Ecosystems

Question 1

Give examples of abiotic factors.

Answer 1

PH level, relative humidity, temperature and the concentration of pollutants.

Question 2

Give examples of biotic factors.

Answer 2

Producers, consumers, decomposers.

Question 3

What is cyclic changes? Give an example.

Answer 3

These changes repeat themselves in a rhythm. For example movement of tides as the water moves forwards and backwards in a continuous cycle.

Question 4

What is directional changes? Give an example.

Answer 4

These changes go in one direction and tend to last longer than the lifetime of organisms with the ecosystem. Such as erosion of coastline.

Question 5

Why can energy transfer between steps in feeding relationships never be 100%?

Answer 5

Energy decreases as it moves up trophic levels because energy is used as heat energy, for life processes such as movement. And some is transferred through faeces and remains are passed to decomposers.

Question 6

What is the calculation for the efficiency of biomass consumption?

Answer 6

Ecological efficiency = ( ( biomass of the higher trophic level) / (biomass of the lower trophic level) ) x 100

Question 7

Define the term niche.

Answer 7

The role of each species in an ecosystem.

Question 8

Define the term biomass transfer.

Answer 8

Transfer of biomass from one trophic level to the next.

Question 9

Define the term trophic level.

Answer 9

The level at which an organism feeds in a food chain.

Question 10

What are the steps in saprotrophic decomposition?

Answer 10

1. Saprotrophs secrete enzymes onto dead and waste material.
2. Enzymes digest the material into small molecules, which are then absorbed into the saprotrophs body.
3. Having been absorbed, the molecules are stored or respired to released energy.

Question 11

What is nitrogen fixation?

Answer 11

To be used by plants, the N2 must be transformed through a process called nitrogen fixation. Fixation converts nitrogen in the atmosphere into forms that plants can absorb through their root systems. There are three ways in which nitrogen gas can be fixated, by nitrogen fixing bacteria, lightning or the Haber process.

Question 12

What is ammonification and nitrification?

Answer 12

When an organism excretes waste or dies, the nitrogen in its tissues. Various fungi and prokaryotes then decompose the tissue and release inorganic nitrogen back into the ecosystem as ammonia. This process is called ammonification.
Some bacteria obtain their energy from oxidising ammonium ions to nitrates, while others obtain it by oxidising nitrites to nitrates. These processes are called nitrification.

Question 13

What is denitrification?

Answer 13

Other bacteria convert nitrates back to nitrogen gas. When the bacteria involved are growing under anaerobic conditions they use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide.

Question 14

Describe the carbon cycle (or draw it).

Answer 14

The series of processes by which carbon compounds are interconverted in the environment, involving the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels.

Question 15

Describe the first step of succession?

Answer 15

Bare rock - very hostile environment, with very little water and few nutrients.

Question 16

Describe the second step of succession?

Answer 16

Primary colonisers - lichens (fungus and algae): fungus breaks down rock surfaces making minerals available, alga provides carbohydrates for fungus. Slow growing and tolerant to extreme conditions. Death and decomposition of lichens release nutrients to create humus, this changes abiotic environment for future organisms.

Question 17

Describe the third step of succession?

Answer 17

Pioneer species -

Question 18

Describe the fourth step of succession?

Answer 18

Herbaceous plants -

Question 19

Describe the fifth step of succession?

Answer 19

Large plants (shrubs) - Grow in good soil. Their fast growth outcompete slower growing species. This provides a greater variety of food and habitats, supporting a large number of organisms.

Question 20

How can humans impact the process of succession?

Answer 20

When landscape is influenced by agriculture it cab be difficult to work out whether a particular location has reaches its climax community. Other ways include grazing, burning, application of fertilisers, application of herbicides and exposure to excessive amounts of wind.

Question 21

Describe the sixth step of succession?

Answer 21

Complex community (trees) - these grow slowly and outcompete the shrubs, replaced by shade tolerant species. This is a stable environment, with very few new species replacing established species. There is generally a dominant plant and animal species present, therefore reduces species diversity.