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Biology Paper 2,May/June 2008.  
Questions: 1 2 3 4 5 6 7 8 Main
General Comments

Question 2

(a) What is transpiration? [3 marks]

(b) (i) Name two types of transpiration. [2 marks]
(ii) List four factors which affect the rate of transpiration. [4 marks]

(c) Describe the mechanisms of opening and closing of the stomata. [7 marks]

(d) State:
(i) two similarities and
(ii) two differences between transpiration and sweating. [4 marks]



Most candidates who attempted this question were able to correctly define transpiration and list four factors which affect the rate of transpiration as well as name the types of transpiration. However, in naming the types of transpiration ( Stomatal, Lenticular and Cuticular) a good number of candidates lost marks due to spelling errors.

Most candidates performed poorly in describing the mechanism of opening and closing of the stomata and where they were able to state some of the processes they did so in a non sequential manner. The proper order of the mechanism is as follows.

- When the solute concentration of the guard cells is high;
- water flows from neighbouring epidermal/cells into the guard cells;
- by osmosis;
- the volume and turgidity of the guard cells increase;
- the thin outer walls of the guard cells stretch more than the thicker inner walls;
- causing the guard cells/stomata to open;
- when the solute concentration is low;
- water flows out of the guard cells by osmosis;
- the volume and turgidity decrease causing the guard cell to become flaccid;
- and the stomatal pore is closed.

In stating the similarities and differences between transpiration and sweating most candidates could only state one similarity namely both processes involve loss of water. Other expected answers include the following:

Similarities between transpiration and sweating
- Both involve loss of water from the body of the organism;
- Both processes result in cooling;
- Water is lost through pores.


Transpiration Sweating
Occurs in plants/through stomata/lenticels             occurs in mammals/skin/through   sweat process
involves only loss of water   loss of water, salts and nitrogenous wastes
water is lost in the form of vapour water is lost in liquid form
occurs during the day            occurs both night and day            

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