The Nutrient Cycle

Question 1

Describe how action of microorganisms in soil produces source of nitrates

Answer 1

1. protein/AA/DNA converted into ammonium compounds
2. by saprobionts
3. ammonia into nitrile
4. nitrile to nitrate
5. by nitrifying bacteria
6. nitrogen gas to ammonia
7. by nitrogen fixating bacteria

Question 2

Describe the role of saprobionts in the nitrogen cycle

Answer 2

• use enzymes to decompose proteins
• releasing ammonia

Question 3

Explain how carbon-containing compounds present in the pine leaves that fall from the trees are absorbed and used for growth by saprobionts/fungi that live in the soil.

Answer 3

• extracellular digestion;
• by secretion of enzymes;
• absorption of digested products
• synthesis of structural compounds
• respiration provides energy for growth

Question 4

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

Describe the role of microorganisms in this process.

Answer 4

• proteins broken down
• ammonification
• By saprobionts
• conversion to nitrates via nitrites;
• by nitrifying bacteria
• nitrates absorbed into roots via active transport

Question 5

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.

Answer 5

1. Amino acid
2. DNA
3. RNA
4. ATP

Question 6

Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant.

Answer 6

• production of phospholipids;
• in cell membranes;
• synthesis of ATP;
• production of DNA;
• production of RNA;
• production of NADP

Question 7

Describe how a lack of phosphates in the soil surrounding a plant can affect its growth

Answer 7

• make ATP, so less respiration
• make nucleotides, so less DNA
• make RuBP, so less CO2 fixed
• make phospholipids for membranes

Question 8

Phosphorus Cycle

Answer 8

1. phospholipids, RNA, DNA from dead organisms into phosphate ions
2. Decomposed by saprobionts
3. Phosphate ions also found in wastes and remains eg. bones / shells
4. phosphate ions are transported by streams, rivers lakes/oceans
5. form sedimentary rock
6. weathering/ erosion of rocks helps phosphate ions dissolve in oceans, lakes, soil
7. phosphate become available for absorption by plants to incorporate into biomass

Question 9

Leaching

Answer 9

Inorganic fertilisers result in more ions applied to the soil than are actually taken up by the plants. This leads to leaching, the ions dissolve in soil water and are washed into streams, rivers and lakes

Question 10

Reduced species diversity

Answer 10

Plants which are adapted to soils with high in Nitrate concentration outcompete other species.

Question 11

Eutrophication

Answer 11

• Nitrates washed away into water
• High concentration of ions causes rapid growth of algal bloom
• Algae block light = less photosynthesis
• Algae die
• Plants that can’t photosynthesise under the surface also die off
• Large increase in population of saprobionts = respiration rate increases
• Bacteria reduce Oxygen concentration of the water
• Oxygen levels depleted resulting in death of other aerobic organisms

Question 12

Outline the advantages of having Mycorrhizae growth near plants

Answer 12

• Mycorrhizae help plants to defend themselves
• Mycorrhizae help plants to take up nitrates/phosphates

Question 13

How do microorganisms make carbon in polymers in dead worm available to cells in a leaf?

Answer 13

1. microorganisms are saprobionts
2. secrete enzymes
3. adsorb products of digestion
4. respiration produces CO2
5. CO2 taken into leaves
6. through stomata

Question 14

Explain what is meant by the term carbon sink.

Answer 14

• Takes up carbon / carbon dioxide (for a long time)
• e.g. coal

Question 15

Explain what is meant by the term global warming.

Answer 15

• Increase in temperature of earth’s surface
• due to an increase in greenhouse gases
• trap heat in the atmosphere
• enhanced greenhouse effect
• leads to climate change

Question 16

The scientists used units of μg g−1 for the concentration of ammonia in soil.
Suggest why, in this investigation, the scientists used these units.

Answer 16

• (μg because) very little ammonia (in soil);
• (μg because) avoids use of (lots of) decimal places (in their results) / avoids the use of powers of 10 / avoids the use of standard form /makes numbers more manageable / Accept makes easier to plot graph
• (g-1) to allow comparisons (between samples);