Two healthy green plants were places in the dark for 24 hours. They were then set up, as shown in the figure, for 4 hours. Then a leaf was taken form each plant and the chlorophyll was removed from the leaves:
(i) What is the next and final step in this experiment?
(ii) What would be the results of the final step?
(iii) Why was it necessary to grease the glass sheet?
(iv) What hypothesis is being tested in this experiment?
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Solution

(i) The next and final step in this experiment is to perform iodine test for the presence of starch.

(ii) The results would be positive for the plant kept outside the jar, i.e., its leaf will turn blue-black on addition of iodine solution, while the result would be negative for the plant kept inside the jar, i.e., there will be no change in the colour of the leaf on addition of iodine solution.

(iii) It was necessary to grease the glass sheet so that no air could enter the jar, thereby no carbon dioxide was made available to the plant.

(iv) The hypothesis that is being tested here is that carbon dioxide is necessary for photosynthesis.

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Similar questions

Two healthy green plants were placed in the dark for 24 hours. They were then set up as shown in the figure and were left for 4 hours. Then a leaf was taken from each plant and the chlorophyll was removed from the leaves.

What hypothesis is being tested in this experiment?

A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept it in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with dark paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.

(a) What aspect of photosynthesis was being investigated ?

(b) Is there any control in this experiment ? If so, state it.

(d) Describe step by step, how the candidate proceeded to test leaf for the presence of starch.

Q. An experiment was set up as shown in the adjoining figure. The twig in the diagram was intact on the plant and it was left as such in sunlight for a few hours.
(i) What is the aim of the above experiment?
(ii) Why was potassium hydroxide placed inside the conical flask?
(iii) What test would you perform on the leaf inside the flask?
(iv) What is the expected result of the above test?
(v) Is it necessary to similarly test on outer leaf also? Give a reason.
Figure

Q. The steps taken for setting up an experiment to demonstrate that ‘light is necessary for photosynthesis’, were as follows :
• A strip of black paper was clipped on the leaf of a potted plant
• The plant was kept in the sun for four hours
• The strip was removed and the leaf was placed in boiling alcohol in water bath
• The leaf was washed and tested for starch
The result was not as expected. Identify the step which had been missed out :
(1) The plant was kept in the dark for 24 hours before starting the experiment
(2) The leaf was boiled in water after placing it in boiling alcohol
(3) The leaf was sprinkled with water before placing it in black paper strip
(4) A transparent strip was used to cover the black paper strip

Q. 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 dept 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.

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