Biology [3 marks Question Answer]

(i) bark
(ii) stems
(iii) gaseous
(iv) carbon dioxide
(v) woody

(i) Hydathode
(ii) Garden nasturtium, grasses
(iii) Guttation

(i) A. Guard Cell, B. Stoma
(ii) The above structure is known as stomatal apparatus.
(iii) The part A is known as guard cell which helps in the opening and closing of stomata.

(i) The given apparatus is Ganong's potometer.
(ii) The experiment takes long time and the twig may not remain alive for this much duration.
(iii) Transpiration is measured with the help of given apparatus.

Four disadvantages of transpiration to the plant are:
(i) Stunted growth- Transpiration reduces the amount of water available to the plant. Plant with water deficit decreases in growth and thus, the plant remain stunted. Hence, excessive transpiration may result in the stunted growth of the plant.
(ii) Wilting-Wilting is the loss of turgidity. It occurs mostly during afternoon when transpiration rate is higher than the rate of water absorption through roots. The leaf cells become flaccid causing wilting of plant. Sometimes, it may be due to diseases also.
(iii) Energy expenditure-As most of the water absorbed is lost through transpiration, and energy is utilised in transpiration and conduction of water goes waste.
(iv) Abscission- When very little water is available to plant, transpiration results in the closing of stomata following the production of abscissic acid. It causes premature leaf fall and delayed flower production.

The rate of transpiration get affected by various internal and external factors. Some of the factors that affect it majorly are:
(i) Wind velocity-Wind will affect the rate of transpiration. Wind blow away the small pockets of humid air that develops when air is still. With the removal of these, wind will increase the movement of water from leaf surface, and thus more transpiration will occur. The higher the wind speed the higher the rate of transpiration.
(ii) Intensity of light- The higher the light intensity, the higher the rate of evaporation. Light intensity stimulates stomatal openings which in turn brings about an increase in transpiration.
(iii) Humidity-Humidity is defined as the water vapour present in the air. For water to evaporate, there must be a water potential gradient between the air in the leaf and the atmosphere. As the humidity increases in the surrounding, the rate of transpiration decreases. Water evaporates easily in drier air than that in more saturated air.

(i) Leaves with thick cuticle - Some desert plants develop a thick waxy cuticle over the epidermis to reduce the loss of water by transpiration.
(ii) Reduced number of stomata - These plants have few stomata and concentrated on the underside of leaves to avoid direct sunlight.
(iii) Presence of epidermal hair - In some plants like cucurbits, leaf surface may be covered by thick coating of epidermal hairs to reduce transpiration.
(iv) Presence of sunken stomata - The stomata of leaves in dry environment sink into the leaf to reduce the surface area of the pores which further reduces rate of transpiration.
(v) Leaves modified into spines - In cactus, leaves are modified into spines to reduce surface area for transpiration, while their stem performs photosynthetic functions.