• IB
  • IB Docs (2) Team
    Logout
  • Maths
  • Biology
  • Chemistry
  • Physics
  • Combined Science
  • English Language
  • Geography
  • Other Subjects
GCSE Maths
Edexcel Topic QuestionsRevision NotesPast PapersPast Papers Questions
AQA Topic QuestionsRevision NotesPast Papers
OCR Topic QuestionsRevision NotesPast Papers
GCSE Biology
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsRevision NotesPast Papers
OCR Gateway Topic QuestionsRevision NotesPast Papers
GCSE Chemistry
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsRevision NotesPast Papers
OCR Gateway Topic QuestionsRevision NotesPast Papers
GCSE Physics
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsRevision NotesPast Papers
OCR Gateway Topic QuestionsRevision NotesPast Papers
GCSE Combined Science
Edexcel Combined: Biology Topic QuestionsRevision NotesPast Papers
Edexcel Combined: Chemistry Topic QuestionsRevision NotesPast Papers
Edexcel Combined: Physics Revision NotesPast Papers
AQA Combined: Biology Topic QuestionsRevision NotesPast Papers
AQA Combined: Chemistry Topic QuestionsRevision NotesPast Papers
AQA Combined: Physics Topic QuestionsRevision NotesPast Papers
OCR Gateway Combined: Biology Topic QuestionsRevision Notes
OCR Gateway Combined: Chemistry Revision Notes
OCR Gateway Combined: Physics Revision Notes
GCSE English Language
AQA Revision NotesPractice PapersPast Papers
Edexcel Past Papers
OCR Past Papers
GCSE Geography
AQA Topic QuestionsRevision Notes
Edexcel Topic Questions
GCSE Other Subjects
AQA English LiteratureBusinessComputer ScienceEconomicsFurther MathsGeographyHistoryPsychologySociologyStatistics
Edexcel English LiteratureBusinessComputer ScienceGeographyHistoryPsychologyStatistics
OCR English LiteratureBusinessComputer ScienceEconomicsPsychology
OCR Gateway GeographyHistory
  • Maths
  • Biology
  • Chemistry
  • Physics
  • Double Science
  • Economics
  • English Language
  • Geography
  • Other Subjects
IGCSE Maths
Edexcel Topic QuestionsRevision NotesPast PapersBronze-Silver-Gold Questions
CIE (Extended) Topic QuestionsRevision NotesPast Papers
CIE (Core) Topic QuestionsPast Papers
IGCSE Biology
Edexcel Topic QuestionsRevision NotesPast Papers
CIE 2020-2022 Topic QuestionsRevision NotesPast Papers
CIE 2023-2025 Topic QuestionsRevision NotesPast Papers
IGCSE Chemistry
Edexcel Topic QuestionsRevision NotesPast Papers
CIE 2020-2022 Topic QuestionsRevision NotesPast Papers
CIE 2023-2025 Topic QuestionsRevision NotesPast Papers
IGCSE Physics
Edexcel Topic QuestionsRevision NotesPast Papers
CIE 2020-2022 Topic QuestionsRevision NotesPast Papers
CIE 2023-2025 Topic QuestionsRevision NotesPast Papers
IGCSE Double Science
Edexcel Double: Biology Topic QuestionsRevision NotesPast Papers
Edexcel Double: Chemistry Topic QuestionsRevision NotesPast Papers
Edexcel Double: Physics Topic QuestionsRevision NotesPast Papers
IGCSE Economics
CIE Topic QuestionsRevision NotesPast Papers
IGCSE English Language
CIE Revision NotesPractice PapersPast Papers
Edexcel Past Papers
IGCSE Geography
CIE Revision NotesTopic QuestionsPast Papers
Edexcel Topic QuestionsRevision NotesPast Papers
IGCSE Other Subjects
CIE Additional MathsEnglish LiteratureBusinessComputer ScienceHistorySociology
Edexcel English LiteratureBusinessComputer ScienceHistoryFurther Maths
  • Maths
  • Biology
  • Chemistry
  • Physics
  • English Language
  • Other Subjects
AS Maths
Edexcel Pure MathsMechanicsStatistics
AQA Pure MathsMechanicsStatistics
OCR Pure MathsMechanicsStatistics
CIE Pure 1Pure 2MechanicsProbability & Statistics 1
Edexcel IAS Pure 1Pure 2MechanicsStatistics
AS Biology
AQA Topic QuestionsRevision NotesPast Papers
OCR Topic QuestionsRevision NotesPast Papers
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Revision Notes
AS Chemistry
Edexcel Revision Notes
AQA Topic QuestionsRevision NotesPast Papers
OCR Revision Notes
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Revision Notes
AS Physics
Edexcel Revision Notes
AQA Topic QuestionsRevision NotesPast Papers
OCR Revision NotesPast Papers
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Revision Notes
AS English Language
AQA Past Papers
Edexcel Past Papers
OCR Past Papers
AS Other Subjects
AQA BusinessComputer ScienceEconomicsEnglish LiteratureFurther MathsGeographyHistoryPsychologySociology
Edexcel BusinessEconomicsEnglish LiteratureFurther MathsGeographyHistoryPsychology
OCR BusinessComputer ScienceEconomicsEnglish LiteratureFurther Maths AGeographyHistoryPsychologySociology
CIE Further Maths
  • Maths
  • Biology
  • Chemistry
  • Physics
  • English Language
  • Economics
  • Further Maths
  • Psychology
  • Other Subjects
A Level Maths
Edexcel Pure MathsMechanicsStatistics
AQA Pure MathsMechanicsStatistics
OCR Pure MathsMechanicsStatistics
CIE Pure 1Pure 3MechanicsProbability & Statistics 1Probability & Statistics 2
Edexcel IAL Pure 1Pure 2Pure 3Pure 4Mechanics 1Mechanics 2Statistics 1Statistics 2Decision 1
A Level Biology
Edexcel Topic QuestionsPast Papers
Edexcel A (SNAB) Revision Notes
AQA Topic QuestionsRevision NotesPast Papers
OCR Topic QuestionsRevision NotesPast PapersGold Questions
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Topic QuestionsRevision NotesPast Papers
A Level Chemistry
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsRevision NotesPast Papers
OCR Topic QuestionsRevision NotesPast PapersGold Questions
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Topic QuestionsRevision NotesPast Papers
A Level Physics
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsRevision NotesPast Papers
OCR Topic QuestionsRevision NotesPast Papers
CIE 2019-2021 Topic QuestionsRevision NotesPast Papers
CIE 2022-2024 Topic QuestionsRevision NotesPast Papers
Edexcel IAL Topic QuestionsRevision NotesPast Papers
A Level English Language
AQA Past Papers
CIE Past Papers
Edexcel Past Papers
OCR Past Papers
Edexcel IAL Past Papers
A Level Economics
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Topic QuestionsPast Papers
OCR Past Papers
CIE Past Papers
A Level Further Maths
Edexcel Topic QuestionsRevision NotesPast Papers
AQA Past Papers
OCR Past Papers
CIE Past Papers
Edexcel IAL Past Papers
A Level Psychology
AQA Topic QuestionsRevision NotesPast Papers
CIE Past Papers
Edexcel Past Papers
OCR Past Papers
Edexcel IAL Past Papers
A Level Other Subjects
AQA BusinessComputer ScienceEconomicsEnglish LiteratureGeographyHistorySociology
CIE BusinessComputer ScienceEconomicsEnglish LiteratureGeographySociology
Edexcel BusinessEconomics AEnglish LiteratureGeographyHistory
OCR BusinessComputer ScienceEconomicsEnglish LiteratureGeographyHistorySociology
Edexcel IAL English LiteratureGeography
CIE IAL History
  • Biology
  • Chemistry
  • Physics
  • Other Subjects
O Level Biology
CIE Topic QuestionsPast Papers
O Level Chemistry
CIE Topic QuestionsPast Papers
O Level Physics
CIE Topic QuestionsPast Papers
O Level Other Subjects
CIE Additional MathsMaths D
  • Maths
  • Biology
  • Chemistry
  • Physics
Pre U Maths
CIE Topic QuestionsPast Papers
Pre U Biology
CIE Topic QuestionsPast Papers
Pre U Chemistry
CIE Topic QuestionsPast Papers
Pre U Physics
CIE Topic QuestionsPast Papers
  • Maths
  • Biology
  • Chemistry
  • Physics
  • Economics
IB Maths
Maths: AA HL Topic QuestionsRevision NotesPractice Papers
Maths: AI HL Topic QuestionsRevision NotesPractice Papers
Maths: AA SL Topic QuestionsRevision NotesPractice Papers
Maths: AI SL Topic QuestionsRevision NotesPractice Papers
IB Biology
Biology: SL Topic QuestionsRevision NotesPractice Papers
Biology: HL Topic QuestionsRevision NotesPractice Papers
IB Chemistry
Chemistry: SL Topic QuestionsRevision NotesPractice Papers
Chemistry: HL Topic QuestionsRevision NotesPractice Papers
IB Physics
Physics: SL Topic QuestionsRevision NotesPractice Papers
Physics: HL Topic QuestionsRevision NotesPractice Papers
IB Economics
Economics: SL Revision Notes

DP IB Biology: HL

Revision Notes

Home / IB / Biology: HL / DP / Revision Notes / 5. Evolution and Biodiversity / 5.1 Evolution & Natural Selection / 5.1.2 Evolution: Evidence


5.1.2 Evolution: Evidence


Evidence for Evolution: Fossils

  • Fossils are the preserved remains of organisms, or the traces left by organisms, such as footprints, burrows and faeces
    • These remains can be preserved, e.g. in rocks, by the process of petrification, during which the tissues of organisms are replaced with minerals
    • The fossil record is small in relation to the number of organisms that have ever lived, due to the conditions for fossilisation being so rare
  • We can tell from fossils that organisms have changed significantly over millions of years
    • Fossils, as well as the rocks they are found in, can be dated, allowing us to accurately put fossil organisms into a sequence from oldest to youngest, and therefore see how organisms have changed through evolutionary time
    • The fossil record shows the kind of progression that the theory of evolution would lead us to expect, with older fossils showing simpler life forms and complexity increasing with time
    • The sequence of fossils aligns with ecology groups:
      • Plant fossils appear earlier in the fossil record than animals
      • Plants with the ability to be pollinated by insects appear before insect pollinators
    • Fossils can show evidence for transitional species, showing how one species could evolve into another e.g. Ambulocetus is a fossil that links amphibians with early whale-like organisms, and Archaeopteryx appears to link reptiles with birds

Evidence for Evolution: Selective Breeding

  • Selective breeding is a process in which humans choose organisms with desirable characteristics and breed them together to increase the expression of these characteristics over many generations
    • The process of selective breeding has enabled humans to produce desirable crop varieties and livestock with exaggerated characteristics from wild varieties and species, e.g.
      • Desirable crop varieties include those with a high yield and disease resistance
      • Exaggerated characteristics in livestock include thick, heavy wool in sheep, and large volumes of milk produced in dairy cattle
  • Selective breeding involves changes to heritable characteristics over many generations, and so it is an example of evolution in action
  • This practice is also known as artificial selection
    • It makes use of the principles of natural selection, but is carried out by humans
      • In natural selection, advantageous alleles are more likely to be passed on because they increase an organism's chances of survival
      • In artificial selection, or selective breeding, desirable alleles are more likely to be passed on because humans decide which individuals will be used for breeding

  • Humans have been selectively breeding organisms for thousands of years, long before scientists understood genes and alleles
  • The process of selective breeding

    1. The population shows variation; there are individuals with different characteristics
    2. Breeders select individuals with the desired characteristics; selected individuals should not be closely related to each other
    3. Two selected individuals are bred together
    4. The offspring produced reach maturity and are then tested for the desirable characteristics; those that display the desired characteristics to the greatest extent are selected for further breeding
    5. The process is repeated over many generations; the best individuals from the offspring are continually chosen for breeding until all offspring display the desirable characteristics

    Selective breeding dogs, IGCSE & GCSE Biology revision notes

    The wolf was bred selectively over thousands of years to produce a wide variety of domesticated dog breeds.

    Evidence for Evolution: Homologous Structures

    • Homologous structures are body parts that may look and function very differently but share structural similarities
    • The limbs of animals are a good example of this; animals have many different mechanisms of motion and limb use, but the basic arrangement of bones in many different types of limbs is very similar
      • E.g. The limbs of birds, bats, crocodiles, whales, horses, and monkeys are used very differently and are visually very different, but are structurally very similar to each other

    • One explanation for the surprising similarities of these different limbs is that of adaptive radiation; the idea that organisms with homologous structures have all evolved from a shared, common ancestor but have adapted to different environments in the process
      • Note that adaptive radiation does not provide proof that these organisms have evolved from a common ancestor, but it is a good explanation for the existence of homologous structures

    A homologous structure: the pentadactyl limb

    • A pentadactyl limb is any limb that has five digits i.e. five fingers or toes
    • Pentadactyl limbs are present in many species from many groups of organisms, including mammals, birds, amphibians, and reptiles
    • In different species, the pentadactyl limb has a similar bone structure but can enable an animal to move in a very different way
      • The human foot evolved for upright walking and running
      • Whale flippers enable them to propel themselves through a marine environment
      •  Bird wings are usually highly adapted for flight
      •  The limbs of frogs allow them to walk, jump and swim
      • Alligator limbs enable them to walk and swim

    • Although the individual bones of the pentadactyl limb in these example animals are very different shapes and sizes due to their different mechanisms of locomotion, their layout is almost exactly the same

    The bone structure of the pentadactyl limb of a human, whale, bird, frog, and alligator; they all have the same basic layout despite having evolved for different functions

    Vestigial structures

    • Note that vestigial structures, while different in nature from homologous structures, can also be explained by common ancestry
      • Vestigial structures are those that no longer have a function in an organism
        • E.g. pelvis bones in snakes and whales and wings in flightless birds

    • These structures tend to be homologous to structures that perform a function in other species
    • The presence of vestigial structures suggests a shared ancestry with those species that possess a fully functioning equivalent of the same structure
    • Vestigial structures are considered to be 'evolutionary leftovers'; they would have had a function in an ancestral organism, but a change in the environment led to loss of use e.g. a group of fish trapped in a dark cave would have no use for eyes
      • The presence of vestigial structures does not harm the species in which they are found, so there is no advantage to be gained by losing them completely; hence their persistence

    NOS: Looking for patterns, trends and discrepancies; there are common features in the bone structure of vertebrate limbs despite their varied use

    • When patterns and trends are observed in nature, scientists seek to find explanations that fit with these observations
      • Here, scientists have observed a pattern in the limb structure of animals; despite differences in appearance and function, the general structure of the pentadactyl limb is repeated throughout the animal kingdom
      • The explanation that best fits this observation is that all animals evolved from a common ancestor that itself had a pentadactyl limb, in the process of adaptive radiation
        • This is the only explanation so far that makes sense of the pattern of homologous structures seen in nature, and it supports the theory that organisms evolve over time

    Evidence for Evolution: Continuous Variation Between Populations

    • Different populations of a species may show small amounts of variation between each population e.g. a few mm in beak length between bird populations
      • Beak length is an example of continuous variation

    • The presence of continuous variation between populations across their geographical range can lead to gradual divergence
      • The term divergence refers to the species becoming separate; this is the process of speciation
    • It can sometimes be difficult to make decisions about the point at which populations showing continuous variation have diverged into different species, and biologists sometimes disagree over whether separate populations are the same species, different subspecies, or separate species
      • E.g. Orca, or killer whale, populations can show different body shapes and markings, and there is debate among scientists around whether there is only one species of orca, several subspecies, or several species

    Evidence for gradual divergence

    • There are several examples around the world of groups of species found in a particular geographical location where the differences between those species are small, e.g.
      • Darwin's finches; many species of small bird observed by Darwin in the Galapagos islands
      • Hawaiian honeycreepers; a group of more than 50 bird species found in the Hawaiian archipelago

    • The presence of continuous variation like this, between species, and across their geographical range, suggests that these species evolved by gradual divergence as a result of continuous variation between historical populations
    • For example, Hawaiian honeycreepers show continuous variation across their geographical range; because of this, they are thought to have evolved from a series of ancestral populations, from which gradual divergence gave rise to many different species

    Continuous Variation Between Populations of Honeycreepers, downloadable IB Biology revision notes

    The Hawaiian honeycreepers show continuous variation across their geographical range, suggesting that they diverged gradually from a common ancestor

    Evidence for Evolution: Melanistic Insects in Polluted Areas

    • Because evolution generally happens over millions of years, it is difficult to see it taking place, and we often have to rely on evidence from the fossil record, and evidence of common ancestry such as homologous structures and continuous variation between species
    • There are, however, some examples of evolution, on a small scale, that show changes in heritable characteristics in a short time frame
      • E.g. in insects and bacteria
      • Examples like this rely on short generation times

    • A famous example of evolution taking place in insects is that of the peppered moth and industrial melanism
      • Melanin is a dark pigment produced in the cells; the more melanin is produced, the more melanistic an individual is said to be, and the darker it will be in colour
    • It has been noted that melanistic peppered moths have become more common than non-melanistic individuals in industrialised parts of the UK where air pollution has increased
      • Air pollution kills organisms called lichens that grow on the bark of trees
      • In areas with clean air, lichens grow on tree bark, causing tree trunks and branches to appear paler in colour
        • In these areas, non-melanistic moths are well camouflaged against the trees, and therefore more likely to survive and pass on the alleles for non-melanism
      • In polluted areas, lichens are killed, causing tree trunks and branches to appear darker in colour
        • Here, melanistic moths are well camouflaged, increasing their chances of surviving and passing on the alleles for melanism

      • The frequency of non-melanistic individuals therefore increases in non-polluted areas, and the frequency of melanistic individuals increases in polluted areas
    • This change in the heritable characteristic of melanin production over generations of moths shows evolution taking place

    In areas with higher levels of air pollution the frequency of melanistic moths increases



    • 1. Cell Biology
      • 1.1 Cells: Theory
        • 1.1.1 Cell Theory
          • 1.1.2 Functions of Life
            • 1.1.3 Surface Area to Volume Ratio
              • 1.1.4 Cell Specialisation
                • 1.1.5 Stem Cells
                  • 1.1.6 Skills: Cell Theory
                  • 1.2 Cells: Origin & Ultrastructure
                    • 1.2.1 Origin of Cells
                      • 1.2.2 Endosymbiotic Theory
                        • 1.2.3 Prokaryotic Cell Structure
                          • 1.2.4 Eukaryotic Cell Structure
                            • 1.2.5 Exocrine Pancreatic & Palisade Mesophyll Cells
                              • 1.2.6 Comparison of Prokaryotic & Eukaryotic Cells
                                • 1.2.7 Microscopes
                                  • 1.2.8 Skills: Drawing Cells
                                    • 1.2.9 Skills: Cell Origin & Ultrastructure
                                    • 1.3 Cells: Membrane Structure & Transport
                                      • 1.3.1 Phospholipid Bilayer Properties
                                        • 1.3.2 Membrane Proteins
                                          • 1.3.3 History of Fluid Mosaic Model
                                            • 1.3.4 Membrane Transport
                                              • 1.3.5 Active Transport & Bulk Transport
                                                • 1.3.6 Skills: Membrane Structure & Transport
                                                  • 1.3.7 Skills: Estimation of Osmolarity
                                                  • 1.4 Cells: Division
                                                    • 1.4.1 Cell Cycle
                                                      • 1.4.2 Phases of Mitosis
                                                        • 1.4.3 Cancer
                                                          • 1.4.4 Skills: Cell Division
                                                        • 2. Molecular Biology
                                                          • 2.1 Metabolism & Water
                                                            • 2.1.1 Molecules
                                                              • 2.1.2 Metabolism
                                                                • 2.1.3 Hydrogen Bonds
                                                                  • 2.1.4 Water
                                                                  • 2.2 Carbohydrates & Lipids
                                                                    • 2.2.1 Carbohydrates
                                                                      • 2.2.2 Fatty Acids
                                                                        • 2.2.3 Lipids
                                                                          • 2.2.4 Skills: Visualising Carbohydrates
                                                                            • 2.2.5 Skills: Calculating BMI
                                                                            • 2.3 Proteins
                                                                              • 2.3.1 Proteins
                                                                                • 2.3.2 Protein Structure & Function
                                                                                  • 2.3.3 The Variety of Proteins
                                                                                    • 2.3.4 Skills: Molecules
                                                                                    • 2.4 Enzymes
                                                                                      • 2.4.1 Enzymes
                                                                                        • 2.4.2 Immobilised Enzymes
                                                                                          • 2.4.3 Skills: Enzyme Experiments
                                                                                          • 2.5 Nucleic Acids: Structure & DNA Replication
                                                                                            • 2.5.1 DNA & RNA Structure
                                                                                              • 2.5.2 DNA Replication
                                                                                                • 2.5.3 Skills: DNA Replication
                                                                                                • 2.6 Transcription & Translation
                                                                                                  • 2.6.1 Transcription
                                                                                                    • 2.6.2 Translation
                                                                                                      • 2.6.3 Biotechnology
                                                                                                        • 2.6.4 Skills: DNA, RNA & Protein Synthesis
                                                                                                          • 2.6.5 Skills: Interpreting Sequences
                                                                                                          • 2.7 Cellular Respiration
                                                                                                            • 2.7.1 Cellular Respiration
                                                                                                              • 2.7.2 Anaerobic Respiration
                                                                                                                • 2.7.3 Aerobic Respiration
                                                                                                                  • 2.7.4 Skills: Respiration
                                                                                                                  • 2.8 Photosynthesis
                                                                                                                    • 2.8.1 Photosynthesis
                                                                                                                      • 2.8.2 Photosynthesis Continued
                                                                                                                        • 2.8.3 Skills: Photosynthesis
                                                                                                                          • 2.8.4 Skills: Separating Photosynthetic Pigments
                                                                                                                        • 3. Genetics
                                                                                                                          • 3.1 Genes & Chromosomes
                                                                                                                            • 3.1.1 Genes
                                                                                                                              • 3.1.2 Alleles
                                                                                                                                • 3.1.3 Mutation
                                                                                                                                  • 3.1.4 Genome
                                                                                                                                    • 3.1.5 Prokaryotic Chromosomes
                                                                                                                                      • 3.1.6 Eukaryotic Chromosomes
                                                                                                                                        • 3.1.7 Chromosome Number
                                                                                                                                          • 3.1.8 Sex Determination
                                                                                                                                            • 3.1.9 Karyograms
                                                                                                                                              • 3.1.10 Skills: Using Databases
                                                                                                                                              • 3.2 Meiosis
                                                                                                                                                • 3.2.1 Meiosis
                                                                                                                                                  • 3.2.2 Stages of Meiosis
                                                                                                                                                    • 3.2.3 Genetic Variation
                                                                                                                                                      • 3.2.4 Non-disjunction
                                                                                                                                                        • 3.2.5 Skills: Meiosis
                                                                                                                                                        • 3.3 Inheritance
                                                                                                                                                          • 3.3.1 Inheritance
                                                                                                                                                            • 3.3.2 Inheriting Alleles
                                                                                                                                                              • 3.3.3 Skills: Inheritance
                                                                                                                                                                • 3.3.4 Inheritance of Genetic Diseases
                                                                                                                                                                  • 3.3.5 Mutations & Disease
                                                                                                                                                                  • 3.4 Genetic Modification & Biotechnology
                                                                                                                                                                    • 3.4.1 Electrophoresis & PCR
                                                                                                                                                                      • 3.4.2 DNA Profiling
                                                                                                                                                                        • 3.4.3 Genetic Modification
                                                                                                                                                                          • 3.4.4 Cloning
                                                                                                                                                                            • 3.4.5 Skills: Genetic Modification & Biotechnology
                                                                                                                                                                          • 4. Ecology
                                                                                                                                                                            • 4.1 Species, Communities, Ecosystems & Energy Flow
                                                                                                                                                                              • 4.1.1 Species & Population
                                                                                                                                                                                • 4.1.2 Methods of Nutrition
                                                                                                                                                                                  • 4.1.3 Community
                                                                                                                                                                                    • 4.1.4 Nutrient Cycling
                                                                                                                                                                                      • 4.1.5 Energy Flow
                                                                                                                                                                                        • 4.1.6 Energy Losses
                                                                                                                                                                                          • 4.1.7 Skills: Species, Communities, Ecosystems & Energy Flow
                                                                                                                                                                                            • 4.1.8 Skills: Chi-squared test & Statistical Significance
                                                                                                                                                                                              • 4.1.9 Skills: Pyramids of Energy
                                                                                                                                                                                              • 4.2 Carbon Cycling & Climate Change
                                                                                                                                                                                                • 4.2.1 Carbon Cycle: Carbon Dioxide
                                                                                                                                                                                                  • 4.2.2 Carbon Cycle: Carbon Dioxide in the Atmosphere
                                                                                                                                                                                                    • 4.2.3 Carbon Cycle: Methane
                                                                                                                                                                                                      • 4.2.4 Carbon Cycle: Organic Matter
                                                                                                                                                                                                        • 4.2.5 Climate Change: Greenhouse Effect
                                                                                                                                                                                                          • 4.2.6 Climate Change: Impact
                                                                                                                                                                                                            • 4.2.7 Climate Change: Causes
                                                                                                                                                                                                              • 4.2.8 Skills: Carbon Cycling & Climate Change
                                                                                                                                                                                                            • 5. Evolution and Biodiversity
                                                                                                                                                                                                              • 5.1 Evolution & Natural Selection
                                                                                                                                                                                                                • 5.1.1 Evolution
                                                                                                                                                                                                                  • 5.1.2 Evolution: Evidence
                                                                                                                                                                                                                    • 5.1.3 Variation
                                                                                                                                                                                                                      • 5.1.4 Natural Selection
                                                                                                                                                                                                                        • 5.1.5 Natural Selection Examples
                                                                                                                                                                                                                        • 5.2 Classification & Cladistics
                                                                                                                                                                                                                          • 5.2.1 Classification System
                                                                                                                                                                                                                            • 5.2.2 Classifying Organisms
                                                                                                                                                                                                                              • 5.2.3 Plant Phyla Features
                                                                                                                                                                                                                                • 5.2.4 Animal Phyla Features
                                                                                                                                                                                                                                  • 5.2.5 Cladistics
                                                                                                                                                                                                                                    • 5.2.6 Reclassification
                                                                                                                                                                                                                                      • 5.2.7 Skills: Classification & Cladistics
                                                                                                                                                                                                                                    • 6. Human Physiology
                                                                                                                                                                                                                                      • 6.1 Digestion & Absorption
                                                                                                                                                                                                                                        • 6.1.1 Digestion
                                                                                                                                                                                                                                          • 6.1.2 Villi & Absorption
                                                                                                                                                                                                                                            • 6.1.3 Absorption
                                                                                                                                                                                                                                              • 6.1.4 Skills: Digestion & Absorption
                                                                                                                                                                                                                                              • 6.2 The Blood System
                                                                                                                                                                                                                                                • 6.2.1 The Blood System: History
                                                                                                                                                                                                                                                  • 6.2.2 The Blood System: Vessels
                                                                                                                                                                                                                                                    • 6.2.3 The Blood System: Double Circulation
                                                                                                                                                                                                                                                      • 6.2.4 The Blood System: Cardiac Cycle
                                                                                                                                                                                                                                                        • 6.2.5 The Heart Rate
                                                                                                                                                                                                                                                          • 6.2.6 Skills: The Blood System
                                                                                                                                                                                                                                                          • 6.3 Defence Against Infectious Disease
                                                                                                                                                                                                                                                            • 6.3.1 Skin
                                                                                                                                                                                                                                                              • 6.3.2 Blood Clotting
                                                                                                                                                                                                                                                                • 6.3.3 White Blood Cells
                                                                                                                                                                                                                                                                  • 6.3.4 Antibiotics
                                                                                                                                                                                                                                                                    • 6.3.5 Antibiotic Resistance
                                                                                                                                                                                                                                                                    • 6.4 Gas Exchange
                                                                                                                                                                                                                                                                      • 6.4.1 Ventilation: Function & Structures
                                                                                                                                                                                                                                                                        • 6.4.2 Ventilation: Mechanism
                                                                                                                                                                                                                                                                          • 6.4.3 Lung Diseases
                                                                                                                                                                                                                                                                            • 6.4.4 Skills: Monitoring Ventilation
                                                                                                                                                                                                                                                                            • 6.5 Neurones & Synapses
                                                                                                                                                                                                                                                                              • 6.5.1 Neurones: Function & Structure
                                                                                                                                                                                                                                                                                • 6.5.2 Nerve Impulses
                                                                                                                                                                                                                                                                                  • 6.5.3 Synapses
                                                                                                                                                                                                                                                                                    • 6.5.4 Skill: Neurones & Synapses
                                                                                                                                                                                                                                                                                    • 6.6 Hormones, Homeostasis & Reproduction
                                                                                                                                                                                                                                                                                      • 6.6.1 Hormones
                                                                                                                                                                                                                                                                                        • 6.6.2 Hormones Continued
                                                                                                                                                                                                                                                                                          • 6.6.3 Reproduction: Background
                                                                                                                                                                                                                                                                                            • 6.6.4 Reproduction: Sex Determination in Males
                                                                                                                                                                                                                                                                                              • 6.6.5 Reproduction: Sex Determination in Females
                                                                                                                                                                                                                                                                                                • 6.6.6 Skills: Reproduction Diagrams
                                                                                                                                                                                                                                                                                              • 7. Nucleic Acids (HL Only)
                                                                                                                                                                                                                                                                                                • 7.1 DNA Structure & Replication
                                                                                                                                                                                                                                                                                                  • 7.1.1 DNA Structure
                                                                                                                                                                                                                                                                                                    • 7.1.2 Mechanism of DNA Replication
                                                                                                                                                                                                                                                                                                      • 7.1.3 Non-coding DNA
                                                                                                                                                                                                                                                                                                        • 7.1.4 DNA Sequencing
                                                                                                                                                                                                                                                                                                          • 7.1.5 Skills: The Hershey & Chase Experiment
                                                                                                                                                                                                                                                                                                            • 7.1.6 Skills: Nucleosomes & Molecular Visualisation Software
                                                                                                                                                                                                                                                                                                            • 7.2 Transcription & Gene Expression
                                                                                                                                                                                                                                                                                                              • 7.2.1 Regulation of Gene Expression by Proteins
                                                                                                                                                                                                                                                                                                                • 7.2.2 Environment & Gene Expression
                                                                                                                                                                                                                                                                                                                  • 7.2.3 Transcription
                                                                                                                                                                                                                                                                                                                    • 7.2.4 Post-transcriptional Modification
                                                                                                                                                                                                                                                                                                                      • 7.2.5 Skills: Analysing DNA Methylation Patterns
                                                                                                                                                                                                                                                                                                                      • 7.3 Translation
                                                                                                                                                                                                                                                                                                                        • 7.3.1 Translation
                                                                                                                                                                                                                                                                                                                          • 7.3.2 Ribosomes
                                                                                                                                                                                                                                                                                                                            • 7.3.3 Translation in Prokaryotes
                                                                                                                                                                                                                                                                                                                              • 7.3.4 Bioinformatics
                                                                                                                                                                                                                                                                                                                                • 7.3.5 Levels of Protein Structure
                                                                                                                                                                                                                                                                                                                                  • 7.3.6 Skills: Polysomes & Ribosomes
                                                                                                                                                                                                                                                                                                                                • 8. Metabolism, Cell Respiration & Photosynthesis (HL Only)
                                                                                                                                                                                                                                                                                                                                  • 8.1 Metabolism
                                                                                                                                                                                                                                                                                                                                    • 8.1.1 Metabolic Pathways
                                                                                                                                                                                                                                                                                                                                      • 8.1.2 Inhibition
                                                                                                                                                                                                                                                                                                                                        • 8.1.3 Bioinformatics & Metabolism
                                                                                                                                                                                                                                                                                                                                          • 8.1.4 Skills: Rates of Reaction & Types of Inhibition
                                                                                                                                                                                                                                                                                                                                          • 8.2 Cell Respiration
                                                                                                                                                                                                                                                                                                                                            • 8.2.1 Oxidation, Reduction & Phosphorylation
                                                                                                                                                                                                                                                                                                                                              • 8.2.2 Overview of the Stages of Respiration
                                                                                                                                                                                                                                                                                                                                                • 8.2.3 Glycolysis
                                                                                                                                                                                                                                                                                                                                                  • 8.2.4 The Link Reaction & The Krebs Cycle
                                                                                                                                                                                                                                                                                                                                                    • 8.2.5 Oxidative Phosphorylation
                                                                                                                                                                                                                                                                                                                                                      • 8.2.6 Mitochondria
                                                                                                                                                                                                                                                                                                                                                        • 8.2.7 Skills: Cell Respiration
                                                                                                                                                                                                                                                                                                                                                        • 8.3 Photosynthesis
                                                                                                                                                                                                                                                                                                                                                          • 8.3.1 Light-dependent Reactions
                                                                                                                                                                                                                                                                                                                                                            • 8.3.2 Photophosphorylation
                                                                                                                                                                                                                                                                                                                                                              • 8.3.3 Light-independent Reactions
                                                                                                                                                                                                                                                                                                                                                                • 8.3.4 Investigating Carbon Fixation in Photosynthesis
                                                                                                                                                                                                                                                                                                                                                                  • 8.3.5 Chloroplast
                                                                                                                                                                                                                                                                                                                                                                    • 8.3.6 Skills: Photosynthesis
                                                                                                                                                                                                                                                                                                                                                                  • 9. Plant Biology (HL Only)
                                                                                                                                                                                                                                                                                                                                                                    • 9.1 Transport in the Xylem of Plants
                                                                                                                                                                                                                                                                                                                                                                      • 9.1.1 Transpiration in Plants
                                                                                                                                                                                                                                                                                                                                                                        • 9.1.2 The Transpiration Stream
                                                                                                                                                                                                                                                                                                                                                                          • 9.1.3 The Roots & Water Transport
                                                                                                                                                                                                                                                                                                                                                                            • 9.1.4 Adaptations of Xerophytes
                                                                                                                                                                                                                                                                                                                                                                              • 9.1.5 Skills: Drawing Xylem Vessels
                                                                                                                                                                                                                                                                                                                                                                                • 9.1.6 Skills: Experiments Investigating the Rate of Transpiration
                                                                                                                                                                                                                                                                                                                                                                                • 9.2 Transport in the Phloem of Plants
                                                                                                                                                                                                                                                                                                                                                                                  • 9.2.1 Translocation in Plants
                                                                                                                                                                                                                                                                                                                                                                                    • 9.2.2 Sucrose Loading
                                                                                                                                                                                                                                                                                                                                                                                      • 9.2.3 Hydrostatic Pressure Gradients
                                                                                                                                                                                                                                                                                                                                                                                        • 9.2.4 Skills: Identifying Xylem & Phloem
                                                                                                                                                                                                                                                                                                                                                                                          • 9.2.5 Skills: Measuring Phloem Transport Rates
                                                                                                                                                                                                                                                                                                                                                                                          • 9.3 Growth in Plants
                                                                                                                                                                                                                                                                                                                                                                                            • 9.3.1 Plant Growth
                                                                                                                                                                                                                                                                                                                                                                                              • 9.3.2 Plant Hormones
                                                                                                                                                                                                                                                                                                                                                                                                • 9.3.3 Micropropagation
                                                                                                                                                                                                                                                                                                                                                                                                • 9.4 Reproduction in Plants
                                                                                                                                                                                                                                                                                                                                                                                                  • 9.4.1 Flowering
                                                                                                                                                                                                                                                                                                                                                                                                    • 9.4.2 Plant Reproduction
                                                                                                                                                                                                                                                                                                                                                                                                      • 9.4.3 Skills: Drawing Plant Structures
                                                                                                                                                                                                                                                                                                                                                                                                        • 9.4.4 Skills: Investigating Factors Affecting Germination
                                                                                                                                                                                                                                                                                                                                                                                                      • 10. Genetics & Evolution (HL Only)
                                                                                                                                                                                                                                                                                                                                                                                                        • 10.1 Meiosis
                                                                                                                                                                                                                                                                                                                                                                                                          • 10.1.1 The Process of Meiosis
                                                                                                                                                                                                                                                                                                                                                                                                            • 10.1.2 Crossing Over
                                                                                                                                                                                                                                                                                                                                                                                                              • 10.1.3 Meiosis I
                                                                                                                                                                                                                                                                                                                                                                                                                • 10.1.4 Meiosis II
                                                                                                                                                                                                                                                                                                                                                                                                                  • 10.1.5 Skills: Drawing Chiasmata
                                                                                                                                                                                                                                                                                                                                                                                                                  • 10.2 Inheritance
                                                                                                                                                                                                                                                                                                                                                                                                                    • 10.2.1 Unlinked Genes
                                                                                                                                                                                                                                                                                                                                                                                                                      • 10.2.2 Skills: Analysing Dihybrid Crosses
                                                                                                                                                                                                                                                                                                                                                                                                                        • 10.2.3 Gene Linkage
                                                                                                                                                                                                                                                                                                                                                                                                                          • 10.2.4 Skills: Identifying Recombinants
                                                                                                                                                                                                                                                                                                                                                                                                                            • 10.2.5 Skills: Chi-squared Test
                                                                                                                                                                                                                                                                                                                                                                                                                              • 10.2.6 Variation
                                                                                                                                                                                                                                                                                                                                                                                                                              • 10.3 Gene Pools & Speciation
                                                                                                                                                                                                                                                                                                                                                                                                                                • 10.3.1 Gene Pools
                                                                                                                                                                                                                                                                                                                                                                                                                                  • 10.3.2 Evolution
                                                                                                                                                                                                                                                                                                                                                                                                                                    • 10.3.3 Speciation
                                                                                                                                                                                                                                                                                                                                                                                                                                      • 10.3.4 Polyploidy & Speciation
                                                                                                                                                                                                                                                                                                                                                                                                                                        • 10.3.5 Skills: Comparing Allele Frequencies Between Populations
                                                                                                                                                                                                                                                                                                                                                                                                                                      • 11. Animal Physiology (HL Only)
                                                                                                                                                                                                                                                                                                                                                                                                                                        • 11.1 Antibody Production & Vaccination
                                                                                                                                                                                                                                                                                                                                                                                                                                          • 11.1.1 Antigens
                                                                                                                                                                                                                                                                                                                                                                                                                                            • 11.1.2 Specific Immune Response
                                                                                                                                                                                                                                                                                                                                                                                                                                              • 11.1.3 Antibodies, Vaccines & Immunity
                                                                                                                                                                                                                                                                                                                                                                                                                                                • 11.1.4 Smallpox Vaccine & Eradication
                                                                                                                                                                                                                                                                                                                                                                                                                                                  • 11.1.5 Zoonosis
                                                                                                                                                                                                                                                                                                                                                                                                                                                    • 11.1.6 Histamines
                                                                                                                                                                                                                                                                                                                                                                                                                                                      • 11.1.7 Monoclonal Antibodies
                                                                                                                                                                                                                                                                                                                                                                                                                                                        • 11.1.8 Skills: Analysing Epidemiological Data
                                                                                                                                                                                                                                                                                                                                                                                                                                                        • 11.2 Movement
                                                                                                                                                                                                                                                                                                                                                                                                                                                          • 11.2.1 Requirements for Movement
                                                                                                                                                                                                                                                                                                                                                                                                                                                            • 11.2.2 Skeletal Muscle
                                                                                                                                                                                                                                                                                                                                                                                                                                                              • 11.2.3 Mechanism of Muscle Contraction
                                                                                                                                                                                                                                                                                                                                                                                                                                                                • 11.2.4 Skills: The Human Elbow & Sarcomeres
                                                                                                                                                                                                                                                                                                                                                                                                                                                                  • 11.2.5 Skills: Analysing Muscle Contractions in Electron Micrographs
                                                                                                                                                                                                                                                                                                                                                                                                                                                                  • 11.3 The Kidney & Osmoregulation
                                                                                                                                                                                                                                                                                                                                                                                                                                                                    • 11.3.1 Osmoregulation in Organisms
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      • 11.3.2 Kidney: Structure & Function
                                                                                                                                                                                                                                                                                                                                                                                                                                                                        • 11.3.3 Conserving Water
                                                                                                                                                                                                                                                                                                                                                                                                                                                                          • 11.3.4 The Role of ADH
                                                                                                                                                                                                                                                                                                                                                                                                                                                                            • 11.3.5 Types of Nitrogenous Waste
                                                                                                                                                                                                                                                                                                                                                                                                                                                                              • 11.3.6 Kidney Failure & Urinalysis
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                • 11.3.7 Skills: Drawing & Annotating the Kidney
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                • 11.4 Sexual Reproduction
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  • 11.4.1 Oogenesis & Spermatogenesis
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    • 11.4.2 Fertilisation
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      • 11.4.3 Pregnancy
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        • 11.4.4 Hormones in Pregnancy
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          • 11.4.5 The Placenta
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            • 11.4.6 Oestrogen Pollution
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              • 11.4.7 Skills: Annotating Sexual Reproduction Diagrams
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Naomi Holyoak

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Author: Naomi

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Naomi graduated in 2007 from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.


                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Save My Exams Logo
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Resources
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Home Join Support

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Members
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Members Home Account Logout

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Company
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            About Us Contact Us Jobs Terms Privacy Facebook Twitter

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Quick Links
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            GCSE Revision Notes IGCSE Revision Notes A Level Revision Notes Biology Chemistry Physics Maths 2022 Advance Information

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            © IB Documents (2) Team & u/aimlesskr
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            IBO was not involved in the production of, and does not endorse, the resources created by Save My Exams.