DP Biology (last assessment 2024)

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Question 23M.2.SL.TZ1.7

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Date May 2023 Marks available [Maximum mark: 15] Reference code 23M.2.SL.TZ1.7
Level SL Paper 2 Time zone TZ1
Command term Describe, Discuss, Outline Question number 7 Adapted from N/A
7.
[Maximum mark: 15]
23M.2.SL.TZ1.7

Plant species discovered in wild habitats are named and classified by taxonomists. Some plants have been genetically modified to make them more suitable for use by humans.

(a)

Describe how plants are named and classified, including recognition features of plant phyla.

[7]

Markscheme
  1. binomial naming
    OR
    genus and species name;
  2. plants constitute a kingdom
  3. plants are eukaryotes/belong to the domain eukaryota
  4. classified using a hierarchy of taxa
    OR
    kingdom, phylum, class, order, family, genus, species
  5. bryophyta/filicinophyta/coniferophyte/angiospermophyta is a phylum (of plants);
  6. bryophytes have only rhizoids/spores (produced in a capsule)/no roots/ no vascular tissue;
  7. filicinophytes have stems/roots/xylem-phloem/reproduce by spores/leaves that uncurl; but no seeds
  8. coniferophytes have seeds in cones/ vascular tissue/xylem-phloem/cambium/ but no flowers/no fruits
  9. angiospermophytes have flowers/produce seeds/produce fruits/vascular tissue/xylem-phloem;
  10. named example showing of the classification of a plant from species to domain or vice versa
  11. cladistics is used to reclassify groups of plants
    OR
    named example of a group of plants reclassified by cladistics;
  12. use a dichotomous key to discriminate among plant features

 

Each phylum of plants requires at least 2 features for the mark.

Mp-e does not require all 4 phyla to be named.

Examiners report

The most challenging part of the question was (a). Although successful candidates characterized the 4 phyla with examples, many did not seem to realize that this component was expected of the question. Most answers contained information about binomial nomenclature and some answers included the divisions in the hierarchy. There was virtually no mention of cladistics. A few candidates wrote about animals. If candidates had paid attention to the number of marks expected, they might have included more information and earned more of the marks.

(b)

Outline the stages of the carbon cycle that involve plants or materials made by plants.

[5]

Markscheme
  1. absorption/diffusion of carbon dioxide from the atmosphere/water by plants;
  2. photosynthesis fixes/converts carbon (dioxide) to carbohydrates/carbon compounds;
  3. respiration in plants converts carbohydrates/carbon compounds to carbon dioxide;
  4. saprotrophs/detritivores digest dead plants/plant matter releasing carbon/carbon dioxide;
    OR
    decomposition returns carbon to the soil/releases CO2 to atmosphere/water/environment
  5. peat forms when decomposition of dead plant matter is incomplete storing carbon/ creating a reservoir;
    OR
    fossilization of carbon stores carbon as coal/oil/natural gas;
  6. forest fires/combustion of plants converts (carbohydrates/carbon compounds) to carbon dioxide;
  7. plants are eaten by consumers (moving carbon in the food chain)
  8. humans use plant products for making cloth/household items/building/arts creating a reservoir for carbon
    OR
    Humans burn fossil fuels releasing CO2;
  9. Plants act as carbon sinks/reservoirs

 

Carbon may be used in place CO2 an carbohydrates

Examiners report

(b) was challenging to the same degree that (c) was. In answers to (b), photosynthesis by plants and respiration by animals was stated even though the question asked about plants not animals. Many candidates wrote about photosynthesis but that it makes oxygen rather than carbon compounds. The most successful answers included the use of carbon (CO2) to make carbon compounds which can be passed up the food chain. Other marking points were variously earned.

(c)

Discuss briefly the potential risks and benefits of the genetic modification of crop plants.

[3]

Markscheme

Award [2 max] for risks and [2 max] for benefits.


Risks:

a. harm to a wild species because the GMO might out compete the wild species removing it from the ecosystem / example of harm to a wild species;

b. spread of the transferred gene has resulted in farmers being sued for growing GMOS without permission / other example

c. consumer resistance to genetically modified crop plants can result in countries experiencing famine not accepting seeds from aid organizations / other reason;

d. some nutritional improvements may result in allergens being introduced;

e. resistance to herbicides is used to kill weeds around crops and this herbicide can cause damage from overspray;


Benefits:

f. higher yields can feed more people / other value;

g. resistance to pests because less pesticide use results;

h. resistance to herbicides results in farmers being able to use herbicides to kill weeds without causing damage to the crops;

i. improved nutritional quality / example of improved nutritional content/shelf life;

j. increased tolerance to drought/salinity allows yields in places where crops were previously unsuccessful;

k. reducing land use for crops makes the land available for other uses;

 

Risk or benefit must be supported to earn the mark.

Other supported risks or benefits may be accepted.

Examiners report

Candidates seem to be concerned about the issues surrounding use of GMOs. Risks and benefits were listed, but how the benefit was a benefit was required as this question had the command term discuss. Some answers were insightful, but many contained seriously erroneous information.

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