Question 1

1.   Explain briefly four factors that affect the diffusion of substances.             [ 8 marks ]
2.   Explain the following terms:
3. active transport;
4. transpiration.                                                                                             [ 4 marks ]

1.      State four ways by which plants can reduce high rate of transpiration  [4 marks  ]
2.      State the features of red blood cells and how these features adapt the cell to perform its functions.                                                                           [ 4 marks ]

 

observation

      Many candidates avoided question 1 and the few who attempted it performed poorly.
     Those who attempted this question could not correctly explain the factors affecting the rate
     of diffusion.  It was evident from the answers given by the candidates   that they had not grasped
     this  concept.
      Most candidates could not explain the term active transport, could not define transpiration as
      loss of water from the plants  in the form of vapour,   a lot of candidates could not state ways by
      which plants can reduce high rate of  transpiration.

 

     In stating how features of red-blood cells adapt the cell to perform its functions, they could
    only state how the presence of haemoglobin adapts the cell to oxygen uptake while the other
    points were not mentioned.
     Expected answers include
     a     Factors Affecting the rate of Diffusion:

• Presence of concentration gradient; when concentration gradient is high the rate of movement of molecules will increase; from the region of high concentration to the region of lower concentration; leading to an increase in the rate of diffusion.
• Surface Area, Large surface area; will allow more molecules of substance to diffuse.
• State/nature of the diffusing substance; molecules in gaseous state diffuse faster than those in liquids or solid states/molecule in solid state diffuse slower than those of liquid and gas.
• Size of the molecules/particles; the smaller molecules will move/ diffuse faster than larger molecules.
• Temperature; increase in temperature increases the movement of molecules/ increases in diffusion/decrease in temperature slows down movement of molecules/decreases diffusion

 
(b)(i)    Active Transport

• This is the movement of molecules from a region of low concentration to a region of high concentration/against a concentration gradient;
• across a living membrane;
• using energy from the cell.

                                                                                    
(c)        Reduction of Transpiration
            -           Closure of stomata during the day;
            -           Reduction of leaf size/leaf modified in spines;
-           Dropping of leaves in the dry season;
-           Development of thick cuticle;
-           Presence of hairs over leave surfaces;
            -           Presence of sunken stomata.           
                                                           
 (d)       Red Blood Cells

• Biconcave shape/disc-like, increases its surface area for oxygen uptake; Elastic membrane; enables it to flow easily through the blood vessels;
• Presence of haemoglobin; for oxygen uptake;
• Thin membrane; for easy diffusion of oxygen/carbon-dioxide.