Nutrient cycles

Question 1

Name 4 substances that animal cells require a source of nitrogen to make.

Answer 1

DNA and RNA
Amino acids and Proteins
NAD and NADH
ATP

Question 2

What is nitrogen fixation?

Answer 2

Nitrogen gas is converted into ammonia/nitrate

Question 3

Name the bacteria that carry out nitrogen fixation

Answer 3

Nitrogen fixing bacteria

Question 4

Where are nitrogen fixing bacteria found?

Answer 4

Free in the soil
In root nodules of legumes

Question 5

What does the term symbiotic relationship mean?

Answer 5

Two organisms of different species interact

Question 6

What does the term mutualistic relationship mean?

Answer 6

Two organisms of different species interact.
Both organisms benefit from the relationship

Question 7

Give the main benefit

Answer 7

Nitrogen fixing bacteria - gain protection in the nodule and a source of organic substances from the plant
Plant gains a source of ammonium/nitrate ions

Question 8

What is ammonification?

Answer 8

Formation of ammonium ions from organic material (eg urea, faeces, dead organisms)

Question 9

Name the organisms that cause ammonification

Answer 9

Saprobiontic bacteria

Question 10

What is nitrification?

Answer 10

Conversion of ammonium ions into nitrites and then nitrates

Question 11

Name the organisms that cause nitrification

Answer 11

Nitrifying bacteria

Question 12

What is denitrification?

Answer 12

Conversion of nitrates in the soil into nitrogen gas

Question 13

Why does dentification take place in waterlogged soils

Answer 13

Denitrifying bacteria require anaerobic conditions.
No air pockets in the soil when saturated with water

Question 14

Name 4 biological molecules that contain phosphate

Answer 14

Phospholipids
DNA
RNA
ATP

Question 15

How do phosphates get into the soil

Answer 15

Weathering of rocks containing phosphate minerals

Question 16

Describe how phosphates or nitrates can get into water bodies

Answer 16

Dissolve in rain water
Leached/run off into the water body

Question 17

Name the process that causes the death of fish in water containing lots of phosphates and nitrates

Answer 17

Eutrophication

Question 18

Describe how the presence of nitrates/phosphates cause the death of fish

Answer 18

Leached into water body
Causes increased growth of algae (algal bloom)
As lack of nitrates and phosphate was a factor limiting their growth
Blocks light so less photosynthesis of plants which causes death of plants
Increase in number of decomposers/bacteria
Increased respiration by bacteria
Reduces oxygen content of water
Anaerobic bacteria increase, releasing toxin into water
Fish die

Question 19

Outline the role of mycorrhizae

Answer 19

Mutualistic relationship between plants and fungus
Increases the surface area for absorption of minerals and water by roots.

Question 20

Give 3 benefits of planting a different crop in the same field each year

Answer 20

Nitrogen fixing crops increase soil nitrate content
Different crops have different pathogen
Different crops removed different proportions of ions

Question 21

Why do farmers add fertiliser to their fields?

Answer 21

Increase primary productivity
More minerals for plant growth

Question 22

What is an organic fertiliser?

Answer 22

Derived from living organisms
eg manure, slurry

Question 23

What is an inorganic fertiliser?

Answer 23

Manufactured fertiliser
Ammonium nitrate

Question 24

Why are organic fertiliser better than inorganic fertilisers?

Answer 24

Minerals released at a slower rate
Minerals available for longer
Less likely to be leached from the soil
Improves soil structure

Question 25

Why are inorganic fertilisers better than organic fertilisers?

Answer 25

Control proportion of nitrates, phosphates and potassium added to the soil