Class 10 – BIOLOGY
About Lesson


1. Plasmolysis & deplasmolysis

Shrinkage of cell contents ( cytoplasm ) & the withdrawl  of plasma membrane from cell wall as one cell is immersed in hypertonic solution, is called is called plasmolysis. The recovery of the cell or reversal of plasmolysis by immersing the cell in the hypotonic solution is called deplasmolysis.

2. Turgour pressure & wall pressure

Pressure of the cell contents on the cell wall is called turgour pressure whereas pressure exerted by cell wall on the cell content is called wall pressure

3. Guttation & bleeding

The loss of water as water drops through the ends of leaf veins. In certain plants like tomato, grass , banana or ferns , the root pressure is high enough to force water all the way through stem . 

 But loss of water (cell sap) through a cut stem is calledbleeding .Here too the cause is root pressure

4.Turgidity & flaccidity

The condition in which the cell reaches a state where it cannot accomodate any more water, it is known as turgidity,

whereas the condition when the cell looses water & shrink from cell wall ,is known as flaccidity.

II What is the difference between flaccid and turgid ? Givre one example of flaccid condition in plants

When cell reaches a state where it cannot accomodate any more water , it is fully distended is called , turgid.

As a result of plasmolysis, the shrinkage of cytoplasm with cell membrane takes place from cell wall is known as flaccid.

Example plants in draught condition

III Give two examples of turgour movements in plants

 Turgour movements in touch- me -not plant is a common example . Here the leaves droop down as one touches the 

plant as a result of loss of water from each cell in the petiole region.

Another example is sleep movements in plants. The closure of leaves of some members of pea family , during night.

IV Explain the mechanism of closing and opening of stomata

Closing and opening of stomata depends upon the turgidity of guard cells.Bean shaped guard cell has thick  wall facing stoma & thin wall on the opposite side. Guard cell contain chloroplast and synthesis glucose during daytime.. As a result chemical changes take place and osmotic pressure of contents of guard cell increases and  the guard cell absorb more water from the neighbouring subsidiary cells., thus become turgid. On account of turgour , the guard cells become more arched outward and the aperture between the guard cell widens, there by opening the stomata. At night, or when there is shortage of water in the leaf , the turgid cells turn flaccid and inner rigid walls become straight, thus closing stomatal aperture.

V Explain how seed soaked seeds swell up and burst their seed coat

Imbibition is the passive absorption of water by substance such as cellulose in the cell wall and startch. Turgour is the pressure set up inside the plant cell due to hydraustatic on the cell walls on account of incoming water as a result of endosmosis. The seeds and grains swell up when soaked in water due to imbibition and endosmosis.

VI What is transpiration pull? How is it caused?

As  the water is lost from the leaf surface by transpiration , more water molecules are pulled up due to the tendency of water molecules to remain joined (cohesion) , and thus produce a continuous column of water through stem. This is called transpiration pull.