waecE-LEARNING
Biology Paper 2,May/June 2011.  
Questions: 1 2 3 4 5 6 7 8 Main
General Comments
Strength
Weakness/Remedies
























Question 3

(a) (i) State the second law of thermodynamics.                                            [3 marks]
(ii)Use the second law of thermodynamics to explain the flow of energy across different trophic levels in a food chain.                     [8 marks]
(b) (i)State three factors that can likely limit the size of human population. [3 marks]
(ii) Outline two ways each by which humans can overcome the factors
named in 3(b)(i).                                                                                   [6 marks]




 




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OBSERVATION

This was the most popular question in this section. Most candidates who answered the question performed fairly well as they could state the second law of thermodynamics and use the law to explain the flow of energy across different tropic levels in a food chain. Some candidates however were talking about loss of heat instead of stating how useful energy is lost from one trophic level to another. expected answers include:

    Flow of energy across different levels in a food chain

    Transfer of energy between trophic levels is not 100% completely efficient;
    Successive levels have less energy;
    And support fewer organisms;
    primary producers/green plants have the highest energy;
    when herbivores/primary consumers feed on primary produces;
    they energy level is reduced;
    when carnivores/secondary consumers feed on herbivores;
    the energy level is further reduced;
    part of the energy is lost as heat at each trophic level;
    not all parts of the preceding organisms are eaten by the predator/organisms at the next
    trophic level;

Energy is lost in the process of respiration/feedinglmovementlmetabolic activities . Most candidates could state factors that can limit human populations and ways of overcoming these factors and scored full marks. Some candidates listed death rate and birth rate as factors that can limit populations instead of reduced birth rate and increased death rate and so lost marks.


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