3.5.4 - Nutrient Cycling

Question 1

What is a saprobiont?

Answer 1

They feed on the remains of dead plants and animals. They secrete enzymes and digest food externally, then absorb the nutrients they need.

Question 2

What are hyphae?

Answer 2

Long, thin strands that make up the fungi.

Question 3

What is a symbiotic relationship

Answer 3

A relationship where two organisms of different species interact.

Question 4

What do plants and animals use nitrogen for?

Answer 4

Making proteins and nucleic acids.

Question 5

What is nitrogen fixation?

Answer 5

When nitrogen gas in the atmosphere is converted into nitrogen-containing compounds.

Question 6

What are Rhizobium?

Answer 6

Bacteria found in root nodules of leguminous plants. They turn nitrogen into ammonia.

Question 7

What is ammonification?

Answer 7

When nitrogen compounds are turned into ammonia. This ammonia then forms ammonium ions.

Question 8

Define nitrification

Answer 8

Ammonium ions in the soil are changed into nitrogen compounds that can be used by plants (nitrates).

Question 9

Name a bacteria that converts nitrites into nitrates.

Answer 9

Nitrobacter

Question 10

Name a bacteria that converts ammonium ions into nitrites.

Answer 10

Nitrosomas

Question 11

What term is used to describe the conversion of nitrates in the soil into nitrogen gas.

Answer 11

Denitrification

Question 12

Why does denitrification occur in waterlogged soils?

Answer 12

Because denitrifying bacteria need anaerobic conditions to convert nitrates into nitrogen gas.

Question 13

How does nitrogen get into an ecosystem?

Answer 13

By lightning, and artificial fertilisers.

Question 14

Name 4 things plants and animals need phosphorus for?

Answer 14

1. phospholipids
2. DNA
3. RNA
4. ATP

Question 15

How does phosphate get into the soil?

Answer 15

Phosphate ions in rocks are released into the soil by weathering.

Question 16

When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake.

(a) (i) Describe how the nitrogen-containing substances get into the lake.

.

Answer 16

dissolve (in soil water) / run-off / leaching

Question 17

Describe how the presence of nitrates in a lake may eventually lead to the death of fish

Answer 17

1. increased growth / algal bloom
2. blocks light; less photosynthesis; plants die;
3. increase in decomposers / bacteria;
4. bacteria respire so less oxygen;

Question 18

It is estimated that, each year, a total of 3 × 109 tonnes of ammonia are converted to nitrate. Only 2 × 108 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures.

Answer 18

1. Ammonia formed by decay of nitrogenous waste by decomposition.
2. by action of decomposers / saprobionts;

Question 19

Describe the role of microorganisms in producing nitrates from the remains of dead organisms.

Answer 19

1. Saprobiotic (microorganisms / bacteria) break down remains into ammonia / ammonium;
2. Ammonia / ammonium ions into nitrite and then into nitrate;
3. (By) Nitrifying bacteria / nitrification;