Ecosystems

Question 1

How would you investigate the population size of an organism in two different areas?

Answer 1

• Measure the total area of the habitats (e.g. fields)
• Use a random number generator to find two different locations, one in each habitat
• Place two 1m² quadrats in both of these locations
• Count the number of plants of the given species found inside each quadrat, and multiply it by the total number of m² of the habitat to find the approximate population size in that habitat
• Compare the results for the two habitats
• The biodiversity in two different areas can be measured by counting the number of species in each quadrat and working out the percentage cover of each organism by measuring what percentage of squares (out of the 100) in the quadrat are occupied by a certain organism

Question 2

What is meant by biodiversity?

Answer 2

• The range and variety of species in an ecosystem
• It takes into account the number of different species, but not the population size
• However it does take into account the distribution - the more evenly distributed the populations of each organism in an ecosystem are, the higher the biodiversity

Question 3

What are the stages of the nitrogen cycle?

Answer 3

• N₂ is very stable and cannot be absorbed from the air
• However nitrogen fixing bacteria in the soil can take nitrogen gas and turn it into nitrates in the soil
• Alternatively, lightning can split the nitrogen atoms apart, where they will then turn into nitrous oxides, dissolve into rainwater and leach as nitrates into the soil
• Plants can then absorb these nitrates and turn them into proteins
• Animals eat plants (or other animals) and derive nitrogen from them for their own use
• When animals or plants die (or egest), the organic matter decays and turns into ammonium compounds which are put into the soil by decomposers
• Amonium cannot be absorbed by plants, but through nitrification, nitrifying bacteria in the soil will turn ammonium compounds into nitrites then nitrates which can be absorbed by plants
• However, another type of bacteria in the soil called denitrifying bacteria can take some of these nitrates and convert them into N₂ gas, releasing it back into the atmosphere

• Nitrogen, which is also finite, is needed by life as it is a fundemental part of proteins
• Farmers will not want denitrifying bateria as they want nitrates in their soil