Biology MCQ

(d) Cobalt chloride paper
Explanation:
Cobalt chloride paper is used to demonstrate unequal transpiration in a dicot leaf. This paper is sensitive to moisture and changes colour when it absorbs water, which makes it useful for showing the areas of the leaf where transpiration is occurring more intensely.

(d) Age of the plant
Explanation:
The factors that significantly affect the rate of transpiration include light, humidity, and wind, but the age of the plant generally does not directly influence transpiration rates.

(b) Hydathodes
Explanation:
Guttation is the process where plants exude drops of xylem sap on the tips or edges of leaves during the night. This occurs through structures called hydathodes, not through stomata.

(a) Open stomata, dry atmosphere and moist soil
Explanation:
Transpiration pull, which helps draw water up through a plant, is maximized under conditions of open stomata (for maximum water loss), a dry atmosphere (which increases the gradient for water evaporation), and moist soil (ensuring water availability).

(b) The turgid and flaccid state of the guard cells
Explanation :
Stomatal opening and closing are primarily controlled by the turgidity changes in the guard cells. When guard cells are turgid, stomata open; when they are flaccid, stomata close.

(c) Guttation
Explanation:
Guttation is the process by which plants release liquid water from specialised structures called hydathodes located at the tips of their leaves. It occurs when there is an excess of water in the plant's root system, typically in conditions of high soil moisture or humidity. Unlike transpiration, guttation involves the release of liquid water in the form of droplets. Guttation often happens during the night or early morning when the plant's stomata are closed, preventing transpiration.

(c) Rate of transpiration
Explanation:
Ganong's potometer is a device used to measure the rate of water uptake by a plant, which indirectly indicates the rate of transpiration, the process of water loss from plants primarily through the stomata in their leaves.

(a) Both A and R are True.
Explanation :
Transpiration is the process of loss of water (in the form of water vapour) from plant aerial parts, such as leaves, stems and flowers. It occurs mostly at the leaves through the minute openings present on the leaves called stomata. At night in some plants, root pressure causes guttation or exudation of drops of xylem sap from the tips or edges of leaves. Thus, guttation is due to root pressure.

(a) Both A and R are True.
Explanation:
Reduced surface area reduces the loss of water by transpiration. In cacti, leaves are modified into spines to reduce the surface area of the leaf lamina, thereby minimising water loss in arid environments due to transpiration. This adaptation is crucial for survival in desert conditions.

(b)


Explanation:
Transpiration is reduced if the air outside is humid. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.

(a) Water loss is greater than water uptake
Explanation:
The wilting condition is found when plant tissues contain insufficient water to hold the cells rigid. This may occur when the rate of transpiration exceeds the rate at which water enters the root system from a soil containing ample water.

(d) Transpiration
Explanation :
Cobalt chloride paper is an indicator of moisture. It is blue when dry and turns pink when exposed to moisture. The initial blue cobalt chloride paper will turn pink only in the case of transpiration in which water vapour is released.

(b)

Wind speed	Light intensity	Humidity	Temperature
✓	✓	✓	x

Explanation:
The rate of transpiration is affected by several factors, including: temperature, humidity, wind speed and light intensity. To investigate the effect of temperature on the rate of transpiration, other factors such as humidity, wind speed and light intensity should be kept constant.

(b) Regulate the opening and closing of stomata
Explanation :
Guard cells are specialised cells in the epidermis of leaves and stems. They function to control the opening and closing of stomata. By adjusting the size of these openings, guard cells regulate gas exchange and water loss in plants.

(a)Stomata help in diffusion of gases in the leaves and in transpiration.
Explanation:
Stomata are tiny openings on the surface of leaves that allow for the exchange of gases (like oxygen and carbon dioxide) necessary for photosynthesis. They also play a key role in the process of transpiration, which is the loss of water vapor from the plant to the atmosphere.

(d) They are present on the surface of hard, old woody stem.
Explanation:
Lenticels are found as raised circular, oval, or elongated areas on stems and roots. In woody plants, lenticels commonly appear as rough, cork-like structures on young branches. Lenticels participate in gaseous exchange and transpiration.

(a) It is the loss of water as water vapour from the aerial parts/stems and leaves of the plants.
Explanation:
Transpiration is the biological process by which water is lost in the form of water vapour from the aerial parts of the plants, like stems and leaves.

(d) Oxygen
Explanation:
Intensity of light, temperature, humidity, wind velocity and carbon dioxide concentration are the factors that affect transpiration.

(b) Xylem
Explanation:
Xylem is the tissue in plants responsible for conducting water and minerals from roots to other parts of the plant.

(c) Reading on the capillary tube indicates the volume of water lost.
Explanation:
As the transpiration proceeds, i.e., as the water is lost from the twig, a suction force is set up which pulls the water from the beaker and the bubble in the capillary tube moves along. The readings on the capillary tube would give the volume of water lost in a given time.

(c) Potometer
Explanation:
A potometer, sometimes known as transpirometer, is a device used for measuring the rate of water uptake of a leafy shoot which is almost equal to the water lost through transpiration.

(d) Provides oxygen
Explanation:
The process of transpiration helps in the exchange of gases; helps in sending out excessively absorbed water by plants; helps in the absorption and distribution of water in plants; and provides coolness to the plant body. It does not provide oxygen.

(b) Turgor Pressure
Explanation:
In a leaf, the cell sap within each cell exerts a turgor pressure outward against the cell wall. This pressure is essential for maintaining the structure and rigidity of plant cells. Turgor pressure results from the osmotic flow of water into the cell, creating outward pressure on the cell-wall.

(c) Stomata
Explanation:
Stomata are minute openings in the epidermal layer of leaves, primarily involved in gaseous exchange.

(b) Transpiration
Explanation:
As the potted plant is covered with polythene bag and kept in the sunlight there will be the loss of water through the stomata present on the leaves. The water drops will appear inside the polythene bag as a result of a loss of water from the stomata. This is due to transpiration.

(c) The spongy mesophyll cells
Explanation:
During transpiration, water vapor is primarily lost through these spaces, making the spongy mesophyll a key site for water evaporation in leaves. These cells are part of the leaf's internal structure and contain large air spaces that facilitate gas exchange.

(b) Loss of water vapour from the leaves and stems of a plant.
Explanation :
Transpiration is the process where plants lose water vapour through small openings in their leaves and stems, known as stomata. This process helps in the movement of water and minerals from roots to leaves and also aids in temperature regulation of the plant.

(a) Open stomata, dry atmosphere and moist soil.
Explanation:
Transpiration pull is highest when stomata are open (allowing water vapour to escape), the atmosphere is dry (creating a greater gradient for water vapour to move from the plant to the air), and the soil is moist (ensuring adequate water supply for transpiration). These conditions collectively maximize the rate of transpiration.

(b) Increase in wind velocity
Explanation :
When the wind velocity increases, it removes the water vapour quickly from the leaf surroundings, reducing the external humidity around the leaf. This enhances the rate of transpiration as water vapour is drawn out of the leaves more rapidly.

(c) Summer
Explanation:
During summer, the higher temperatures, increased light intensity, and often lower humidity levels lead to greater evaporation of water from the soil and increased water loss from the plant leaves. This combination of factors makes transpiration rates highest in the summer compared to other seasons.

(c) Out of the leaf by transpiration
Explanation :
Transpiration is the process by which water vapour is lost from a plant to its environment. On a dry, sunny day, the rate of transpiration is generally higher because the warmer temperature and lower humidity outside the leaf encourage water vapour to diffuse out of the leaf into the atmosphere.