- Assertion : Selectively permeable membranes allow
passage of solvent molecules, only upto a certain
extent.
Reason : all plant and animal cell membranes, egg
membranes and parchment membrane are selectively
permeable. - Assertion : The upper layer of ground water is called
water table, where soil is completely saturated with
water, and air is excluded.
Reason : all plants can send their roots upto the fringe
of water table. - Assertion : The osmotic pressure of a solution largely
depends upon the ratio between the number of solute
and solvent particles present in a solution.
Reason : The instrument used for measuring osmotic
pressure is called osmometer.
- Assertion : Pure water has maximum water potential.
Reason : The osmotic potential is zero in pure water.
Short Answer Type Questions
- fill in the blanks.
(i) In a fully turgid cell, DPD equals , while in a
flaccid cell, DPD equals .
(ii) The passive absorption of water, from the soil by root
hairs occurs due to _____.
(iii) The metabolic state of the root directly affects the
_____ pathway of water absorption.
(iv) _____ pressure developed during germination of
seeds can break asphalt roads.
(v) _____ is a type of diffusion of solvent.
- Out of the following forms of soil water – hygroscopic
water, capillary water and combined or bound water,
which of these is available to the plants? - Why both water potential and osmotic potential of pure
water is zero? - Why dry wooden stakes, driven into small cracks in a
rock, when soaked, cause the rock to split? explain the
phenomenon responsible for this.
Answer Key
New MCQs- (d) 2. (a) 3. (d) 4. (a) 5. (b)
- (a) 7. (c) 8. (b) 9. (a) 10. (b)
Exam Section- (b) 2. (d) 3. (a) 4. (a) 5. (c)
- (b) 7. (c) 8. (c) 9. (a) 10. (b)
- (c) 12. (d) 13. (a) 14. (a) 15. (e)
- (e) 17. (b) 18. (b) 19. (a) 20. (a)
Assertion & Reason- (a) 2. (d) 3. (c) 4. (d) 5. (c)
- (b) 7. (a)
Short Answer Type Questions- (i) zero, OP (ii) transpiration (iii) symplast
(iv) imbibition (v) osmosis - Hygroscopic water is the water that occurs in the form
of thin film on the soil particles and is not available
to the plants. Capillary water fills the spaces between
non-colloidal soil particles and forms films around them.
This is the only available water to the plants. Combined
water is that water which is chemically bound with soil
materials and is not available to plants. - Water potential (yw) is the difference between the
chemical potential of the water in a biological system
and the chemical potential of pure water at the same
temperature and pressure. The water potential of
pure water is zero, aqueous solutions of increasing
concentration have increasingly negative values. Osmotic
pressure is the pressure required to stop the flow of
pure water into a solution across a partially permeable
membrane. It is also zero for pure water. - Imbibition is the phenomenon of adsorbing water
by certain materials, particularly in dry or semi-dry
conditions. This is also a type of diffusion, which is
performed like osmosis.
In this process, there is a great difference between
diffusion pressure of the liquid of imbibing cell and
the liquid of external medium. Due to this reason the
process of imbibition takes place and it continues till the
pressures of cell-liquid and external medium becomes
equal or balanced. The swelling of dry seeds when
placed in water, the swelling of wooden windows, tables,
doors, etc., due to moisture during rainy season are the
examples of imbibition. So, if such dry wooden stakes
are driven into a small crack in a rock and then soaked,
they develop enough pressure due to imbibition, to split
the rock.
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