Ecosystems

Question 1

4 steps of the nitrogen cycle

Answer 1

1. Nitrogen fixation
2. Nitrification
3. Ammonification
4. Denitrification

Question 2

1. Nitrogen fixation

Answer 2

• nitrogen fixing bacteria convert nitrogen gas in the atmosphere into ammonia
• azobacter convert ammonia into ammonium ions in the soil
• rhizobium live in root nodules of legumes, and directly transfer ammonia into the plant

Question 3

2. Nitrification

Answer 3

• in the soil, Nitrosomonas convert ammonium ions into nitrites
• nitrobacter convert nitrites into nitrates
• these bacteria are called nitrifying bacteria
• requires oxygen

Question 4

3. Ammonification

Answer 4

• nitrogen containing compounds is waste & decaying matter are broke down by decomposers (saprobionts)
• this forms ammonia which is released into the soil
• ammonia combines with water and forms ammonium ions (which can be converted into nitrates)

Question 5

4. Denitrification

Answer 5

-denitrifying bacteria carry out anaerobic respiration
- takes in nitrates and converts it into nitrogen gas

Question 6

Carbon Cycle

Answer 6

1. Producers take in carbon dioxide and use for photosynthesis
2. During photosynthesis carbon dioxide is converted into organic carbon containing compounds in the process called carbon fixation
3. Producers also release carbon dioxide back into the atmosphere through respiration
4. Consumers eat the producers and the organic carbon containing compounds pass along the food chain (e.g. rabbit eats plant, fox eats rabbit)
   - consumers also release carbon dioxide back into the atmosphere through respiration
5. When producers and consumers die, the carbon containing compounds remain in their waste matter - these compounds are broken down by decomposers (e.g. bacteria and fungi) in process called decomposition - releases carbon back into the atmosphere
6. Waste matter that isn’t decomposed will form fossil like oil. When fossil fuels are burnt in combustion, they release carbon dioxide back into the atmosphere

Question 7

Ecosystem

Answer 7

Made up of all the living organisms that interact with one another in a defined area and all the physical factors present in that region

Question 8

Factors influencing ecosystems

Answer 8

Biotic factors
- predation
- competition
- hunting
- disease

Abiotic factors
- light
- temperature
- pH
- oxygen availability
- water availability

Question 9

Edaphic factors (soil)

Answer 9

Clay: has fine particles, easily waterlogged and forms clumps when wet

Loam: different sized particles, retains water but won’t become waterlogged

Sandy: coarse, well separated particles, doesn’t retain water and easily eroded

Question 10

Cyclic, directional and erratic changes

Answer 10

Cyclic changes and repeat in a regular pattern

Directional changes do not repeat, tend to be long lasting and go in one direction e.g. erosion

Erratic changes cannot be predicted and are neither cyclic or directional e.g. effects of lightning

Question 11

Ecological efficiency

Answer 11

Efficiency with which biomass is transferred from one trophic level to the next

Question 12

Ecological efficiency calculation

Answer 12

energy/biomass available after transfer x 100
energy/biomass available before transfer

Question 13

Net production calculation

Answer 13

Gross production - respiratory losses

Question 14

Succession

Answer 14

A natural directional change in species composition in an area over a period of time

• happens in a series of recognisable stages (sere)
• one community changed the conditions for the next e.g. soil depth

Question 15

Primary succession

Answer 15

Begins with bear ground

Question 16

Pioneer species

Answer 16

E.g. algae, moss - colonises first

Stabilises the environment by:
- developing the soil
- cause an increase in availability of water
- causes more minerals to be available
- creates habitats and provides shelter
- change soil pH

Question 17

What happens as succession continues

Answer 17

• a development of deeper soil
• soil accumulates more minerals and is more fertile
• dominant species get larger
• plant species get larger

Question 18

Climax community

Answer 18

Final stage in succession
- community is in equilibrium with environment
- stable, doesn’t change

Question 19

What might prevent succession occurring

Answer 19

• trampling
• grazing
• human activities
  -natural disasters e.g. forest fires, flood
• agriculture

Question 20

Deflected succession

Answer 20

When something e.g. grazing, burning, trampling of plants prevent succession and therefore the establishment of the next community

Question 21

Secondary succession

Answer 21

When succession takes place on previously colonised, but damaged habitat
- it does not start from bare ground