Module 5- Nutrient cycle

Question 1

What are saprobionts?

Answer 1

They are a type of bacteria that break down dead organisms or waste material.
They are also involved in extracellular digestion.

Question 2

2 marks

Describe the role of saprobionts in the nitrogen cycle

Answer 2

1. They use enzymes to decompose proteins, DNA, RNA, ATP, urea
2. Producing ammonium ions

Question 3

What are the 4 key stages in the nitrogen cycle?

Answer 3

Nitrogen fixation, ammonification, nitrification and denitrification

Question 4

Explain what nitrogen fixation is

Answer 4

This is when mutualistic nitrogen fixing bacteria breaks down the nitrogen gas from the atmosphere into ammonia. This then gets broken down to form ammonium ions. Some bacteria can be found in root nodules of leguminous plants

Question 5

What is nitrogen fixation

Answer 5

• Atmospheric nitrogen gas is converted into nitrogen-containing compounds
• This biological nitrogen fixation is carried out by nitrogen-fixing bacteria
• The bacteria convert nitrogen into ammonia, which forms ammonium ions that can then be used by plants
• These nitrogen-fixing bacteria are found inside the root nodules of leguminous plants such as peas, beans and clover
• The bacteria have a symbiotic (mutually beneficial) relationship with these plants - the bacteria provide the plants with nitrogen-containing compounds and the plants provide the bacteria with organic compounds such as carbohydrates

Question 6

Explain what ammonification is

Answer 6

This is when saprobionts break down dead organisms or waste material into ammonia. These then get turned into ammonium ions.

Question 7

Explain what nitrification is

Answer 7

This is when nitrification converts ammonium ions in the soil into nitrogen compounds that can be used by the plant. These are turned coverted nitrites. The, another bacteria will turn these into nitrates which can be used by the plant

Question 8

Explain what denitrification is?

Answer 8

This is when denitrifying bacteria breaks down nitrates into nitrogen gas. This happens under anaerobic conditions

Question 9

What can inhibit nitrogen fixation

Answer 9

The presence of oxygen inhibits nitrogenase.
Inhibits nitrogen fixation process

Question 10

What is the phosphorus cycle?

Answer 10

This is the recycling of phosphate

Question 11

2 marks

Suggest and explain why a poor supply of phosphate ions results in poor growth of plants

Answer 11

1. Required to make ATP, so less respiration for growth;
2. Required to make nucleotides, so less DNA for cell division for growth
3. Required to make RuBP / NADP, so less CO2 fixed
4. Required to make phospholipids for membranes
   5.Required to make nucleotides, so less RNA for production of protein for growth

Question 12

3 marks

Why are mycorrhizae beneficial for plant growth

Answer 12

1. The fungi increases surface area for water and mineral aborportion
2. Acts like a sponge so holds water and minerals around the roots
3. Makes plants more drought resistant and able to take up more inorganic ions

Question 13

What does assimilated mean?

Answer 13

Absorbed and then used to make more complex molecules

Question 14

The first stage of the phosphate cycle is weathering. What is this?

Answer 14

This is when rocks are broken down which causes the release of phosphate ions into the soil. These are then taken up by planta through the mycorrhizae.

Question 15

ways the UK is actually trying to reduce absolute and relative poverty

What are mycorrhizae

Answer 15

This is a form of symbiotic relationship which is when long thin filaments attach to the roots of plants - known as hyphae which increase the rate of absorption of water and ions

Question 16

What is the second stage of the phosphorus cycle?

Answer 16

The phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.

Question 17

How can phosphate ions get lost through organisms?

Answer 17

They can be lost through excretion or when organisms die, saprobionts will break dowm the organisms causing the release of phosphate ions into the soil

Question 18

How can aquatic producers obtain phosphate ions?

Answer 18

Weathering of rocks releases phosphate ions into the sea, lake and rivers. These phosphate ions can be taken up by aquatic producers and passed along the food chain

Question 19

An example of a natural fertiliser and how this can be used to give phosphate back into soil and rocks.

Answer 19

Bird faeces is known as guano and contains a high proportion of phosphate ions back into the soil which can therefore be used as a natural fertiliser

Question 20

How can harvesting remove nutrients?

Answer 20

When plants and animals are harvested. This prevents them from decomposing in the fields and therefore nitrogen and phosphate cannot be returned back into the soil. Furthermore, animal excretion is removed from the soil.

Question 21

What is an example of a natural fertiliser

Answer 21

Manure and compost

Question 22

What is an example of an artificial fertiliser?

Answer 22

Made out of chemicals containing the correct proportions of ions needed

Question 23

What is leaching?

Answer 23

This is when water-soluble compounds in the soil are washed away into near by waterways

Question 24

Why is leaching less likely to occur in natural fertiliser?

Answer 24

Natural fertiliser has to be decomposed by saprobionts and therefore uptake by plants is more controlled then artifical fertilisers

Question 25

Which ion is more likely to be leached and why?

Answer 25

Nitrates because they are less soluble in water

Question 26

Explain the 5 steps of eutrophication?

Answer 26

Minerals are leached from fertilised fields which stimulate rapid growth of algae.
Large amounts of algae block the light
The plants die because they cannot receive light for photosynthesis
Bacteria feed on dead matter and reduce oxygen conc because they respire.
Fish and other organisms die because there isnt enough oxygen

Question 27

Why may too much artificial fertiliser cause a reduction in crop yield?

Answer 27

The water-soluble minerals inside the fertiliser will create a lower water potential in the soil around the plant. This will cause water to move out into the soil from the plant, killing it

Question 28

1 mark

Give one advantage of using natural fertiliser produced in the digester rather than an artifical fertiliser

Answer 28

1. Improves drainage/ increases organic content of soil
2. Contains wider range of elements
3. Production of artificial fertiliser energy-consuming
4. Less leaching