TOPIC 5 - Nutrient cycles

Question 1

What is nitrogen essential for?

Answer 1

Amino acids
Proteins
Nucleic acids

Question 2

What are the 4 main stages of the nitrogen cycle?

Answer 2

Nitrogen fixing
Feeding
Decomposition
Ammonification
Nitrification/ denitrification

Question 3

What is ammonification?

Answer 3

Nitrogen compounds from dead organisms and animal waste are tuned into ammonia by saprobionts which is then converted to ammonium ions

Question 4

What is nitrification?

Answer 4

Oxidising of ammonium ions into nitrate by nitrifying bacteria
ammonium ion –> nitrite –> nitrate

Question 5

What is nitrogen fixing?

Answer 5

Nitrogen fixing bacteria convert nitrogen into ammonia - forms ammonium ions which plants can use

Question 6

What is denitrification?

Answer 6

Nitrates in the soil are converted to nitrogen gas by denitrifying bacteria (anaerobic conditions e.g. waterlogged soil)

Question 7

What do saprobionts do?

Answer 7

1. Secrete enzymes externally onto dead organisms/waste products
2. Breaks down the biological molecules
3. Absorb SOME of the nutrients

Question 8

What is extracellular digestion?

Answer 8

Enzymes are secreted onto the food and it is digested externally

Question 9

What do mycorrhizae do ?

Answer 9

Their hyphae connect to plant roots and increase the surface area
This helps the plant absorb more ions from the soil/ take up more water

Question 10

What are mycorrhizae?

Answer 10

Fungi which have formed a symbiotic relationship with plant roots
Made up of long thing strands (hyphae) which connect to plant roots

Question 11

What do mycorrhizae get out of their symbiotic relationship with plant roots?

Answer 11

Obtain organic compounds from the plant e.g. glucose

Question 12

How do phosphate ions initially enter ecosystems?

Answer 12

Phosphorous in rocks dissolves in oceans

Question 13

What are the stages of the phosphorus cycle?

Answer 13

1. Phosphate ions released into soil from rocks
2. Plants taken up ions through roots
3. Ions transferred through food chains and lost as waste/death
4. Decomposition

Question 14

What is guano?

Answer 14

Waste produced by sea birds which is very high in phosphate ions

Question 15

How are nutrients lost from ecosystems?

Answer 15

Harvested crops/animals are removed from fields
Mineral Ions not returned to the soil by decomposition of plants/waste by saprobionts

Question 16

What do fertilisers do?

Answer 16

Replace lost minerals so more energy from the ecosystem can be used for growth

Question 17

What is an example of natural fertiliser?

Answer 17

ORGANIC MATTER
Manure, compost, crop residues, sewage sludge

Question 18

What do artificial fertilisers consist of?

Answer 18

INORGANIC
Pure chemicals as powders of pellets

Question 19

What is leaching?

Answer 19

Water soluble compounds in the soil drain into aquatic ecosystems

Question 20

What is eutrophication?

Answer 20

The addition of extra nutrients such as nitrate/phosphate ions to aquatic ecosystems

Question 21

Why is leaching less likely with organic fertilisers?

Answer 21

The ions are contained in biological molecules which need to be decomposed by saprobionts before plants can absorb them

Question 22

What are the 5 stages of eutrophication?

Answer 22

1. Mineral ions leached from fertilised field stimulate rapid growth of algae in ponds/rivers
2. Large amounts of algae block light from reaching plants below
3. Plants cannot photosynthesise enough and die
4. Bacteria feed on dead plants and aerobically respire, reducing oxygen concentration
5. Fish and other orhanisms die due to lack of dissolved oxygen