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nitrogen from atmosphere is fixed denitrification returns nitrogen to the atmosphere plants / autotrophs make organic compounds / biomass heterotrophs / decomposers break down organic compounds / biomass numbers of prey controlled by numbers of predators numbers of predators controlled by numbers of prey energy In sunlight continually supplied to blosphere energy lost from blosphere as heat 4, Explain the factors that cause a population to follow the sigmoid ( S-shaped) growth curve. (8 max) during exponential growth the population grows at an increasing rate all / most / many offspring survive / birth rate higher than death rate all / most / many offspring reproduce each generation produces more offspring that the last plateau reached eventually / population levels off / birth rate equals death rate when carring capacity of environment is reached e.g. when no more food / nutrients / resources available e.g. when no more space for nesting / space for another purpose is available e.g. when numbers of predators have Increased e.g. when levels of parasites / diseases have become very high transitional phase when limits to growth are starting to act (for exponential growth phase, accept converse examples) 5. Describe a method for measuring the size of a population of plants using quadrats. (4 max) random positions for the quadrats use of random numbers fro co-ordinates / other randomisation procedure many repeats / quadrats size of quadrat depends on size / density of plants count number of plants in each quadrat find mean number of plants per quadrat multiply number per unit area by total area to obtain total population 6. Apply the concept of carrying capacity to the struggle for survival resulting from overproduction of offspring. (5 max) . ®:'. 0. ' 0-® the environment can only support a certain maximum population this population is sometimes exceeded (due to overproduction of offspring) food | space / resources are insufficient / competition for resources some indlviduals fail to obtain enough deaths / failure to reproduce / survival of the fittest population falls to carrying capacity reference to evolution by natural selection 7. Outline the international system used for naming species of living organisms. (4 max) binomial system devised by Linnaeus the first name is the genus name the second name is the specles name genus name can be abbreviated genus consists of a group of (closely related) species upper case for first letter of genus name and the rest of the binomial is lower case Sequoia sempervirens / other example first published name is the correct one local / colloquial names can be very confusing / helps international communication 8. Discuss the definition of the term species. (8 max) . a species is a group of organisms