Transpiration in Plants Test - 2

This loss of water in the form of vapour from living plants, particularly from the aerial parts, is known as transpiration. The process is in principle one of evaporation and diffusion.

Transpiration is the process of evaporation of water through aerial parts ( leaves and stem ) of plants. 97-99 % of water absorbed through roots is lost by transpiration. In leaves, there are pores called stomata for transpiration.

In dorsiventral leaves, these leaves have somewhat difference in anatomy like no. of stomata. On the lower side or ventral side more no. of stomata are present in comparison to the dorsal side to reduce transpiration. As sunlight can not directly approach the stomata present at the lower side.  

So the correct answer is 'Reduction in transpiration'.

Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 97–99.5% is lost by transpiration and guttation. Leaf surfaces are dotted with pores called stomata (singular "stoma"), and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells and their stomatal accessory cells (together known as stomatal complex) that open and close the pore. Transpiration occurs through the stomatal apertures, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots. Two major factors influence the rate of water flow from the soil to the roots: the hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil. Both of these factors influence the rate of bulk flow of water moving from the roots to the stomatal pores in the leaves via the xylem.

Blue and red light stimulate the stomatal opening. Among this, blue is the most effective light for the opening of stomata, it is perceived by phototropins that promote the increase in the solute concentration of guard cells. It also increases the phototropic response.

The rate of transpiration is roughly inversely proportional to atmospheric humidity. When there is diffusion of water vapors through stomata, it is in accordance with the law of simple diffusion, meaning, the rate of transpiration is greatly reduced when the atmosphere is very humid.

Transpiration, the loss of water vapor from plants, is a physical process that is under control of both external physical and physiological factors. Solar radiation provides the energy source for transpiration. Most water loss is from leaves and stomata largely control leaf transpiration.

The three major types of transpiration are: (1) Stomatal Transpiration (2) Lenticular Transpiration and (3) Cuticular Transpiration. Transpiration mainly takes place through surface of leaves. It is known as Foliar transpiration (more than 90%).

When the leaves are greased, the rate of transpiration is decreased drastically. So, when both the surfaces are greased, irrespective of where the stomata are present, transpiration will be highly reduced as a result, these leaves would dry up last.

Stomata are tiny holes found in the underside of leaves. They control water loss and gas exchange by opening and closing. They allow water vapour and oxygen out of the leaf and carbon dioxide into the leaf.

The guard cells swell when water flows into them , causing the stomata pore to open.

Aquatic plants float on the surface of the water and therefore stomata are not found in the lower epidermis. Stomata are found on the upper epidermis because for direct exchange of gases between the leaf and the atmosphere. But in the terrestrial plants, stomata are at the lower epidermis because this is an adaption to reduce the excessive loss of water through transpiration.

Therefore, the correct answer is option D.

Transpiration pull will be maximum under open stomata, dry atmosphere and moist soil.

Relative humidity – Relative humidity (RH) is the amount of water vapor in the air compared to the amount of water vapor that air could hold at a given temperature. A hydrated leaf would have a RH near 100%, just as the atmosphere on a rainy day would have. Any reduction in water in the atmosphere creates a gradient for water to move from the leaf to the atmosphere. The lower the RH, the less moist the atmosphere and thus, the greater the driving force for transpiration. When RH is high, the atmosphere contains more moisture, reducing the driving force for transpiration. The rate of transpiration increases in dry atmosphere. 

Therefore, the correct answer is option D.

Transpiration is a process by which the moisture is carried through plants from the roots to the stomata where it is converted into vapour and is released out to the atmosphere that is the evaporation of water from plant leaves. The water which is lost annually is pure water.

Maximum transpiration takes place from leaves. It is known as foliar transpiration. The leaves have stomata. Stomata are small openings on the leaves which helps in transpiration and gaseous exchange.