1973-11-23 — Page 15

育教轝 真三第張四第一日九廿月十年丑癸服夏 WAH KIU

堅道書院主編

1974中學會考試題預習專欄

生物科(課程乙)(三) 卓唐慕儀

BIOLOG

(3)

III. Source of Energy used by

Living Things.

Look at the diagram and write

a short summary to explain the processes.

b) What is meant by the term

c.)

photosynthesis'?

) Why is this process so import-

ant in nature?.

d) Describe two experiments to support your answer in (b).

[Kinetic Eu].

Water Vapour

Free Energy

↑

Lost to Space

BRARY

報日僑華

Solar

Light Energy

Stored En

Water absorbed.

from soil roots

Photos.

Respication

esynthewis

←← EARTH

[Stored EN].

AIR

→ Sugar+O2

- CLoups ←← AIR ←

Energy

The diagram shows that if there were no sun, all living things would die owing to lack of energy.. Note the exchange of energy in the diagram..

Solar energy

stored energy (potential En

kinetio En.

(released for work)

Note how. plante obtain raw

日三廿月一十年三七九一公年二十六國民華中

五期星

materials for photosynthesis and how animals use the food made by plants (food chain) to obtain energy.

Note how plants help to remove

00. from air thus maintain.the.

composition of air constant.

b. Photosynthesis can be regarded as the only process which make organisms alive. All living things require food. Plants have to make its own food. Photosynthesis is such a food- making process. It builds up: carbohydrates from carbon dioxide and water with: chlorophyll acting as an

enzyme to absorb the necessary energy from the sun.

sunlight

Equation: 6H20 + 6002 chlorophyll

C6H1200 +602个

As mentioned above, plants: manufacture food necessary all living organisms. It is the store-house of energy. A13. things rely directiy (herbivor- es) or indirectly (carnivore & omnivore) on plant as its source of

energy

supply food ann) A good

ahare of what economists term wealth originates directly as a consequence of photosynthesis Our heritage of coal, oil and gas from mother earth are deriv wed from the remains of Tiving organisms and thus from:: photosynthesis.

To conclude, man"s very exist-

ance depends largely on. photosynthesis.

d. This question is quite familiar.

to you. I would like to stress

here a few pointers thet are important in doing such experiments.

(i) Prior to using any green

plants or variegated plants for photosynthesis experiments, they must be first destarched (Kept in the dark for at least 24 hours) Next test one of their leaves for any presen -ce of starch (should be none) before start of experiment otherwise there can be no prove that: photosynthesis. occur during the experiment. (ii) There must be a control

experiment for every. controlled experiment (the one which you control the factor to be: proved).

(1) Th proving photosynthesis:

occurred, we can only prove that starch was or was not. made thus starch test is. necessary. In doing this, remember that we use iodine solution and NOT iodine; that the colour changed from brown to blue-black: indicates a positive result ie starch is present. Pre-reading topic:-

Source of Energy used by Living organisms. contd.

Experiments on Photosynthesis.

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The

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