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DP IB Biology: HL

Revision Notes

Home / IB / Biology: HL / DP / Revision Notes / 6. Human Physiology / 6.1 Digestion & Absorption / 6.1.2 Villi & Absorption


6.1.2 Villi & Absorption


Villi: Increasing the Surface Area

  • The ileum (the second section of the small intestine) is adapted for absorption
    • It is very long
    • It has a highly folded surface 
    • It has millions of villi (singular villus)
      • Finger like projections on the internal intestinal walls

    • The epithelium of each villus is covered in microvilli
      • Foldings of the cell surface membrane of the epithelial cells
  • All of these features significantly increase the surface area of the ileum, allowing absorption to take place faster
  • Villi_ Increasing the Surface Area, downloadable IB Biology revision notes

    A villus is covered in microvilli which provide a huge surface area to maximise absorption in the small intestine

    Villi: Absorption

    • Absorption takes place in the ileum
    • Absorption is the movement of digested food molecules, vitamins and mineral ions from the digestive system into the blood and lymph
    • This includes the following products of digestion:
      • Simple monosaccharides e.g. glucose, fructose, galactose
      • Amino acids
      • Fatty acids, monoglycerides and glycerol
      • Nucleotide bases
    • And the following additional substances:
      • Mineral ions e.g. calcium, potassium, sodium
      • Vitamins e.g. vitamin C
    • Water is absorbed in both the small intestine and the colon, but most absorption of water occurs in the small intestine

    Absorption of unwanted substances

    • The epithelium provides a barrier to prevent absorption of some harmful substances
    • However, some unwanted substances can still pass into the blood. This includes:
      • Some harmless chemicals found in food colourings and flavours; these are removed by the kidney and lost in the urine
      • Small numbers of bacteria - these are engulfed and digested by phagocytes in the blood
      • Some other harmful substances - these are removed from the blood and broken down by the liver

    Dialysis Tubing Experiment

    Investigating the absorption of the products of digestion using dialysis tubing

    • Dialysis tubing (sometimes referred to as Visking tubing) is a non-living, partially permeable membrane made from cellulose
    • It is sometimes used to model the process of digestion and absorption that occurs in the small intestine
    • Pores in the membrane are small enough to prevent the passage of large molecules (such as starch and sucrose) but allow smaller molecules (such as glucose) to pass through by diffusion

    Dialysis Tubing Experiment, downloadable IB Biology revision notes

    Dialysis tubing can be used to model the epithelium of the small intestine

    Method

    • Fill a section of dialysis tubing (tube 1) with a mixture of:
      • 1 ml 1% amylase solution
      • 10 ml 1% starch solution

    • Tie up the tubing tightly with a piece of thread
    • Suspend the tubing in a beaker of water for a set period of time at 40°C
    • Take samples from the liquid outside the dialysis tubing at regular intervals and test for the presence of starch and glucose
      • Iodine is used to test for the presence of starch. A blue-black colour is produced in the presence of starch
      • Benedict's reagent is used to test for the presence of glucose. An orange-red precipitate is formed in the presence of glucose when Benedict's solution is added and the solution is heated to 90°C or above

    • Repeat the same method in a second dialysis tube (tube 2) with a mixture of:
      • 1 ml distilled water
      • 10 ml 1% starch solution

    Results

    • Tube 1:
      • The amylase present inside the dialysis tube breaks down starch into glucose
      • Over time the concentration of glucose in the liquid outside the dialysis tube should increase as more starch is digested
        • Glucose is small enough to diffuse across the partially permeable membrane
        • The amount of precipitate produced from the Benedict's reagent test will increase over time
      • No starch should be found in the liquid outside the dialysis tubing
        • Starch molecules are too large to diffuse across the partially permeable membrane
        • The iodine test will be negative
    • Tube 2:
      • Without amylase present, the starch is not broken down into glucose
      • The glucose tests done on the water outside the dialysis tube show no glucose is present as no precipitate is formed
      • Starch molecules are too large to diffuse across the partially permeable membrane, so the iodine test will be negative

    Limitations

    • This test is qualitative, so does not show the rate of enzyme activity
      • The rate of digestion can be investigated quantitatively by using the semi-quantitative Benedict’s test
        • Comparisons can be made at time intervals using a set of colour standards (known glucose concentrations) or a colorimeter to give a quantitative set of results
        • A graph could be drawn showing how the rate of diffusion changes with the concentration gradient between the inside and outside of the tubing

    Other investigations using dialysis tubing

    • Dialysis tubing can also be used to investigate other features of digestion such as
      • The effects of different factors on the rate of digestive enzyme activity
        • Investigating the effect of pH
          • Eg. multiple dialysis tubings are set up containing solutions of starch and amylase kept at different pH levels using buffer solutions
        • Investigating the effect of temperature
          • Eg. multiple dialysis tubings are set up in water baths of different temperatures

      • The effect of membrane permeability on absorption
        • E.g. using cola to show how some smaller particles (glucose) can diffuse through the partially permeable membrane whilst larger molecules (food colouring) cannot

    Using Models to Represent Real Life

    NOS: Use models as representations of the real world; dialysis tubing can be used to model absorption in the intestine

    • Models are often used to study living systems which may be too complicated to observe in reality and achieve meaningful results
      • There may be too many factors influencing a system at any one time
    • Scientists may have access to specialist equipment that enables them to carry out computer based models e.g. the Dynamic Gastric Model, used to analyse factors influencing digestion
    • It is also possible to model some systems using much simpler equipment, such as the dialysis tubing model from the experiment above
      • The dialysis tubing membrane is used to represent the membrane of the small intestine:
        • It is an accurate model because both are partially permeable so smaller particles can pass through the membrane whilst larger particles cannot; the membrane therefore allows the passive movement of solutes in diffusion, and water molecules in osmosis
        • However, the small intestine has a much larger surface area due to the presence of villi
        • Additionally, dialysis tubing is limited in the processes it can mirror and cannot show active transport 
      • Distilled water is used to represent blood:
        • This is a good model because both have an initially low solute concentration
        • However, the distilled water does not flow in the same way as blood and so does not maintain the concentration gradient as blood does


    • 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
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Ruth Brindle

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Author: Ruth

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.


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