(A) Multiple Choice Type 

Question 1: Transpiration pull will be maximum under which set of the following conditions? 

(a) Open stomach, dry atmosphere and moist soil. 

(b) Open stomata, high humid atmosphere and well irrigated soil. 

(c) Open stomata, high humid atmosphere and dry soil. 

(d) closed stomata, dry atmosphere and dry soil. 

Solution 1: (a) Open stomata, dry atmosphere and moist soil 

Question 2: With decrease in atmospheric pressure, the rate of transpiration will 

(a) increase 

(b) decrease rapidly 

(c) decrease slowly 

(d) remain the same 

Solution 2: (a) increase 

Question 3: The rate of transpiration is more when 

(a) atmosphere is dry 

(b) temperature is high 

(c) humidity is high 

(d) atmosphere is dry and temperature is high 

Solution 3:(b) temperature is high 

Question 4: One of the internal factors which affect the rate of transpiration is 

(a) big size of the leaf 

(b) colour of the leaf 

(c) sunken stomata 

(d) sunny day 

Solution 4: (c) sunken stomata 

Question 5: Guttation takes place through 

(a) stomata 

(b) lenticels 

(c) lower epidermis of leaves 

(d) hydathodes 

Solution 5: (d) hydathodes 

Question 6: The loss of water as water vapour from the aerial parts of a plant is known as 

(a) evaporation 

(b) perspiration 

(c) guttation 

(d) transpiration 

Solution 6: (d) transpiration 

Question 7: Transpiration will be fastest when the day is 

(a) cool, humid and windy 

(b) hot, humid and still 

(c) hot, humid and windy 

(d) hot, dry and windy 

Solution 7: (d) hot, dry and windy 

Question 8: Most of the transpiration in tall trees occurs through 

(a) stomata 

(b) Lenticels 

(c) cuticle 

(d) Bark 

Solution 8: (b) Lenticels 

Question 9: Transpiration is best defined as 

(a) loss of water by the plant 

(b) evaporation of water from the surfaces of a plant 

(c) loss of water, as water vapour, by a plant 

(d) release of water by a plant into the atmosphere 

Solution 9: (b) evaporation of water from the surfaces of a plant 

B. Short Answer Type 

Question 1: Name the following: 

(a) Openings on the stem through which transpiration occurs 

(b) The process by which the intact plant loses water in the form of droplets. 

(c) An instrument used to find the rate of transpiration 

(d) A plant in which the stomata are sunken 

(e) The apparatus to record the rate of transpiration in a cut shoot. 

(f) Any two parts of a leaf which allows transpiration. 

(g) The structure in a leaf that allows guttation. 

(h) Loss of water as droplets from the margins of certain leaves. 

Solution 1: 

(a) Lenticels 

(b) Guttation 

(c) Potometer

(d) Nerium 

(e) Ganong's photometer 

(f) Stomata and cuticle 

(g) Hydathodes 

(h) Guttation 

Question 2: Fill in the blanks: 

(a) Transpiration is the loss of water as water ________ from the _______ parts of the plant. 

(b) Closing of ............... and shedding of leaves reduce ........... 

(c) Transpiration helps in Creating ... ............ force and in eliminating excess........... 

Solution 2: 

(a) vapour, aerial 

(b) stomata, transpiration 

(c) suction, water (heat) 

Question 2: State whether the following statements are True (T) Or False (F)? 

(i) Most transpiration occurs at midnight. 

(ii) Transpiration creates a pull for upward movement of the sap. 

(iii) Wind velocity has an effect on transpiration. 

(iv) Voltmeter is an instrument used for measuring the rate of transpiration in green plants. 

(b) Rewrite the false statements, in 2 above, in the correct form by changing either the first or the last word only. 

Solution 2:

(i) False 

(ii) True 

(iii) True 

(iv) False 

(b) (i) Most transpiration occurs at mid-day. 

(iv) Potometer is an instrument used for measuring the rate of transpiration in green plants. 

Question 3: Differentiate between guttation and bleeding in plants. 

Solution 3:

Guttation:

i) It is the removal of water from the plants because of excess water buildup in the plant.

ii) water escapes from specialized structures called hydathodes.

Bleeding:

i) It is the removal of water from the plant because of injury.

ii) Water escapes in the form of sap from the injured part of the plant.

Question 1: What is wilting? Some plants show wilting of their leaves at noon even when the soil is well watered, Why is it so? 

Solution 1: Wilting refers to the loss of cellular turgidity in plants which results in the drooping of leaves or plant as a whole because of lack of water. 

During noon the rate of transpiration exceeds the rate of absorption of water by roots. Due to the excessive transpiration, the cells of leaves lose their turgidity and wilt. 

Question 2: Why are the stomata in most plants more numerous on the lower surface of a leaf instead of being on the upper surface? 

Solution 2: The lower surface of leaf is sheltered from direct sunlight. If more stomata are on the upper surface of a leaf, then excessive transpiration would occur, resulting in quick wilting of the plant. Hence most plants have more numerous stomata on the lower surface of a leaf to control the rate of transpiration. 

Question 3: What is photometer?

Potometer is a device that measures the rate of water intake by a plant. This water intake is almost equal to the water lost through transpiration. Potometers do not measure the water lost due to transpiration but measure the water uptake by the shoot. 

Question 4: What is lenticular transpiration? Mention one major difference between lenticular transpiration and stomatal transpiration. 

Solution: Transpiration occurring through lenticels i.e. minute openings on the surface of old stems is called lenticular transpiration. 

Stomatal transpiration is controlled by the plant by altering the size of the stoma, where as this does not happen in case of lenticular transpiration. This is because the lenticels never close, but remain open all the time. The amount of stomatal transpiration is much more than the amount of lenticular transpiration. 

Question 5: List any three major factors that accelerate the rate of transpiration. 

Solution: The factors that accelerate the rate of transpiration are: 

(i) High intensity of sunlight 

(ii) High temperature 

(iii) Higher wind velocity 

(iv) Decrease in atmospheric pressure (Any three) 

Question 6: List the four advantages of transpiration to the plants. 

Solution: The advantages of transpiration to the plants are: 

(i) Transpiration brings about a cooling effect to the plant body since evaporation of water reduces the temperature of leaf surface. 

(ii) Transpiration helps in the ascent of sap by producing a suction force acting from the top of the plant. 

(iii) Transpiration helps in distributing water and mineral salts throughout the plant body. 

(iv) Transpiration helps in eliminating excess water. 

Question 7: Mention any three methods by which the plants tend to reduce transpiration. 

Solution 7: (i) lf the water content of the leaves decreases due any reason, the guard cells turn flaccid, thereby closing the stomatal opening and transpiration stops. 

(ii) Some plants have sunken stomata whereas others have reduced number of stomata to reduce transpiration. 

(iii) In some plants, leaves may be dropped or may be absent or changed into spines as an adaptation to reduce transpiration. 

(iv) The leaves may be covered by thick cuticle such as in Banyan tree, so as to reduce transpiration. 

Question 8: Droplets of water may sometimes be seen along the margins of the leaves of a banana plant, growing in wet soil, in the mornings. Are these dew drops? Comment upon your answer. 

Solution 8: No, they are not dew drops. 

This is water given out by the plant body through guttation. Since the banana plant is growing in humid environment, transpiration is hampered. But the roots continue to absorb water from the soil. This builds up a huge hydrostatic pressure within the plant and forces out the excess water from the hydathodes, which are pores present at the tips of veins in the leaf. This is observed especially during the mornings. 

Question9 : Briefly explain how the rate of transpiration is affected by (a) Intensity of light (b) Humidity of the atmosphere 

Solution: (a) Intensity of light - During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. At night they are closed. Hence more transpiration occurs during the day. During cloudy days, the stomata are partially closed and the transpiration is reduced.