DP Biology (last assessment 2024)

Test builder »

Question 22N.2.SL.TZ0.6

Select a Test
Date November 2022 Marks available [Maximum mark: 15] Reference code 22N.2.SL.TZ0.6
Level SL Paper 2 Time zone TZ0
Command term Describe, Explain, Outline Question number 6 Adapted from N/A
6.
[Maximum mark: 15]
22N.2.SL.TZ0.6

The continued survival of all living organisms depends on sustainable communities in which plants play a vital role.

(a)

Outline how energy flows in an ecosystem.

[4]

Markscheme
  1. energy from the sun is captured by plants/autotrophs;
  2. light energy is converted to chemical energy by photosynthesis;
  3. energy is passed to animals/consumers/along the food chain;
  4. at each stage in the food chain energy is lost by respiration/as heat;
  5. much less energy/only about 10 % is available at each stage/trophic level of the food chain;
  6. some energy is made available to decomposers when organisms die/parts fall to the ground;
  7. energy cannot be recycled;
Examiners report

Explaining the energy flow in part (a), was one of the best answered questions on the paper. However, the 
conversion of light energy to chemical energy was missed by many. Some weaker candidates are still confusing energy with biomass, and lost marks due to contradictory statements such as saying that in the end the energy goes into the soil and is taken up by the plants again.

In both (a) and (b) many students drew diagrams, Carbon cycles etc. Some of these aided the explanation, but the majority contributed nothing.

(b)

Describe how plants affect the amount of carbon dioxide in the atmosphere.

[4]

Markscheme
  1. plants reduce the amount of carbon dioxide in the atmosphere by photosynthesis;
  2. carbon dioxide is fixed/converted into organic substances/sugars/ OWTTE;
  3. plants respire which releases carbon dioxide into the atmosphere;
  4. plant decomposition may release CO2
  5. carbon in dead plants is trapped/ stored in fossil fuels / peat
  6. combustion of plants/wood/ fossil fuels adds to the amount of carbon dioxide in the atmosphere;

OR Shows correct equation

Examiners report

In (b) many saw the words 'Carbon Dioxide' and immediately treated it as a long answer on greenhouse gases, thus putting their quality mark in jeopardy for superfluous content. Most were aware of photosynthesis removing CO2 from the atmosphere by fixing it into organic compounds and many mentioned plant respiration as increasing it. However, there were some disturbing answers where students mixed up photosynthesis and respiration. The question was about plants, but many answered in terms of animals.

(c)

Explain how a newly discovered plant species would be classified and named.

[7]

Markscheme

      Naming:

  1. binomial nomenclature / (plant is) given a binomial/double name;
  2. first name is the genus and second name is the species / genus initial upper case and species lower case;
  3. names (of plant species) are international/are universally understood/are published in journals;

    Classification:
  4. study the characteristics/structure/reproduction/chemical properties/DNA (of the plant);
  5. put/classify (the plant) in a group/genus with other similar species;
  6. natural classification corresponds with evolution / natural classification is based on many features;
  7. analogous features/features due to convergent evolution should not be used;
  8. hierarchy of groups/taxa (in traditional classification / 3 or more taxa in correct sequence (kingdom-phylum-class);
  9. two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named;
  10. a clade is a group of organisms evolved from a common ancestor;
  11. base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships;
  12. cladograms show the relationships between clades/likely evolutionary divergence of clades;
  13. each branch point/node represents where species are formed via divergent evolution;
  14. species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa);

Mpi accept common names, mosses, ferns etc.

Examiners report

There were a few G2 comments that part (c) on classification was above the level expected at Standard Level. This part was in common with Higher Level, but did only contain material from the Core (cladistics appears in section 5.4). There were a large number of marking points to score on. The naming was well known, as was classification into taxa and the different plant phyla. Some weaker students tried to go all the way back to eukaryotes and prokaryotes and animalia and plantae, giving far too much superfluous information. Good explanations of the use of clades were seen by better candidates.

Syllabus sections