[5 Mark Question Answer]

Question 15 Marks

The diagram alongside represents an experiment conducted to prove the importance of a factor in photosynthesis.

Study the same and then answer the questions that follow:
(i) Name the factor being studied in his experiment.
(ii) Why was the plant kept in a dark room before conducting the experiment?
(iii}Why was the experimental leaf then kept in
1. boiling water 2. methylated spirit?
(iv) Name the solution used to test for the presence of starch in the leaf.
(v) What will we observe in the experimental leaf at the end of the starch test?
(vi) Give a balanced chemical equation to represent the process of photosynthesis.

Answer

(i) Sunlight
(ii) To destarch the leaf.
(iii) (1) The leaf was kept in boiling water to kill the cells/ releases the starch grains.
(2) It is kept in methylated spirit to remove chlorophyll.
(iv) Iodine
(v}At the end of the starch test it is observed that the covered part of the leaf remains brown and the exposed part of the leaf remains blue-black.
(vi) $\ce {6CO2 + 12H2O ->[Sunlight][Chlorophyll]C6H12O6 + 6O2 + 6H2O}$

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Question 25 Marks

Complete the following by filling in the blanks numbered 1 to 10 with the appropriate word/term:
Photosynthesis involves light reaction and dark reaction. During light reaction, the chlorophyll present in the (1) ______ gets activated by absorbing light energy. This energy splits (2) ______ molecules to (3) ______ and oxygen and releases two electrons. This process is called (4) ______. The (5) ______ ions are picked up by NADP to form (6) ______. The ADP is converted to (7) ______. This process is called (8) ______. During the dark phase, the compound produced at the end of the light reaction reacts with carbon dioxide to form (9) ______. This product is converted to starch. The process is called (10) ______.

Answer

Photosynthesis involves light reaction and dark reaction. During light reaction, the chlorophyll present in the leaves gets activated by absorbing light energy. This energy splits water molecules to hydrogen ion and oxygen and releases two electrons. This process is called photolysis. The hydrogen ions are picked up by NADP to form $N A D P H _2$. The ADP is converted to ATP. This process is called photophosphorylation. During the dark phase, the compound produced at the end of the light reaction reacts with carbon dioxide to form glucose. This product is converted to starch. The process is called polymerization.

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Question 35 Marks

How does carbon dioxide return to the atmosphere? Explain.
A student in order to study the importance of certain factors of photosynthesis took a potted plant and kept it in the dark for over 24 hours. Then in the early hours of the morning the student covered one of the leaves with black paper in the centre only. Student placed the potted plant in the sunlight for a few hours, and then tested the leaf which was covered with black paper for starch.
(i) What aspect of photosynthesis was being investigated?
(ii) Is there any control in this experiment? If so, state the name.
(iii) Why was the plant kept in the dark before the experiment?
(iv) Describe step by step how the candidate proceeded to test the leaf for the presence of starch.

Answer

(a) Carbon dioxide is returned back to the atmosphere mainly through the following ways:
(i) Respiration - Animals and plants respire and release carbon dioxide in the atmosphere.
(ii) Decay - Plants and animals decay organic matter with the help of bacteria and fungi and release carbon dioxide.
(iii) Combustion - Plants and animals which got buried under the soil changed into coal and oil and releases carbon dioxide when these are burnt.
(iv) Ocean water - Carbon dioxide occurs in the form of lime stone in molluscan shells and as by product of photosynthesis in marine water.
(b) (i) To show that sunlight is needed for photosynthesis.
(ii) Yes, the uncovered portion of the experimental leaf is the control.
(iii) To destarch the leaf.
(iv) 1. Boil the leaf in alcohol.
2. Wash the leaf in water to make it soft.
3. Add iodine solution on the leaf. The portion uncovered shows blue-black colour and the portion covered shows brown colour. This indicates that sunlight is needed for photosynthesis.

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Question 45 Marks

Match the terms of column I with those in column II:

Column I	Column II
(i) Stomata closed	(a) decomposers
(ii) Autotrophs	(b) light reaction
(iii) By-products of photosynthesis	(c) animals
(iv) Photolysis	(d) during night
(v) Bacteria and fungi	(e) green plants
	(f) oxygen

Answer

(i) (d) During night
(ii) (e) Green plants
(iii) (f) Oxygen
(iv) (b) Light reaction
(v) (a) Decomposers

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Question 55 Marks

(i) Fill in the blanks in the following equations of two chemical reactions:
(a) $\ce{---+12H2O->[Light energy]C6H12O6 + --- + ----}$
(b) $\ce{--- 6O2->[Chlorophyll] 6 --- +6 ---- + Energy}$
(ii) Name the two processes represented by the above two reactions.
(iii) State any two differences in these processes other than those already indicated in the reactions.
(iv) Which one of these two reactions is the supporter of all life on earth?

Answer

(a) $\ce{6CO2 + 12H2O ->[Sunlight][Chlorophyll] C6H12O6 + 6O2 + 6H2O}$
(b) $\ce {C6H12O6 + 6O2 -> 6CO2 + 6H2O} + Energy$
(ii) Photosynthesis and respiration.
(iii) Difference between Photosynthesis and respiration :

Photosynthesis	Respiration
(a) It is an anabolic process.	(a) It is a catabolic process.
(b) It results in a gain in dry mass.	(b) It results in a loss in dry mass.

(iv) Photosynthesis

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Question 65 Marks

Describe fully one experiment with potted green plant to show that starch is not produced in the leaves when carbon dioxide is not available (diagrams essential)

Answer

Experiment to show that starch is not produced in the leaves when carbon dioxide is not available:
a. A potted plant is kept in the dark for two days to destarch the leaves.
b. Take a wide mouth bottle and fill 1/ 3'd of it with caustic potash solution.
c. Insert half part of the leaf of potted plant in the bottle and do not let the leaf to
touch the solution in the bottle.
d. The apparatus is kept in sunlight for few hours.
e. The leaf is plucked and tested for starch.
f. Only the portion of the leaf which is outside the bottle turns blue and the part of
the leaf inside the bottle remains colourless because it did not get C0 2 for
photosynthesis. All the C02 present in the bottle was absorbed by caustic
solution.

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Question 75 Marks

Describe an experiment to prove that sunlight is necessary for photosynthesis.

Answer

Experiment to prove that sunlight is necessary for photosynthesis:
a. A potted plant is kept in the dark for two days to destarch the leaves.
b. A part of a leaf is covered with a black paper by clip.
c. Now the plant is kept in the light for few hours.
d. The leaf is plucked and is boiled in water and is then decolourized with
alcohol.
e. The portion of leaf which received light turns blue with iodine because
photosynthesis took place in that part of leaf.
f. The part of leaf which was covered with black paper remains colourless
because photosynthesis could not take place in the absence of sunlight.

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