Question 21N.2.SL.TZ0.3
| Date | November 2021 | Marks available | [Maximum mark: 10] | Reference code | 21N.2.SL.TZ0.3 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Compare and contrast, Draw, Explain, State | Question number | 3 | Adapted from | N/A |
Compare and contrast the mode of nutrition of detritivores and saprotrophs.
[2]
Accept not autotrophic/not photosynthetic instead of heterotrophic.
Do not accept that both groups are decomposers or consumers for the similarity.
Knowledge of detritivores and saprotrophs was good in 3a, with many of the poorer answers describing them as feeding on inorganic material.
The image shows an example of a soil food web.
[Source: Anon., n.d. The Soil Food Web. [image online] Available at: https://www.nrcs.usda.gov/wps/portal/nrcs/
photogallery/soils/health/biology/gallery/?cid=1788&position=Promo [Accessed 11 March 2020].]
Draw a food chain from this food web, showing at least three organisms.
[1]
food chain of three or more organisms starting with plants;
Many took the word ‘draw’ literally in the food chain, and the drawings of the nematodes and fungi amused the examiners. A food chain must start with a plant. The stem did say “three organisms”. Detritus was not taken as an organism, so negated the mark.
Explain the reasons for food chains rarely containing more than four or five trophic levels.
[3]
a. energy is lost between the trophic levels;
b. transfer between levels is only usually 10% efficient
OR
energy transformations take place in living organisms / the process is never 100% efficient;
c. energy is lost by the organism/used in respiration / released as heat/movement;
d. energy is lost as waste/feces/urine/undigested food/uneaten parts;
e. as energy is lost between trophic levels and so (higher ones) have less biomass / less biomass available for next level;
Most were able to gain at least two marks for the explanation of energy loss through the trophic levels.
The amount of food passing into food chains can be affected by the rate of photosynthesis. Explain the effect of one limiting factor on photosynthesis.
[3]
a. the rate of reaction will be limited by the limiting factor that is nearest to its minimum value;
temperature:
b. enzymes that control photosynthesis are influenced by temperature;
c. as temperature increases, reaction rate will increase;
d. above a certain temperature, the rate of photosynthesis will decrease;
e. (where temperature is limiting) essential enzymes begin to denature/not working to optimum;
light intensity:
f. light is source of energy / converted into chemical energy;
g. as light intensity increases reaction rate will increase;
h. at a certain light intensity, rate of photosynthesis will plateau;
i. another factor becomes limiting;
CO2 concentration:
j. CO2 is fixed to form organic molecules;
k. as CO2 concentration increases, reaction rate will increase;
l. at a certain concentration of CO2, rate of photosynthesis will plateau;
m. another factor becomes limiting;
Accept answers using an annotated graph to explain
Only accept the first factor described
Do not accept pH as a limiting factor
In 3c, most knew that temperature/CO2 concentration/light affect photosynthesis but could not explain the idea of acting as a limiting factor. Only the better students gained all 3 marks.
All of the leaves in the image are from Solanum, a wild genus of tomato.
[Source: Courtesy: National Science Foundation, Credit Leonie Moyle.]
State one cause of variation in a plant such as the tomato.
[1]
a. mutations;
b. meiosis/crossing over/random assortment of homologous pairs;
c. sexual reproduction/recombination/random fertilisation;
In 3d there was a great deal of variety in the leaf shape, so an answer in terms of sexual reproduction was looked for.
