1Define an ecosystem.
A characteristic community of interdependent species and their abiotic environment.
2What is a niche?
The specific role or function an organism plays in its ecosystem.
3Define carrying capacity.
The maximum population size that an ecosystem can support.
4What is the difference between interspecific and intraspecific competition?
Interspecific competition is between different species; intraspecific competition is between members of the same species.
5Define succession.
The change in species composition in a community over time.
6What is a pioneer species?
The first species to colonise bare rock or barren land, such as lichens.
7Define a climax community.
The stable, final stage of succession that remains unchanged unless the environment changes.
8What is Gross Primary Productivity (GPP)?
The rate of production of chemical energy in organic molecules by photosynthesis.
9How is Net Primary Productivity (NPP) calculated?
NPP = GPP − respiration.
10Why is energy transfer between trophic levels inefficient?
Energy is lost as heat, in faeces or urine, or because parts of organisms are not eaten.
11What is the role of Nitrosomonas?
To convert ammonium ions into nitrites.
12What is the role of Nitrobacter?
To convert nitrites into nitrates.
13Define nitrogen fixation.
The conversion of atmospheric nitrogen gas into ammonium ions by bacteria such as Rhizobium.
14What are the conditions for denitrification?
Anaerobic conditions, such as waterlogged soil.
15What is eutrophication?
The enrichment of water with nutrients, causing algal blooms and oxygen depletion.
16Where is Rhizobium found?
In the root nodules of leguminous plants.
17Define a biotic factor.
A living factor that affects an ecosystem, for example predation.
18What is primary succession?
Succession that occurs on land where no soil has ever existed.
19What is secondary succession?
Succession that occurs on land where soil is already present, such as after a fire.
20What is the role of decomposers?
To break down organic matter into ammonium ions in ammonification.
21Define a trophic level.
The position of an organism in a food chain.
22Why are food chains rarely more than five levels?
There is insufficient energy at higher levels to support a population.
23What is humus?
Decaying organic matter that improves soil structure and fertility.
24Name a denitrifying bacterium.
Pseudomonas.
25How does ploughing help the nitrogen cycle?
It aerates the soil, providing oxygen for nitrifying bacteria and inhibiting denitrifying bacteria.
26Define abundance.
The number of individuals of a species in a given area.
27What is the light compensation point?
The light intensity at which the rate of photosynthesis equals the rate of respiration.
28What is a transect?
A line across a habitat used to study the distribution of species.
29Define distribution.
The area or range in which a species is found.
30What is the main source of carbon for plants?
Atmospheric carbon dioxide.