NCERT Book Class 10 Science Lab Manual The World of the Living

The World of the Living

AIM

To prepare temporary mounts of leaf peels to observe stomata and to differentiate between dicot and monocot stomata.

THEORY

In plants, physiological processes such as respiration and photosynthesis involve exchange of gases between plant tissues and the external atmosphere. This occurs through minute microscopic pores called stomata (singular; stoma) present in the leaf. Stoma is an elliptical pore with two kidney shaped guard cells on either side. The guard cells have thin outer and thick inner walls. When guard cells are turgid, the stoma opens and it closes when the guard cells are flaccid.

The number, distribution and type of stomata varies in different plants. Within a plant, the number and distribution may vary between the upper and lower surfaces of leaf. However, the type of stomata remains the same in a particular plant species. Stomata are either absent or non-functional in submerged aquatic plants. In this experiment we shall prepare the temporary mounts of leaf peels of dicot and monocot plants to observe their stomata.

MATERIALS REQUIRED

Fresh leaves of a dicot plant (such as Petunia, Dianthus, Solanum) and a monocot plant (such as lily, maize, grass), compound microscope, slide, cover slip, needle, brush, a piece of blotting paper, and a razor blade.

PROCEDURE

1. Remove a peel from the lower surface of a dicot leaf. This can be easily done by folding or tearing the leaf and pulling out the thin membranous transparent peel. Leaf peels can also be obtained by carefully scratching the leaf surface with a razor blade.

2. Mount the peel on a slide in a drop of water and place a cover slip on it. Avoid air bubbles. Blot the excess water from the slide.

3. Focus the peel under the low power of compound microscope and observe the stomata, guard cells and epidermal cells.

4. Count the number of stomata, and epidermal cells in the field of microscope without disturbing the slide.

5. Observe and identify the contents of guard cells under high power.

6. Move the slide and again count the number of stomata and epidermal cells. Record your observations.

7. Calculate the average number of stomata and epidermal cells in the field of the microscope.

8. Draw the diagram of a stoma and label its parts.

9. Repeat the process with peels removed from a monocot leaf. Record your observations.

10. Following the same procedure, study the stomata of other dicot and monocot plants.

QUESTIONS

• What is the function of guard cells in stomata?

• Why is the number of stomata greater on the lower surface of a leaf?

• Why are stomata absent in roots?

• What is the shape of guard cells in stoma of grass leaf?

• Do guard cells have rigid or elastic walls? Justify your answer

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

• Will you get the same result if you perform the experiment without de-starching the plant? Give reason.

• Why do we warm the leaves in alcohol?

• 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;

• Why do we keep the experimental plant in bright sunlight?

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

• Why do we de-starch the leaves before the experiment?

• What is the role of KOH in the experiment? Can you suggest any other substance that can be used in place of KOH?

• How does the carbon dioxide gas enter the leaves?

• If carbon dioxide gas is essential for photosynthesis, do you think that plants growing in places with high CO2 concentration have an advantage over plants growing in less polluted areas?

• What is the role of KOH in this experiment?

• When we say that plants and animals respire, where exactly is the process occurring?

• Why do we use germinating seeds in this experiment?

• Why do we take a fruit juice (or a sugar solution) for this experiment? Can we use any other food material in place of fruit juice or sugar solution?

• How does the lime water turn milky in this experiment?

• What are the industrial products that are manufactured by the process of fermentation?

• What are the end products of fermentation?

• Which by-product of the fermentation process is useful in baking industry?

• Which by-product of fermentation is useful in brewing industry?

Please refer to attached file for NCERT Class 10 Science Lab Manual The World of the Living