Mark Scheme Assessed Lab 3
Sample Result
A. Mean distance moved per 5 min interval = 10.6 mm
( 1 mark)
Mean distance moved per minute = 2.1 mm min–1
( 1 mark)
B. Volume of water lost per minute = 6.6 mm3 min–1
( 2 marks)
C. The calculated value of volume of water lost per minute may not necessarily be the
actual volume of water lost from the leaves because:
- some water is used in photosynthesis
( 1 mark)
- some water is stored within the plant cells.
( 1 mark)
D. Functions of transpiration:
- cooling
( 1 mark)
- transport of minerals/water to leaves.
( 1 mark)
- support.
( 1 mark)
E. The potometer is set up underwater to avoid unwanted air bubbles in the xylem of the
plant which may disrupt the transpiration stream.
( 1 mark)
F. It varies with each time interval roughly 0.3 to 5mm distance movement ( 1 mark)
There are factor that affects the distance movement per interval such at heat, light
intensity and humidity
( 1 mark)
G..1 If the leaves are wet, this may block the pores/stomata.
( 1 mark)
This means transportation cannot occur, so the leaves need time to dry. ( 1 mark )
G.2 As the light intensity increases the rate of water movement increases. ( 1 mark)
This is because plants open their stomata in response to light, ( 1 mark)
thus, allowing water vapour to escape from the leaves. ( 1 mark)
G.3 Introducing the air bubble is not very easy. (Any 2 mark)
The twig may not remain fully alive for a long time.
Any changes in the temp of atmosphere may affect the position of the air bubble in
the capillary tube.
( 4 marks)