Detailed explanations in West Bengal Board Class 9 Life Science Book Solutions Chapter 3.1C Transpiration offer valuable context and analysis.
WBBSE Class 9 Science Chapter 3.1C Question Answer – Transpiration
Very Short Questions and Answers : (1 mark for each question)
Which tiny pores, present on the leaf surface help in gaseous exchange and liberation of excess water as vapour?
Stomata are the tiny pores, present on the leaf surface, helping in gaseous exchange and liberation of excess water as vapour.
Which cells control the opening and closing of stomata?
Guard cells control the opening and closing of stomata.
Name the small lens-shaped pores present on the stems of plants, which serve as site of transpiration.
The small lens-shaped pores present on the stems of plants, which serve as site of transpiration, are called lenticels.
Which layer on the leaf surface prevents transpiration in desert plants?
Cuticle layer on the leaf surface prevents transpiration in desert plants.
At which time of a day does transpiration occurs at the maximum rate?
During mid-day, transpiration occurs at the maximum rate.
Why does transpiration occur mainly during the daytime?
Light helps in opening of the stomata, therefore, transpiration occurs mainly during the daytime.
In which type of plants do stomata open at night?
In some desert plants stomata open at night.
Why do stomata of some desert plants open at night?
To prevent excess water loss during daytime, stomata of some desert plants open at night.
In lotus, on which surface of the leaf are stomata present?
In lotus, stomata are present on the dorsal surface of the leaf.
In which season of the year does transpiration in terrestrial plants reaches the peak?
In dry summer season, transpiration in terrestrial plants reaches the peak.
Why are the leaves of many desert plants modified into spines?
The leaves of many desert plants are modified into spines in order to prevent water loss by transpiration.
Why do many desert plants possess dense hairs on the body surface?
Dense hairs prevent direct air contact on leaf surface and thus, reduce the rate of transpiration, therefore, many desert plants possess dense hairs on the body surface.
How does air flow affect the rate of transpiration?
Rate of transpiration increases with the increase in air flow.
Why is the rate of transpiration low in pine leaves?
Needle-shaped pine leaves possess lesser number of stomata, which are slightly sunken in nature, so rate of transpiration is low in pine leaves.
Which instrument is used to measure the rate of transpiration?
Ganong’s potometer is used to measure the rate of transpiration.
Why is rate of transpiration higher on the ventral surface of the leaves of dicotyledonous plants?
Leaves of dicotyledonous plants possess more stomata on the ventral surface, therefore, the rate of transpiration is higher on that side.
Mention the phenomenon through which plants give out excess water in the form of droplets?
The phenomenon through which plants give out excess water in the form of droplets, is known as guttation.
In which side of an isobilateral leaf, do we find more number of stomata?
In an isobilateral leaf, stomata are distributed equally on both sides of the leaf.
How is the rate of transpiration affected on a rainy day?
Since the percentage of water vapour is high in the atmosphere on a rainy day, the rate of transpiration decreases.
Short Questions and Answers : (2 marks for each question)
How do guard cells control the opening and closing of stomata?
In the presence of light, hygroscopic pressure increases inside the guard cells. Due to unequal elasticity of cell walls of the two opposite sides of each guard cell, the cells bend like beans. As a result, the space between two guard cells widens to open the stomata. In the absence of light, hygroscopic pressure decreases inside the guard cells and the stomata close.
Why is the stomata of lotus plant present on the dersal surface of the leaves?
The lotus leaves float on the water surface and the stomata are present on the dorsal surface to keep direct contact with air. This typical placement of stomata helps lotus leaves to maintain gaseous exchange with atmosphere and thus, perform transpiration.
Therefore, a plant with wider leaves shows higher rate of transpiration than a plant with narrow leaves. Also, in some plants (e.g. cactus) leaves are modified into spines to reduce transpiration. Thus, shape of leaves influence the rate of transpiration.
Why do plants with wider leaves wilt in summer but a pine tree remains unaffected?
Plants with wider leaves have more number of stomata, through which they lose excess water in form of vapours due to transpiration on summer days. This loss of water makes the cells turgid and the protoplasm shrinks. This results into wilting of these plants. Whereas, a pine tree possesses needle-like leaves with very little number of sunken stomata. Therefore, pine trees lose much less water by transpiration and remain unaffected even on a summer day.
Why is transpiration called a necessary evil?
Transpiration helps plants in the ascent of sap, removal of excess water, cooling the plant body, maintaining the water balance. On the other hand, excessive transpiration causes decrease in protoplasmic water content and thus, resulting into shrinkage of cells followed by wilting of leaves and tender branches. This is why, transpiration is called a necessary evil.
How does shape of leaves influence the rate of transpiration?
Number of stomata is directly proportional to the rate of transpiration. A wider leaf has more stomata than a leaf with narrow leaf lamina. Therefore, a plant with wider leaves shows higher rate of transpiration than a plant with narrow leaves. Also, in some plants (e.g. cactus) leaves are modified into spines to reduce transpiration. Thus, shape of leaves influence the rate of transpiration.
If all the leaves of a plant are applied with a layer of vaseline, what will happen to it?
If all the leaves of a plant are applied with a layer of vaseline, the stomatal openings will be sealed completely. In this situation, the plants will not be able to carry out gaseous exchange for photosynthesis and respiration. The excess water in the plant body will not be expelled out. This will affect many necessary physiological activities of the cells and the cells will die and eventually the whole plant.
What is wilting?
In case of excess transpiration during daytime in summer, the plants lose large amount of water. As a result, protoplasm of cells lose turgidity and shrink. Hence, leaves and tender branches droop. This is called wilting. If the whole plant wilts and remains in that state for several hours, it may die.
How does transpiration control environmental condition?
By transpiration, water vapour is released in the atmosphere. This increases the relative humidity, which in turn helps in the formation of clouds. Therefore, transpiration initiates rainfall in an area and thus, regulates atmospheric temperature and soil water content of that environment.
What are hydathodes? What is the function of hydathodes?
- Hydathodes: Several plants, specially herbs, possess small pores on the apices and edges of their leaves. These small pores are known as hydathodes.
- Function: Hydathodes help the plants to dispose excess water from the body in the form of droplets, by a process called guttation but they do not take part in transpiration.
State the relationship between transpiration and root-shoot ratio.
The rate of transpiration is reduced if the rootshoot ratio is less i.e root system is less branched and less deep or shoot is larger in size.
Long Questions and Answers : (5 marks for each question)
What is transpiration? Mention the differences between transpiration and evaporation.
Transpiration is a life process, by which terrestrial plants eliminate excess water from the aerial parts of the body in form of water vapour, into the atmosphere.
Differences between transpiration and evaporation
|It is a physiological process
|It is a physical process
|Occurs in plants through stomata, lenticels and cuticle
|Occurs in any free surface
|Vapour pressure, diffusion pressure and osmotic pressure are the main controlling factors of this process
|Relative humidity and air current are the main controlling factors of this process
|It is a slow and controlled process
|It is a quick process
How do plants eliminate excess water from their body? Give the difference between transpiration and guttation.
Elimination of excess water from plant body Plants release maximum amount of the excess water from their body in the form of water vapour by the process of transpiration. This occurs through the stomata, cuticular pores and lenticels. Some herbs dispose excess water as droplets through small pores, present at the edges of their leaves, called hydathodes. This process of disposal of water by plants is known as guttation.
Differences between transpiration and guttation
|1. Disposition of mineral salts
|Excess water is given out in the form of vapour
|Excess water is given out in the form of small droplets
|2. Site of occurrence
|Stomata, lenticels, cuticle
|Small pores on the edges of leaves, called hydathodes
|Mineral salts are not disposed in this process
|Mineral salts are disposed along with water in this process
Mention one difference between stomata and hydathodes. Give a brief account of different structures involved in transpiration of plants.
Difference between stomata and hydathodes:
One difference between stomata and hydathodes is that, stomata usually, open during the day and remain closed during the night (and in some desert plants, like Aloe vera, remain closed during the day, and open during the night). Whereas, hydathodes remain open all the time.
Different structures involved in transpiration:
Transpiration occurs through three different parts of plant body-stomata, lenticels and cuticle. Based on this, the process is divided into the following types.
1. Stomatal transpiration: Stomata are small pores, present mainly on leaves and a few other parts of tender shoot. Each of these pores is surrounded by two guard cells, that help to open the stomatal pores during the day and close at night. Maximum amount of excess water (about 90-97% ) is eliminated through the stomata.
2. Cuticular transpiration: Cuticle is a layer of waxy coating present on the epidermis of leaves. Very little amount of water (about 3-10% ) is eliminated through the minute pores of the cuticle.
3. Cuticular transpiration: Cuticle is a layer of waxy coating present on the epidermis of leaves. Very little amout of water (about 3-10%) is eliminated through the minute pores of the cuticle.
3 Lenticular transpiration: Lenticels are permanent, minute lens-shaped pores, found on the cracked bark of the trees. Negligible amount of water (about 0.1% ) is eliminated through these pores.
Mention the roles of different external factors regulating the rate of transpiration.
External factors regulating transpiration
Various external factors control the rate of transpiration. These are discussed below.
1. Intensity of light: The most important external factor which regulates the rate of transpiration is the intensity of light. Stomata open during daylight in the presence of light and close at night. Thus, light controls transpiration by regulating the opening and closing of stomata. Increase in the intensity of light, increases the rate of transpiration. But decrease in light intensity decreases the rate of transpiration.
2. Temperature: Rate of transpiration increases with the rise in temperature. But when temperature rises above 35°C, the stomata start closing, in order to prevent excess water loss.
3. Humidity: Increase in relative humidity decreases the rate of transpiration and decrease in relative humidity increases transpiration rate. Therefore, transpiration is inversely proportional to the rate of humidity.
4. Wind flow: In airy environment, transpiration occurs at a faster rate. Therefore, wind flow is directly proportional to the rate of transpiration.
5. Density of carbon dioxide: Rate of transpiration also depends on the density of CO2 in the atmosphere. When density of CO2 increases and more CO2 accumulates in leaves, stomatal pores close, and rate of transpiration decreases and when density of CO2 is less, rate of transpiration increases. Thus, density of CO2 in the atmosphere is inversely proportional to the rate of transpiration.
Mention the roles of different internal factors regulating the rate of transpiration.
Internal factors regulating transpiration
Various internal factors control the process of transpiration. These are discussed below.
1. Surface area and number of stomata in the leaves: Leaves with larger surface area possess more number of stomata. Therefore, transpiration rate is higher in plants with broader and larger leaves.
2. Size of stomata: Size of stomata is directly proportional to the rate of transpiration of a plant.
3. Position of stomata: Stomata, present on the surface of leaves, facilitate transpiration, but in some plants, stomata is slightly sunken below the surface of leaves. This type of stomata helps to reduce the rate of transpiration.
4. Cuticle: A plant with thick and waxy cuticle reduces cuticular transpiration. On the other hand, a thin and porous cuticle enhances transpiration rate.
5. Age of leaves: In older leaves, many stomata become clogged. So age of leaves is inversely proportional to the rate of transpiration.
6. Protoplasm: Increased density of cellular protoplasm results in an increase in the rate of transpiration and vice versa. Thus, density of protoplasm in the cell is directly proportional to the rate of transpiration.
7. Presence of hormones: Hormones such as abscisic acid control the rate of transpiration by regulating the opening and closing of stomata.
Explain the beneficial effects of transpiration. Mention its harmful effects.
Beneficial effects of transpiration
The beneficial effects of transpiration are as follows-
- Ascent of sap: Transpiration results in transpiration pull by which water and minerals reach the top leaves of the trees.
- Elimination of excess water: By transpiration, excess water from the plant body is removed. It eases the physiological activities within the cells.
- Cooling plant body: By this process, latent heat of evaporation is lost from the plant body, which cools the plant.
- Maintaining water balance: Due to the removal of excess water from plant body, water balance is maintained within it.
Harmful effects of transpiration:
The harmful effects of transpiration are as follows-
- Drying of leaves and twigs: Excess transpiration reduces water content in plant cells. As a result, leaves and softer parts of plants become dry.
- Wilting: In case of excess transpiration, the cells loseturgidity and shrink. Hence, leaves and tender branches droop. This is called wilting. If the whole plant wilts and remains in that state for several hours, it may die.
- Wastage of energy: Plant utilises only about 5% of the total absorbed water for various functions of its body. The rest (about 95% ) is given out by transpiration. Thus, there is a wastage of energy.
- Inhibition of gaseous exchange: Due to excess stomatal transpiration, gaseous exchange during photosynthesis and respiration through stomata, is inhibited.