nutrient cycles

what is a saprobiont?

a microorganisms which secretes hydrolytic enzymes, then absorbing the products of digestion- extra-cellular digestion 

what is a saprobiont’s role in the nitrogen cycle?

use enzymes to decompose proteins/DNA/RNA/urea to release ammonia/ammounium compounds/ions

What are mycorrhizae? And what is their role?

Fungi associated with the roots of plants

• mutualistic relationship between plant and fungi to increase surface area of root system = increase uptake of water and mineral ions

How do mycorrhizae facilitate the uptake of water and ions by plants?

• extend out from roots of plants increasing area from which ions and water can be absorbed

• able to grow into rocks in soil and extract phosphates which the plants would not be able to access otherwise

What is nitrogen fixation?

• N_² gas from the atmosphere converted into ammonia nitrogen fixation

• nitrogen-fixing bacteria eg Rhizobium 

• this is found in EITHER root nodules of legumes (convert toxic NH3 into amino acids) or nitrogen fixing bacteria is free living in the soil 

• have a mutualistic symbiotic relationship 

How is NH₃ converted into NH^₄₊ ?

Dissolves into water or soil 

What is nitrification? Describe the bacteria involved and the processes. 

By nitrifying bacteria 

NH4+ —> NO2- 

NO2- —> NO3- 

How are nitrate ions transported into animals and then nitrogen compounds? 

Nitrate ions are absorbed by the soil via active transport and then eaten by the animals because pants are primary producers, assimilated to form nitrogen-containing compounds, eg DNA, RNA ATP etc

Then the animals die and are left as highly nitrogen concentrated compounds

What is ammonification?

• when saprobionts (bacteria and fungi) do saprobiotic digestion by secreting proteases which digest molecules eg proteins —> amino acids

• Decompose animal excretion and animals dead matter-ammonifying bacteria form ammonium ions by deanimating amino acids and urea 

Explain the process of denitrification

• nitrates (NO3-) form back into atmospheric N2 gas by denitrifying bacteria

• Occurs in anaerobic conditions (denitrifying bacteria uses NO3- instead of O2 in respiration

describe the process of the phosphorus cycle

1. Phosphate ions in rocks are released into soil by weathering

2. Phosphate ions are taken into plants through roots. Mycorrhizae greatly increase the rate at which phosphorus can be assimilated (high SA)

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

4. Phosphate ions are lost from animals in waste products

5. When plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. These microorganisms also release the phosphate ions from urine and faeces.

6. Weathering of rocks also releases phosphate ions into seas, lakes and rivers, taken up by aquatic producers, eg algae, & passed along food chain to birds

7. waste produced by sea birds- guano contains a high proportion of phosphate ions, returns a significant amount of phosphate ions to soils (particularly in coastal areas), often used as a natural fertiliser

why is phosphorus important?

Plants and animals need it to make biological molecules eg phospholipids (cell membranes), ATP and DNA

What is the benefit of planting a different crop on the same field each year?

• nitrogen-foxing crops eg legumes make soil more fertile by increasing soil nitrate content

• different crops have different pathogens

• different crops use different proportions of certain ions