12th biology chapter 6 MCQs ( plant water Relations )

 1 Multiple Choice Questions

1. In soil, water available for absorption
by root is ...................
    a. gravitaional water
    b. capillary water
    c. hygroscopic water
   d. combined water

Answer : capillary water 
Explanation : Plants absorb water and minerals through roots from soil for metabolism and their life. This soil water comes to the upper level of soil through a fine tube-like gap in the soil. So this water is called capillary water. So the correct answer is 'Capillary water'


2. The most widely accepted theory for
ascent of sap is ..............
    a. capillarity theory
    b. root pressure theory
    c. diffusion
    d. transpiration pull theory

Answer : Transpiration pull theory 
Explanation : 
Transpiration pull cohesion theory for ascent of sap in trees is most widely accepted.


3. Water movement between the cells is due to .............
    a. T. P.
    b. W. P.
    c. DPD
    d. incipient plasmolysis

Answer : DPD 
Explanation : Water movement between cells is due to DPD. If a cell is placed in pure water it shows endosmosis and as a result water enters into the cell.


4. In guard cells, when sugar is converted into starch, the stomatal pore .............
    a. closes almost completely
    b. opens partially
    c. opens fully
    d. remains unchanged

Answer : Closes almost completely.
Explanation : In guard cells when sugar is converted into starch, the stomatal pore closed completely. At night time, the CO2 released during respiration accumulates. As a result, the acidity of the guard cells increases and pH decreases. The decreased pH favours conversion of sugar to starch



5. Surface tension is due to ..............
    a. diffusion
    b. osmosis
    c. gravitational force
    d. cohesion

Answer : Cohesion 


6. Which of the following type of solution has lower level of solutes than the solution?
    a. Isotonic
    b. Hypotonic
    c. Hypertonic
    d. Anisotonic

Answer : Hypitonic 
Explanation : A hypotonic solution has a lower concentration of solutes than another solution. In biology, a solution outside of a cell is called hypotonic if it has a lower concentration of solutes relative to the cytosol.


7. During rainy season wooden doors warp and become difficult to open or to close because of ...............
    a. plasmolysis
    b. imbibition
    c. osmosis
    d. diffusion

Answer : Imbibition
Explanation : Humidity increases during rainy season. because of Imbibition.


8. Water absorption takes place through
.............
    a. lateral roots
    b. root cap
    c. root hair
    d. primary root

Answer : Root Hair
Explanation : Plants absorb water through the entire surface using roots, stems and leaves. However, mainly the water is absorbed by roots. The area of young roots where most absorption takes place is the root hair zone.



9. Due to low atmospheric pressure the
rate of transpiration will .............
    a. increase
    b. decrease rapidly
    c. decrease slowly
    d. remain unaffected

Answer : Increase 
Explanation : If atmospheric pressure is low, water will move out of the plant into the atmosphere as water vapour. Plants will lose water at higher rate by transpiration process. Hence, at low atmospheric pressurerate of transpiration increases.


10. Osmosis is a property of ..................
    a. solute
    b. solvent
    c. solution
    d. membrane

Answer : Membrane
Explanation : Osmosis is defined as the movement of solvent or water molecules from a region of their higher concentration to a region of their lower concentration through a semipermeable membrane. Hence, osmosis depends upon the semipermeable nature of membrane..