Page 16 - Focus PT3 2020 Science ( BI Version )

Science PT3 Chapter 2 Cell as the Basic Unit of Life
Photosynthesis

1. Green plants are able to make their own Ethanol
food through the process of photosynthesis. Leaf Boiling Hot water
water
Photosynthesis is the process by which Bunsen burner Form
green plants make food from carbon (turned off)
Form
dioxide and water in the presence of light 1
and chlorophyll. A leaf is immersed The leaf is placed
into a beaker of into a boiling
boiling water for a tube containing
2. Chloroplasts are the cell structures involved few minutes to break ethanol which is
in photosynthesis and contain chlorophyll down the cell walls then placed into a
that absorbs sunlight. and soften the leaf. beaker of hot water
for a few minutes
3. Green plants use carbon dioxide and to decolourise the
water in the presence of sunlight and leaf (to remove
chlorophyll to make food in the form of chlorophyll).
glucose. Oxygen is released as the by-
product of photosynthesis.

Iodine
Carbon dioxide Hot solution
water
is absorbed
Sunlight White
tile
Chlorophyll The decolourised The leaf is placed
Glucose leaf is then dipped on a white tile. A
produced into a beaker of few drops of iodine
hot water for a few solution are added
Oxygen released seconds to get the on to the leaf to test
ethanol off the leaf. for starch.
Water absorbed
by roots

Figure 2.17 Steps involved in the iodine test for starch
Figure 2.16 The process of photosynthesis
7. The presence of starch in the leaf can be
4. The whole process of photosynthesis can be tested using iodine solution after removing
summarised by the following equation: the chlorophyll using an alcohol.

Sunlight 8. Starch is present if the brown colour of
6H O + 6CO C H O + 6O 2
2
2
12
6
6
Water Carbon Chlorophyll Glucose Oxygen iodine solution turns blue-black.
dioxide
9. Experiments 2.1 – 2.4 are carried out to
show the factors required for photosynthesis
5. Excess glucose is stored in the form of such as light, carbon dioxide, chlorophyll
starch in leaves, stems, fruits and roots.
and water.
6. We can determine whether photosynthesis
has taken place in a plant by testing the
presence of starch in the leaf using the
iodine test.

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