Viva Voce: Light is Necessary for Photosynthesis | Lab Manuals for Class 10 PDF Download

Q.1. Will you get the same result, if you perform the experiment without de-starching the plant. Give reason.

No, the results will not be the same because the starch stored in plants will interfere with the result.

Q.2. Arrange the following steps in correct sequence
(i) De-starching the plant
(ii) Treatment with iodine
(iii) Attaching black paper strips to the leaf
(iv) Keeping the set up in sunlight

1, 3, 4 and 2

Q.3. Can this experiment be performed with a de-starched leaf detached from the plant? Give reasons.

No, because another raw material, i.e. water is supplied byxylem from roots to the leaves for photosynthesis. Thus, leaf detached from plant cannot perform photosynthesis.

Q.4. During the process of photosynthesis, glucose is released as the end product, then why is the iodine test performed?

In plants, carbohydrates are used and stored in the form of starch by polymerisation of glucose molecules. The presence of starch can be easily detected by change in colour of leaf by iodine solution. Hence, iodine test is performed over glucose test.

Q.5. During photosynthesis, the light energy is trapped by which cell organelle?

Chloroplast (i.e. a type ofplastid) traps the light energy.

Q.6. Which fraction of light is used during the photosynthesis by plants?

Visible light

Q.7. Why does the portion of leaf covered with black paper strips not respond to iodine test?

It is so because iodine test is positive only with starch. This portion did not have starch due to non-availability of light for photosynthesis so, it does not respond or show blue-black colour to the iodine test.

Q.8. What are the features present in green leaves that make it suitable site for photosynthesis?

These features include:

• Large leaf surface area for absorbing maximum light.
• Numerous stomata.
• Presence of chloroplasts in mesophyll cells.

Q.9. Black paper strips are used to cover a portion of leaves in this experiment. Why?

Black colour is a good absorber of light, thus it blocks the light rays to reach the covered part and stop photosynthesis process.

Q.10. Photosynthesis occurs in which ceils of plants?

Mesophyll cells

Q.11. Why do we keep the experimental plant in bright sunlight?

The plant will perform photosynthesis when kept in bright sunlight.

Q.12. Why do we warm the leaves in alcohol?

Alcohol is used because it removes the chlorophyll pigment and decolourise the leaves which help in clear detection of changes during iodine test.

Q.13. What is meant by de-starching? Why do plants get de-starched when kept in continuous darkness for about forty eight hours?

De-starching refers to the complete removal of starch from a plant. Plants kept in darkness for long duration are not able to carry out photosynthesis process due to the absence of light. The plant then uses its stored starch supply leading to de-starching.