Chapter 3 (3.4)

Question 1

Explain the phenomenon of plant wilting. (5)

Answer 1

• excessive use of fertilisers may cause wilting in plants
• dissolved fertiliser causes soil water to be hypertonic to the sap cell of roots
• water diffuse by osmosis from the roots’ cell sap to the soil
• cells become plasmolysed
• if period of plasmolysis is prolonged, wilted plants will eventually die

Question 2

What are the applications of movement of substances across a plasma membrane in our daily life? (4)

Answer 2

• rehydration drinks help to recover loss of water & electrolytes in individuals with diarrhoea
• isotonic drinks help athletes recover water loss & electrolytes through perspiration
• saline solutions are isotonic to the blood plasma
• liposomes (vesicles that contain aqueous solution surrounded by phospholipid bilayer membrane) are used to protect drug/active substances taken orally from being destroyed by gastric juices. Hence, drugs can reach they’re target cells

Question 3

What is reverse osmosis & how is it done? (4)

Answer 3

• a technology used to extract fresh water from seawater using desalination process
• pressure is applied to push the seawater through a semi-permeable membrane
• the membrane allows water particles to pass through it but not foreign particles, salt & microorganisms
• Hence, only pure fresh water is released