The Nutrient Cycle

Question 1

What is the nutrient cycle?

Answer 1

Nutrients are recycled within the natural ecosystems between the abiotic and biotic phases where they exist as inorganic or organic compounds

Question 2

Why is nitrogen needed?

Answer 2

Component of DNA, RNA, ATP, ADP, amino acids, proteins

Question 3

What are the 4 stages of the nutrient cycle?

Answer 3

1) Nitrogen Fixation
2) Nitrification
3) Saprobiotic Digestion
4) Denitrification

Question 4

What happens during nitrogen fixation?

Answer 4

Nitrogen fixing bacteria reduce N2 into NH3/NH4+
Bacteria live in legumes or in the soil
Symbiotic relationship between bacteria and plant

Question 5

What happens during nitrification?

Answer 5

Nitrifying bacteria oxidise NH4+ into nitrites and they are oxidised into nitrates
Plants uptake the nitrates via active transport through the roots

Question 6

What happens during symbiotic nutrition?

Answer 6

Organisms die, excrete urea, or egest faeces
Decomposed by saprobionts
NO3- coverts to NH4+
Extracellular digestion (s excrete enzymes on detritus)
NH4+ either absorbed by bacteria or dissolves in soil

Question 7

What happens during dentrification?

Answer 7

Loss of NO3- from soil into N2
Via denitrifying bacteria
Aerating soil reduces denitrification

Question 8

What is a symbiotic relationship?

Answer 8

A mutually beneficial relationship

Question 9

Give an example of a symbiotic relationship.

Answer 9

Nitrogen-fixing bacteria on legumes and plants

Question 10

Why is nitrogen gas useless to plants?

Answer 10

It is inert so would not be taken up by plants

Question 11

Why is phosphorous required?

Answer 11

Component of the biological molecules, phospholipids, ATP, nucleic acids

Question 12

What happens during the phosphorous cycle?

Answer 12

1) Saprobionts decompose dead animals, plants, and algae via extracellular digestion
2) The bacteria absorb the products of digestion and release PO4- back into the soil, water, river, and lakes where it dissolves
3) Plants absorb the PO4- to make biological compounds such as phospholipids
4) PO4- is passed along the food chains where it is absorbed and assimilated
5) Some dissolved PO4- in the ocean form sedimentary rocks which can only enter the cycle if geographical upheaval and erosion occurs

Question 13

What are mycorrhizae?

Answer 13

Fungi that grow with association on the plant roots
They produce hyphae which provide a large surface area for increased absorption of mineral ions and H2O
Plant provides fungi with sugars

Question 14

Why do we need fertilisers?

Answer 14

Mineral ions are not replaced in the soil due to intensive harvesting of crops
Plants are not left to die and decompose so minerals are not recycled

Question 15

What are natural fertilisers?

Answer 15

Made of organic plant or animal matter containing organic compounds

Question 16

What are artificial fertilisers?

Answer 16

Manufactured, with a mineral ion concentration inorganic compound

Question 17

What is leaching?

Answer 17

Excess ions from fertiliser are washed away from the soil by the rain into lakes and rivers
Leading to eutrophication

Question 18

What is eutrophication?

Answer 18

Excess mineral ions wash away into rivers and lakes
Causes excess growth and an algal bloom absorbs and blocks sunlight
Reduced rate of photosynthesis in plants leads to reduced production of oxygen and death of plants
Algae start to die out due to an increase in competition
Saprobionts decompose dead plants leading to an increased rate of aerobic respiration so increased uptake of oxygen
Decreased concentration of dissolved oxygen for aquatic life