Quiz

Detailed Description of Topics Covered in the MCQs

1. Transport of Water in Plants

Water transport in plants occurs primarily through xylem, which consists of vessels and tracheids. This process is driven by:

• Transpiration pull: A force created by the evaporation of water from the leaves.
• Cohesion and adhesion: Cohesion refers to the attraction between water molecules, while adhesion refers to the attraction of water molecules to xylem walls.
• Root pressure: A minor force generated by the active uptake of ions in the roots.

2. Transpiration

• The process by which plants lose water as water vapor from aerial parts, especially through stomata.
• Factors affecting transpiration include temperature, humidity, wind speed, and light intensity.
• Benefits: Helps in nutrient transport, cooling the plant, and maintaining turgor pressure.

3. Osmosis and Water Absorption

• Osmosis is the movement of water across a semipermeable membrane from a region of higher water potential to lower water potential.
• Root hairs absorb water from the soil by osmosis, providing a steady supply to the plant.

4. Ascent of Sap

• Movement of water and minerals from roots to aerial parts is called the ascent of sap.
• Explained by the Transpiration-Cohesion-Tension theory, which highlights the roles of transpiration pull, cohesion, adhesion, and root pressure.

5. Transport of Minerals

• Minerals are absorbed by the roots through active transport, which requires energy in the form of ATP.
• They move through xylem to various parts of the plant, supporting growth and metabolic functions.

6. Phloem Transport

• Phloem is responsible for transporting organic nutrients like sucrose from source (e.g., leaves) to sink (e.g., roots, fruits).
• This movement is called translocation and is explained by the Pressure Flow Hypothesis, where pressure gradients drive the flow of nutrients.
• Sieve tube elements and companion cells play critical roles in this process, with companion cells supplying energy.

7. Energy for Transport Processes

• Energy in the form of ATP is required for:
  • Active transport of minerals into roots.
  • Loading and unloading of sucrose in the phloem.

8. Cuticle and Epidermis

• Cuticle: A waxy layer on the leaf surface that prevents excessive water loss.
• Epidermis: Protects against pathogens and helps in water retention.

9. Stomata and Gaseous Exchange

• Stomata are small pores primarily on the leaf surface involved in:
  • Transpiration: Water vapor loss.
  • Gas exchange: Uptake of carbon dioxide and release of oxygen during photosynthesis.
• Guard cells regulate the opening and closing of stomata.

10. Root Pressure

• Root pressure is generated by the active transport of ions into the root xylem, creating an osmotic gradient that drives water upward.
• Plays a role in water transport during low transpiration conditions, like at night.

11. Environmental Factors Affecting Transpiration

• Temperature: Higher temperatures increase the rate of transpiration.
• Humidity: High humidity reduces transpiration by lowering the water potential gradient.
• Wind speed: High wind speeds increase transpiration by removing the water vapor near the leaf surface.
• Light intensity: Promotes stomatal opening and thereby increases transpiration.

12. Guttation

• The loss of liquid water through specialized structures called hydathodes, occurring in conditions of high root pressure and low transpiration (e.g., at night).
• Different from transpiration as it involves liquid water rather than water vapor.