NCERT MOST IMPORTANT QUESTIONS CLASS – 11 | BIOLOGY IMPORTANT QUESTIONS | CHAPTER -11 | TRANSPORT IN PLANTS | EDUGROWN |

In This Post we are  providing Chapter-11 TRANSPORT IN PLANTS NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS  can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.

NCERT MOST IMPORTANT QUESTIONS ON TRANSPORT IN PLANTS

Question 1.
What are the advantages of transpiration?

Answer:

1. Ascent of sap: Transpiration pull created in leaves is responsible for ascent of sap.
2. Absorption of water: Transpiration pull is also responsible for passive absorption of water.
3. The distribution of minerals in different parts of the plant is done by transpiration.
4. Cooling effect: Transpiration lowers the temperature of the leaf and causes a cooling effect.
5. The increased rate of transpiration favours the development of tissue, which provides strength to the plant.
6. Excessive transpiration induces hardness which imparts resistance of plants to drought.

Question 2.
What is the diffusion pressure? What are the factors which affect the rate of diffusion?

Answer:
The pressure exerted by the particles due to their tendency to diffuse from the region of higher concentration to the region of lower concentration.

Various factors affect the rate of diffusion:

• Diffusion pressure gradient
• Temperature
• The density of diffusing substance
• The density of the medium.

Question 3.
Define water holding capacity or field capacity of the soil.

Answer:
After heavy rainfall or irrigation, the amount of water actually retained by soil even against the force of gravity is termed as water holding capacity or field capacity of the soil. It is expressed in terms of the percentage of water present per unit dry weight of soil.

Question 4.
Describe osmosis as a special case of diffusion.

Answer:
Uptake and distribution of water, solutes, and gases occur in a plant as a result of diffusion. The diffusion of water through a semipermeable membrane is known as osmosis. The diffusion of water molecules continues across the membrane until an equilibrium is attained. Osmosis can be demonstrated by a simple experiment as follows

A thistle funnel is taken and tied with a semipermeable membrane (parchment paper) to the wide mouth of the thistle funnel and made tight.

The thistle funnel is filled with concentrated sugar solution and its wide mouth is dipped into water contained in a beaker. The membrane allows water molecules to pass through and not the sugar molecules. The level of sugar solution will rise in the funnel from ‘A’ to ‘B’. This demonstrates osmosis.

A demonstration of osmosis. A thistle funnel is filled with sucrose solution and kept inverted in a beaker containing water,
(a) Water will diffuse across the membrane (as shown by arrows) to raise the level of the solution in the funnel
(b) Pressure can be applied as shown to stop the water movement into the funnel.

Question 5.
What is the factor which affects the rate of transpiration?

Answer:
There are two factors.
A. External (Environmental) factors.
B. Internal (Living factors).

A. External factors:

1. Light: Causes stomatal opening
2. Temperature: High temperature decreases relative humidity increasing transpiration.
3. Humidity: It directly affects the rate of transpiration that is related to the vapour pressure of the atmosphere.
4. Wind: High velocity of wind causes closure of stomata.
5. Soil moisture: The rate of transpiration is directly proportional to the quantity of available moisture in the soil.

B. Internal factor:

1. Root Shoot Ratio: Roots absorbs water, should transpire water, hence their ratio affects transpiration.
2. Leaf area: Smaller plants tend to transpire more rapidly per unit area than larger plants.
3. Leaf Anatomy: Modification of leaves affects transpiration.

Question 6.
Describe the role of osmotic potential in regulating the water potential of plant cells.

Answer:
Osmotic potential is the amount by which the water potential of pure water is reduced by the presence of the solute. The osmotic potential has a negative value.

If we apply additional pressure, the water can be flown out of the solution.

Osmosis is driven by two factors:

1. The concentration of dissolved solutes in solution,
2. Pressure difference.

Water potential is the driving force for water movement in plants. Water potential represents the free energy associated with water. Osmotic potential regulates the flow of water molecules through the membrane.

Question 7.
Describe the theories related to the translocation of water.

Answer:
There are three most important theories related to the translocation of water.

1. Root pressure theory
2. Capillarity
3. Cohesion theory.

1. Root pressure theory: Water flows from higher water potential to low water potential. Water from the soil is absorbed by root hairs and conducted through xylem vessels. Mineral ions from the soil are taken up by roots and get deposited in the xylem vessels.

When the stem of a plant is cut transversely above the soil surface, a drop of the xylem sap will exude from the cut surface. This indicates the presence of positive pressure in the xylem. This pressure is known as Root Pressure.

2. Capillarity: Capillarity means a rise in water in tubes of small diameter kept in a water vessel. The uptake of water through xylem vessel is possible in small size plants through capillarity. This is due to the forces of adhesion and cohesion.

Adhesive forces attract molecules of different kinds whereas cohesive forces attract molecules of the same kind to each other. According to this theory, water is taken due to the force of adhesion and flows upward due to the force of cohesion.

3. Cohesion: This is the most important theory of water movement through plants. It is based on the force of cohesion between water molecules. This sets up a continuous water column from the top to the root tip of the plant. According to this theory water evaporates from the leaf to the atmosphere, results in a decrease in the water potential of epidermal cells.

This loss of water is balanced by water moving from adjacent cells along a water potential gradient. The movement of the water occurs from the soil to the root. Uptake of water is termed as cohesion theory and also known as transpirational pull.

Question 8.
Is there a general mechanism to explain the opening and closing of stomata? Justify your answer.

Answer:
There is no general mechanism to explain the opening and closing of stomata. Because opening and closing of stomata are regulated by the accumulation of solute in the guard cells. Solutes are taken in the guard cells, as a result, osmotic potential and water potential of guard cells are lowered, the guard cells become turgid and swell size, resulting in the stomatal opening. With a decline in guard cell solutes, water moves out, resulting in the stomatal opening.

There are two theories to explain the mechanism of opening and closing of stomata.

1. Classical starch sugar conversion theory: According to this theory, the change in osmotic concentration is brought about due to the conversion of starch into glucose and vice-versa.
2. K+ Influx and Efflux theory: According to this theory when the leaf is exposed to light, the pH of the guard ceils rises due to the active transfer of H+ ions from the cytoplasm into chloroplast’s utilization of CO. in photosynthesis. In the majority of plants, stomata remain open during the day and close at night.

Hence, there is no general mechanism to explain the stomatal opening and closing.

Question 9.
Mention some factors that influence stomatal opening and closing. How are these factors involved in regulating stomatal behaviour?

Answer:
Factors affecting stomatal movements:

1. Light: In most of the plant’s stomata open during the day. The effect of light causes the opening of stomata or it may be either due to the hydrolysis of starch into glucose.
2. The water content of leaves: A decrease of water content in stomatal cells results in an increase in their D.P.D. Water from guard cells moves into these cells and stomata close.
3. CO₂ concentration: Low CO₂ concentration in guard cells causes the opening of stomata.
4. pH: High pH stimulates the opening of stomata and low pH causes closure of stomata and high concentration of CO₂ causes closure of stomata.
5. Temperature: High temperature stimulates the opening of the stomata.
6. Atmospheric Humidity: Humid environment favours opening and dryness causes closure of stomata.
7. Minerals: Minerals like P, Mg, Ca etc. affect the stomatal opening. A high concentration of K+ ions causes the opening of stomata.
8. Growth Hormones: Cytokinins stimulates the opening of stomata. Abscisic acid induces the closure of stomata.

Question 10.
Write short notes on:
(i) Cohesion-Tension and Transpiration pull theory.

Answer:
Transpiration pull theory: Ascent of sap has been explained satisfactorily by Dixon with the help of a theory called Transpiration pull theory. According to this theory water continuously evaporates from the turgid and moist cell walls of mesophyll cells in the leaves.

It makes the mesophyll air saturated. The air outside the leaf is dry. So a gradient is set up which allows the water vapours to go out from the interior of the leaf to the outside through the stomata. The mesophyll cells draw water from the deeper tissue, which in turn take water from the xylem of the leaf. It creates a kind of pull in the leaf called transpiration pull.

The xylem of the leaf is connected to the xylem of the stem and further to the xylem of the roots. Since there is a continuous column of water in the plant, water is virtually lifted up due to transpiration pull a situation similar to one like drawing a bucket of water from a well. The column of water does not break because of the great force of cohesion among the water molecules. This theory is also called the cohesion of water molecules theory.

(ii) Mass flow hypothesis.
Answer:
Mass flow hypothesis: The carbohydrates prepared in the leaves are translocated to other parts of the plant in the form of sucrose through phloem at the expense of metabolic energy. Munch’s mass flow hypothesis is the most accepted theory for the translocation of organic food.

According to this hypothesis, organic substances move from the region of high osmotic pressure to the region of low osmotic pressure due to the development of a gradient of turgor pressure. This can be proved by taking two interconnected osmometers. One of the osmometers has a high solute cone than the other. The whole apparatus is placed in water.

Water enters the osmometer with a high solute cone. It creates high turgor pressure in it. High turgor pressure forces the solution to move through the tube to the other osmometer. It is called mass flow. If somehow, the solute is continuously added to the donor osmometer and converted into the osmotically inactive compound in the other osmometer, this system can work indefinitely.

Munch’s mass flow apparatus.