1. Define the term "community".
Answer
A community is the populations of different species within a given area.
2. What is meant by an ecosystem's carrying capacity ?
Answer
It is the size of population of a species that an ecosystem can support.
3. How can you estimate the number of plants of one species in an area ?
Answer
Random sampling using a quadrat. Random number generator used to determine co-ordinates. Calculate a mean number per quadrat, then multiply by the number of times the quadrat fits into the area being studied.
4. Describe the process of succession starting from bare land.
Answer
Pioneer species colonise an area by seeds or spores being brought in by wind or dropped by birds. At each stage a certain species changes the environment to make it less hostile and more suitable for the next species by adding humus to the soil. The earlier species is then out-competed by the later species. This continues until a climax community is reached. At each stage biomass and biodiversity is increased, increasing the variety of habitats and food supply.
5. Describe how a population size can be estimated using mark-release-recapture.
Answer
Capture a number of animals in an area, and mark them harmlessly so that they can be recognised again. Release the marked animals. After a series of time has passed, collect a second sample in the same area. Count the number of marked and unmarked animals in second sample. Then carry out calculation: number of organisms in first sample × (total number of organisms collected in second sample ÷ number of marked organisms in second sample).
6. What assumptions are made when carrying out mark-release-recapture ?
Answer
The animals all come from the same population, marking does not harm the animal and doesn't make them more likely to be caught by predators, there is no migration in or out of the population during the time period the samples are being taken. No animals die and no new ones are born.
7. Organisms within an ecosystem experience both interspecific and intraspecific competition. Explain what the difference is between these two types.
Answer
Interspecific competition is between two different species, intraspecific is between organisms of the same species.
8. The table below shows the yields of some common vegetable oils. Suggest how scientists could calculate the figures for yield given in the table.
Answer
Select a hectare at random then measure mass of oil from all the crop plants in that area.
9. Explain how deforestation contributes to climate change.
Answer
Carbon dioxide is a greenhouse gas that contributes to climate change, the greenhouse effect, and global warming. Trees absorb carbon dioxide during photosynthesis. Because they live for a long time, trees store large amounts of carbon in their biomass. Deforestation prevents this process from occurring. Burning trees releases carbon dioxide into the atmosphere. Crops that replace trees absorb much less carbon dioxide during photosynthesis.
10. A group of students carried out a belt transect along a sand dune system. The figure below shows some of their results. The students measured percentage cover of each species rather than counting individual plants. Suggest why.
Answer
For comparison because plants vary in size.
11. Explain why a kite diagram is especially useful for this kind of study.
Answer
You can compare populations of different species across the transect. This allows you to see which species are competing with each other.
12. A different group of students carried out a belt transect in the same area at the same time but their kite diagram was not the same. Explain why.
Answer
By chance, because plants do not grow uniformly, the transect may miss some species or over-represent others.
13. Bird's-foot trefoil is a leguminous plant. This means it has root nodules containing nitrogen-fixing bacteria in its roots. Suggest how this plant is important in the sand dune succession.
Answer
Bird’s-foot trefoil can grow in soils that are poor in nutrients or nitrates because its root nodules contain nitrogen-fixing bacteria. When the plants die, they add humus and nutrients to the soil, which allows other species to establish and grow, making it important in sand dune succession.