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Biology Paper 3,Nov/Dec 2010  
Questions:   1 2 3 4 Main
General Comments
Weakness/Remedies
Strength

















































Question 1

Study the diagram below and use it to answer questions l(a) to l(e)


 

(i) Identify the instrument in the diagram

…………………………………………........................................................................................... [1 mark ]

 

Name the parts labelled I to VI:

I…………………………………………… IV……………………………………

II. …………………………………………  V.…………………………………

III. ………………………………………… VI.…………………………………  [ 3 marks]

(b)   (i)  Outline the process for taking readings with the instrument.

                     ………………………………………………………………………………… …

                      ……………………………………………………………………………………  [7 marks]

(ii)   State two precautions necessary to get correct readings in the experimental set-up .

                         …………………………………………………………………………………
                
                      ………………………………………………………………………………………………………………………………….[2 marks]
(c) (i)  What is the limitation of using this instrument?

                        ………………………………………………………………………… ……. [ 2 mark]
(ii) State two other methods that can be used to measure the process taking place in the part labelled I in the diagram.

  ………………………………………………………………………………………………………………………………………….

   ………………………………………………………………………………………………………………………………………… 

   ……………………………………………………………………………………………………………………………………….. [ 2 marks]

(d)   List four factors that can affect the process being measured

   ………………………………………………………………………………………………………………………………………..

   ………………………………………………………………………………………………………………………………………..

   ………………………………………………………………………………………………………………………………………..

   ………………………………………………………………………………………………………………………………………..

   ………………………………………………………………………………………………………………………………………..[ 4 mark]

(e) State the importance of the process being measured in nature.

                 ………………………………………………………………………………………………………………………………………….

                 ………………………………………………………………………………………………………………………………………….   [4 marks]

_____________________________________________________________________________________________________
OBSERVATION

This was the less popular question in this section and candidates performed poorly on the question. A large number of candidates could not correctly identify the potometer and some who did, lost the mark due to spelling errors. Most of the candidates seemed unfamiliar with the instrument as they could not properly label the parts of the instrument, could not outline the process of taking readings, the precautions to be taken in using the instrument as well as the limitations of using the instrument.

Expected answers include:

Identification of Instrument
Potometer

Name of labelled parts

I - leafy shoot IV - tap to control reserviour
II - bent glass tube V - air bubble
III - water reserviour VI - graduated scale/metre rule.


How to take readings
- as the plant loses water by transpiration;
- more water is absorbed to maintain the transpiration stream;
- which causes the air bubble to move;
- from one point to another;
- in the tube;
- the distance travelled by the bubble;
- in a given time interval is read on the scale;
- this reading is taken several times;
- during the duration of the experiment;
- the rate of transpiration is calculated by average distance travelled per unit time.

Precautions necessary for correct readings
- The shoot must be cut under water to prevent the blocking of the xylem vessels by air.
- The air bubbles should not move out of the graduated region, this is controlled by refilling the
- reservoir.

Limitations of the instrument
- The instrument measures the rate of water absorption;
- The instrument does not measure the amount of water transpired.

Some candidates were able to correctly state the factors that could affect the process of transpiration but nearly all the candidates could not correctly state the importance of transpiration in nature. Expected answers include:

- it enhances the movement of water within the xylem vessels for distribution to plant cells for cellular activity/photosynthesis;
- it enables the uptake of mineral salts dissolved in water to be distributed to the leaves/all parts of the plants for - the synthesis of complex substances;
- cools the plant;
- regulates the volume of water in plants.

 

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