Exam Questions for Ecological Cycles

Question 1

With reference to an example, explain what is meant by carbon sink. (2 marks)

Answer 1

1. Takes up/locks up CO2 for a long time

2. E.g.peat/coal/limestone/trees/fossil fuel/chalk/ shells

Question 2

Pouring a dilute solution of washing up liquid on soil causes earthworms to come to the surface. Describe how you could use this technique to compare the population density of earthworms in different habitats. (3 marks)

Answer 2

1. Quadrats
2. Large sample
3. Calculate a mean

Question 3

Burrows produced by earthworms improve drainage and aeration of of the soil. Suggest how theesse burrows help to increase the rate of leaf decompsitiion. (2 msarks)

Answer 3

1. Provides oxygen for aerobic respiration

2. By bacteria/microorgansms

Question 4

Apart from affecting the number of earthworms, suggest how a decrease in the ph of the soil slows down the rate of leaf decomposition. (2 marks)

Answer 4

1. Fewer bacteria/decomposers
2. Acid conditions inhibit enzymes/enzymes denatured
3. H+ ions affects enzymes active site

Question 5

How is carbon dioxide removed form the air into the oceans? (2 marks)

Answer 5

1. Carbon dioxide dissolves in the oceans
2. For carbon-fixation/light-dependetn reaction
3. By photosynthesis of seaweed

Question 6

How is CO2 returned to the air from the ocean? (1 mark)

Answer 6

1. Decomposition/respiration

Question 7

Describe the role of bacteria in decomposition? (3 marks)

Answer 7

1. Decomposition/breakdown of organic material
2. Bacteria produces enzymes for digestion.
3. Respiration of bacteria produces CO2

Question 8

Suggest why more carbon is entering the air than leaving it. (3 marks)

Answer 8

1. The rate of productioin of CO2 is greater than the rate of removal of CO2.
2. Using fossil fuels releses CO2.
3. This carbon in fossil fuels was locked up years ago.
4. Deforestation results in less photsynthesis/carbon fixation

Question 9

Explain why there is a decrease in the mass of the leaves. (4 marks) 7 points

Answer 9

1. Bacteria release enzymes for decomposition
2. Formation of monomers/glucose/amino acids
3. That are soluble/dissolve
4. Some soluble molecules soak into the ground/ taken up by organisms.
5. respiration of glucose by decomposers
6. CO2 released
7. Water evaporates from the leaves
8. Animals eat the leaves.

Question 10

What effect would increasing the temp have on the rate of decomposition? (4 marks)

Answer 10

1. Increasign the temp would increase the rate of decomposition.
2. Enyzmes are involved in decompostion
3. Increase in ke results in an increas in number of collisions between enzymes and substrates.
4. Increased temp increases rate at which bacteria increase.
5. Above a certain temp teh rate of decmopsiton wold stop/decrease.
6. At higher temps enzymes become denatured. OR bacteria killed.

Question 11

When leaves are added to compost heaps, explain why it is important that the compost is not allowed to become waterlogged or compacted? (2 marks) 4 points

Answer 11

1. The conditions in the soil need to be anaerobic
2. As aerobic respiration is not possible.
3. For denitrifying organisms
4. to turn nitrogen compounds into nitrogen

Question 12

Suggest how woodlice are involved in the recycling of carbon. (3 marks)

Answer 12

1. Ref to carbon compunds in plant material
2. Idea that digestion provides respiratory substrates
3. CO2 released from respiration
4. This CO2 is available for photsynthesis.
5. Woodlice eaten/decompose

Question 13

Suggest 2 abiotic factors that might influence behaviour and distribution of woodlice in her garden. (2 marks)

Answer 13

1. Temp

2. Air currents/wind

Question 14

Suggest why taking photos is a sutiable method of counting woodlice. (1 mark) (3 points)

Answer 14

1. Woodlice move about
2. So are difficult to count
3. Some might be counted more than once

Question 15

Explain why it would be difficult to determine which abiotic factor is influencing the behaviour and distribution of the woodlice in a garden environment.
(3 marks) (6 points)

Answer 15

1. For results to be scientifically valid
2. Only 1 factor needs to be varied
3. Other factors need to be kept constant.
4. Ref to many biotic factors in the garden
5. These factors are difficult to control
6. Difficult to set test factor values.

Question 16

Each year a total of 310^9 tonnes of ammonia are converted to nitrate. Only 210^8 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures. ( 2 marks)

Answer 16

1. Ammonia formed by decay/ by action of of decomposers/saprobionts
2. on nitrogenous waste/urea or nitrogen compounds(e.g proteins, amino acids)

Question 17

Conversion of ammonia to nitrate involves oxidation. (1 mark)

Answer 17

1. Oxidation added/hydrogen removed

Question 18

Explain why the roots of Papillionaceae, such as peas and beans, are ploughed into the soil before planting a different crop. (2 marks) (3 points)

Answer 18

1. Root nodules contain nitrogen fixing bacteria.
2. Therefore mroe ammonia/more nitrogen compounds are available
3. So less fertiliser is needed.

Question 19

Explain why soil needs to be well drained to avoid waterlogging. (2 marks)

Answer 19

1. Waterlogging creates anaerobic conditions
2. Denitrifying bacteria is more active in low oxygen conditions while nitrifying bacteria is less active in low oxygen conditions.
3. This leads to reduction of ammonia in the soil/fewer nitrates available for plants.

Question 20

Describe the process of denitrification. 2 marks

Answer 20

1. Covnersion of nitrates or any nitrogen containng compound into nitrogen gas
2. By denitrifying bacteria

Question 21

Exaplain how the digestion of insects help a venus flytrap’s to obtain additional nitrogen compounds. (2 marks)

Answer 21

1. Insects contain proteins
2. Digested to amino acids
3. Which can be absorbed/diffuse into the leaf

Question 22

In plant tissue ratio of carbon to nitrogen was 40:1. In animal tissue ration was 8:1. Explain why the ratio is much higher in the plant tissue than in the animal tissue. (2 marks)

Answer 22

1. High proportion of carbs/starch in plant tissues
2. Cellulose in cell walls
3. More protein in animal cells such as muscle

Question 23

Describe how nitrogen in compounds in a dead plant is made available for use by other plants. (6 marks)

Answer 23

1. Proteins/amino acids are broken down
2. by saoprobionts/decomporsers
3. To form ammonia
4. Ammonia is then converted to nitrate
5. By nitrifying bacteria
6. Nitrite is an intermediate
7. Nitrate can be absorbed by roots

Question 24

Leguminous crop plants have nitrogen-fixing bacteria in their root nodules. On soils with a low conc of nitrate ions, leguminous plants grow better than other crops. Explain why. (2 marks)

Answer 24

1. They can convert nitrogen gas into ammonia (and then to nitrate)
2. Which produces protein/amino acids

Question 25

Applying very high conc of fertiliser to the soil can reduce plant growth. Use your knowledge to explain why. (2 marks)

Answer 25

1. Soil will have lower water potential due to the fertilisers and the roots will have a higher water potential.
2. Osmosis from plant/ water diffusion from plant

Question 26

Describe how microorganisms produce nitrates. (3 marks)

Answer 26

1. Oxidation
2. of ammonia/ammonium to nitrate
3. via nitrite
4. by nitrifying bacteria

Question 27

Describe how microorganisms produce nitrogen gas. (2 marks)

Answer 27

1. Reduction
2. Of nitrates to nitrogen gas
3. By denitrifying bacteria

Question 28

Explain whats meant by biomass. (1 mark)

Answer 28

1. Mass of organisms/mass of organic material

Question 29

Name and describe the process by which ammonium compounds are converted into nitrates in well-aerated soil. (4 marks)

Answer 29

1. Nitrification/ref to nitrifying bacteria
2. Ammonia/ammonium into nitrite
3. by Nitrosomonas
4. Nitrite to nitrate
5. by nitrobacter