Monday, 3 February 2014

TEXTBOOK ANSWERS AND SOLUTIONS CBSE-SCIENCE- CLASS XI Plant Physiology. Chapter – 11 (Transport in plants)

Plant  Physiology.

Chapter – 11 (Transport in plants)


            This chapter deals with the transportation of water, minerals and other nutrients to each and every parts of plant – Do you know that plants transport are of two types. So come and look in the world of plant’ transportation.

Transport in plant-----

 A ) Shorter transport 

1.    Diffusion

2.    Osmosis

               3. Facilitated diffusion 

       B) Longer Transport

                                         1. Translocation by xylem and phloem


            Some Important definitions:-

1) Translocation – The transport of substances over long distances through the vascular tissue i.e. xylem and phloem is called translocation. It is unidirectional in case of water froot to steam, leaves, flowers, fruits.
            Unidirectional in case of minerals and organic solutes.


Q. 1) what are the factors affecting the rate of diffusion?

            I) Density of the substance ii) density or the permeability of the medium. Ii) Temperature IV) diffusion pressure v) pressure

[Imp not – According to Graham’s law of diffusion the rate of diffusion is inversely proportionate to the square root of the density of the diffusing substance.
Q. 2) what are poring? What role do they play in diffusion?

             Poring are generally channel proteins. They are protein lined hydrophilic channels present in the occur membrane of plastids, mitochondria & some bacteria. They are large proteins forming pores and allow passage of large bio molecules’ & even small protein to pass through along concentration gradient.

             They are involved in faccillited diffusion Aquoporins are water channels for diffusion of water molecules across the plasma membrane as per as osmotic gradients.

3)         Describe the role of protein pumps during active transport in plants?

            They are carrier proteins which take part in transport of solutes across the cell membrane with the help of energy even against concentration gradient. ATP supplies the required energy. On being actionaned with energy, the protein pump picks up solute particles from outside & throws the same to the inner side of the tyro plasma through no of pumps e.g. – Na+, -K+, Ca2+ pumps.

4)         Why pure water has maximum water potential? Explain

            Pure water has the maximum water potential due to the absence of solute particles which to dues the free energy of water & decreases the water potential (-ve value)

[Note – Water potential of solutions is determined using pure water as a standard reference, pure water potential = 0]

5) Differentiate –

a) Guttation

i) It is uncontrolled phenomenon

ii) Water loss in liquid form

iii) Occurs during night or early morning

iv) Through hydathodes

v) loss of Impure water

It is controlled phenomenon

ii) Water loss is vapor form

iii) Occurs during day time.

iv) Through stomata or a epidermis cuticle or lenticels.

v) loss of pure water about 98-99%


It occurs in any medium.

I) Hydrostatic or turgor pressure do not oppose

ii) It doesn’t require any semipermiable membrane

iv) It do not

v) Movement of we hypes of substance from higher conc. To lower conc.

1) It occurs in only liquid medium

ii) It is opposed by turgor or hydrostatic pressure of the system.

ii) It must have a semipermiable membrane to operators

iv) Depends upon solute potential.

v) Most of only water or solvent from higher to lower conc.

c) Osmotic Pressure

i) It is the pressure which develops in an osmotic systems due to entry of water into it

ii) It develops only in confined system.

ii) the value is +eve & numerically equal to osmotic potentials

Osmotic Potential

It is lowering of free energy of water in a system due to the presence of solute particles.

It is present whether the soln. occurs in confined or an open system.

The value is –vie equal to osmotic pressure

d) Transpiration

i) It take place in plants

ii) It is both a physical & physiological process

iii) Formation of vapors continues for some time in after the saturation of outside air because temp of leaf is lightly higher than air

iv) Water vapors are formed mostly in internal tissues at plants


I) In non-living objects

ii) It is environmentally controlled physical process

iii) It stops often the saturation of outside air.

iv) It forms at the free surface of the water.


I) Absorption of water by particles of a solid without forming a soln.

ii) An absorbent is absent.

iii) Energy is not liberated

iv) No change in volume

v) little change in pressure

I) amount. Of substance from the region of higher to lower conc.

ii) It occurs in the presence of absorbent (imbibes)

iii) heat is liberated

iv) The imbibents swell up but the swelling is less than the volume. Of imbibe.

v) Huge pressure develops.

Apoplast pathway

I) Faster

ii) It consists of non-living parts of plant body i.e. Cell wall & intracellular spaces

Little resistance in the amount of water.

iv) Metabolic state of root doesn’t affect apoplast pathway.
Symplast pathway

I) Slightly slower

ii) It consists of living parts of plant body i.e. protoplast connected to plasmodesmata

iii) Some resistance occurs in the amount of water.

iv) Metabolic state of root directly affect symplast pathway.

6) Briefly describe water potential & Factors affecting it?

            The difference between the free energy of water molecules in pure water & the energy of water in any other system (e.g. – plant cell or tissue ) is termed as water potential.

·         Factors affecting

I) Solute potential
ii) Pressure
iii) Metric Potential
iv) Loss or gain of water
v) temperature
vi) Pressure potential

Q. 7) What happens when a pressure greater than the atmospheric pressure is applied to pure water or soil?

            Pressure applied to pure water or a sol, is a=vie pressure that will increase the diffusing of water whether in pure water or in soln. it sol it will reduce or prevent the entry of water from outside. If the sol is very delivered, pressure can cause nurse osmosis.

Q. 8) a) Diagram of plasmolysis

Fig – Plant cell plasmolysis

b) Explain what will happen to a plant cell if it is kept in a solution having high water potential?

            Higher water potential occurs in a hypotonic or delivered soln. a plant cell present in such a sol will absorb water due to endue-osmosis. It will become turgid or swollen. The swelling protoplast develops a wall pressure that becomes equal to water potential of the system. At this time further endo-osmosis stops –

9) How are the cortical associations helpful in absorption of water & minerals in plants?

            In mycorrhiza a large no of fungal hype are assured with young roots. The fungal hypalextyend to sufficient distance into the soil. They have a large surface area. The hype are specialized to absorb water and minerals.

15) Explain pressure flow hypothesis of translocation of sugar in plants

            The most accepted mechanism used for the translocation of sugars from source to sink is called the pressure flow or mass flow hypothesis. as glucose is prepared at the source in leaves) it is converted to sucrose (disaccharides). The sugar is then moved in the form of sucrose. Into adjacent comprising cells by active transport.

10) What role does the root pressure playing water most in plants?

            I) Being a positive pressure, it puts the water deficit of the cell created due to transpiration less.

            ii) certain workers believe that root pressure helps in ascent of water in small – sized plants.

            iii) It dissolves & removes the air bubbles formed during transpiration pull.

Q. 11) a) Describe transpiration pull model of water transport in plants.

b) Factors affecting   a) relative humidity
                                    b) Atmospheric temperature
                                    c) light
                                    d) Air movements
                                    e) Atmospheric pressure
                                    f) Availability of water.

c) uses of transpirationPhotosynthesis
                                                b) Maintain turgidity
                                                c) improve quality of

12) Discuss the factors responsible for ascent of xylem in plants

            i) Capillary      It is limited rise of water in narrow tubes or capillaries due to force of erosion amongst molecules of water & their property of adhesion to other substances.

            ii) Imbibitions             it is the ability of hydrophilic colloids to attract & hold water on the surface & inside their interspaces.

            iii) Root Pressure       It is positive pressure that pushes sap from below due to active transport roots.

            iv) Transpiration pull            Transpiration in air at parts brings the xylem sap under –vie pressure or tension due to continuous windrow of water by them. Water column doesn’t breaks due to its high tensile strength relayed to high force of cohesion & adhesion

13) What essential role does the root endodermis plays during mineral absorption in plants?

I) Regulates the amount of minerals passing into vascular strands due to presence of casparian strips. Minerals have to pass through symplest pathway and then special sets of carrier proteins & ion channels present in the plasma membrane of endodermic cells.

ii) Endoderm’s doesn’t allow the flow of minerals back from vascular strand into cortex of root.

14) Explain why xylem transport is unidirectional & phloem transport is bi-directional.

Xylem transport – It is unidirectional & upward from roots to shoot hps the force for upward

amount. Develop in the aerial parts due to loss of water in transpiration. It creates a tension or –vie pressure in the water column latter is, pulled upwards.

Phloem transport:     Organ nutrients are loaded in the phloem in the region of manufacture (leaves) or storage. It draws water in to the area creation a high turgid pressure. A low turgid pressure exists in the area of utilization of nutrients (e.g.  roots, shoot tips) because of regular widrawal.

            So transport occurs in both directions due to gradient of turgid pressure.

16) What causes the opening & closing of guard will of stomata during transpiration?

            Opening and closing of stomata occurs due to influx & efflux of ions into or out of guard cells.