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Define the term “ecosystem”.

All living organisms and the non-living conditions in an area.


Define the term “community”.

All the populations of living organisms in a particular habitat.


Define the term "habitat”.

An area inhabited by a species.


Define the term population.

A group of organisms of one species that live in the same place at the same time.


Define the term species.

A group of organisms which have a common ancestor and can interbreed to produce fertile offspring.

It is the smallest and most specific taxonomic group.


Define the term ecology.

A branch of biology that deals with the distribution, abundance, and interactions of living organisms at the level of communities, populations and ecosystems as well as at a global scale.


Explain what is meant by the phrase “ecosystems are dynamic”.

They are constantly changing.


Define the term “biotic factor”.

The living components of an ecosystem.


Define term abiotic factor.

The non-living conditions in a habitat.


Give some examples of biotic factors.

- presence of organism (as predator or prey)
- the size of the populations of organisms
- the competition between organisms.


Give some abiotic factors.

- amount of rainfall
- yearly temperature range
- availability of light
- availability of water
- availability of oxygen
- salinity
- PH


Define the term “edaphic factor”.

the soil factors - the type and condition of the soil.


Give three examples of edaphic factors.

Clay - this has fine particles, is easily waterlogged, and forms clumps when wet
Loam - this has different-sized particles, it retains water and but does not become water logged.
Sand - this has coarse, well-separated particles that allow free draining, sand soil does not retain water and is easily eroded.


Define the term “food web"

Food webs are systems of interlinked food chains used to show the transfer of biomass, and therefore energy, through the organisms in an ecosystem.


Define the term “food chain”.

Chains used to show the transfer of biomass and therefore energy through organisms in an ecosystem. Each stage in the chain is known as a trophic level.


Define the term "trophic levels".

The stages in a food chain. Starting with a producer, the rest are consumers.


Define the term “heterotroph”.

Organisms that acquire nutrients by the ingestion of other organisms.


Explain what the arrows represent in a food web.

The transfer of energy, they point in the direction that the energy is being transfered.


Define the term “consumer”.

Organisms that attain their energy by feeding on other organisms.


Define the term producer.

Organism that converts light energy into chemical energy.


Define the term “detritivore”. Give two examples and explain their role in food webs.

Organism that speeds up decay by breaking down detritus into smaller pieces.
- Woodlice, breaks down wood.
- Earthworms, breaks down dead leaves.
Detritivores increase the surface area of organic material for decomposers to work on. They perform internal digestion.


Define the term “decomposer”. Give 2 examples of and explain their role in food webs.

Organism that breaks down dead organisms, releasing nutrients back into the ecosystem.
They are primarily microscopic fungi and bacteria e.g oyester mushrooms which decompose wood.
Decomposers obtain their energy by saprobiotic nutrition. This means that they digest waste externally by secreting enzymes. This process releases stored inorganic compound and elements back into the environment.


Define the term “biomass”.

The mass of living material.


Define the terms “dry mass”.

The mass of living material without its water content.


Explain why dry mass is a better indicator of biomass than fresh mass.

Dry mass excludes fluctuating water concentrations which could affect the overall mass.


Explain how to calculate the dry mass of each trophic level in a food chain.

1) Kill the organism and then place it in an oven at 80oC until all water has evaporated.
2) Weigh the organism to find the dry mass.
3) Multiply the dry mass present in each organism by the total number of organisms in that trophic level.


Explain how to experimentally measure the energy content of organic matter.

The energy available at each trophic level is measured in kilojoules per metre sqaured per year.


Suggest suitable units for the biomass in an ecosystem (both terrestrial and aquatic).

g/m2 - terrestrial
g/m3 - aquatic


Explain how pyramids of numbers, biomass and energy represent data about an ecosystem and the relative merits of each.

Pyramid of numbers - producers are always placed at the bottom of the diagram with subsequent trophic levels added above. Shows the actual number of organims in each trophic level.
Sometimes misleading as the shapes will not consistently get smaller the further up the pyramid you go.

Pyramid of biomass - usually a pyramid shape, because each trophic level normally has less biomass than the trophic level before it.

Pyramid of energy - very similar to biomass so will likely show a pyramid. Level of energy is roughly equal to level of biomass.

Neither pyramid of biomass nor pyramid of energy will be representative of the number of individuals at each trophic level.


Suggest suitable units for the energy at each trophic level in a food chain and explain why these units are appropriate.

kJ m-2 yr-1 (kilojoules per metre squared per year)