K.C.S.E Biology Q & A - MODEL 2017PP2QN06

K.C.S.E Biology Q & A - MODEL 2017PP2QN06

In an investigation, two potted plants G and H belonging to the same species were exposed to increasing light intensities at different temperatures, 30°C and 20°C respectively. The rate of photosynthesis was measured for each plant and results recorded as shown in the table below:

​(a) On the same axis, plot graphs of rate of photosynthesis against light intensity for plants G and H. 
(b) State the aim of the investigation. 
(c) Account for the difference in the rate of photosynthesis in the two plants.
(d) Account for the difference in the rate of photosynthesis in the two plants between the following light intensities:
(i) 1—4 units 
(ii) 4—8 units. 
(e) (i) Predict the rate of photosynthesis at light intensity of 16 units. 
(ii) Give a reason for your answer in (e) (i) above. 
(f) State one internal and one external factor that could be limiting in the investigation.

answers

b) To investigate/compare the effect of (varying) light intensity/temperature on the rate of photosynthesis;
c) Rate of photosynthesis is higher in plant G (than H); (Photosynthesis being an enzymatic process), enzymes were subjected to favourable/optimal temperatures (of 30°C): hence more activated, unlike in plant H where temperatures were lower (20C); 
d) (i) 1-4 units
Rapid increase in rate of photosynthesis increases with the increase in light intensity; due to increase in light energy for photosynthesis/formation of more ATP molecules;
(ii) 4 — 8 units 
Slower/gradual increase in the rate of photosynthesis as the light intensity increases: because other factors become limiting/some chlorophyll molecules start bleaching;
e) i) Slight increase/no significant increase/remains constant;
ii) The optimum light intensity has been exceeded/some chlorophyll could be destroyed;
f) Internal factor — Chlorophyll/enzyme concentration;
External factor — Carbon (IV) oxide concentration/amount of water;