Biology [2 Mark Question Answer]

Plasmolysis : Living cells of leaf of aquatic plants remain in turgid condition, but when they are kept in salt or sugar solution, they lose their turgid form, protoplasm shrinks and plasma membrane is withdrawn. This shrinkage of protoplasm is called plasmolysis and the cell is said to be plasmolysed.
Application of plasmolysis in our daily life : Preserving food items in highly concentrated sugar solution as in the case of jams and jellies.

(i) Turgor pressure helps the plants to push through the hard ground as in mushrooms and in a seedling.
(ii) Sometimes, the roots of certain trees crack the walls or a concrete floor of an adjoining building. This happens due to the turgor pressure.

When a cell loses water from its cytoplasm and the plasma membrane is withdrawn, it is said to be flaccid, e.g., when stomata closes.
Turgidity is a condition when a cell is fully stretched with water and all its walls are in a state of tension. Such cell is called turgid cell. e.g. when stomata is open.

Transpiration pull of the aerial parts of the plants, cohesive forces between water molecules, adhesive forces between water and xylem vessels, and root pressure are the various forces involved in the absorption of water from the soil.

Plants begin to die when excess of soluble fertilisers are added to the soil. This is because the concentration of soil solution becomes very high. This causes the water to move out from the root hair due to exosmosis. Due to this, plants initially wilts but later begin to die.

Freshwater fish cannot survive in sea water. This is because in freshwater, a fish is hypertonic to its surrounding. It means fish is "more salty" and water continually flows into the fish's body through osmosis. But in sea water, a fish is hypotonic or "less salty" compared to its surrounding. This means water flows out of the fish's body. Thus, freshwater fish cannot survive in sea water.

Resins swell up when kept in water. It is because of both imbibition and osmosis. Imbibition is the passive absorption of water by the dead surface. The resins swell up due to imbibition and endosmosis when kept in water.

Potato cubes when placed in water become firm and increase in size. This is because of endosmosis i.e., diffusion of water. The concentration of water in the potato is less than water outside. So, water molecules move from a region of higher concentration to low concentration and thus, the potato swell up and increase in size.

Lawn grass is killed if salt is sprinkled on it. This is because the surrounding water (in which grass is grown) becomes hypertonic, hence, water from root hair cells comes out by the process of exosmosis and cells get plasmolysed and die. This causes the death of lawn grass.