WAEC Biology 2013 Theory — Question 3

Model answer

(a)(i) Ecological succession refers to a long-term, gradual or progressive series of changes occurring in the structure, composition, variety and number of species in an area until a stable/climax community is established. (ii) The first set of organisms to inhabit a plot of land are known as the pioneers. As the pioneers die, they are broken down and nutrients are added to the soil. Higher plants and animals are now found there as the soil is more fertile. When these species die, they are also broken down to release more nutrients to the soil, and more advanced species emerge. Eventually, a stable community known as the climax community is established. (b)(i) The biosphere refers to the part of the environment where life exists. The biosphere is divided into the atmosphere, lithosphere and hydrosphere. (ii) Population refers to the total number of organisms of the same species living in a particular place at a particular time. (iii) A community is a group of organisms of different species living and interacting in a given habitat. (iv) Ecosystem refers to living organisms and their non-living environment interacting together. (c)(i) The instrument used for measuring relative humidity is the hygrometer. (ii) The instrument used for measuring the speed of wind is the anemometer. (Note: while the anemometer measures the speed of the wind, the wind vane measures the direction of the wind.)