6. PLANT WATER RELATION
MULTIPLE CHOICE QUESTIONS (1 MARK EACH)
1 Water present in the form of hydrated oxides of
Silicon, Aluminium is
called ......................... _______________
A Hygroscopic Water
B Gravitational Water
C Combined Water
D Capillary Water
2 Most plant cells and tissues constitutes ................_%
water
A 90-95 %
B 70-80 %
C 10-25 %
D 0-20 %
3 .......................type of tissues are present in
epiphytic roots
A Meristematic
B Parenchyma
C Velamen
D Epithelial
4 In the zone of absorption, epidermal cells form
unicellular hair like
extensions called ........................
A Epiblema cells
B Roots
C Root hairs
D Velamen tissues
5 Outer layer of root hair is made up of .......................
A Cellulose
B Lignin
C Starch
D Pectin
6 Inner layer of root hair is made up of ......................
A Cellulose
B Lignin
C Starch
D Pectin
7 Cell wall is ..................
A Selectively Permeable
B Freely Permeable
C Non Permeable
D Impermeable
8 Plasma Membrane is ..................
A Selectively Permeable
B Freely Permeable
C Non Permeable
D Impermeable
A
Cytoplasmic
B Protoplasmic
C Nucleoplasmic
D Cellulosic
10 Fine soil particles imbibe or absorb water and hold
it. This is called as ..............
A Hygroscopic Water
B Gravitational Water
C Combined Water
D Capillary Water
11 To carry out plasmolysis, a cell must be
placed in ..................
A. Pure water
B. Hypertonic water
C. Hypotonic solution
D.
Hypertonic solution
12 The liquid adsorbed during imbibition is known as
A. Solid
B. Imbibant
C.
Imbibate
D. Colloids
13 Water moves either by apoplast or symplast
pathway across the root.
Ultimately it becomes
symplastic at...............
A. Pericycle
B.
Endodermis
C. Xylem
D. Phloem
14 The positive hydrostatic pressure which
develops due to absorption of water is
called as ..............
A. Capillary force
B. Transpiration pull
C.
Root pressure
D. Transpiration
15 The example of amphi-stomatic leaf is .................
A. Nerium
B. Lotus
C.
Grass
D. opuntia
VERY SHORT NASWER TYPE QUESTIONS (1 MARK EACH)
1 Why water acts as a thermal buffer?
Ans: Because, water has high
specific heat, high heat of vaporization and high heat of fusion.
2 Define: Root hair.
Ans: The unicellular hair like cytoplasmic
extension of epiblema cell in the region of absorption is called root hair.
3 What is meant by Gravitational water?
Ans: The water which percolates
deep, due to gravity, in the soil is called gravitational water.
4 What is meant by Hygroscopic water?
Ans: The water which is imbibed
and hold by fine soil particles is called hygroscopic water.
5 What is meant by Combined water?
Ans: Water which is present in
the form of hydrated oxides of silicon, aluminium, etc., is called combined
water.
6 What is meant by Capillary water?
Ans: The water which is held in
pores present between the neighbouring soil particles, due to capillarity is
called capillary water.
7 What is the composition of outer layer of root hair?
Ans: Pectin
8 What is the composition of inner layer of root hair?
Ans: Cellulose
9 From which type of cells, root hair is originated?
Ans: Epiblema cell in the
region of absorption.
10 Which type of tissue is present in
epiphytic roots?
Ans: Velamen tissue
11 Define imbibition.
Ans: Imbibition is swelling up
of hydrophilic colloids due to absorption of water.
12. What is DPD?
Ans: The difference in the
diffusion pressure of pure solvent and the solvent in a solution is called
diffusion pressure deficit.
13 Which symbol is used to denote water
potential?
Ans: The Greek letter psi(ψ)
is used to denote water potential.
14 What do you understand by the term lateral
conduction of food?
Ans: The transport of food occurs in the root and
stem from phloem to pith and phloem to cortex is called lateral translocation
of food.
15 Which organ is mainly involved in
guttation?
Ans: Water stomata or
hydathodes involved in guttation.
SHORT ANSWER TYPE QUESTIONS (SA-I) (2 MARKS EACH)
1 Why water is called as ‘Elixir of Life’?
Ans: Because,
· Water constitutes almost 90 to 95% of most
plant cells and tissues.
· It helps the cells to maintain turgidity
and shape.
2 What are the different types of water?
Ans: Types of Water:
1. Gravitational water 2.
Hygroscopic water
3. Combined water 4. Capillary water
Ans: Structure of Root
Hair:
4 Explain the structure of root hair.
Ans: Structure of Root
Hair:
— Root hair is cytoplasmic extension
(prolongation) of epiblema cell.
— Each root hair may be approximately 1
to 10mm long and tube-like structure.
— It is colourless, unbranched,
short-lived (ephemeral) and very delicate.
— It has a
— large central vacuole surrounded by
thin film of cytoplasm,
— plasma membrane and
— thin cell wall, which is two layered.
— Outer layer is composed of pectin and
— inner layer is made up of cellulose.
— Cell wall is freely permeable but
plasma membrane is selectively permeable.
5 In which forms water is
available to roots for absorption?
Ans: Water which is held in pores present between the neighbouring soil
particles, due to capillarity is called capillary water. This water is
available to roots for absorption.
6 Explain the different properties of water.
Ans: Properties of Water:
— It is in the liquid form at room temperature.
— It is the best solvent for most of the
solutes.
— It is inert inorganic compound with
neutral pH when in pure form.
— Due to this, --is best transporting
medium for dissolved minerals and food molecules.
— It is best aqueous medium for all
biochemical reactions occurring in the cells.
— It is an essential raw material for
photosynthesis.
— Water has high specific heat, high
heat of vaporization and high heat of fusion.
— Due to this, it acts as thermal
buffer.
— These various properties are due
to hydrogen bonds between the water molecules.
— Water molecules have good adhesive and
cohesive forces of attraction.
— Due to high surface tension and high
adhesive and cohesive force,
— it can easily rise in the capillaries.
7 Define imbibate and imbibant.
Ans: Imbibate: Water/ liquid that gets imbibed is called as
imbibate.
Imbibant: Substance that absorbed water/ liquid is
called imbibant.
8 Give importance of diffusion to plants.
Ans: Diffusion is significant in plants in the
◦
absorption
of water, minerals,
◦
conduction
of water against the gravity,
◦
exchange
of gases and
◦
transport
and distribution of food.
9 Differentiate between exosmosis and endosmosis.
Ans:
|
Exosmosis |
Endosmosis |
|
1. It is the migration of solvent from the cell
outside. 2. It causes flaccidity of cell. |
1.
It is the migration of the solvent into the cell. 2. It causes turgidity of cell i.e.,
cytoplasm becomes turgid. |
10 Mention various factors affecting water
absorption.
Ans: Factors affecting water
absorption:
◦
i.
Presence of capillary water is essential.
◦
ii.
Rate of water absorption is maximum at soil temperature between 200
to 300C.
◦
iii.
High concentration of solutes in soil water reduced the rate of absorption of
water.
◦
iv.
Poorly aerated soil shows poor absorption rate.
◦
v.
Increased transpiration accelerates the rate of absorption of water in the
irrigated soil.
11 Give various objections to root pressure
theory.
Ans: Objections to Root Pressure Theory:
i. It
is not applicable to plants taller than 20 meters.
ii. Ascent of sap can also occur even in the
absence of root system.
iii. Root pressure value is
almost nearly zero in taller gymnosperm trees.
iv. In actively transpiring plants, no root
pressure is developed.
v. Xylem sap under normal condition is under
tension i.e., it shows negative hydrostatic pressure or high osmotic pressure.
12 Draw a well labelled diagram of structure
of stomata.
Ans: Structure of Stomata:
13 Give advantages of transpiration.
Ans: Advantages of Transpiration:
i. It removes excess of water.
ii. It helps in the passive absorption of water and
minerals from soil.
iii. It helps in the ascent of sap.
iv. As stomata are open, gaseous exchange required for
photosynthesis and respiration, is
facilitated.
v. It maintains turgor of the cells.
vi. Transpiration helps in reducing the temperature of leaf
and in imparting cooling effect.
SHORT ANSWER TYPE QUESTIONS (SA-II) (3MARKS EACH)
1 Draw a neat and labelled diagram of Root tip showing root
hair zone.
Ans: Root tip showing root hair zone:
2 Draw a neat and labelled diagram of Root hair.
Ans: Root Hair:
Ans:
- · Roots shows root hair region.
- · In this region the outer epiblema cells
shows cytoplasmic extensions called root hairs.
- · Root hairs increases surface area of water
absorption.
- · Root hair cell shows two layered cell wall
made up of pectin and cellulose.
- · Pectin and cellulose acts as imbibant.
- · Water enters root hair due to imbibition
and osmosis.
- · From root hair cell water moves toward xylem tissue.
- · Thus roots can acts as a water absorbing organ.
4 Why capillarity theory was discarded?
Ans: The capillary theory
wad discarded due to following objections raised –
i. Capillary tube (xylem)
must be continuously and completely hollow from one end to the other end but
tracheids in the xylem show closed end-walls.
ii. The lower end of capillary tube i.e., xylem must be in
direct contact with soil water.
However,
there exists a barrier of root cortex between xylem and soil water.
iii. Narrower the capillary tube, greater is the height to
which water column is raised.
Thus,
taller trees should show xylem vessels with very narrow bore (diameter).
However,
in nature the tall trees show xylem vessels having wider bore.
Hence,
to sum up capillarity cannot be the sole mechanism to explain ascent of sap in
all the plants of varying heights.
5 Explain the concept of water potential.
Ans: Water Potential:
· According to the principle of thermodynamics,
o every component of a system
is having a definite amount of free energy which is used to do work.
·
Osmotic
movement of water is based on free energy.
·
Free
energy per molecule in a chemical system, is called its chemical potential.
·
Chemical
potential of water is called water potential.
·
It
is represented by Greek letter psi (ψ).
·
Water
potential of protoplasm is equal but opposite in sign to DPD.
·
It
has negative value.
·
The
unit of measurement is in bars/ pascals / atmospheres.
·
Water potential of pure water is always zero.
·
Addition of any solute in it, decreases its psi
(ψ) value.
·
Therefore, it has negative value.
·
Water always flows from less negative
potential to more negative water potential (i.e., from high water
potential area to low water potential area).
·
Difference between water potential of the
adjacent cells decides movement of water through plasmodesmata across the
cells.
Ans: Types of
Transpiration:
Accordingly, three types
of transpiration are recognized viz. cuticular, stomatal and lenticular.
i.
Cuticular transpiration:
· Cuticle is a layer of waxy
substance- cutin, present on outer surface of epidermal cells of leaves and
stem.
· Cuticular transpiration
occurs by simple diffusion.
· It contributes 8-10% of the
total transpiration.
· Cuticular transpiration
occurs throughout the day.
· Its rate is inversely
proportional to thickness of cuticle.
ii.
Lenticular transpiration:
·
Lenticels
are small raised structures.
·
They
are composed of loosely arranged complementary cells.
·
Each
lenticel is a porous tissue consisting of cells with large intercellular
spaces.
·
They
are situated in the
o periderm of the secondarily
thickened organs
o bark of woody stems
o pericarp of woody fruits
o bark of roots of
dicotyledonous flowering plants.
·
Lenticels
are absent in leaves.
·
Lenticular
transpiration contributes only about 0.1-1.0% of total transpiration.
·
Rate
of lenticular transpiration is very slow.
·
It
also occurs throughout the day.
iii.
Stomatal transpiration:
·
Stomata
are minute apertures formed of two guard cells and accessory cells.
·
They
are located in the epidermis of young stem and leaves.
·
Leaves
generally show more number of stomata on the lower surface.
·
Depending
upon distribution of stomata on leaves, leaves are categorized into three types
namely-
o Epistomatic – on upper
epidermis (Hydrophytes. e.g., Lotus),
o Hypostomatic - on lower
epidermis (Xerophytes-
e.g., Nerium)
o Amphistomatic - on both surfaces (Mesophytes-
e.g., Grass).
·
Stomatal
transpiration occurs only during daytime. (Exception: Desert plants).
·
90
to 93% of total transpiration occurs through stomata and that too during day
time only.
7 Describe the path of water across the root with the help
of labelled diagram
Ans: Path of Water across the Root:
· Water
is absorbed by root hair cell through imbibition à diffusion à
osmosis, sequentially.
· Consequently,
the cell becomes turgid.
· Its
turgor pressure increases, but its DPD value decreases.
· However,
the immediately adjacent cortical cell inner to it, has more DPD value, because
its O. P. is more.
· Therefore,
cortical cell will suck water from the turgid root hair cell.
· It
then becomes turgid.
· The
flaccid root hair cell now absorbs water from soil.
·
Water from the turgid cortical cell is sucked
by inner cortical cell and the process goes on.
·
Thus, a gradient of suction pressure (DPD) is
developed from cells of epiblema to the cortex of the root.
·
Consequently, water moves rapidly across the
root through-
o loosely arranged living cells of cortex,
o followed by passage cells of endodermis and finally
o into the cell of pericycle.
·
Protoxylem is in the close proximity with
pericycle.
·
Absorption of water being a continuous
process, a sort of hydrostatic pressure is developed in living cells of root.
·
This is called root pressure.
·
It is due to root pressure, water from
pericycle is
o not only forced into the xylem,
o but also conducted upwards against the gravity.
·
Pathway of water across the root essentially
occurs in two ways viz, apoplast and symplast.
·
When some amount of water passes across the
root through the cell wall and the intercellular spaces of cortical cells of
root, it is then called apoplast pathway.
·
This pathway occurs up to endodermis.
·
When water passes across from one living cell
to other living cell through plasmodesmata, then it is called symplast pathway.
·
It is also called transmembrane pathway.
8 Differentiate between passive and active absorption.
Ans:
|
Passive Absorption |
Active Absorption |
|
1.
Water is absorbed
through roots. 2.
Driving force is
transpiration pull. 3.
No expenditure of
energy. 4.
Rate of respiration
is not affected. 5.
Water moves in
accordance to the concentration gradient. 6.
About 98% water absorption
occurs passively. 7.
It occurs during
daytime. 8.
It stops at night. |
1. Water is absorbed by roots. 2. Driving force is root pressure
developed in the living cells of root. 3. Needs expenditure of energy. 4. Rate of respiration is affected. 5. Water moves against the concentration
gradient. 6. About 2% water absorption occurs
actively. 7. It occurs during night. 8. It stops during daytime. |
LONG ANSWER TYPE QUESTIONS(LA) (4 MARKS EACH)
1 Explain the structure of root hair with the help of neat
and labelled diagrams.
Ans: Structure of Root
Hair:
— Root hair is cytoplasmic extension
(prolongation) of epiblema cell.
— Each root hair may be approximately 1
to 10mm long and tube-like structure.
— It is colourless, unbranched, short-lived
(ephemeral) and very delicate.
— It has a
— large central vacuole surrounded by
thin film of cytoplasm,
— plasma membrane and
— thin cell wall, which is two layered.
— Outer layer is composed of pectin and
— inner layer is made up of cellulose.
— Cell wall is freely permeable but
plasma membrane is selectively permeable.
Ans: Transpiration Pull Theory of Ascent of Sap:
Ø This
is presently widely accepted theory explaining ascent of sap in plants.
Ø It was put forth by Dixon
and Joly (1894).
Ø This theory is based on two
principles.
Cohesion and adhesion, and
Transpiration pull
Ø A strong force of
attraction between water molecules, is called cohesive force.
Ø While a strong force
of attraction between water molecules and lignified wall of lumen of xylem
vessel, is called adhesive force.
Ø Due to combined cohesive and adhesive
forces a continuous water column is developed (formed) in the xylem right from
root up to the tip of the topmost leaf in the plant.
Ø Transpiration pull :
Ø The transpiration pull developed in the
leaf vessel is transmitted down to root and thus accounts for the ascent of
sap.
Ø Excess water is lost in the form of vapour, mainly through
the stomata found on leaf.
Ø This water loss increases D. P. D.
of mesophyll cells.
Ø These cells withdraw water
ultimately from xylem in the leaf.
Ø In other words, due to continuous transpiration,
a gradient of suction pressure (i.e. D. P. D.) is developed right from guard
cells up to the xylem in the leaf.
Ø This will create a tension
(called negative pull or transpiration pull) in the xylem.
Ø Consequently, water column is pulled
out of xylem.
Ø Thus, water is pulled upwards
passively against the gravity leading to the ascent of sap.
3 Explain the mechanism of transport of food through phloem
with suitable diagram,
Ans: Mechanism of
Food Transport through Phloem:
•
Several mechanisms/ theories like diffusion,
activated diffusion, protoplasmic streaming, electro-osmosis, pressure-flow,
etc. are put forth.
•
The most convincing theory is Munch’s
pressure flow theory or mass flow hypothesis.
•
Ernst Munch proposed that photosynthetic cell synthesizes
glucose.
– Hence, its osmotic concentration increases.
•
Due to endo-osmosis water from surrounding
cells and xylem, is absorbed.
•
The cell becomes turgid.
•
Due to increase in turgor pressure, sugar
from photosynthetic cell is forced ultimately into the sieve tube of the vein.
•
This is called loading of Vein.
•
At the sink end, root cell utilizes sugar and
also polymerizes excess sugar into the starch.
– Its osmotic
concentration is lowered.
– Exo-osmosis occurs.
•
Water in the root cell is lost to surrounding
cells, thereby decreasing the turgidity of cell.
•
Turgor pressure is lowered.
•
Hence, a turgor pressure gradient is
developed from sieve tube in the leaf to the root cell.
•
Consequently, food is translocated along the
concentration gradient, passively.
•
This is Vein unloading.
•
At the sink end, sugar is used and excess water exudes into the xylem.
4 Explain the mechanism of opening and closing of stomata.
Ans: Mechanism of Opening and Closing of Stomata:
· Opening and closing of stoma is controlled
by turgor pressure of guard cells.
· During day, guard cells become turgid due
to endosmosis.
· Thus, turgor pressure is exerted on the
thin walls of guard cells.
· Being elastic and thin, lateral walls are
stretched out.
· Due to kidney or dumb-bell like shape,
inner thick walls are pulled apart to open (widen) the stoma.
· During night, guard cells become flaccid
due to exosmosis.
· Flaccidity closes the stoma almost completely.
· Endosmosis and exosmosis occur due to
diurnal changes in osmotic potential of guard cells.
·
Different
theories are proposed to explain diurnal changes in osmotic potential.
·
According
to starch-sugar interconversion theory (Steward 1964),
§ During day, enzyme phosphorylase
converts starch to sugar,
·
Thus, increasing osmotic potential of guard cells causing
entry of water there by guard cells are stretched and stoma widens.
§ The reverse reaction occures
at night brining about the closure of stoma.
·
According
to theory of proton transport (Levitt-1974), stomatal movement occurs due to
transport of protons H+ and K + ions.
·
During
daytime, starch is converted into malic acid.
·
Malic
acid dissociates to form Malate and protons.
·
Protons
are transported to subsidiary cells and K+ ions are imported from
them.
·
Potassium
malate is formed that increases osmolarity and causes endosmosis.
·
Uptake
of K+ ions is always accompanied with Cl¯ ions.
·
At
night, uptake of K+and Cl- ions is prevented by abscisic
acid, changing the permeability of guard cells.
·
Due
to this guard cells become hypotonic and thereby become flaccid.
