Levels of organisation from individual to ecosystem, food chains and predator prey cycles, and the required practical using quadrats and transects.
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1.What are the levels of organisation in an ecosystem?
Individual organism, population, community, then ecosystem.
2.What is a population?
All the organisms of one species living in a habitat.
3.What is a producer?
An organism, usually a green plant or algae, that makes its own food by photosynthesis. All food chains begin with one.
4.What is a primary consumer?
A herbivore that eats the producer.
5.What are secondary and tertiary consumers?
Carnivores that eat the primary consumers, and carnivores that eat the secondary consumers.
6.What is an apex predator?
A carnivore at the top of a food chain, with no predators of its own.
7.What do the arrows in a food chain represent?
The transfer of biomass and energy, pointing from the organism being eaten to the organism eating it.
8.Describe a predator prey cycle.
Prey numbers rise, so predators have more food and their numbers rise. More predators eat more prey so prey numbers fall, then predator numbers fall too, and the cycle repeats.
9.Why do predator numbers peak after prey numbers?
It takes time for predators to breed and grow in response to the extra food, so their rise lags behind.
10.What is a quadrat used for?
Sampling the number or percentage cover of slow moving or non-moving organisms in a defined area.
11.Why do ecologists sample rather than count everything?
Counting every organism in a habitat is impractical, so a sample is used to estimate the whole population.
12.How do you use random sampling with quadrats?
Lay two tape measures at right angles, generate random coordinates, place the quadrat at those coordinates, and record what is inside.
13.Why must the sampling be random?
To avoid bias. Choosing where to place the quadrat would tend to favour areas that look interesting and would not represent the habitat.
14.How do you estimate a population size from quadrat data?
Find the mean number per quadrat, then multiply by the total area divided by the area of one quadrat.
15.The mean is 5 daisies per 1 m squared quadrat and the field is 400 m squared. Estimate the population.
5 x 400 = 2000 daisies.
16.How can results from quadrat sampling be made more reliable?
Take a larger number of samples and calculate a mean.
17.What is a transect?
A line across a habitat along which samples are taken, used to study how the distribution of organisms changes.
18.When would you use a transect rather than random quadrats?
When you are investigating how distribution changes across a gradient, for example from the edge of a pond to dry land.
19.How do you carry out a transect?
Lay a tape measure along the gradient, then place a quadrat at regular intervals along it and record the organisms in each.
20.What is percentage cover?
The proportion of the area inside the quadrat that is covered by a particular species, estimated as a percentage.
21.When is percentage cover more useful than counting?
For plants such as grass or moss, where individual organisms are hard to distinguish and count.
22.Name an abiotic factor you might measure alongside a transect.
Light intensity, soil moisture, soil pH or temperature.
23.Why measure abiotic factors during a transect?
To look for a relationship between the changing conditions and the distribution of organisms.
24.Why can a correlation from a transect not prove causation?
Several abiotic factors change together along a gradient, so you cannot tell which one is responsible from the transect alone.
25.What is meant by biomass?
The mass of living material in an organism or at a trophic level.
26.Why can food chains rarely have more than five trophic levels?
So little biomass is transferred at each stage that eventually there is not enough to support another level.
27.What would happen to a food web if one species were removed?
Species that fed on it would decline, and species it fed on would increase, so the effect spreads through the whole web.
28.Why is repeating a sample at a different time of year useful?
Populations change with the seasons, so samples from several times give a truer picture of the community.
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