With the aid of diagrams, describe an experiment to show that chlorophyll is necessary for photosynthesis to take place.

• Stoma: Regulates gas exchange (carbon dioxide intake, oxygen and water vapor release) between the plant and the atmosphere.
• Synovial fluid: Lubricates the joint, reducing friction between articular cartilages, and provides nutrients to the cartilage.
• Tendon: Connects muscle to bone, transmitting the force generated by muscle contraction to move the bone.
• Root hair: Increases the surface area of the root for efficient absorption of water and mineral salts from the soil.

b) ii)

Halophytes are plants adapted to grow in saline environments.

• They possess salt glands on their leaves to excrete excess salt.
• They have succulent leaves or stems to store water and dilute the accumulated salts.
• They can exclude salt at the root level, preventing its uptake.
• They have a high tolerance for internal salt concentrations.

b) iii)

Proteins are essential macromolecules with diverse roles in the body.

• Enzymatic function: Act as biological catalysts (enzymes) to speed up biochemical reactions.
• Structural support: Provide structural components for cells and tissues (e.g., collagen in connective tissue, keratin in hair and nails).
• Transport: Facilitate the transport of substances (e.g., hemoglobin transports oxygen, membrane proteins transport ions).
• Immune defense: Form antibodies that protect the body against pathogens.
• Hormonal regulation: Some hormones are proteins (e.g., insulin) that regulate physiological processes.
• Movement: Components of muscle fibers (actin and myosin) are proteins responsible for muscle contraction.

c)

This experiment uses a variegated leaf (a leaf with green and non-green areas) to demonstrate the necessity of chlorophyll for starch production, a product of photosynthesis.

• Materials: A potted variegated plant (e.g., Coleus or Croton), beaker, test tube, ethanol, iodine solution, white tile, Bunsen burner, tripod stand, gauze mat, water bath.

• Procedure:

  1. Destarching: Place the potted variegated plant in a dark room for 2-3 days. This ensures that any pre-existing starch in the leaves is used up.
  2. Exposure to light: Transfer the plant to bright sunlight for several hours (e.g., 6-8 hours).
  3. Leaf selection and drawing: Pluck a variegated leaf from the plant. Make a clear drawing of the leaf, indicating the green (chlorophyll-containing) and non-green (chlorophyll-lacking) areas.
  4. Boiling in water: Immerse the leaf in boiling water for a few minutes. This kills the leaf cells and breaks down cell membranes, making it permeable to iodine.
  5. Decolorization: Transfer the leaf to a test tube containing ethanol. Place the test tube in a hot water bath (do not heat ethanol directly over a flame as it is flammable). Boil until the leaf becomes pale white or yellowish, indicating that the chlorophyll has been extracted.
  6. Washing and softening: Remove the decolorized leaf from the ethanol and wash it thoroughly with cold water to remove any residual ethanol and to soften the leaf, making it less brittle.
  7. Iodine test: Spread the softened leaf on a white tile and add a few drops of iodine solution over its entire surface.

• Observation:

  • The parts of the leaf that were originally green (containing chlorophyll) will turn blue-black, indicating the presence of starch.
  • The parts of the leaf that were originally non-green (lacking chlorophyll) will remain yellowish-brown (the color of the iodine solution), indicating the absence of starch.

• Conclusion: This experiment demonstrates that starch, a product of photosynthesis, is only formed in the areas of the leaf that contain chlorophyll. Therefore, chlorophyll is essential for photosynthesis to occur.

• Diagrams:

  • Diagram 1: Variegated Leaf Before Iodine Test
    • A simple outline of a leaf showing distinct regions: one part labeled "Green area (with chlorophyll)" and another part labeled "White/Yellow area (without chlorophyll)".
  • Diagram 2: Variegated Leaf After Iodine Test
    • A similar outline of the leaf. The area corresponding to the original green part should be shaded dark and labeled "Blue-black (starch present)". The area corresponding to the original white/yellow part should be left unshaded or lightly shaded and labeled "Yellowish-brown (starch absent)".