Chapter 11 Transport in Plants

Class 11 Biology Chapter 11 Important Extra Questions Transport in Plants

Transport in Plants Important Extra Questions Very Short Answer Type

Question 1.
Define heat of wetting or hydration.
Answer:
Imbibition of water is always associated with heat generation is called wetting or hydration.

Question 2.
What phenomenon is always associated with imbibition?
Answer:
Heating of wetting or hydration.

Question 3.
Which solution de-plasmolyse the plasmolyse solution?
Answer:
Hypotonic solution.

Question 4.
What is the full form of D.P.D.?
Answer:
Diffusion pressure deficit.

Question 5.
Name the element that regulates turgidity in guard cells.
Answer:
Potassium.

Question 6.
Which type of guard cells are found in grasses?
Answer:
Dumb bell-shaped.

Question 7.
Which is the important factor that affects water potential?
Answer:
Solute concentration.

Question 8.
Why do plants growing in arid regions bear small leaves with sunken stomata?
Answer:
To reduce transpiration.

Question 9.
Name two antitranspirants.
Answer:
Abscisic acid (ABA), Phenyl Mercuric Acetate (PMA).

Question 10.
When does wilting occur?
Answer:
When the rate of evaporation of water exceeds the rate of uptake of water by roots.

Question 11.
What is water potential?
Answer:
The capacity of a solution to hold the maximum amount of water is called water potential.

Question 12.
What will be the water potential of distilled water at normal pressure and temperature?
Answer:
Zero.

Question 13.
What are the porins?
Answer:
The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through.

Question 14.
Define the water potential.
Answer:
Water potential is a concept fundamental to understanding water movement.

Question 15.
What is antiport?
Answer:
In an antiport, both molecules move in opposite directions.

Question 16.
What is flaccid?
Answer:
When the water flows into the cell and out of the cell are in equilibrium the cells are said to be flaccid.

Question 17.
Define isotonic.
Answer:
If the external solution balances tire osmotic pressure cytoplasm it is said to be isotonic.

Question 18.
Define translocation.
Answer:
The bulk movement of substances through the conducting or vascular tissues of plants is called translocation.

Question 19.
Define Casparian strip.
Answer:
The inner boundary of the cortex, the endodermis, is impervious to water because of a bond of suberised matrix called the Casparian strip.

Question 20.
Define cohesion.
Answer:
The mutual attraction between water molecules.

Question 21.
What is transpiration?
Answer:
Transpiration is the evaporative loss of water by the plants. It occurs mainly through the stomata in the leaves.

Transport in Plants Important Extra Questions Short Answer Type

Question 1.
What is osmosis?
Answer:
It is the movement of water molecules from a region of its higher concentration to low concentration through the plasma membrane. It is a vital process. Various physiological process in plants takes through osmosis.

Question 2.
What is the active transport of water?
Answer:
It is the transport of water molecules against the concentration gradient with the utilization of energy (ATP). The molecules from low to high concentration move through the active transport of water.

Question 3.
How does transpiration differ from guttation?
Answer:

Transpiration	Guttation
1. It is the process of loss of water in the form of water vapour from the aerial part of the plant body.	1. It is the process of elimination of water in the form of water droplets from leaf margins.
2. It mostly takes place through stomata.	2. It takes place only through hydathodes.

Question 4.
Define permanent wilting co-efficient or permanent wilting percentage.
Answer:
The percentage of water on a dry weight basis of the soil that still remains at the time when the plant shows permanent wilting is termed as permanent wilting co-efficient. It various between 1-1.5% depending upon the texture of the soil. It is higher in clayey soil than sandy soil.

Question 5.
What are the conditions for imbibition to take place?
Answer:
There are two conditions necessary for imbibition to take place:

1. Water potential gradient between the surface of the adsorbent and the liquid imbibed.
2. The affinity between the adsorbent and the imbibed liquid. It is a type of diffusion by which the movement of water takes place.

Question 6.
Give an account of the water relations of a plant cell when it is placed in
(a) Hypertonic solution,
Answer:
When the cell is placed in hypertonic solution exosmosis occurs, the protoplast contracts and the cell membrane detaches from the cell wall and contracted protoplast. This contraction of the protoplast by ex¬osmosis is termed plasmolysis.

(b) Hypotonic solution.
Answer:
When a plasmolysed cell is placed in water or hypotonic solution, endosmosis occurs and the protoplast regains the original position. This phenomenon is termed de-plasmolysis.

Question 7.
What is the ascent of sap?
Answer:
Water and minerals absorbed by the plants through roots from the soil are transported to different parts of the plant as these play a vital role in their growth. Water along with various dissolved inorganic substances in it are termed sap. The upward translocation of sap (water and dissolved inorganic substances) from the roots to the aerial parts of the plant is termed ascent of sap.

Question 8.
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 9.
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 10.
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 11.
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 12.
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 13.
In what way does the concept of water potential help in explaining water movement?
Answer:
The additional pressure (more than osmotic pressure) is applied so that water can be made to flow out of the solution.
There are two factors

1. The concentration of dissolved solutes in a solution,
2. Pressure difference determines the chemical potential of water, which is the driving force for water movement in plants.

This chemical potential is the water potential. It is the difference in the free energy of water molecules in solution and in the pure state at the same temperature and pressure.

Question 14.
Of what importance is potassium in the opening and closing of stomata?
Answer:
The opening and closing of stomata are controlled by the accumulation of solutes in the guard cells. In the guard cell solutes are taken from neighbouring epidermal and mesophyll cells. The major solute which is taken in by the guard cells is potassium.

The rise in potassium level causes the stomatal opening and a decrease in level causes stomatal closing. The uptake of potassium controls the water potential. The extent of K⁺ accumulation in guard cells determines the size of the stomatal opening.

Question 15.
Does transpiration serve any useful function in the plants?
Answer:
Transpiration helps in the movement of xylem sap. It increases the absorption of mineral nutrients by the roots from the soil. Solar radiation absorbed by the leaves is used in photosynthesis but some radiations will cause heating of leaves. Transpiration, however, reduces the heating of the leaves.

Question 16.
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 17.
Explain the facilitated diffusion.
Answer:
In facilitated diffusion special proteins help move substances across membranes without the expenditure of ATP energy. Facilitated diffusion cannot cause net transport of molecules from a low to high concentration-this would require the input of energy.

The transport rate reaches a maximum when all of the protein transporters are being used (saturation). Facilitated diffusion is very specific: it allows the cell to select substances for uptake. It is sensitive to inhibitors that react with protein side chains.

Question 18.
What is active transport? Explain with an appropriate example.
Answer:
Active transport is carried out by membrane proteins. Hence different proteins in the membrane play a major role in both active as well as passive transport. Pumps are proteins that use energy to carry substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration.

The transport rate reaches a maximum when all the protein transporters are being used or are saturated. Like enzymes, the carrier protein is very specific in what it carries across the membrane. These proteins are sensitive to inhibitors that react with protein side chains.

Question 19.
What is imbibition?
Answer:
Imbibition is a special type of diffusion when water is absorbed by solids-colloids-causing them to enormously increase in volume. The classical examples of imbibition are absorption of water by seeds and by dry wood. The pressure that is produced by the swelling of wood has been used by prehistoric man to split rocks and boulders.

If it were not for the pressure due to imbibition, seedlings would not have been able to emerge out of the soil into the open; they probably would not have been able to establish.

Question 20.
What is turgor pressure? Give its two roles in plants.
Answer:
The pressure exerted by the cell sap on its wall when it has absorbed the maximum amount of water is called turgor pressure.

1. Leaves stand erect and look fresh due to turgor pressure.
2. The movement of soluble food in phloem is due to turgor pressure.

Question 21.
What is guttation?
Answer:
Oozing of droplets along the leaf margin on the vein endings at night is called guttation. In the morning when water evaporates, a layer of salts remains on the leaf which may cause burning.

Guttation occurs through the hydathodes. Education occurs when absorption exceeds transpiration and water pressure builds up in the xylem vessels. It forces the water outward through the hydathode.

Transport in Plants Important Extra Questions Long Answer Type

Question 1.
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 2.
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 3.
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 4.
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.