waecE-LEARNING
Agricultural Science Paper 3, Nov/Dec 2013  
Questions: 1 2 3 4   Main
General Comments
Weakness/Remedies
Strength













































Question 2

The diagram below shows some of the causes and effects of deforestation in West Africa.
  Study it carefully and use it to answer the questions that follow.

State the reason why more food and firewood are needed in most parts of West Africa.                                                                                                   [ 1 mark ]

  1. State the four causes of soil erosion                                                   [ 4 marks ]
  2. Explain the term overgrazing as shown in the diagram                      [ 2 marks ]
  3. Explain how the need for more food lends to deforestation                [ 2 marks ]

 

  1.   The illustration below shows a cooking device which uses biogas.

   Explain how the use of this device could help check deforestation.               [2marks ]

  1.   The diagram below is an illustration of a disc plough. Study it carefully and answer

   the questions that follow.


  1. Name the parts of the diagram labeled I, II and III.                         [3 marks]
  • Give one reason why disc ploughs are widely used in the forest regions of West Africa.                                                                                    [1 mark ]
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OBSERVATION

This question was fairly attempted by the candidates. In 2(a)(i-ii), majority of the candidates were able to state the reason why more food and firewood are needed in most parts of West Africa, and state the causes of soil erosion.  Although majority of the candidates could not explain the term overgrazing as required in 2(a)(iii – iv).
 Also, in 2(b) most of the candidates could not explain how the use of the device (gas cooker) could help check deforestation. Further to this, majority of them could neither name the parts of the disc plough nor give a reason why disc ploughs are widely used in the forest regions of West Africa as required in 2 c(i – ii)
The expected answers include:

  1. Explanation of overgrazing

-   Overgrazing is the excessive removal of vegetative cover of pasture
     rangeland through grazing
-   leading to the exposure of the land to agents of erosion.

  (b)     Explanation why the use of cooking device could help check deforestation
           -   The cooking device doses not use wood or charcoal to generate heat needed
                for cooking,
           -    hence no need for the harvesting of firewood (deforestation).
(c)(i)    Name of parts labelled I,II and III
            I.   Beam
            II.    Disc scraper
            III.   Furrow wheel

    (ii)    Reasons for using disc plough in the rain forest regions of West Africa.
            -     Disc ploughs can work on hard soil conditions where penetration is  difficult
            -     Disc ploughs do not completely turn over soil slices, so grass turfs which
                   help to protect the soil from erosion are left on the soil surface
            -     Disc ploughs can roll over hidden rocks or stumps
            -     It works better in sticky soils due to the presence of scrapers that clean  attached soil
             -    Can make deep cut into the soil

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