Seconday 4 (MYE) - Essay (6)

6. (a) Based on your knowledge in Biology, explain the following processes:

(i) excessive use of fertiliser on crop plants

· The excessive use of fertiliser causes the soil to become hypertonic to the cell sap of the plant root cells [1]
· This causes water to diffuse out of the root cells by osmosis [1]
· As a results, the root cells undergo plasmolysis and the plant will wilt [1]

(ii) absorption of glucose in the small intestines

· After digestion, the concentration of glucose in the ileum increases [1]
· Glucose is a large molecule that is transported across the epithelial cells of ileum by facilitated diffusion [1]
· Glucose molecules move across the transport protein down the concentration gradient into the blood capillaries [1]
[6 marks]

(b) Blood is a medium to transport respiratory gases in human beings. Explain how the transport of oxygen and carbon dioxide takes place between the alveolus and the body cells. [6 marks]

· In the alveolus, the concentration of oxygen is higher than that of the blood capillary [1]
· Therefore, oxygen diffuses from the alveolus into the blood capillary down its concentration gradient by simple diffusion [2]
· In the blood capillary, the concentration of carbon dioxide is higher than that of the alveolus [1]
· Therefore, carbon dioxide diffuses from the blood capillary into the alveolus down its concentration gradient by simple diffusion [2]

(c) For each type of food in Diagram 10 below explain one method in which it can be preserved for a long period of time. [8 marks]

Diagram 10 - FISH, CARROTS

· Fish can be preserved by dehydration [1]
· Fish is smoked or dried under the sun to remove water [1]
· Fish can also be dried by adding salts which causes water to diffuse out from fish into hypertonic surrounding [1]
· Dehydrated fish has low water content that prevents growth of microbes [1]

· Carrot strips are soaked in a vinegar syrup solution [1]
· The cell sap of the carrot cells is hypotonic to the external solution [1]
· Water diffuses out of the carrot cells into the hypertonic surroundings [1]
· The dried and shrunk carrot strips prevent the growth of microbes [1]