Chapter 4: Transpiration - Practice worksheet with complete answer key
According to your class and board
- Board: ICSE
- Class/Year: 10
- Subject: Biology
- Book + Publisher: Selina Biology (ICSE)
- Chapter: Transpiration
- Difficulty: Standard
- Goal: Practice
A1. Define transpiration.
A2. Name the pores through which transpiration mainly occurs.
A3. What is the function of guard cells?
A4. Which surface of a dorsiventral leaf has more stomata — upper or lower?
A5. Name the instrument used to measure the rate of transpiration.
B1. Distinguish between transpiration and evaporation.
B2. Explain the structure of a stoma with the help of a labelled diagram.
B3. List three factors that affect the rate of transpiration.
B4. What is meant by 'transpiration pull'? How does it help in water transport?
B5. Why do plants wilt on a hot, dry afternoon even when the soil has sufficient water?
B6. Describe the role of potassium ions (K⁺) in the opening and closing of stomata.
B7. What is guttation? How does it differ from transpiration?
B8. Why is transpiration called a 'necessary evil'?
B9. Name the three types of transpiration. Which is the most significant?
B10. What is the effect of high humidity on the rate of transpiration?
C1. A potted plant was kept in a dark room for 24 hours. Predict the effect on its transpiration rate and explain why.
C2. Why do desert plants have sunken stomata and thick cuticles? Relate this to transpiration.
C3. An experiment shows that a leafy shoot loses more water than a shoot with leaves coated in petroleum jelly. Explain.
C4. If you place a polythene bag over a potted plant in sunlight, you observe water droplets inside the bag. Explain the process.
C5. Why do gardeners often prune (cut back) leaves when transplanting a plant?
C6. Explain how wind speed affects transpiration. What would happen on a very windy day?
C7. A student set up two potometers — one in bright sunlight and one in shade. Predict and explain the results.
C8. Why is transpiration higher during daytime than at night?
D1. Describe an experiment to demonstrate that transpiration occurs more from the lower surface of a dorsiventral leaf. (3 marks)
D2. Explain the mechanism of opening and closing of stomata with labelled diagrams. (3 marks)
D3. State three significances of transpiration for the plant. How does excessive transpiration harm a plant? (3 marks)
D4. Draw a well-labelled diagram of a potometer. Describe how you would use it to compare the rate of transpiration under different conditions. (3 marks)
D5. Differentiate between lenticular transpiration and stomatal transpiration. (2 marks)
E1. "Transpiration is the loss of water from all parts of the plant." Is this statement correct?
E2. A student claims that closing stomata completely stops transpiration. Is this accurate?
A1. Transpiration is the loss of water in the form of water vapour from the aerial parts (mainly leaves) of a living plant.
A2. Stomata.
A3. Guard cells regulate the opening and closing of stomata, thus controlling gas exchange and water loss.
A4. The lower (abaxial) surface has more stomata.
A5. Potometer (Ganong's potometer).
B1. Transpiration: physiological process, occurs only in living plants, through stomata/lenticels/cuticle, regulated by guard cells. Evaporation: physical process, occurs from any wet surface, not regulated by living cells.
B2. A stoma consists of two bean-shaped guard cells surrounding a pore (stomatal opening). Guard cells have thickened inner walls and thin outer walls. Chloroplasts are present in guard cells. (Diagram should label: guard cell, stomatal pore, epidermal cells, inner thick wall, outer thin wall, chloroplast.)
B3. (i) Light intensity (ii) Temperature (iii) Humidity (iv) Wind speed (any three).
B4. Transpiration pull is the suction force created by transpiration in leaves that pulls water upward through the xylem. It is the main driving force for water ascent in tall trees.
B5. The rate of transpiration exceeds the rate of water absorption by roots on hot, dry days. Even with sufficient soil water, the roots cannot absorb water fast enough, causing temporary wilting.
B6. In light, K⁺ ions are actively pumped into guard cells → osmotic concentration increases → water enters by osmosis → guard cells become turgid → inner walls pull apart → stoma opens. Reverse happens in dark: K⁺ moves out, water exits, guard cells become flaccid, stoma closes.
B7. Guttation is the exudation of liquid water from the margins/tips of leaves through hydathodes, usually at night or early morning when humidity is high and transpiration is low. Unlike transpiration (vapour), guttation involves liquid water.
B8. It is "necessary" because it creates transpiration pull for water transport, cools the leaf, and helps mineral absorption. It is an "evil" because it results in significant water loss, which can be harmful in dry conditions.
B9. Stomatal, cuticular, and lenticular transpiration. Stomatal transpiration is most significant (accounts for ~80-90% of total).
B10. High humidity reduces the rate of transpiration because the difference in water vapour concentration between the leaf interior and the surrounding air decreases, reducing the driving force for water loss.
C1. Transpiration rate would decrease significantly. In darkness, stomata close (no photosynthesis), reducing stomatal transpiration. Some cuticular transpiration would still occur.
C2. Sunken stomata create a pocket of moist air above the pore, reducing the humidity gradient and thus reducing water loss. Thick cuticle prevents cuticular transpiration. Both are adaptations to conserve water in dry environments.
C3. Petroleum jelly blocks stomata, preventing stomatal transpiration. The coated shoot loses water only through cuticular and lenticular transpiration, which is much less than stomatal transpiration.
C4. The plant transpires water vapour from its leaves. This vapour condenses on the inner surface of the polythene bag (which is cooler), forming visible water droplets. This demonstrates transpiration.
C5. Pruning reduces the leaf surface area, thereby reducing water loss through transpiration. This helps the newly transplanted plant survive as its damaged root system cannot absorb water efficiently.
C6. Moderate wind increases transpiration by removing the humid air layer around leaves (boundary layer), maintaining a steep humidity gradient. On a very windy day, transpiration increases further but may also cause stomata to close due to excessive water loss, eventually reducing it.
C7. The potometer in bright sunlight will show faster movement of the air-water meniscus (higher transpiration rate) because light causes stomata to open. The one in shade will show slower water uptake.
C8. During daytime, stomata are open (for photosynthesis), temperature is higher, light intensity is greater, and humidity is generally lower — all factors that increase transpiration. At night, stomata are mostly closed.
D1. Experiment: Take a dorsiventral leaf. Apply petroleum jelly (vaseline) on the upper surface of one leaf and the lower surface of another. Keep both in sunlight. Weigh both leaves at intervals or use cobalt chloride paper (turns pink to blue when dry). The leaf with jelly on the lower surface shows less water loss, proving more transpiration occurs from the lower surface.
D2. Opening: Light triggers K⁺ influx into guard cells → increased osmotic pressure → water enters by endosmosis → guard cells become turgid → thin outer walls stretch more than thick inner walls → stoma opens. Closing: In darkness, K⁺ moves out → osmotic pressure drops → water exits → guard cells become flaccid → stoma closes. (Two labelled diagrams: open and closed stoma.)
D3. Significances: (i) Creates transpiration pull for water transport (ii) Cools leaf surface (evaporative cooling) (iii) Helps in absorption and transport of minerals. Excessive transpiration causes wilting, reduced growth, and may lead to plant death if water loss exceeds absorption for prolonged periods.
D4. Diagram of potometer: graduated capillary tube, rubber tubing, leafy shoot, water reservoir, air-water meniscus. Method: set up the leafy shoot, note initial meniscus position, measure movement over time under different conditions (wind, humidity, light). Rate = distance moved / time.
D5. Stomatal: through stomata on leaves, regulated by guard cells, accounts for ~80-90% of water loss, occurs mainly during day. Lenticular: through lenticels on bark of woody stems, unregulated, accounts for very small percentage, occurs both day and night.
E1. Not exactly correct. Transpiration is the loss of water specifically from the aerial parts (leaves, stems, flowers) of the plant, not from "all parts." Roots do not transpire. — Why students get this wrong: They confuse transpiration with general water loss and forget the specific definition refers only to aerial parts.
E2. No. Closing stomata stops stomatal transpiration (~80-90%) but cuticular transpiration and lenticular transpiration still continue, albeit at much lower rates. Transpiration cannot be completely stopped while the plant is alive. — Why students get this wrong: They assume stomata are the ONLY route for water loss, forgetting about cuticle and lenticels.