Unit-III: Adaptive Anatomy and Plant Physiology

This unit provides practical exposure to the structural adaptations of plants to their environments and the physiological processes maintaining plant metabolism.

Observation of internal structural changes that allow plants to survive in extreme moisture conditions.

A. Hydrophytes (e.g., Hydrilla, Nymphaea)

• Aerenchyma: Presence of large air cavities in the cortex of stem and roots to provide buoyancy and facilitate gas exchange.
• Reduced Xylem: Since water is abundant, the vascular tissue, especially xylem, is highly reduced.

B. Xerophytes (e.g., Nerium, Casuarina)

• Sunken Stomata: Stomata are located in deep pits (stomatal crypts) to reduce water loss by transpiration.
• Thick Cuticle: A thick waxy layer on the epidermis to minimize non-stomatal water loss.
• Mechanical Tissue: Well-developed sclerenchyma to provide support and prevent wilting during drought.

This experiment determines the osmotic potential of plant cell sap using the plasmolytic method.

Procedure:

• Prepare a series of sugar or salt solutions of known molarity (e.g., 0.1M to 1.0M).
• Place epidermal peels (e.g., Rhoeo or Onion) in each solution for 20-30 minutes.
• Identify the "incipient plasmolysis" stage where 50% of cells show detached protoplasts from the cell wall.

Calculation:

Osmotic Potential (Ψs) = -miRT

Where:
m = molarity of solution at incipient plasmolysis
i = ionization constant (1 for sucrose)
R = gas constant (0.083 bars/mole deg)
T = absolute temperature (273 + room temperature)

Determining the water potential of a tissue (like potato tuber) by measuring weight changes in different osmotic environments.

• Observation: If the tissue gains weight, the external solution has a higher water potential than the tissue. If it loses weight, the tissue has a higher water potential.
• Equilibrium: The molarity where no weight change occurs indicates that the water potential of the tissue is equal to the water potential of the solution.

Quantitative analysis of stomata on leaf surfaces to compare adaptations between mesophytes and xerophytes.

Key Parameters:

• Stomatal Frequency: The number of stomata per unit area of leaf.
• Stomatal Index (SI): The percentage of the total number of epidermal cells that are stomata.
  Formula: SI = [S / (E + S)] x 100 (where S = number of stomata, E = number of epidermal cells).

Study of physiological triggers in early plant growth.

• Effect of Light: Observation of how light quality and duration affect the percentage of seed germination.
• Amylase Induction: During germination, gibberellins induce the synthesis of α-amylase in the aleurone layer to break down starch into maltose for the growing embryo.