energy transfers and the nutrient cycle

Question 1

one farming practice used to maintain high crop yields is crop rotation

This involves growing a different crop each year in the same fields
Suggest two ways in which crop rotation may lead to high crop yields

Answer 1

1. it allows different nutrients to enter the soil
2. grow crops/ plants with nitrogen-fixing bacteria
3. different pests/ pathogen

Question 2

explain why the scientist sterilised the surface of the seeds and for them in soil that had been heated to 85 C for 2 days

Answer 2

1. to kill any bacteria on the surface of the soil

2. so only the fungus has any effect on the growth of the plant

Question 3

explain why it was important that the soil contained no mineral ions useful to the plants

Answer 3

1. so only the type of fertiliser effects growth

Question 4

Explain how groups A and C act as controls

Answer 4

1. so the effect of the nitrate or the ammonium could be seen
2. so that the effect of the fungus could also be seen

Question 5

suggest what the scientist should have done during the drying process to be sure that all the water gad been removed from the plant

Answer 5

weigh samples at intervals during drying

to see if weighing becomes constant by 3 days

Question 6

applying a very high concentration of fertiliser to the soil can reduce plant growth

Use your knowledge of water potentials to explain why

Answer 6

soil has lower wp than the roots

osmosis from the plant’s roots into the soil

water is used in important metabolic processes

Question 7

during the dry season, the PROTEIN of the plants decreases.

Suggest one way in which a lack of rain could account for this charge

Answer 7

as it is talking about PROTEINS you must refer to nitrates

fewer nitrates are taken up
so less protein synthesis

Question 8

explain how including leguminous plants in a crop rotation reduces the need to use artificial plants

Answer 8

Leguminous plants contain nitrogen-fixing bacteria in their roots

so they don’t need extra compounds added to the soil

Question 9

If scientists could transfer the gene that codes for nitrogenase to cereal plants, these cereal plants would be able to fix nitrogen. However, scientists would expect these genetically engineered cereal plants to grow more slowly than cereal plants that get their nitrogen from fertiliser.

Explain why they would grow more slowly

Answer 9

ATP used for nitrogen fixation
so less ATP is available for growth

one thing limits the growth of another thing

Question 10

explain how farming practices increase the productivity of agricultural crops

Answer 10

1. Fertilisers / minerals / named ion (added to soil);

Accept any named examples of natural fertilisers for mark point 1 e.g. manure, bone meal etc. Ignore named elements

2. Role of named nutrient or element e.g. nitrate / nitrogen for proteins / phosphate / phosphorus for ATP / DNA;

Accept fertilisers / minerals / named nutrient / element removes limiting factor for mark point 2

3. Selective breeding / genetic modification (of crops);

Accept idea of choosing particular variety of crop for mark point 5

4. Ploughing / aeration allows nitrification / decreases denitrification;
5. Benefit of crop rotation in terms of soil nutrients / fertility / pest reduction;

Question 11

Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in spring

Describe the role of microorganisms in this process

Answer 11

Saprobinats break down proteins and the ammonium ions are released into the soil by saprobiansts

The ammonium ions are oxidised to nitrates by nitryfing bacteria

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