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ICSE BIOLOGY TRANSPIRATION NOTES

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Avalon Heights International School, Mumbai
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DishaEducentre Biology for X ICSE Exhaustive Notes ~ 1 ~~ 1 ~ 4. Transpiration DishaEducentre Exhaustive Notes TRANSPIRATION Scope of Syllabus: Mechanism of stomatal transpiration must be explained so that the concept of the process is clear. Adaptations in plants to reduce transpiration to be discussed. A brief idea of guttation and bleeding should be given. I. Definitions and Explanations 1. Transpiration 2. Potometer 3. Stomatal Transpiration 4. Cuticular Transpiration 5. Cuticle 6. Lenticular Transpiration 7. Lenticels 8. Guttation 9. Hydathode 10.Bleeding 11.Antitranspirants II. The evaporative loss of water in the form of water vapour from the aerial parts of the plants is known as transpiration. A potometer is a device that measures the rate of water intake by a plant. (Latin: poton means to drink and meter means to measure ) The loss of water which takes place though the stomatal openings on the leaves of plants is known as stomatal transpiration. The loss of water which takes place directly through the surface of the leaves and stems is known as cuticular transpiration. Cuticle is a waxy layer present on the underside of some leaves to prevent transpiration. The loss of water which takes place from the lenticels, which are minute openings on the surface of stems of old plants, is known as lenticular transpiration. Lenticels are minute openings on the bark and root of old trees. Guttation is the loss of water in the form of droplets of water along the leaf margins of certain plants. Hydathodes are pore-bearing structure present along the margins of leaves of some plants through which guttation takes place. The escape of plant sap from the ruptured surfaces of a plant is known as bleeding. Substances that are applied to plants to control their loss of water through transpiration are known as anti-transpirants. Example: silica gel. Questions-Answers Describe an experiment to demonstrate transpiration by polythene bag method. ANSWER Aim: To demonstrate transpiration in plants. Procedure: A medium-sized well-watered plant is taken. It is covered with a transparent polythene bag with its mouth tied up quite securely. The plant is kept in sunlight for 1-2 hours. 1. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 2 ~~ 2 ~ DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes Observation: Drops of water begin condensing on the inner wall of the polythene bag. Inference: Plants perform transpiration, i.e. loss of water through their leaves. Describe an experiment to demonstrate transpiration by using cobalt chloride paper. ANSWER Aim: To demonstrate transpiration in plants. Procedure:Three different setups are taken as follows:(i) Setup A A small well-watered potted plant with broad leaves is taken. The whole pot is enclosed in a polythene bag and firmly tied at the mouth. This is to prevent any water loss from the pot. The entire setup is kept under a bell jar. (ii) Setup B Another similar plant is set up and covered with a bell jar in the same manner. A piece of dry cobalt chloride paper is kept inside the bell jar. It is stuck on a wooden stick propped inside the bell jar. (iii) Setup C A third bell jar is taken without the plant inside. A similar piece of dry cobalt chloride paper is kept inside the bell jar in a similar manner. This is a control setup. All three bell jars are kept in the sun for a few hours. Observations: (i) The first bell jar A shows water vapour condensing on its inner walls. (ii) The second bell jar B shows similar water condensation, and also the blue cobalt chloride paper turns pink. (iii) The third bell jar C does not show any change. There is no water condensation and the cobalt chloride paper remains blue. Inferences:Plants lose water by transpiration. There is double visual proof for that:(i) The water droplets that condense on the inner side of the bell jar A and B and (ii) The pink coloration of the cobalt chloride paper in bell jar B. 2. How is loss of water due to transpiration measured by the Weighing Method? ANSWER Method 1 A lightweight potted plant is fully covered at its soil surface to prevent water loss by evaporation. The plant is weighed. Then it is kept for some time and weighed again. The difference between the initial and final weights gives a direct measure of the amount of water loss through transpiration. Method 2 A test tube is filled with some water. Some amount of oil is added on its surface to prevent evaporation. A leafy shoot (without roots) is inserted into the test tube. The whole apparatus is weighed. Then the test tube is allowed to stand for some time and weighed again. It will be found that this weight will be lower. The difference in the weights is a measure of the water loss through transpiration. This method gives a better measure of transpiration loss because there are no roots to absorb water. Whatever weight is lost is only that of the water lost by transpiration. 3. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 3 ~~ 3 ~ DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes 4. Sketch a Ganong s photometer. Answer the following questions based on it:What is it used for? State its principle of working. Describe it s working. Write the drawbacks of the photometer. What are the difficulties in using a photometer? (i) (ii) (iii) (iv) (v) ANSWER Use A potometer is an apparatus that is used for measuring the rate of transpiration. Principle The potometer is based on the Fluid Dynamic Principle. The potometer is based on the assumption that water transpired through leaves is equal to the water absorbed by roots. Working A twig of some suitable plant such as coleus is cut with a sharp knife and introduced into the apparatus. The entire apparatus is filled with water so that no air spaces remain. An air bubble is introduced into the capillary. This is done by lifting the bent capillary tube above the surface of water and then immediately dipping it into the water again. As the leaves lose water by transpiration, the bubble is pulled nearer to the twig. The movement of bubble through the capillary tube is noted on a calibrated scale. This gives the measure of the rate of transpiration. By measuring the distance travelled by the bubble in a specific time interval, we can measure the rate of transpiration. Drawbacks (Shortcomings/Disadvantages) Potometer does not measure the water lost during transpiration but measures only the water uptake by the cut shoot. This is not an exact measure of transpiration because some of the water is used by the tissues of the plant for other metabolic activities. Limitations (Difficulties in Use) It is not easy to introduce the air bubble into the capillary. The twig may not remain fully alive for a long time. Any change in the outside air temperature may affect the position of the air bubble. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 4 ~~ 4 ~ Transpiration DishaEducentre Exhaustive Notes Note: It would be more appropriate to say that the potometer measures the rate of evaporation and not purely transpiration. What are the different kinds of transpiration? Briefly describe them. ANSWER There are three different kinds of transpiration based on where the water exits from:Type of Description Exit Organ Transpiration Stomatal Water loss occurs from leaves through their stomata on Transpiration stomata. leaves Cuticular Water loss occurs directly from leaves and surface of Transpiration stems. leaves and stems Lenticular Water loss occurs from lenticels, which are lenticels Transpiration minute openings on the stems of old plants. 5. Describe the structure of stomata. ANSWER Stomata (singular: stoma) are small pores present on the epidermis of leaves. Each stoma is surrounded by two bean-shaped guard cells in dicots. The inner wall of the guard cells is thicker than the outer wall. The guard cell contains a nucleus and many chloroplasts. 6. 7. How does water loss occur through the stomata? entire process of water loss through stomata is through diffusion. During the daytime, the stomata are open. Water from the cells of the leaves reaches the sub-stomatal space through imbibition. Once it reaches the stomatal openings, there is a high concentration of water in the sub-stomatal space and a low concentration in the outer environment. Diffusion takes place and water is dispelled into the atmosphere. ANSWER The 8. Describe the path followed by water owing to transpiration pull. transpiration occurs through the stomatal openings in the leaves, it causes an upward movement of the water throughout the plant. This leads to a transpiration pull on the water. Every cell has turgor pressure due to the water in it. Due to this pressure, water is forced out from the cell into the intercellular space. The water from the intercellular spaces in the mesophyll evaporates and enters the sub-stomatal space. From there, it diffuses into the environment. This is then replaced by more water brought from the nearest vein. Thus, most of the water travels along the cell wall and only a little amount of water enters the cells through osmosis. When the water from the leaves evaporates, more water is pulled upward through the xylem vessels. ANSWER When Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 5 ~~ 5 ~ DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes This kind of transpiration pull can draw water even up to 50 metres in tall trees. State the functions of stomata. ANSWER Stomata is concerned with the following two main functions: They play an important role in the process of transpiration. They provide a pathway for gaseous exchange during photosynthesis and respiration. 9. Under what conditions can the stomatal opening get closed even in the daytime? ANSWER The stomatal opening can get closed even in the daytime if the weather is excessively hot, and if the plant has already lost a lot of water through transpiration. This is a protective measure for the plant to retain the water present in it. 10. Describe an experiment to show that transpiration occurs at different rates from the two surfaces of a dicot leaf. ANSWER Aim: To demonstrate different rates of transpiration from the two surfaces of a dicot leaf. Procedure:A strip of dry cobalt chloride paper is attached to two different surfaces of a leaf. The strip is held in place by two glass slides on either side of the leaf, connected by clips. The leaf should remain attached on the plant. Observation:The strip of cobalt chloride paper that is attached on the upper surface of the leaf does not turn pink. The strip that is attached on the lower surface turns pink. Inference:The different surfaces of the leaf perform transpiration at different rates. The upper surface shows negligible transpiration while the lower surface shows a high amount of it. This is because there are numerous stomatal openings on the lower surface of the leaf. 11. Explain the mechanism of opening and closing of stomata. ANSWER The opening and closing of stomata are controlled by guard cells. These guard cells are turgor operated valves. When the guard cells are turgid, they are open; and they close when flaccid. During the daytime, the chloroplasts of the guard cells begin photosynthesis. Due to this, the sugar concentration in the guard cells increases. This increases their osmotic pressure, and water from the surrounding cells enter the guard cells. This endosmosis makes the guard cells turgid and they open. When the stomata are open, exchange of gases takes place through them and water loss through transpiration also takes place. During night or because of any other reason when the photosynthesis stops, the guard cells lose their osmotic pressure and become flaccid. This causes them to close. 12. State the functions of stomata. ANSWER Stomata is concerned with the following two main functions: They play an important role in the process of transpiration. 13. 14. Describe cuticular transpiration. transpiration takes place directly through the surface of leaves and stems via a layer known as cuticle. The cuticle is a waxy layer which is secreted by the epidermis on the two surfaces of the leaf. Its function is to prevent evaporation of leaves from the plant surfaces. ANSWER Cuticular Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 6 ~~ 6 ~ DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes Different plants have different layers of cuticles. A thicker cuticular layer can prevent transpiration water loss to a greater extent. Desert plants (xerophytes) have thick cuticles to prevent loss of water by transpiration. 15. Describe lenticular transpiration. transpiration takes place through special openings on the older stems of plants, which is known as lenticel. Lenticels develop on older stems. They are openings which allow direct diffusion of water into the outside environment. ANSWER Lenticular Compare the amount of water loss through the three modes of transpiration. ANSWER The water loss through stomatal transpiration is the highest and that through cuticular transpiration is the lowest. Hence, the water loss in the three modes of transpiration can be arranged in an ascending order as follows:Water loss by Water loss by Water loss by cuticular stomatal transpiration > lenticular transpiration > transpiration 16. Describe briefly the external factors that affect transpiration. ANSWER The following are the external factors that affect transpiration:Factor Effect Intensity Stomata open in daytime and close at night. of Sunlight Hence, rate of transpiration increasesduring the day. Temperatu When weather is hot, rate of evaporation increases. re Hence, rate of transpirationincreaseswith temperature. Velocity of If wind blows faster, it can carry more water with it. Wind Hence, rate of transpiration increases with wind velocity. Humidity If air is humid, it cannot retain more water vapour in it. Hence, rate of transpiration decreases in humid conditions. Carbon When CO2 level in air increases beyond 0.03%, stomata close. dioxide Hence, rate of transpiration decreases due to excess CO2 in air. Atmosphe When air pressure is high, it is difficult for more water to be ric held in it. Pressure Hence, rate of transpiration decreases when air pressure is high. 17. 18. Describe how transpiration is influenced by water content of leaves. content of leaves is an internal factor that influences the rate of transpiration. If water content of leaves decreases, then leaves wilt. This makes the guard cells flaccid and they close. Hence, rate of transpiration decreases when leaves have less water content. ANSWER Water What adaptations do some plants, such as desert plants, show to reduce transpiration? ANSWER Some plants show the following adaptations to reduce transpiration. Adaptation Effect Sunken In plants such as nerium, the stomata is sunken or Stomata covered by hairs. Fewer Stomata Some plants have fewer stomata. 19. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 7 ~~ 7 ~ DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes Narrow Leaves Some plants have narrow leaves. This reduces the surface area of the leaves, and that Reduced Exposed Surface Loss of Leaves Thick Cuticle 20. directly reduces the number of stomata on their lower epidermis. In some plants, leaves are wavy, rolled or folded. This reduces the surface area of the leaves, and that directly reduces the number of stomata on their lower epidermis. Some plants lose leaves by dropping them in hot seasons. Some plants do not have leaves at all or have them in the form of spines, such as in most cacti. Some leaves have a thick waxy layer known as cuticle. This reduces the transpiration water loss. This adaptation is seen in banyan and many evergreen trees. Discuss the significance of transpiration in plants. is significant to plants in many ways as follows:Cooling Effect Evaporation causes cooling of the surface. When water loss takes place by transpiration, the leaf is cooled down. This is beneficial to plants on hot days as it saves the enzymes from being destroyed due to heat. Suction Force Transpiration helps in ascent of sap. It provides a suction force acting from the top of the plant. This concentrates cell sap in the leaves and increases their osmotic pressure. As a result, water from the lower level cells moves into the leaf cells by osmosis. This facilitates the uptake of water by the roots at the lowest level. Distribution of Water and Mineral Salts Leaves are present at the tips of all branches and twigs. As water is drawn into them through transpiration, it is distributed to all parts of the plant. Thus, the dissolved minerals and salts are distributed throughout the plant. ANSWER Transpiration (i) (ii) (iii) 21. How does transpiration affect climate? amount of water lost by transpiration is quite significant. A small plant like a sunflower plant can lose half a litre of water per day, while a full-grown big plant like an apple tree can lose up to 30 litres of water per day. Thus, transpiration drastically affects the amount of moisture in the atmosphere and brings rain. In this manner, transpiration can affect climate. ANSWER The 22. What is guttation? What conditions favour the guttation process? is the direct loss of water from plants. This exudation occurs as droplets of water seen along the margins of leaves especially in the mornings. Guttation is mostly observed in plants in the early mornings. Guttation takes place through special pore-bearing structures along the margins of leaves, which are known as hydathodes. Some examples of plants that show guttation are nasturtium, banana and strawberry. ANSWER Guttation Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 8 ~~ 8 ~ Transpiration DishaEducentre Exhaustive Notes Conditions Favouring Guttation Large amount of water in the plant. Suitable temperature (at very low temperatures, no guttation takes place). Any condition that inhibit (restrict) transpiration can increase guttation. 23. What is meant by bleeding in plants? is the exudation of sap from the injured parts of the plants. When an incision is made in the stem of a plant growing in well-watered soil, the xylem sap starts oozing out of it due to root pressure. This kind of bleeding is common in the mulberry plant. Other plants that show bleeding (of milky white latex) are Calatropis and Euphorbia(rubber plant). ANSWER Bleeding What are the similarities between stomata in plants and sweat pores in animals? ANSWER The following similarities exist between stomata in plants and sweat pores in animals: Both are minute openings in the outside surface layer (epidermis). Both remove water from the body of the organism. 24. 25. What are hydathodes? Where are they present? are special pore-like structures present in some grasses and angiosperms through which loss of water takes place through guttation. They are also known as chalk glands. They are present at the margins and tips of leaves. ANSWER Hydathodes What are anti-transpirants? ANSWER Anti-transpirants are transpiration retardants. They slow down the process of transpiration and are used in cases transpiration is undesirable in plants. They help to retain water in the plant. Anti-transpirants are of two types:(i) Those that inhibit the metabolic process of transpiration: Examples:abscissic acid, phenyl mercuric acetate, aspirin (ii) Those that form a film on the surface of the leaf: Examples: silica gel, petroleum jelly 26. Reasons and Justifications Transpiration is the price a plant has to pay for photosynthesis. OR: Transpiration is incidental to photosynthesis. ANSWER For preparing sugars through photosynthesis, the plants needs carbon dioxide. In order to get this gas from the atmosphere, the stomata need to be open. The primary function of the stomata is to exchange gases needed for photosynthesis and respiration. However, when the stomata open up, the water in the sub-stomatal openings also gets removed through the process of diffusion. The plant cannot avoid this water loss. Thus, it is said that transpiration is the price the plant has to pay for photosynthesis. 1. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 9 ~~ 9 ~ Transpiration DishaEducentre Exhaustive Notes Cork and bark of trees help in preserving water. ANSWER Cork and bark of trees are made of dead cells. They do not have any openings such as stomata that may facilitate transportation. Hence, the water remains within the plant. 2. Leaves of some plants wilt during midday and recover in the evening. ANSWER At midday, the rate of photosynthesis is high in the guard cells of the stomata. Hence, the sugar concentration in them in high too, and they have high osmotic pressure. Due to this, the rate of transpiration increases and the leaves lose water. This makes them wilt. But during night, photosynthesis stops. The osmotic pressure of the guard cells goes down and they become flaccid and close. Transpiration rate lowers. The leaves retain the water brought due to uptake and their shape is restored. 3. 4. Transpiration is not an excretory process. is the loss of water from a plant through the stomatal openings in its leaf. In transpiration, it is not the excess water that is removed. Excretion refers to the elimination of wastes; i.e. the removal of unwanted substances. But, the water lost through transpiration is necessary to the plant. This removal happens only because the stomata need to open up for performing exchange of gases. Thus, transpiration is not an excretory process. ANSWER Transpiration 5. Transpiration is sometimes undesirable in plants. transpiration is necessary to plants for a host of reasons, it is also true that it causes loss of water in the plant. In hot climate, this is undesirable because plants need to store water. Excessive elimination of water from the plant can lead to wilting of the leaves. ANSWER Though Distinctions and Comparisons 1. (i) (ii) (iii ) (iv ) (v) 2. Transpiration and Evaporation Transpiration Transpiration is a physiological process occurring only in plants. Transpiration occurs only through openings known as stomata. Transpiration involves diffusion of water molecules into the atmosphere. Evaporation Evaporation is a physical process occurring at the surface of any liquid. Evaporation occurs throughout the exposed surface of a liquid. Evaporation involves loosening and breaking the bonds of surface liquid molecules. Transpiration involves the elimination Evaporation can take place in any of only water. liquid. Transpiration is a slow process. Evaporation is a quicker process. Stomatal Transpiration, Respiration Cuticular Respiration and Lenticular Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes (i) (ii) (iii) ~ 10 ~~ 10 ~DishaEducentre Exhaustive Transpiration Notes Stomatal Transpiration It occurs through stomata, which are openings on the leaves. Cuticular Transpiration It occurs through cuticle, which is a waxy coating on the various parts of leaves. It occurs through leaves. It occurs through all leafy parts that are covered by cuticle. Highest amount of water Lowest amount of water is lost. is lost. Lenticular Transpiration It occurs through lenticels, which are openings on the stems of plants. It occurs through stems. Amount of water lost is more than cuticular but less than stomatal transpiration. (iv) It occurs only in the It occurs at all times of It occurs at all times of daytime when the the day. the day. stomata are open. (v) It occurs in all plants, It occurs in plants which It occurs in older plants, irrespective of their age. have significant amount because lenticels of cuticle, such as desert develop only on older plants. stems. (vi) Less exchange of gases No exchange of gases More exchange of gases and more loss of water and least loss of water and less loss of water takes place. takes place. takes place. (vii 70-80% of total 5-10% of total 15-20% of total ) transpiration of a plant transpiration of a plant transpiration of a plant is stomatal. is cuticular. is lenticular. 3. (i) (ii) (iii ) (iv ) (v) 4. (i) (ii) (iii ) (iv ) Open Stomata and Closed Stomata Open Stomata Stomata open in the daytime. When open, the guard cells are turgid. Closed Stomata Stomata close in the night time. When closed, the guard cells are flaccid. Exchange of gases takes place No exchange of gases takes place through open stomata. through closed stomata. Guard cells perform photosynthesis in Guard cells do not perform this condition. photosynthesis in this condition. Transpiration takes place in this Transpiration does not take place in condition. this condition. Transpiration and Guttation Transpiration Transpiration is the loss of water in vapour state. Transpiration occurs through stomata, cuticle or lenticels. Transpiration happens in the daytime. Guttation Guttation is the loss of water in liquid state, as droplets. Guttation occurs through hydathodes on the leaf margins. Guttation occurs in the night, and the droplets are seen in the early mornings. In transpiration, there is only water In guttation, there is water loss along loss. with essential mineral salts. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 11 ~~ 11 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes 5. Transpiration in Plants and Perspiration in Animals (i) (ii) (iii ) (iv ) Transpiration in Plants Transpiration is the loss of water in plants. Transpiration takes place through stomata, cuticle and lenticels. Transpiration is not a form of excretion. Only water loss takes place. (ii) (iii ) (iv ) Stomata Stomata are present in the epidermis of leaves. They are openings surrounded by two guard cells. They give out water by transpiration. Hydathodes Hydathodes are present along the margins of tips of leaves. They are glands. They eliminate only water. They exude water along with some mineral salts. (ii) (iii ) (iv ) They give out water by guttation. Stomata and Sweat Pores 7. (i) Water is lost along with several minerals and salts that the body does not require. Stomata and Hydathodes 6. (i) Perspiration in Animals Perspiration is the elimination of sweat in animals. Perspiration takes place through sweat glands on the skin. Perspiration is a form of excretion. Stomata Sweat Pores Stomata are present in the epidermal Sweat pores are present in the layer of the leaves in plants. epidermal layer of the skin in mammals. The opening and closing of stomata Sweat pores do not have any guard are regulated by guard cells. cells. Stomata are open in the daytime and Sweat pores are open throughout the closed in the night. day. Through stomata, exchange of gases No exchange of gases takes place takes place. through sweat pores. Diagram-based Questions 1. (i) (ii) (iii) (iv) (v) Observe the experimental setups in (A) and (B) and answer the questions:What is the aim of the experiment? Why has oil been put in each test tube? What will be the observation in the two test tubes after about 2-3 days? Explain why the change occurs after the time period, if any. Why has the test tube (B) been taken without any plant? ANSWER Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 12 ~~ 12 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes (i) The aim of the experiment is to demonstrate transpiration. (ii) Oil has been added to the test tubes to prevent any evaporation occurring from (iii) (iv) (v) 2. (i) (ii) (iii) (iv) (v) ANSWER (i) (ii) (iii) (iv) (v) 3. (i) (ii) (iii) (iv) (v) ANSWER (i) (ii) (iii) the water surfaces in the test tubes. The level of water in test tube (A) falls while the level of water in test tube (B) remains the same. The water level in test tube (B) falls because it loses water by transpiration through the aerial parts of the plant. Test tube (B) is used as a control setup. No change occurs in it, and hence it can be used as a standard to measure the change in the experimental test tube (A). Observe the experimental setup and answer the questions:What is the colour of the dry cobalt chloride paper? Is the experimental leaf a monocot or a dicot? Justify. Why are glass slides placed over the CoCl 2 paper? After about half an hour, what changes, if any, would you expect to find in the CoCl2 paper placed on the dorsal and ventral sides of the leaf? What does the experiment prove? Blue The experimental leaf is a dicot because it has reticulate venation. The slides prevent atmospheric moisture from coming in contact with the CoCl 2 paper. The paper on the ventral side turns pink. The paper on the dorsal side remains blue as it is. This is because leaves have stomata only on their ventral (lower) side. Thus, transpiration occurs only on this side. The water lost through transpiration turns the paper pink. No transpiration occurs on the dorsal side and hence the paper there remains as it is. The diagram shown alongside shows a physiological process in plants. Answer the questions below:Name the process. What is the structure named X? What change will X show in the course of the experiment? Why is the potted plant covered with a polythene bag? Will this experiment yield results if conducted in the night time? Explain your answer. Transpiration Cobalt chloride paper The cobalt chloride paper X will change from blue to pink during the experiment. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 13 ~~ 13 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes (iv) In order to prevent direct water loss from the soil surface via evaporation. (v) No. This is because transpiration occurs only in the daytime through stomata as they are only open then. BOARD EXAMINATION QUESTIONS 2002 Match the items in column I with column II. Column I Column II Stomata stimulated by light Grana diffusion of gases ANSWER Stomata diffusion of gases Grana stimulated by light 1. 2003 Give the technical terms for the following:Loss of water in the form of water droplets from the margins of the leaves. ANSWER Guttation 2. Given below is the diagram of an experimental setup to study the process of transpiration in plants. Study the same and then answer the questions that follow:(i) What is the colour of dry cobalt chloride paper? (ii) Is the experimental leaf a monocot or a dicot? Give a reason to support your answer. (iii) Why are glass slides placed over the dry cobalt chloride papers? (iv) After about half an hour, what change, if any, would you expect to find in the cobalt chloride paper placed on the dorsal and ventral sides of the leaf? Give a reason to support your answer. (v) Define the term transpiration. ANSWER (i) The colour of dry cobalt chloride paper is blue. (ii) The experimental leaf is a dicot. It has reticulate venation. (iii) The glass slides serve two purposes:a) They prevent atmospheric oxygen from interfering with the experiment. b) They provide better contact between the leaf and the cobalt chloride paper. (iv) The following changes are observed:a) The cobalt chloride paper on the dorsal side of the leaf turns pink slower. b) The cobalt chloride paper on the ventral side of the left turns pink much faster. This shows that the leaf contains more stomata on the lower surface and hence transpiration occurs at a much faster rate from the lower surface. 3. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 14 ~~ 14 ~DishaEducentre Exhaustive Transpiration Notes 2004 Rewrite the correct form of the statement by inserting a suitable word/words at the right place. Transpiration is the loss of water from the leaves of the plant. ANSWER The corrected statement is:Transpiration is theevaporative loss of water in the form of water vapour from the aerial parts of the plant. 4. Give one point of difference between the following pairs:Cobalt chloride paper and Goat s bladder ANSWER The difference is:Cobalt Chloride Paper Goat s Bladder It is a type of indicator that is used to detect It is a semipermeable the presence of water such as in experiments membrane used to selectively related to transpiration. It is blue in colour but pass solvent molecules through turns pink in presence of water. it during osmosis. 5. 6. Draw a neat labelled diagram of the stomatal apparatus found in the epidermis of leaves and label the following parts:Stoma, guard cells, chloroplast, epidermal cells, cell wall, nucleus ANSWER 2005 Study the diagram given alongside and answer the questions that follow:(i) Explain the physiological process being studied. (ii) What will be observed in the two test tubes after two to three days? (iii) Give reason for your answer in (ii) above. (iv) Why is the surface of water covered with oil? (v) State the purpose for setting up test tube B. ANSWER (i) The process being studied is transpiration. Transpiration is the evaporative loss of water in the form of water vapour from the aerial parts of the plants. (ii) The water level in test tube A will decrease, but the water level in test tube B will remain the same. (iii) This happens because the plant in test tube A undergoes transpiration. Due to this loss of water takes place in this test tube. (iv) The surface of water is covered with oil so that evaporative loss of water does not take place. (v) The test tube B acts as a control. It helps to compare the water loss in the test tube A. 7. What is Ganong spotometer used for? Write any two limitations of this apparatus. ANSWER Use:A potometer is an apparatus that is used for measuring the rate of transpiration. Limitations: It is not easy to introduce the air bubble into the capillary. The twig may not remain fully alive for a long time. 8. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 15 ~~ 15 ~DishaEducentre Exhaustive Transpiration Notes 2006 9. Give the exact location and function of stoma. Stoma are located on the surface of the leaves. They are present in greater number on the lower surface (ventral surface) of the leaf. Function: Stoma are the openings through which exchange of gases takes place from the plant to the external environment. ANSWER Location: 10. Explain the term bleeding. is the exudation of sap from the injured parts of the plants. When an incision is made in the stem of a plant growing in well-watered soil, the xylem sap starts oozing out of it due to root pressure. This kind of bleeding is common in the mulberry plant. Other plants that show bleeding (of milky white latex) are Calatropis and Euphorbia (rubber plant). ANSWER Bleeding Explain briefly:- Xerophytes have their leaves modified to spines or reduced in size. ANSWER Xerophytes have leaves modified into spines to minimise loss of water through transpiration. Xerophytes are plants like cacti that grow in areas of water scarcity. They need to conserve as much water in their bodies as possible. Transpiration takes place through the stomatal openings on the underside of leaves. If the leaf lamina are reduced in size, the number of stoma also reduce and that reduces transpiration. Hence, water is conserved. 11. 2007 12. Study the diagram below and answer the questions that follow:(i) Name the apparatus. (ii) Mention one limitation of this apparatus. (iii) Which phenomenon is studied with the help of this apparatus? (iv) What is the function of the part marked reservoir? (v) What is the role of the air bubble in the experiment? ANSWER (i) (ii) (iii) The apparatus is Ganong spotometer. Limitation: It is not easy to introduce the air bubble into the apparatus. The phenomenon studied is transpiration. Potometer helps to measure rate of transpiration. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 16 ~~ 16 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes (iv) The reservoir helps to fill water into the apparatus. (v) The air bubble helps to measure the rate of transpiration. We calculate the distance moved by the air bubble and note the time taken. Dividing the two, we get the rate of transpiration. 13. Explain the term guttation. is the loss of water in the form of droplets of water along the leaf margins of certain plants. Guttation takes place through organs at the leaf margins known as hydathodes or chalk glands. ANSWER Guttation 2008 Given below is an experimental setup to study a particular process. (i) Name the process being studied. (ii) Explain the process named in (i) above. (iii) Why is the pot covered with a plastic sheet? (iv) Mention one way in which this process is beneficial to the plant. (v) Suggest a suitable control for this experiment. ANSWER (i) The process being studied is transpiration. (ii) Transpiration is the evaporative loss of water in the form of water vapour from the aerial parts of the plants. (iii) The pot is covered with plastic sheet to prevent entry of water from the outside environment. Thus, the water drops formed on the inside of the plastic sheet is only that which is lost by the plant during transpiration. (iv) Transpiration brings about cooling of the aerial parts of the plant. As the water evaporates, it cools down the surface. This helps plants bear hot temperatures. (v) For control, we can take another plastic bag and keep it in the sunlight, empty with its mouth tied. 14. Give the technical/biological term for the following:(i) Respiratory openings found on the stem of woody plants. (ii) Exudation of sap from injured parts of plant. ANSWER (i) Lenticels (ii) Bleeding 15. 2009 Give the specific function of the following structure found in the body of plants/animals:-Hydathodes. ANSWER The function of hydathodes is to exude water from the plants. They are present along the margin of leaves through which loss of water takes place. They are also known as chalk glands. 16. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 17 ~~ 17 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes 17. The diagram below represents a structure found in a leaf. Study the same and answer the questions that follow:(i) Name the parts labelled A and B. (ii) What is the biological term for the above structure? (iii) What is the function of the part labelled A? (iv) Mention two structural features of A, which help in the function mentioned in (iii) above. (v) Where is this structure likely to be found in a leaf? (vi) The above structure helps in the process of transpiration. Explain the term transpiration. (vii) How many other cells are found surrounding this structure as seen in the diagram? ANSWER (i) A: guard cells B: stoma (ii) The biological name for the above structure is stomata. (iii) The part A, guard cells, control the opening and closing of the stomata. Thus, their function is to control the exchange of gases and transpiration. (iv) Two structural features of guard cells that makes them control the opening and closing of stomata are:a) Their inner walls are thickened while their outer walls are thin. b) They are different from other epidermal cells in shape. (v) This structure is found on the lower surface (ventral surface) of a leaf. (vi) Transpiration is the evaporative loss of water in the form of water vapour from the aerial parts of the plant. (vii) We see five cells surrounding the stomata in the diagram. Explain how the rate of transpiration is affected on:(i) A windy day (ii) A foggy day. ANSWER (i) On a windy day, rate of transpiration increases. This is because water vapour is carried away faster from the stomatal openings. (ii) On a foggy day, rate of transpiration decreases. This is because air around the leaves is humid. Due to this, water vapour from the leaves does not diffuse into the leaves easily. 18. 2010 Name a plant with sunken stomata. ANSWER Nerium is a plant with sunken stomata. 19. Rearrange the following terms so as to be in a logical sequence:Stoma, mesophyll cells, xylem, substomatal space, intercellular space (loss of water due to transpiration) ANSWER Mesophyll cells intercellular space xylem substomatal space stoma 20. Choose the correct answer:Loss of water as droplets from hydathodes is called ________________ (transpiration/bleeding/guttation) ANSWER Guttation 21. Explain bleeding in plants. ANSWER Bleeding is the exudation of sap from the injured parts of the plants. When an incision is made in the stem of a plant growing in well-watered soil, the xylem sap starts oozing out of it due to root pressure. 22. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva ~ 18 ~~ 18 ~DishaEducentre Exhaustive DishaEducentre Biology for X ICSE Exhaustive Transpiration Notes Notes This kind of bleeding is common in the mulberry plant. Other plants that show bleeding (of milky white latex) are Calatropis and Euphorbia (rubber plant). Account for the following:- Leaves of certain plants roll up on a bright sunny day. ANSWER During bright sunny days, the rate of transpiration increases. This causes some plants to have a higher rate of transpiration than the rate of water uptake. That means, the plants lose more water than they take in. In order to prevent this loss of water through transpiration, the leaves of some plants roll up on bright sunny days. 23. 24. Name four anti-transpirants. following are examples of anti-transpirants:Those that inhibit the metabolic process of transpiration: Examples: abscissic acid, phenyl mercuric acetate, aspirin Those that form a film on the surface of the leaf: Examples: silica gel, petroleum jelly ANSWER The (i) (ii) 2011 Give the exact location of hydathodes. ANSWER Hydathodes or chalk glands are present on the margins of the leaves. 25. 26. Study the diagram given alongside and answer the questions that follow:(i) Name the process being studied in the following experiment. (ii) Explain the process mentioned in (i) above. (iii) Why is oil placed over water? (iv) What do we observe with regard to the level of water when this setup is placed in (1) bright sunlight (2) humid conditions (3) windy day? (v) Mention any three adaptations found in plants to overcome the process mentioned in (ii) above. ANSWER (i) (ii) (iii) (iv) (v) The process being studied is transpiration. Transpiration is the evaporative loss of water in the form of water vapour from the aerial parts of the plant. Oil is placed over water to prevent direct loss of water through evaporation. (1) In bright sunlight, the level of water decreases rapidly. This is because the rate of transpiration is high. (2) In humid conditions, the level of water decreases slowly. This is because the rate of transpiration slows down when humidity is high. (3) On a windy day, the level of water decreases rapidly. This is because the wind velocity helps in removing more water vapour from the stomatal openings of the leaves. The following are adaptations seen in plants to reduce the rate of transpiration:a) Sunken stomata, such as in Nereis, b) Narrow leaves or leaves reduced to spines, such as in cacti, c) Thick cuticle, such as in xerophytes. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 19 ~~ 19 ~DishaEducentre Exhaustive Transpiration Notes Write down the difference between the following pair as indicated within brackets:Guttation and Bleeding (cause) ANSWER The difference is:Guttation Bleeding Guttation takes place from hydathodes Bleeding is the exudation of cell sap due to low temperature and high from the injured parts of the plants. humidity. 27. 2012 28. Give the exact location of lenticels. are present on the bark and root of old trees. ANSWER Lenticels 29. Given alongside is an experimental setup to demonstrate a particular process. Study the same and answer the questions that follow:(i) Name the physiological process being studied. (ii) Explain the process mentioned above. (iii) What is the aim of the above experiment? (iv) What would you observe in the experimental setup after an hour? Give a reason to support your answer. (v) Mention any three adaptations found in plants to overcome the physiological process mentioned in (i) above. ANSWER (i) (ii) (iii) (iv) (vi) The process being studied is transpiration. Transpiration is the evaporative loss of water in the form of water vapour from the aerial parts of the plant. The aim of the experiment is to demonstrate the different rates of transpiration from the two surfaces of the leaves of plants. We observe that more transpiration occurs from the lower surface (ventral surface) of the leaf. This is shown by the cobalt chloride paper turning from blue to pink. Reason: Leaves have more stomatal openings on their ventral surface than on their dorsal surface. Hence, the lower surface has a higher rate of transpiration. The following are adaptations seen in plants to reduce the rate of transpiration:a) Sunken stomata, such as in Nereis, b) Narrow leaves or leaves reduced to spines, such as in cacti, c) Thick cuticle, such as in xerophytes. 2013 Name the following:The waxy layer on the epidermis of the leaf meant to reduce transpiration. ANSWER Cuticle. 30. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva DishaEducentre Biology for X ICSE Exhaustive Notes ~ 20 ~~ 20 ~DishaEducentre Exhaustive Transpiration Notes Rearrange the following so as to be in a logical order:Spongy cells, upper epidermis, stoma, palisade tissue, substomatal space. ANSWER Upper epidermis palisade tissue spongy cells substomatal space stoma 31. Give the biological term for the following:Permanently open structures seen on the bark of an old woody stem. ANSWER Lenticels 32. Notes Prepared by Neil Valentine D SilvaNotes Prepared by Neil Valentine D Silva

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