Biology 3 Nov/Dec 2012 - Candidates Weakness

Biology Paper 3,Nov/Dec 2012

Questions:		1	2	4		Main

General Comments
Weakness/Remedies
Strength

Question 2

Two identical leafy shoots E and F from a shrub, were each connected to a potometer. One was placed under normal laboratory conditions and the other under a fan in the laboratory. The distance moved by each bubble in each potometer was recorded at regular time intervals.

The results obtained are shown in the table below.

Study the information in the table carefully and use them to answer question 2(a) to 2(f).

Time after start of experiment (mins)	Distance moved by each bubble (mm)
Time after start of experiment (mins)	Shoot E (normal) laboratory condition)	Shoot F (in the laboratory under the fan)
0	0	0
5	3	5
10	5	10
15	8	18
20	11	28
25	13	33

Plot two graphs, one for each shoot on the graph sheet provided, with the distance

moved by the bubble on the vertical axis (y) and the time on the horizontal axis (x).

(i) Under which condition did the bubble move faster?

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

(ii)    Explain the effect of the fan on the shoot.

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

………………………………………………………………………………………
[ 3 marks ]

What is the aim of the experiment?

Aim of experiment:
……………………………………………………………………………………
……………………………………………………………………………………
[2 marks ]

(i) Name the physiological process experienced by the leafy shoots

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

Name one structure of the leaf associated with the process named in 2(c)(i) above.

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

_____________________________________________________________________________________________________

COMMENT

             Most candidates performed below average in this question because most of them could not give the correct title to the graph; identify the vertical axis (y), and horizontal axis (x); give the correct scale used; plot correct points and rule the lines of the graph. Some candidates also plotted two graphs separately instead of being on the same section of the graph sheet.
          Many candidates could give the condition under which the bubble moved faster.
          but were not able to explain the effect of the fan on the shoot and
          the aim of the experiment. Many candidates wrote ‘osmosis,’; photosynthesis’ as
          the physiological process; and some also wrote ‘lenticel’ instead of ‘stomata’as the
          part of the plant associated with the process.

             Expected answers include
           2 (a)       Graph

Title (TL) of the Graph – Effect of wind/fan on water loss/transpiration from plant shoots/Effect of fan on the movement of air bubble in a potometer
Labelling of axis (LA)

Scale for X and Y (SC)
Labelling of graphs (LG)

Correct points plotted (CP)

Ruled lines (RL) to pass through the points
Note: The scales must correspond to the graphs.

(b)(ii) Effect of fan/breeze/wind on shoot

Wind/breeze generated by the fan removes water vapour, above the stomata;
Creating a greater moisture gradient/transpiration pull;
In the external environment/atmosphere of the shoot;
Making water vapour move faster out of the leaf;
Causing more water to be absorbed by the shoot/root of shoot.

(ii)    Aim of experiment

To study the effect of environmental conditions/wind/breeze; on the rate of
   transpiration/water loss by shoots.

          (c) (i) Physiological process

Transpiration

Part of leaf

Stomata/stoma
Guard cell(s)