Question

Assertion (A) : Transpiration lowers down plant temperature.

Reason (R): Transpiration reduces the concentration of mineral salts.​

Answer 1

Answer:

• Assertion is right but Reason is wrong

Transpiration is of immense importance in plant life as it is of great benefit to the plant.

Beneficial roles of transpiration

Gaseous exchange:

Transpiration is essential in the life of land plants. It helps in the absorption of carbon dioxide (CO2) from the atmosphere during photosynthesis as the openings of stomata in day time facilitate gaseous exchange.

Cooling effect:

The leaves absorb the radiant energy. Some of the light energy is utilised in photosynthesis, rest is converted into heat energy resulting in an increase in leaf temperature. However, rapid loss of water in the form of water vapour from the aerial parts of the plant through transpiration brings down their temperature. Transpiration thus provides a significant cooling effect which keeps the plant from being overheated.

Effect on mineral transport:

Mineral salts remain dissolved in the soil water and are absorbed by the roots. Minerals that are absorbed and accumulated in the xylem duct of the root move up and are distributed in the plant by the transpiration stream.

Effect on water movement:

The absorbed water is transported from roots to leaves through the xylem vessels which is greatly influenced by transpiration pull. Water loss due to transpiration results in the development of low water potential in the leaf tissues. Thus water moves from the xylem vessels to the leaf cells and helps in the ascent of sap.

Answer 2

The Assertion is true and Reason is false.

TRANSPIRATION -

• The process of evaporation or water loss through stomatal pores present on the leaves of the plant.
• The cohesion force between water molecules helps in the pull of the water in the upward direction.
• The advantages of the process of transpiration are -

1. Water Absorption - Helps in the ascent of sap and absorption of water from the soil.

2. Water Removal - The extra water is removed by transpiration from the plant body.

3. Cooling effect - It lowers the plant temperature by 10 - 15 degrees celsius.

4. Mechanical strength - It facilitates the growth of tissue to provide strength to the plant.

5. Increasing concentration of the mineral salts - Due to evaporation of the water from the ascent of sap the mineral concentration increases.

6. Root system - The transpirational pull helps in the absorption from soil and the development of the root system.

7. Photosynthesis - The pull facilitates the absorption of more water from the soil and is used in the process of food formation.

8. Resistance and turgidity - Maintain the shape of the cell and make them hard and resistant during droughts.