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Question-1

Define water potential?

Solution:
Water potential is the potential energy of water.

Question-2

what are the factors affecting the rate of diffusion?

Solution:
The main factors that affect the rate of diffusion are,

(i) Temperature: The rate of diffusion increases with rise in temperature. This is because a rise in temperature increases the kinetic energy of the diffusing particles.

(ii) Density of diffusing substance: The rate of diffusion of a substance is inversely proportional to the square root of its density (i.e.) heavier the molecule, slower is the rate of diffusion.

(iii) Density of the medium: The rate of diffusion is slower, if the medium is concentrated. Thus, a gas would diffuse more rapidly in vacuum than in air.

(iv) Diffusion pressure gradient: The rate of diffusion is directly proportional to the difference of diffusion pressure at the two ends of a system and inversely proportional to the distance between the two.

Question-3

What will happen to water potential when solutes are added?

Solution:
Water potential is lowered when solutes are added.

Question-4

Write the significance of plasmolysis.

Solution:
Plasmolysis is a vital phenomenon and has the following importance:

(i) The osmotic pressure of a cell can be measured by plasmolysis. The osmotic pressure of a cell is roughly equal to the osmotic pressure of a solution that causes incipient plasmolysis in the cell.

(ii) Salting of pickles, meat, fishes, etc. and addition of sugar to jams, jellies, cut fruits, etc., prevent their decay by microbes, as the latter get killed due to plasmolysis.

(iii) Plasmolysis is helpful in determining whether a particular cell is living or dead as plasmolysis does not occur in a dead or non-living cell.

Question-5

Which fractions of soil water are readily available to plants for absorption?

Solution:
Capillary water is the fractions of soil water are readily available to plants for absorption.

Question-6

Distinguish between active and passive absorption of water.

Solution:

Active absorption

Passive absorption

(i) Active absorption of water occurs due to the activity of root and root hairs. (i) Passive absorption occurs due to the activity of the upper part of the plant such as shoot and leaves.
(ii) Water is absorbed by the osmotic or non-osmotic processes along or against DPD gradient. (ii) Water is absorbed as a result of tension created by transpiration pull.
(iii) It involves symplast movement of water. (iii) It involves apoplast movement of water (i.e.) through cell walls and intercellular spaces.
(iv) It utilizes metabolic energy. (iv) It utilizes solar energy for transpiration.
(v) During active absorption of water, the root cells play an active role. (v) During passive absorption of water, the root cells play a passive role.
(vi) It is independent of transpiration. (vi) It takes place when transpiration is fast.
(vii) It creates a positive pressure in xylem channels. (vii) It produces a negative pressure in xylem channels.

 

Question-7

Distinguish between transpiration and evaporation.

Solution:

Transpiration

Evaporation

(i) This is a physiological process that occurs in plants. (i) This is a physical process that occurs from any free surface.
(ii) It involves living tissues. (ii) It may involve both living and non-living surfaces.
(iii) It is controlled by environmental factors as well as by plant factors such as osmotic pressure of the cells, thickness of cuticle, number and position of stomata, etc. (iii) It is influenced only by environmental factors.
(iv) It moistens the surface of leaves and young stems and protects them from the burning Sun. (iv) It causes dryness of free surfaces.
(v) It is comparatively a slow process. (v) It is comparatively a faster process.

 

Question-8

Mention two ways of absorption of water in plants?

Solution:
Two ways of absorption of water in plants are, (i) apoplast pathway and (ii) symplast.

Question-9

What are the factors affecting water absorption?

Solution:
The absorption of water is affected by a number of factors. They are

(i) Availability of soil water: Water uptake is directly affected by the amount of water available to the roots for absorption. The water content between field capacity and permanent wilting percentage is often termed as readily available water, because it can be absorbed readily by plants. If water is present in the soil below the permanent wilting percentage or beyond field capacity, the rate of water absorption will be reduced.

(ii) Concentration of soil
Solution:
The amount of soluble salts in the soil also affects water uptake by the roots. If the concentration of soil solution is more than that of the cell sap of root cells, water will tend to move out due to exosmosis. It is due to this reason that a field is irrigated properly after addition of fertilizers.

(iii) Soil temperature: Most plants require temperatures ranging from 20-35oC for optimum water absorption. A temperature above 35oC reduces water uptake by reducing the permeability of the plasma membrane. Low temperature of the soil reduces absorption of water.

(iv) Aeration of soil: The roots of plants absorb water more efficiently in well aerated soils than in poorly aerated soils. In poorly aerated soils, the growth and metabolic activities of the roots are slowed down. Accumulation of CO2 in soil air increases the viscosity of the protoplasm and decreases its permeability. This decreases the rate of water absorption.

Question-10

Define wall pressure?

Solution:
The pressure extended by the rigid cell wall on the protoplasm of cell opposite to the turgor pressure is called wall pressure.

Question-11

Write the importance of diffusion in plants.

Solution:
(i) Exchange of gases (CO2 and O2) through stomata takes place by diffusion.

(ii) Transpiration or loss of water from the aerial parts of the plant involves the process of diffusion.

(iii) Diffusion is involved in the passive uptake of mineral salts.

(iv) Fragrance from the flowers, to attract the pollinating animals, spreads in the air by diffusion.

(v) Diffusion plays an important role in imbibition and osmosis.

Question-12

Name the pores through which guttation occur?

Solution:
Hydathodes are the pores through which guttation occur.

Question-13

What is the value of water potential of pure water at normal temperature and pressure?

Solution:
The value of water potential of pure water at normal temperature and pressure is zero.

Question-14

What is transmembrane pathway?

Solution:
Transmembrane is the movement through the cell membrane.

Question-15

Mention two factors that affect water potential.

Solution:
The two factors that affect water potential are, (i) the amount of solute and (ii) the external pressure.

Question-16

Mention two external factors, which affect transpiration.

Solution:
The two external factors, which affect the rate of transpiration, are atmospheric humidity and light.

(i) Atmospheric humidity: The diffusion of water vapour from the intercellular spaces of leaves to the outside atmosphere depends on the moisture content of the atmosphere. If the moisture content of the atmosphere is high, the rate of transpiration is relatively low but as the moisture in the air decreases, the rate of transpiration increases rapidly.

(ii) Light: Light indirectly affects the rate of transpiration by regulating (a) the opening of stomata and (b) increasing the leaf temperature. In most plants, stomata open in the presence of light and close in darkness. Thus, the rate of transpiration increases in light and decreases in the dark.

Question-17

Define wilting.

Solution:
Wilting is the loss of turgidity of leaves and other soft aerial parts of a plant, thereby causing them to droop.

Question-18

Mention any two uses of transpiration of plants.

Solution:
The two uses of transpiration to plants,

(i) It maintains the turgidity of cells.

(ii) It reduces negative tension downwards to the roots and this help in the ascent of sap.

Question-19

Which part of root is related with the absorption of water?

Solution:
Root hairs are the part of root which is related with the absorption of water.

Question-20

What is wall pressure?

Solution:
In plants, due to turgor pressure, the protoplast of a plant cell presses the cell outwards. The cell wall being elastic, pushes the protoplast back with a pressure equal in magnitude but opposite in direction. This pressure is called wall pressure.

Question-21

Describe the thistle funnel experiment to demonstrate osmosis.

Solution:
The phenomenon of osmosis can be demonstrated by a thistle funnel experiment. Take a long stemmed thistle funnel. Fill it with 10% sugar solution by closing the opening of the stem with finger. Close the mouth of the funnel tightly with semi permeable animal membrane by means of a waxed thread. Scissor the free edges of the membrane. Invert the funnel in a beaker containing water so that the membrane is completely immersed. Mark the level of the solution as A by means of glass marking pencil. After a couple of hours, the level of water falls down in the beaker. The water in the beaker does not taste sweet. The rise in the level of the sugar solution in the stem of the thistle funnel is due to osmosis. The concentration of water molecules in the beaker is more than their concentration inside the thistle funnel. Therefore, water molecules move from the region of their higher concentration to the region of their lower concentration.

Question-22

Name the forces involved in absorption of water by roots?

Solution:
Osmotic pressure and transpiration pull are the forces involved in absorption of water by roots.

Question-23

Name the two factors that affect water potential.

Solution:
The two factors that affect the water potential are, (i) amount of solute and (ii) transpiration pull.

Question-24

Define diffusion pressure.

Solution:
The pressure exerted by the tendency of molecules of gases, liquids or solids to diffuse from the area of their higher concentration to the area of lower concentration is called diffusion pressure.

Question-25

Write the types of osmosis.

Solution:
The osmosis is of two different types. They are

(i) Endosmosis and

(ii) Exosmosis

(i) Endosmosis: The osmotic inflow of water into a cell, when it is placed in a solution, whose solute concentration is less than the cell sap, is called endosmosis.

(ii) Exosmosis: The osmotic outflow of water from a cell, when it is placed in a solution, whose solute concentration is more than the cell sap is called exosmosis.

Question-26

Mention the osmotic relationship of cell when it is put in.

(i) hypotonic solution

(ii) hypertonic solution

(iii) an isotonic solution.

Solution:
  (i) Endosmosis, 

(ii) Exosmosis, 

(iii) No net movement.

Question-27

Write the different types of osmotic concentration.

Solution:
A solution can be termed as hypotonic and hypertonic or isotonic depending upon its osmotic concentration, with respect to another solution or cell sap.

(i) Hypotonic
Solution:
A solution, whose osmotic concentration is less than that of another solution or cell sap is called hypotonic solution.

(ii) Hypertonic
Solution:
A solution, whose osmotic concentration is more than that of another solution or cell sap is called hypertonic solution.

(iii) Isotonic
Solution:
A solution, whose osmotic concentration is equal to that of another solution or cell sap, is called isotonic solution.

Question-28

Which molecules can move freely across the semi permeable membrane of plant cell.?

Solution:
Water molecules can move freely across the semi permeable membrane of plant cell.

Question-29

What is turgor pressure?

Solution:
Turgor pressure is the pressure, which develops in a confined part of an osmotic system due to the osmotic entry into it.

Question-30

Name the tissue through which ascent of sap takes place.

Solution:
Xylem tissue is the tissue through which ascent of sap takes place.

Question-31

State any two significance of turgidity.

Solution:
(i) Turgidity keeps the cell and their organelles fully distended. This is essential for plants to live and grow normally.

(ii) The opening and closing of stomata are regulated by the turgidity of the guard cells.

Question-32

Name two antitranspirants.

Solution:
The two antitranspirants are, phenyl mercuric acetate, and abscisic acid.

Question-33

Describe pressure potential.

Solution:
The positive pressure operating in the plant cell is termed as pressure potential. It is usually positive and increases the water potential in the system. The water potential (Ψ) in a plant cell can be written as sum of the solute potential (Ψs), the matric potential (Ψm) and the pressure potential (Ψp).

Ψ = (Ψs) + (-Ψm) + (Ψp)

   = Ψs + Ψm + Ψp

Since, matric potential is often discarded because it is not significant in osmosis, the above relationship can be simplified as

Ψ = Ψs + Ψp

Question-34

What determines the direction of flow of water from one cell to another cell?

Solution:
Water potential of the cells which is represented by Greek letter psi (y ), determines the direction of flow of water from one cell to another cell.

Question-35

What is the water potential of pure water?

Solution:
Zero bar is the water potential of pure water.

Question-36

What is holard?

Solution:
The total amount of water present in the soil is called holard.

Question-37

What are anti-transpirants?

Solution:
The chemical substances, which reduce transpiration without affecting gaseous exchange, are called anti-transpirants.

Question-38

What is turgor pressure?

Solution:
Turgor pressure is the pressure responsible for pushing the cell membrane against the cell wall due to the entry of water by osmosis.

Question-39

What is wall pressure?

Solution:
The pressure extended by the turgid cell wall on the protoplasm of cell opposite to the turgor pressure is called wall pressure.

Question-40

Demonstrate an experiment to show how the root pressure exists.

Solution:
Root pressure can be demonstrated experimentally by cutting the stem of a well-watered herbaceous plant, near its base. The xylem sap is seen to flow out through the cut end with a pressure. The pressure of exudation can be noted by fixing a vertical glass tube half filled with water, with the help of a rubber tuber to the cut end of the stem. A column of sap is seen to rise in the tube. If a manometer is fixed to the cut end of the stem, the rise in the level of the mercury of the manometer will be a measure of the root pressure.

Question-41

Which of the following has the highest water potential.

(a) IM salt solution

(b) IM sugar solution

(c) Distilled water

(d) IM sugar solution with 2.3 bars pressure applied to it.?

Solution:
(d) IM sugar solution with 2.3 bars pressure applied to it.

Question-42

Name the force of attraction which keeps the water molecules united in the plants.

Solution:
Cohesive force is the force of attraction, which keeps the water molecules united in the plants.

Question-43

Name the part of root concerned mainly with absorption of water.

Solution:
Root hair.

Question-44

What is hygroscopic water ?

Solution:
The thin film of water, which covers the soil particles, is called hygroscopic water.

Question-45

What will happen to a plant cell when it is kept in a higher water potential ?

Solution:
In a plant cell when it is kept in higher water potential, water will move from higher potential to lower potential.

Question-46

What happens to a plat cell if it is put in a hypertonic solution ?

Solution:
Plant cell if it is put in a hypertonic solution, water moves out causing shrinkage of a cell.

Question-47

Name the structure through which water is lost from the plants ?

Solution:
Stomata.

Question-48

Define permeability

Solution:
Permeability is the extent to which the membrane allows or restricts the movement of a substance.

Question-49

Name the theory proposed by Dixon for ascent of sap.

Solution:
Transpiration pull theory

Question-50

Expand DPD.

Solution:
Diffusion Pressure Deficit

Question-51

Name the plants where sunken stomata are present ?

Solution:
Opuntia and Ruscus, etc.

Question-52

Name the hormone which signals the closure of stomata during severe drought or intense solar drought.

Solution:
Abscissic acid (ABA) is the hormone, which signals the closure of stomata during severe drought or intense solar drought.

Question-53

What is the common measurement unit of water potential ?

Solution:
Pascal (Pa) is the common measurement unit of water potential.

Question-54

When root pressure is high and the transpiration is low, some plants lose water. Where from does the water ooze out and what is this process called ?

Solution:
The water oozes out from hydathodes and the process is called guttation.

Question-55

A plat cell when kept in a certain solution got plasmolysed. What was the nature of the solution ?

Solution:
Hypertonic.

Question-56

Name the apparatus to know the relative size of stomata.

Solution:
Potometer.

Question-57

Why is energy required to develop root pressure (or) why does generation of root pressure requires energy ?

Solution:
The generation of root pressure is an active process. It is because only when minerals are accumulated against concentration gradient by active absorption using metabolically produced energy.

Question-58

Why is salt added in excess to pickles ?

Solution:
(i) High concentration of salts prevents the growth of microorganisms and thus it prevents spoilage of pickles.

(ii) Kills microorganism by exosmosis.

Question-59

What is potometer ?

Solution:
Apparatus to measure the rate of transpiration from the leaves of plants.

Question-60

Name one plant having sunken stomata ?

Solution:
Nerium.

Question-61

Name one tallest plant.

Solution:
Eucalyptus.

Question-62

What makes the raisin to swell up when kept in water ?

Solution:
Endosmosis.

Question-63

What is stomatal frequency ?

Solution:
It refers to the number of stomata per square mm of leaf surface.

Question-64

What is stomatal transpiration ?

Solution:
Transpiration by stomatal pores in plants.

Question-65

Name the quantity of water transpired by a unit area of leaf surface in a unit time.

Solution:
Transpiration flux.

Question-66

What is the role of root pressure in the ascent of sap ?

Solution:
Root pressure does play a significant role in the ascent of sap during the day time because the suction pressure is much greater than the root pressure. But, during the night time, when the rate of transpiration decreases, the root pressure causes guttation in herbaceous plants.

Question-67

Why is transpiration in higher plants considered a necessary evil ?

Solution:
Transpiration in higher plants is considered a necessary evil because major portion of the water absorbed by plants is evaporated into atmosphere from the aerial part of plants through this process. Only a small amount of water absorbed is actually used by plants to perform various biological activities. But we cannot stop this evil. Because of this evil, various biological activities are possible only in the presence of water. However, these days to reduce the role of transpiration, various anti-transpirants are used.

Question-68

Differentiate between osmosis and imbibition.

Solution:
Osmosis Imbibition
Osmosis is a non reversible phenomenon. Imbibition is a reversible phenomenon.
Semipermeable membrane is essential. No need of semipermeable membrane.
Osmosis takes place in living cells. Imbibition takes place in living as well as dead cells.
Movements of the solvent from the higher concentration to lower concentration. Water absorption by general body surface.

 

Question-69

List the factors which balance the uptake of K+ions.

Solution:
(i) Uptake of Cl-

(ii) Transport of H+ ions released from organic acids such as malic acid, 

(iii) The negative charges of organic acids when they lose H+ ion.

Question-70

What is wilting ? Differentiate between temporary and permanent wilting.

Solution:
When the rate of transpiration is more than the rater of absorption of water by the roots, the leaves and branches droop down. This flaccid condition of the plant body is known as wilting.
Temporary wilting Permanent wilting
It commonly occurs during mid-day only. It occurs through out day and night.
Plant recovers from temporary wilting after sometimes. Automatic recovery is not possible but it may recover if water is provided soon after the first signs of wilting is noticed.
Much damage is not caused. Much damaged is caused which may lead to death.

 

Question-71

What is root pressure ?

Solution:
Root pressure is a pressure exerted by the root cells due to which water is forced into the xylem vessels under turgid conditions. Root minerals, which results in flowering the water potential, causes the movement of water towards root cells. The root pressure is measured in a negligible amount in actively transpiring plants like conifers. It is nearly about 1 to 6 atmospheres in various herbaceous plants. The exudation of liquid at the cut of stem is also caused by the root pressure.

Question-72

Write a note on the significance of transpirations.

Solution:
(i) Transpiration produces negative tension downwards to roots and this helps in the ascent of sap.

(ii) The circulation of water inside the plant is efficiently maintained by transpiration.

(iii) It causes cooling of leaf surface and thereby protects the leaves from heat injury by intense sunlight.

(iv) It maintains the turgidity of the cells.

(v) Rapid transpiration results in the development of mechanical tissues in plants. This makes the plant healthier, thick and cutinised as well as enables it to resist the attack of various foreign materials.

(vi) During rapid transpiration, the cell sap inside the cells becomes concentrated. This causes the sugar content to increase inside the fruit. Thus, the fruit becomes sweeter during gusts of hot wind.

Question-73

State the significance of plasmolysis.

Solution:
(i) It explains osmosis.

(ii) Essential to know the biotic nature of the cell.

(iii) Essential in killing of weeds.

(iv) To determine the osmotic pressure of the cell.

(v) As a proof of cell wall permeability.

Question-74

Name and explain the factors affecting absorption of water by plants.

Solution:
Factors affecting water absorption by the plants:

Soil aeration: In aerated soil water absorption rate is more as compared to those that are not. It is due to low O2 concentration in the soil.

Soil temperature: In cooler climates, the rate of water absorption is less than warm climate.

Concentration of soil
Solution:
It is dependent upon the presence of soluble substances in the soil. Halophytes grow in soils having high content of salts.

Available water content of soil: It depends upon the DPD (Soil moisture stress).

Question-75

Write a brief note on water potential. How is it represented ?

Solution:
Water potential is the capacity of a given solution to hold maximum amount of water. The water potential of pure water is zero. It can hold maximum amount of water but on adding solutes, its value get lowered. That is why it is represented by negative sign. The value of water potential for 0.1 M solution containing any solute has a value of y = -2.3. Thus, water potential is measurable in BARS and is represented by Greek letter Ψ. It determines the direction of movement of water in two given cell sap of plants. If two plant cells are adjacent to each other, the water moves from the region of higher water potential to the lower water potential.

Question-76

Differentiate between the Diffusion Pressure Deficit (DPD) and water potential.

Solution:
Diffusion pressure deficit Water potential
It is abbreviated as DPD. It is called Ψ (Psi).
It was originally called as suction pressure by Renner. It is the chemical potential of water which is equivalent to DPD with negative sign.
Unit of measurement is atmospheres. Unit of measurement is bars with negative sign.
DPD is the difference in the diffusion pressure of solution and pure solvent. It is the difference between free energy of water molecules in pure water and solution.
Water moves from lower DPD to higher DPD. Water moves energetically downhill side (i.e.) from higher water potential to lower water potential.

 

Question-77

Describe the adaptations of the leaves which reduce transpiration in plants growing in arid regions.

Solution:
Various adaptations found in the leaves of plants growing in dry conditions are,

(i) Presence of thick cuticle.

(ii) Modification of leaves into spines. E.g. Opuntia.

(iii) Presence of waxy or hairy covering.

(iv) Sunken stomata.

(v) Hard and leathery surface over the leaf.

Question-78

Describe the plant cell as an osmotic system.

Solution:
The plasma membrane in plant cell with the vacuolar membrane and cytoplasmic film or alone is more or less semi permeable in nature. This membrane allows the water molecules to get through it freely whereas it allows certain molecules to enter and prevent others.

The cytoplasm is surrounded by the cell wall. It possesses very much higher concentration than the solutions entering the plant cells via osmosis. So the plant cell functions as an osmotic system if it fulfils the following two conditions:

(i) It has a semi permeable membrane.

(ii) It possesses a liquid substance having much higher concentration. Therefore, the plant cells act as osmotic systems.

Question-79

Why is a cell called an osmotic system ?

Solution:
A cell is called osmotic system because,

(i) It has all the components of an efficient osmotic system, i.e. a semipermeable membrane and different concentration of sap on the two sides of the membrane.

(ii) Flow of water occurs from higher water potential to lower water potential.

Question-80

Differentiate between hypertonic and hypotonic solutions.

Solution:
Hypertonic solution Hypotonic solution
Hypertonic solution has higher concentration of solute molecules and lower concentration of solvent molecules (water) than the compared solution. Hypotonic solution has lower concentration of solute molecule and a higher concentration of solvent molecules than the compared solution.

 

Question-81

Distinguish between transpiration and evaporation.

Solution:
Transpiration Evaporation
It is a physiological process where loss of water occurs through the aerial parts of the plants. It is not physiological process but simple a physical process.
It takes place during the day time. It takes place at all the times.
It is regulated by the activity of guard cells around the stomata. It is not so.

 

Question-82

What is the role of antitraspirants in stomata closure ?

Solution:
The antitranspirants blocks the active excretion of H+ from guard cells. Due to the presence of CO2, a rapid acidification of cytoplasm occurs and thus leading to stomata closure. Abscisic acid sensitizes the stomata for CO2. Milbarrow (1974) has described the formation of these chemicals in the chloroplasts. It moves to stomata, where it is responsible for checking the intake of K+ or induces loss of K+ from guard cells.

Question-83

Devise an experiment to demonstrate the process of osmosis.

Solution:
Take a thistle funnel. Fix a big bladder with a thread on its wide mouth. Fill salt or sugar solution in the funnel in such a way that the solution rises a few cms in the stem of the thistle funnel. Now place this thistle funnel in a beaker containing water. Mark the initial reading in the stem of thistle funnel. Keep the apparatus without disturbing for some time after which take another reading. You will note that the level of solution has risen in the stem of the funnel. This due to the osmosis.

Question-84

What are the antitranspirants ? How they help in reducing the rate of transpiration in plants ?

Solution:
The high rate of transpiration causes wilting in the crop plant and thus results in a poor yield. The rate of transpiration in these crop plants can be reduced by spraying chemicals called antitranspirants. These can be used in two ways:

Metabolic inhibitors: These inhibitors reduce the stomata opening, thus checking the rate of transpiration. Chemicals like PMA (Phenyl mercuric acetate), ABA (Abscisic acid) and Aspirin are used for this purpose. These substances increase the leaf resistance to water vapour diffusion without affecting carbon dioxide uptake.

Film forming antitranspirants: They form a colourless transparent film on the leaf surface which allows the diffusion of O2 and CO2 but not water vapour e.g. Silicon emulsions and some low viscosity waxes.

Question-85

List the factors regulating the loss of water.

Solution:
Wind: High wind velocity causes high rate of loss of water.

Light: Stomata open during light and close during night, hence light increases loss of water.

Temperature: More the temperature, greater is loss of water.

Humidity: More humidity, less rate of transpiration.

Question-86

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

Solution:
Osmotic potential is called solute potential. It has a negative sign. It refers to the pressure which is needed to stop the movement of water from inside into the solution. An isolated solution which is not bounded by any membrane has no osmotic pressure. It has only the potential to result into a pressure when placed in an osmometer.

Question-87

Why do raisins swell up in the water ?

Solution:
Raisins swell up in the water due to the process of endosmosis. Raisins form the concentrated solution (hypertonic) whereas water is a hypotonic and water always moves from the region of hypotonic to hypertonic until the concentration may not become the same. That is why resins swell up in the water.

Question-88

Why do red blood cells begin to burst when placed in distilled water ?

Solution:
Red blood cells burst in distilled water due to the phenomenon of turgidity. Red blood cells form the hypertonic turgidity. Red blood cells forms the hypertonic solution whereas distilled water is hypotonic and water always move from hypotonic to hypertonic solution. That is why red blood cells begin to burst when placed in distilled water.

Question-89

What is the importance of water in the life of a plant.

Solution:
The importance of water in the life of a plant,

(i) The various plant tissues in the active form contain about 80-90 per cent water.

(ii) Water is essential for the transport of inorganic minerals from the soil to various organs of the plant body.

(iii) It helps in the transport of organic substances from the leaves to other organs of plant.

(iv) It is required in various metabolic activities.

(v) It maintains the turgidity of the cells.

(vi) The hydrogen of water gets combined with CO2 to form carbohydrates during photosynthesis.

(vii) The oxygen evolved during the process of photosynthesis also comes from water.

(viii) Water is essential for germination of seeds.

(ix) It is essential for the translocation of food.

Question-90

Differentiate between turgor pressure, osmotic pressure, wall pressure and diffusion pressure deficit.

Solution:

Turgor pressure

Osmotic pressure

Wall pressure

Diffusion pressure deficit

It is the pressure (hydrostatic), which develops in the cell due to the osmotic entry of water into it. It is the actual pressure, which develops in a solution if it is separated from the water by semipermeable membrane. It is the pressure exerted by the cell wall over the protoplast with equal and opposite force. It is the measure of decrease in the diffusion pressure of pure solvent or water due to addition of solute molecules.
Turgor pressure maintains the shape and size of plant parts. A fully turgid cell has maximum turgor pressures. Osmotic pressure is measured by bar and it is equal to the osmotic potential having a positive value. It equals to turgor pressure at a specific time. Diffusion pressure deficit is equal to difference between osmotic pressure and

 

Question-91

Give an account of imbibition.

Solution:
It refers to " the absorption of hydrophilic colloids in the cells". Imbibitional pressure is the pressure that increases the volume of imbibant due to increase in volume of water in the cell. Water moves along a diffusion gradient. DPD = Imbibitional pressure – Turgor pressure. It is affected by the temperature. Some energy is lost during the process of imbibition. If there is increase in temperature, the rate of imbibition is increased. The cells of plants have proteins, starch and cellulose etc. When the seeds came in contact with water, they swell up. Dry gum, if kept in water, swells up. The degree of cohesion of water molecules determine the quantity of water absorbed. There are three aspects of imbibition, they are, production of heat, change in volume and imbibitional pressure. The swelling substance produces an imbibitional pressure developed by imbibition process.

Question-92

Differentiate between Stomata and Hydathodes.

Solution:
Stomata Hydathodes
Stomata are the pores present in the epidermis of leaves and young shoots. They are the specialized pores present at the leaf tips or margins of some plants.
They are surrounded by two guard cells which regulate opening and closing of stomata. They are surrounded by a ring of cuticularised cells which do not regulate opening and closing of hydathodes, so hydathodes always remain open.
The stomata lead into an air cavities surrounded by spongy parenchyma. Beneath the hydathode is a small cavity subtended by loosely arranged parenchyma and endings of xylem vessels of veins of leaf.
The water is lost in the form of vapours called transpiration. The water is lost in the form of droplets called guttation.

 

Question-93

What is the meaning of the following statement ? Minerals are actively transported into root cells to develop root pressure.

Solution:
The minerals are actively transported into the root cells as they move from lower concentration towards higher concentration. i.e. against concentration gradient by the utilization of energy (Adenosine Triphosphate).

Question-94

Describe the mechanism of transpiration.

Solution:
Mechanism of transpiration - Cells of mesophyll enclose big air cavities which communicate to outside by stomatal pores. Their turgidity is maintained by osmotic diffusion of H2O from xylem vessels. The air becomes saturated with water vapours due to loss of water by moist cells. For it energy is derived by the sun in daylight. The water potential is high also. Out side the leaf the unsaturated air has low water potential. So water as vapours move to outside by the stomata of the leaf. In air cavities water potential is lowered. Water comes out from the mesophyll cells.

Question-95

Demonstrate the osmosis by a simple experiment.

Solution:
Take a beaker and fill water into it. It is separated by a solution filled in the thistle funnel by a semipermeable membrane. The water moves across the membrane and the level of solution is increased till the equilibrium is obtained. On the upper part of funnel pressure may be applied to prevent the water movement through the membrane. To stop flow of water fully, the pressure applied is known as osmotic pressure. It is also called solute potential or osmotic pressure. The osmotic potential of a solution is negative of osmotic pressure (p).

In reverse osmosis, water flows out of the solution into the beaker. Salt and saline water are removed by reverse osmosis. The pressure difference and concentration of dissolved solutes in a solution affects osmosis. The chemical potential of water is called water potential.

Question-96

Mention two conditions necessary for imbibition to occur.

Solution:
(i) Water potential gradient between the surface of adsorbent and the liquid imbibed.

(ii) The affinity between absorbent and imbibed liquid.

Question-97

What is osmosis ? How do raisins swell up in water ?

Solution:
Osmosis is the movement of water molecules from a region of its higher concentration to a region of its lower concentration through plasma membrane.
Raisins swell up in water due to endosmosis. Raisins swell up in water due to endosmosis. Raisins form the concentrated solution whereas water is a hypotonic and water always moves from the region of hypotonic to hypertonic until concentration may not become the same. Thus, raisins swell up in water.

Question-98

What is passive absorption of water ? Describe the following with reference to water absorption.

Solution:
(a) Apoplast pathway

(b) Symplast pathway and

(c) Tran membrane pathway

Passive absorption of water: A force develops in the shoot system where transpiration is occurring. The transpiration then creates a tension in xylem due to loss of water from its aerial parts. Tension spreads in all the xylem channels of the roots. This may be due to (i) Rate of water absorption follows closely the rate of transpiration. (ii) Amount of water absorbed is almost equal to the amount of water transpired. (iii) The shoot may continue to absorb water even in the absence of root if the cut end of the root is in contact with water. (iv) The water does not spill from the cut end of the shoot showing that water column present in it is under negative pressure.

(a) Apoplast pathway: The water moves from soil to cell walls of root hair cells, cortex, endodermis, pericycle, xylem parenchyma and xylem channels. Water in the xylem channel is under more negative pressure. So it draws water from soil through intervening apoplast along the gradient. It takes place through the cell wall exclusively without crossing any membrane.

(b) Symplast pathway: In the young root hair zone, xylem vessels are not fully empty. They have a thin layer of living cytoplasm according to Hinginbotham et al., around a central cavity having water under tension. This lining layer of cytoplasm is attached to xylem parenchyma, pericycle, endodermis, cortex and root hair cells through plasmodesmata. Tension created in xylem due to transpiration causes movement of water passively from cytoplasm of these cells. The cells of root hairs withdraw water from soil capillaries. When the water passes through symplast and the absorption is influenced by soil temperature, air and metabolic inhibitors.

(c) Tran membrane pathway: It is the movement of water through the cell membrane. Root hair cells have a water potential of –3 to –8 bars. Soil water has a potential of –0.1 to –0.3 bars. Root hair cells absorb soil water through osmosis. It increases their water potential. The cortical cells adjacent to root hair cells absorb water from them due to lower water potential. Absorption of water by these cells increases their water potential as compared to next cortical cells. In this water passes from outside to root interior along the gradient of water potential with individual cells acting as osmotic systems. They water reaches xylem parenchyma.
 

Question-99

How does the absorption and loss of potassium in the guard cells bring about the opening and closure of stomata ?

Solution:
Increased concentration of K+ in the guard cells causes sufficient osmotic pressure to absorb water from the surrounding cells by endosmosis. It increases the turgidity of the guard cells. It results in the stretching out of outer thin walls. Inner thick walls are put apart and causes the opening of the stomata. When K+ ions are transported out of the guard cells. As a result of it, the water flows out and the exosmosis occurs to the neighbouring epidermal cells. It causes the closing of stomatal pores.

Question-100

What is the role of K+ ions in opening and closing of stomata.

Solution:
Levitt explained the mechanism of stomatal action in 1967. In light, starch produced during photosynthesis is converted into organic acids, which causes low concentration of K+ ions. When concentration of organic acids is increased in guard cells, this increases concentration of cell sap followed by subsequent absorption of water. In dark, photosynthesis stops accompanied by increased concentration of CO2, the organic acids are converted into starch. The water comes out of guard cells. It reduces the turgor pressure and stomata get closed.

Question-101

What forces are involved in the absorption of water from the soil by root hairs ?

Solution:
(a) A negative tension is exerted down the roots due to transpiration pull by the aerial parts of the plants. This causes decrease in water potential of the roots which favours uptake of water from the soil.

(b) The decrease of water potential in the root cells than the soil favours absorption of water from the soil.

(c) The cohesive forces among the water molecules and adhesive forces between the water and xylem vessels maintain a unbroken column of water in capillaries of xylem vessels. The gradient of water potential exists in the xylem vessel starting from leaf to roots which favours uptake of water from the soil.

(d) The water from the soil enters into the root hairs and from there it reaches the xylem vessel with lower water potential. It results in the formation of root pressure. This root pressure pushes water to the aerial parts of the plant body.

Question-102

Define osmosis and explain how it influences other components of cell water relations in plants.

Solution:
Osmosis: when two solutions having two different concentrations with a common solvent are separated by a semipermeable membrane, the solvent molecule passes from region of higher concentration to a region of lower concentration till a state of equilibrium is achieved. This movement of solvent molecules through semipermeable membrane is known as osmosis.

If during osmosis the flow of water from the surroundings into a living cell takes place the process is known as endosmosis.

If during osmosis the water of solvent from the living cell diffuses out, the phenomenon is termed as exosmosis.

Plasmolysis: The cell, if placed in an isotonic solution of the same concentration as that of the cell sap, does not show any change. However, if the cell is placed in solution with higher concentration than that of the cell sap, hypertonic solution will show a vast change. In such a case, there shall be a movement of water from cell into the outer concentrated solution. This loss of water will result in the shrinkage of the vacuole and cell contents. The cytoplasm will leave the walls and will shrink to accumulate at a place. This phenomenon is plasmolysis and the cell is said to be plasmolysed.

On keeping a plasmolysed cell in a hypotonic solution or pure water, the water starts moving into the cell and the cell remains the normal turgidity. The process of regaining turgidity of a plasmolysed cell is called deplasmolysis.

Question-103

What are guard cells ? Explain their role in regulating transpiration ?

Solution:
The stomata are small openings in the epidermis of leaves. They are guarded by bean shaped epidermal cells known as guard cells. The shape and size of guard cells alter by the change in their water content which controls the opening and closing of the stomata.

(i) In monocots the stomata are dumbbell shaped. There are thick walls in the intervening walls of the cells and thin walls in the inflated part of the cells. On increasing the turgor pressure of guard cells the thin wall regions bulge, which draws the thick walls and opens the pore.

(ii) In dicotyledonous plants the inner walls of the guard cells bordering the aperture are thicker than the outer wall. The outer wall becomes more convex on increase of turgor of guard cells, these drawing the inner walls apart and open the stomata pore. As soon as the turgor of the guard cells decrease the inner wall attain this original position, thereby causing the closure of the stomata pore. Reversible absorption and loss of potassium ions results in the changes in turgor pressure which in turn opens and closes stomata. Stomata open when the guard cells take up K+ions from the surrounding cells. The uptake of K+ions is balance by, 

(i) uptake of chloride. 

(ii) Transport H+ions released from organic acids (such as malic acid). 

(iii) By the negative charges of the organic acids when they lose H+ions.

The exodus of K+ions leads to osmotic loss of water from the guard cells, which results in the closure of stomata.

Question-104

Describe the closing and opening mechanism of the stomata in dicotyledonous stomata. Explain the role of K+ions in the opening and closing of stomata.

Solution:
The stomata are small openings in the epidermis of leaves. They are guarded by bean shaped epidermal cells known as guard cells. The shape and size of guard cells alter by the change in their water content which controls the opening and closing of the stomata.

(i) In monocots the stomata are dumbbell shaped. There are thick walls in the intervening walls of the cells and thin walls in the inflated part of the cells. On increasing the turgor pressure of guard cells the thin wall regions bulge, which draws the thick walls and opens the pore.

(ii) In dicotyledonous plants the inner walls of the guard cells bordering the aperture are thicker than the outer wall. The outer wall becomes more convex on increase of turgor of guard cells, these drawing the inner walls apart and open the stomata pore. As soon as the turgor of the guard cells decrease the inner wall attain this original position, thereby causing the closure of the stomata pore. Reversible absorption and loss of potassium ions results in the changes in turgor pressure which in turn opens and closes stomata. Stomata open when the guard cells take up K+ ions from the surrounding cells. The uptake of K+ ions is balance by, 

(i) uptake of chloride. 

(ii) Transport H+ ions released from organic acids (such as malic acid). 

(iii) By the negative charges of the organic acids when they lose H+ions.

The exodus of K+ ions leads to osmotic loss of water from the guard cells, which results in the closure of stomata.

Question-105

Describe the adaptations of plants to lower the transpiration rate.

Solution:
Transpiration is a process by which water is lost from the small pores situated on the surface so the leaves. Transpiration is a necessary evil, because it helps in the flow of water, provides a system of transport of minerals from the soil, cools the plans and maintains proper temperature for other physiological activities. 

For transpiration, plants must have sufficient supply of water. If the plant does not get sufficient amount of water it wilts. So to keep the plant in proper shape, under short supply of water the plant develops certain adaptations to reduce the rate of transpiration. This normally happens under xerophytic conditions. The following adaptations take place in plants for this purpose:

(i) Reduction in the surface of leaves. In this the surface of leaves get reduced. Sometimes the leaves get modified into spines, so that no transportation may take place. In certain plants leaves become needle like, in some leaves develop a kind of waxy layer on it to avoid loss of water through transpiration.

(ii) Under dry conditions the leaves become rolled up, this results in the decrease of transpiration as majority of the stomata are not exposed to atmosphere.

(iii) In some plants, the stomata get sunk. This also reduces the rate of transpiration.

(iv) In some leaves, the epidermal hair also helps in the prevention of transpiration.

Question-106

How does a plant lose water ? What are the factors that control the loss ?

Solution:
Plants lose water by the following methods:

(i) Transpiration: The process of loss of water through the aerial parts of a plant through stomata is termed as transpiration. Water may be transpired directly through the cuticle or through a large number of small opening called stomata.

(ii) Through lenticels: Water is also lost through lenticels which are small openings in a corky tissue covering stems and twigs.

(iii) By guttation: Under this method the water is lost in the liquid form and not in the form of water vapour as in the above two cases. This occurs through hydathodes situated at the tip of the veins of leaves.

Factors controlling loss of water: The following are the important factors that control transpiration:

(a) Light: It is one of the most important factor. During daytime, the stomata remain open and in the dark they close down.

(b) Temperature: If the temperature is more, the rate of transpiration increase.

(c) Humidity: If there is humidity in air the rate of transpiration decreases. If less water vapour is present in the air the rate of transpiration increases.

(d) Wind: During high wind transpiration becomes very active because the water vapour around the leaves is instantly removed.

Question-107

List the conditions under which maximum amount of water can be absorbed and retained by the plant.

Solution:
The plants absorb the water from the soil with the help of root hairs present on the roots. The water absorbed by the root hairs is passed on to the cortical cells from where it goes on to the xylem and moves upward on the plant through the conducting vessels.
This phenomenon of absorbing of water take place because of the root pressure. The root pressure can be explained as the pressure exerted on the liquid contents of the cortical cells of the root, under fully turgid condition, forcing a quantity of them into the xylem vessels and through them upwards into the stem up to certain height. The amount of water absorbed by the plant depends upon root pressure. The root pressure in turn depends upon the following conditions.

(i) Temperature: The temperature of the air as well as the soil effects root pressure. If the amount of oxygen, is less than the activity of the root decreases.

(ii) Oxygen: There must be sufficient supply of oxygen in the soil for respiration of the roots. If the amount of oxygen is less, then the activity of the root decreases.

(iii) Moisture in the soil: Sufficient moisture should be present in the soil.

(iv) Salt in the soil: Preponderance of salts making the soil saline greatly interferences with the adsorption of water.

Water in the plant can be retained if the rate of transpiration is less. There are many factors that control the rate of transpiration in plants.

Question-108

Describe the different forms of water found in the soil.

Solution:
The different forms of water found in the soil are,

(i) Hygroscopic water: This type of water encircles the soil particles by making a thin film. It is not available to the plants.

(ii) Gravitational water: During rainy season most of the water percolates down towards the water table percolates down towards the water table under the force of gravity and is known as gravitational water. It is not also available to plants.

(iii) Runaway water: When rain falls on the soul this type of water is drained away and so it is beyond the reach of soil.

(iv) Capillary water: It is the main type of water available to plants from the soil because it lies in between the spaces of soil particles and held up against the force of gravity.

(v) Combined water: It is not available to the plants. It is mixed with the hydrated oxides of silicon, iron etc, in the soil.

Question-109

How do potassium ions regulate the opening and closing of stomata ? Enumerate the three factors which balance the uptake of potassium ions.

Solution:
The reversible absorption and loss of potassium ions by the guard cells of stomata result in the changes in the changes in the turgor pressure, which in turn opens and closes the stomata. The guard cells take up K+ from the surrounding. It results into the entry of water into the guard cells making them turgid and the stomata open.
As soon as the turgor of guard cell decreases the inner wall attain their original position, thereby closing the stomatal pore.

The uptake of K+ is balanced by:

(i) Uptake of chloride ions by guard cells.

(ii) Transport of hydrogen ions, released from organic acid like malic acid, out of the guard cells.

(iii) By the negative charges of organic acids when they loss hydrogen ions.

Question-110

What is root pressure? How do you demonstrate it?

Solution:
The pressure exerted by cortical cells of the root into the xylem vessels, resulting to raise the water column in ascending parts of the plants is called root pressure.
According to Priestly the upward flow of water occur due to a hydrostatic pressure developed in the roots system during exudation, which is called "root pressure".
The root pressure, being a vital phenomenon depends upon the activity of living cells of the root. If the root cells are killed by the addition of poisonous substances or anesthetics to the soil, the root pressure ranges from 3 to 5 atmospheres. It may vary from 5 to 10 atmospheres. It has been considered that the root pressure is absent in actively transpiring plants and conifers. The magnitude of the root pressure is insufficient to raise water to the tops of the tall trees.

Demonstration of root pressure: If we cut a stem of a well-watered plant, we observe the water and cell sap coming out of the cut surface with a force. It is due to root pressure. The cell sap contains dissolved carbohydrate substances.

Experiment: The shoot of a well –watered young plants is cut in spring season and then the stump is attached to a glass tubes having water or a dye solution through a rubber tube. After some time one can observe that water or methylene blue level rises in the glass tube. It is due to the cell sap of the root exuded from the cut end.

Question-111

Explain the cohesive force theory of ascent of sap in plants.

Solution:
Cohesive force theory: This theory was proposed by Dixon and Jolly in 1894 and Askenary in 1895. And this is known as Dixon Jolly’s theory of cohesion or the transpiration pull theory. To date this is the most accepted theory of ascent of sap. This theory was supported by Curtis Clark (1951), Galston and Reuter (1952).

Main aspects of transpiration pull theory: It can be studied into following headings:
(i) Strong cohesive force or tensile strength of water – The water molecules attract each other by mutual force, which is called the "cohesive force". The attraction between the walls of the xylem elements and the water molecules is called "adhesion". The cohesive force helps to maintain a long column of water under tension which may be greater than 100 atmospheres pressure. Only 10 to 20 atmosphere is sufficient for ascent of sap upto a height of more than 100 metres.

(ii) Continuity of the water column in the plant: Scholander after confirming Dixon’s assumption in 1957, found that air breaks do not hinder the total cohesive system and the trees are able to maintain a rapid flow of sap. The water or the sap can be pulled up by the transpiration force like a rope.

(iii) Transpiration pull or tension of the unbroken water column: As a result of transpiration, water is drawn in the intercellular spaces from the mesophyll cell, which consequently draw water osmotically from the nearby cells and thus a diffusion pressure deficit or a suction force is developed. Due to this suction force the adjacent cells take water from the xylem of there veins of the leaves. As the xylem of vein of the leaf are connected with the xylem of roots through stem xylem, a tension is set up in the water column of the xylem and the whole column in physically pulled up.

The tension developed in the xylem sap of trees was estimated to be as high as – 77bars. About 13 atmospheric pressure would be required to raise water to the top of a 416 feet high tree, as one atom. of pressure can raise water to a height of more than 32 feet.

Question-112

Describe the passage of water in root or pathway of water in root.

Solution:
Pathway of water in root: The entry of water into the root hair dilutes the cell sap. Thus, water molecules in root hair increase as compared to adjacent cortical cells. At this stage DPD of root hairs is lower than that of adjacent cortex. Due to higher DPD in cortex, water enters in these cell. Process continues till the water reaches the passage cells of endodermis. These passage cells lie opposite the protoxylem. They allow water to enter the pericycle. In xylem, turgor pressure is lacking. So, water enters the xylem from pericycle for upward movement of sap.

Question-113

Describe the process of transpiration. How do you measure it?

Solution:
Transpiration: Most of the water is lost by the aerial parts of the plants in the form of water vapours. The loss of water from the surface of aerial part of the plants known as transpiration. Transpiration is mainly of two types: 

(i) Cuticular through cuticle and

(ii) stomatal through stomata.

Measurement of transpiration: Following methods are used for measurement of transpiration. It is based on

(i) water absorbed and

(ii) water vapour transpired by a plant.

(a) Potometer method: It is based on the fact that water transpired is equal to water absorbed.

Ganong’s potometer, consists of a vessel filled with water. It contains a cut stem or a plant. The vessel connected to a water reservoir and a capillary tube. A bubble is introduced into the capillary tube. The rate of transpiration occurs throughout the walls except at the pits in the most advanced tracheary elements.

In protoxylem, normally there are annular, spiral and reticulate thickenings whereas in metaxylem the secondary wall thickenings are helical, reticulate and pitted.

Question-114

Define imbibition and how is it important to the plants ? Give suitable examples ?

Solution:
Imbibition can be defined as the absorption of water molecules by dry hydrophilic surfaces. There are three important aspects of this process:

Change in volume, change in pressure and production of heat.

Importance of imbibition:

(i) Helps in the movement of water in plant body.

(ii) Helps in germination of seeds.

(iii) During rainy season wooden doors and windows swell up.

Suitable examples of imbibition are,

(i) Germinating seeds break their seed coats.

(ii) Gum swelling.

(iii) Heat liberation when kneading wheat flour with water.

Question-115

How do rise in temperature and wind velocity affect transpiration ? Write any two adaptations shown by plants to reduce transpiration.

Solution:
Temperature: If the temperature is more, the rate of transpiration increase. An increase in the temperature of leaf increases the rate of transpiration in the leaf. The water is lost rapidly from the leaf. If we increase 10oC in temperature, the rate of transpiration is doubled.

Wind velocity: During high wind the transpiration becomes very active because the water vapour around the leaves is instantly removed. At very high wind velocity the stomata are closed because the rapid loss of water from the guard cells and the rate of transpiration is declined.

Two adaptations shown by plants to reduce transpiration are,

(i) Reduction in the surface of leaves: The surface of leaves get reduced. The leaves are modified into spines and so no transpiration takes place. In some plants the leaves may become needle like, e.g. Opuntia, Euphorbia and Globe cactus.

(ii) Sunken stomata: In some, the stomata get sunk. This also reduces the rate of transpiration. E.g. . Nerium and Agave.

Question-116

Differentiate between turgor pressure and wall pressure in plants cells. List any four ways in which turgidity seems as a useful purpose in the plants.

Solution:
Difference between turgor pressure and wall pressure:
 
Turgor pressure Wall pressure
It is the pressure which develops in a confined part of an osmotic system due to osmotic entry of water into it. I.e., the pressure exerted by the protoplast of the cell on its cell wall in a turgid condition. The pressure exerted by cell wall over the protoplast with an equal and opposite force is called wall pressure.
It is designated as TP. It is designated as WP.

Turgidity serves useful purpose in the plants:

(i) It maintains the shape and size of plant cells.

(ii) It keeps the leaves erect.

(iii) It is useful in opening and closing of stomata.

(iv) Leaf movements are caused in Mimosa pudica.

Question-117

Root system is related to water absorption by plants. "Comment upon the statement".

Solution:
Water is mostly absorbed by roots of plants. The root tip has four zones – root cap, meristematic zone, cell elongation zone and the zone of root hairs. At the apex of the root is root cap. Below the root cap cell divides continuously. Above this zone cells enlarge. Above this zone are projections of piliferous layer. The cell wall of root hair is a double layer. The cell wall is permeable to water. The cytoplasm contain vacuoles which have cell sap of higher osmotic potential. The cell membrane function as a semi permeable membrane.

Question-118

Differentiate between diffusion and osmosis.

Solution:
Characters Diffusion Osmosis
Definition Movement of molecules or ions of gas soldier liquid from the region of higher concentration to the lower concentration is called diffusion. Movement of solvent or water molecules from the region of higher concentration to the region of lower concentration through the semipermeable membrane is called osmosis.
Medium It occurs in solids, gases or liquids. It takes place only in liquid medium.
Membrane No need of semipermeable membrane. Semipermeable membrane is required for osmosis to occur.
Pressure Not influenced by pressure expect diffusion pressure. Influenced by turgor or hydrostatic pressure.
Factors Solute potential, water potential and pressure potential has no effect. Solute potential, water potential and pressure potential has no effect on it.
Other substances Do not affect. Affected by the presence of other substances.
Equilibrium In free energy of diffusion molecules is gained. In free energy of solvent molecules is never gained.

 





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