Activity 1.1: Sunlight and Photosynthesis

Aim/Objective: To demonstrate the necessity of sunlight for the process of photosynthesis and the production of starch in leaves.

Materials Required:

• Two potted plants of the same kind.
• Iodine solution.
• Dropper.
• Water.
• A dark room or a large cupboard.

Procedure:

1. Take two healthy potted plants.
2. Keep one plant in a dark room (or a black box) for 72 hours to de-starch the leaves.
3. Keep the other plant in regular sunlight.
4. After 72 hours, perform the iodine test on a leaf from each plant.
5. To perform the iodine test: Pluck a leaf, boil it in water first, then in alcohol (to remove chlorophyll), and then add a few drops of iodine solution.
6. Record the color change.
7. Now, place the plant that was in the dark in sunlight for 3-4 days.
8. Perform the iodine test again on its leaves and record the observations.

Observation:

• The leaf from the plant kept in sunlight turns blue-black when iodine is added, indicating the presence of starch.
• The leaf from the plant kept in the dark does not turn blue-black (it remains brownish), indicating the absence of starch.
• After keeping the "dark" plant in sunlight for a few days, its leaves also test positive for starch (turn blue-black).

Explanation:

• Photosynthesis is the process by which green plants synthesize their food (glucose) using carbon dioxide and water in the presence of sunlight and chlorophyll.
• The glucose produced is stored in the form of starch. Sunlight is a critical energy source for this chemical reaction.
• In the absence of light, the plant uses up its stored starch and cannot produce more, which is why the iodine test (which detects starch) is negative. When returned to sunlight, the plant resumes photosynthesis and begins producing starch again.

Conclusion:

• Sunlight is essential for plants to carry out photosynthesis and produce starch.

Activity 1.2: Observing Stomata

Aim/Objective: To observe the presence of stomata and guard cells on the surface of a leaf.

Materials Required:

• A fresh leaf (e.g., Tradescantia or Lily).
• Microscope.
• Glass slide and cover slip.
• Forceps.
• Water.

Procedure:

1. Peel off a small, thin layer from the underside (lower epidermis) of a fresh leaf using forceps.
2. Place the leaf peel on a glass slide with a drop of water.
3. Carefully place a cover slip over it to avoid air bubbles.
4. Observe the slide under the low power and then the high power of a microscope.
5. Identify the tiny pores and the cells surrounding them.

Observation:

• Tiny, pore-like structures are visible on the leaf surface.
• Each pore is surrounded by two kidney-shaped or bean-shaped cells.

Explanation:

• The tiny pores observed are called stomata (singular: stoma).
• The bean-shaped cells surrounding each stoma are called guard cells.
• Stomata are primary sites for gas exchange (CO2 entry and O2 release) and transpiration (loss of water vapor).
• Guard cells regulate the opening and closing of the stomatal pore by changing their turgidity (swelling and shrinking), which controls the rate of gas exchange and water loss based on the plant's needs and environmental conditions.

Conclusion:

• Leaves contain microscopic pores called stomata, regulated by guard cells, which facilitate gas exchange and transpiration.