Nutrient Recycling

Question 1

what are the 3 key processes in nutrient recycling?

Answer 1

1) uptake - eg through roots
2) feeding - eg eating other plants/animals
3) decomposition

Question 2

what are saprobionts? what do they do?

Answer 2

micro-organisms involved in decomposition

• bacteria
• fungi

they decompose dead material (detritus) and faeces.

Question 3

what is extracellular digestion?

Answer 3

saprobionts secrete digestive enzymes (eg proteases) and absorb the products of digestion (eg amino acids)

Question 4

what are mycorrhizae?

Answer 4

Fungi that live in close association with plant roots. The fungal hyphae provide a very large surface area for uptake of minerals from the soil. In return for their minerals, the plant provides carbohydrates

this is an example of mutalism

Question 5

what is mutualism?

Answer 5

a relationship between two organisms where both benefit

Question 6

what is nitrogen used for in organisms?

Answer 6

to make amino acids and nucleic acids

Question 7

why can nitrogen gas not be used directly by plants to make organic molecules?

Answer 7

its triple covalent bond is too strong - bacteria help overcome this problem

Question 8

label the 4 stages of the nitrogen cycle

Answer 8

Question 9

where do nitrifying bacteria live?

Answer 9

• some live in soil but many live inside the roots of plants in root nodules
• in return for providing ammonia, bacteria receive carbohydrates from the plant (example of mutalism)

Question 10

Name and describe the first stage of the nitrogen cycle

Answer 10

Nitrogen Fixation

• nitrogen fixing bacteria convert atmospheric nitrogen into nitrogen compounds in plants and animals

Question 11

Name and describe the second stage of the nitrogen cycle

Answer 11

Ammonification

• nitrogen containing compounds in dead plants and animals and in faeces are used by saprobionts in the soil
• they digest proteins using secreted enzymes and absorb amino acids which they then use
• they excrete nitrogen containing ammonia (NH3) and ammonium ions (NH4+)as waste products of amino acid metabolism into the soil

Question 12

Name and describe the third stage of the nitrogen cycle

Answer 12

Nitrification

• ammonia and ammonium compounds are absorbed and used by nitrifying bacteria living in the soil
• convert into nitrites (NO2-) and then nitrates (NO3-)
• bacteria release the nitrates as a waste product, which is a form of nitrogen that can be absorbed and used by plants directly

Question 13

Name and describe the final stage of the nitrogen cycle

Answer 13

Denitrification

• denitrifying bacteria in waterlogged soils absorb and convert nitrates into nitrogen gas
• can only occur in absence of nitrogen

Question 14

why are denitrifying bacteria bad for agriculture?

Answer 14

reduce amount of soil nitrate which are essential for the growth of all plants that do not possess nitrogen fixing bacteria

Question 15

what are ways of increasing soil nitrate concentration?

Answer 15

1) use of artificial fertilisers
2) natural fertilsers eg manure
3) ploughing plants with nitrogen fixing bacteria which leads to decomposition producing nitrates
4) land drainage - reduces activity of dentrifying bacteria

Question 16

what are ways of decreasing soil nitrate concentration?

Answer 16

1) waterlogged soils leads to more denitrifation
2) harvesting crops prevents decomposition and therefore reduces nitrates returning to soil

Question 17

describe the phosphorus cycle (terrestrial)

Answer 17

1) weathering of rocks releases phosphate ions into soil
2) uptake into plants by roots
3) plants make ATP, DNA, phospholipids etc. Then they are eaten by anilmals and transfer the phosphate ions throughout the food chain
4) some are lost in animal waste products
5) saprobionts decompose detritus + faeces and urine - release phosphate back into soil

Question 18

describe the phosphorus cycle (marine)

Answer 18

1) weathering of rocks releases phosphate ions into seas/lakes/rivers
2) taken up by algae and other primary aqautic producers
3) passed along the food chain to fish and then too birds
4) bird guano contains a high concentration of phosphate ions and lands on soil

Question 19

what are the types of fertilisers?

Answer 19

1) artificial - inorganic chemicals eg ammonium nitrate
- these come in powder, pellet andliquid forms.
- they are water soluble

2) natural - eg manure or compost
- they decompose slowly to release minerals
- are not soluble until decomposed

Question 20

what is leaching?

Answer 20

Artificial fertilisers are easily washed off the land when it rains (as they are soluble). Eventually dissolved ions end up in waterways -can cause eutrophication

Question 21

what is the process of eutrophication?

Answer 21

1) nitrates and phosphates from artificial fertilers are leached off the land by rainwater to end up in ponds/rivers
2) algae reproduce rapidly to form slimy mats on the water surafce caleld algal bloom
3) plants beneath the surface die from less light for phoyosynthesis because they are shaded by the algae
4) algae die off due too light and temp conditions becoming less suitable later in year and/or because algae have used up all nitrates and phosphates in water
5)bacteria in mud at bottom of pond decompose the bodies of plants and algae multiply. they use up oxygen for aerobic respiration
6) the water becomes low in oxygen and animals start to die. As the algae and dead animals decompose the nitrates and phosphates are released - the cycle continues

Question 22

what is the key point of eutrophication?

Answer 22

the primary harm to aquatic life is caused by lack of oxygen which leads to suffocation. The lack of oxygen is caused by aerobic respiration of huge numbers of saprobiont bacteria and fungi feeding off dead plants, algae and animals

Question 23

what is the summary of causes of eutrophication?

Answer 23

• artificail nitrate and phosphates fertiliser being le3ached from the land
• phosphates in washing powders in waste domestic water
• also , raw sewage: decomposers will use this and release nitrates and phosphates as waste products