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

Plant  Physiology.
– 11 (Transport in plants)
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.

in plant—–

 A ) Shorter

1.    Diffusion

2.    Osmosis

               3. Facilitated diffusion 

       B) Longer

                                         1. Translocation by xylem and phloem

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.
in case of minerals and organic solutes.
1) what are the factors affecting the rate of diffusion?
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.


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)
– 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
ii) Water loss in
liquid form
iii) Occurs during
night or early morning
iv) Through
v) loss of Impure
It is controlled
ii) Water loss is vapor
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
v) Most of only water
or solvent from higher to lower conc.
c) Osmotic
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
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
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
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
iii) Energy is not
iv) No change in
v) little change in
I) amount. Of
substance from the region of higher to lower conc.
ii) It occurs in the
presence of absorbent (imbibes)
iii) heat is
iv) The imbibents swell
up but the swelling is less than the volume. Of imbibe.
v) Huge pressure develops.
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.
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
Solute potential
Metric Potential
Loss or gain of water
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
– 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
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?
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.
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.
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.