Page 281 - Biology_F5

Biology for Advanced Level Secondary Schools

Enzymes (b) Describe the pattern of the colour of
Photosynthesis is an enzyme controlled the patches of the leaf.
process. For example, the enzyme PEP (c) Place the leaf in the beaker containing
carboxylase is crucial for fixation of hot water and boil it for about 10
carbon dioxide in the mesophyll cells. minutes.
Similarly, RuBP carboxylase is an (d) Take out the leaf and place it in boiling
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important enzyme necessary for carbon ethanol in a water bath for about 10
dioxide fixation in bundle sheath cells minutes.
during dark reaction. Another enzyme (e) Remove the leaf from ethanol and
wash it with running water.
is ATP synthase found in the thylakoid
membrane. This enzyme is vital for ATP (f) Place the leaf on a white tile and add a
synthesis during photophosphorylation few drops of Iodine solution.
process. These enzymes perform their role (g) Record any observable colour changes.
actively under optimal condition below (h) Describe the colour pattern after being
which they become inactive and above stained with iodine solution.
which they are denatured. If the enzymes (i) Compare the colour pattern of the

are inactive, the rate of photosynthesis patches with that of the original leaf
proceeds very slowly. In contrast, when in b).
the enzymes are very active, the rate of
photosynthesis becomes very high. Safety precaution
Avoid direct flame near ethanol because
it is highly flammable.
Activity 5.2: Investigating the role of
chlorophyll in photosynthesis Questions

Materials 1. Why was the variegated leaf used in
Variegated plant, Iodine solution, bea- the above experiment?
ker, ethanol, water, burner, and white tile 2. What was the reason for boiling the
leaf in ethanol?
Procedure 3. From the observations made in the
(a) Pick a variegated leaf from a plant experiment, what is the role of chlo-
(Figure 5.8) which has been exposed rophyll in the leaf?
to sunlight for three to four hours.
b) External factors
The external factors, which are also known
as environmental factors that affect the rate
of photosynthesis, include atmospheric
carbon dioxide concentration, water
availability, wind, temperature, mineral
and nutrients supply as well as light.

Figure 5.8: Variagated leaves

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