PRIVATE SCHOOL BIOLOGY ESSAY QUESTIONS AND ANSWERS

I. Photosynthesis

1.Write an essay describing the process of photosynthesis.

Photosynthesis occurs in two stages,that is,light stage and dark stage. During light stage, light energy is trapped by chlorophyll in the chloroplast and converted into chemical energy. The chemical energy isused to split water molecules into hydrogen and oxygen atoms. The hydrogen is used in the dark stage, while oxygen molecules are released into the atmosphere as oxygen gas or used for aerobic respiration. Some of the chemical energy is used to combine a molecule called adenosine diphosphate with a phosphate group to form the rich energy molecule called adenosine tri-phosphate.

During dark stage, the hydrogen atoms formed in light stage are combined with carbondioxide to form glucose using energy from ATP.

2.Describe any five ways in which a plant leaf is adapted to its function. Your answer should be in essay form.

Firstly, the leaf has broad and flattened surface. This increases the surface area for absorption of carbondioxide and sunlight.

Secondly, the leaf is supported by a stem and a petiole. This exposes as much of the leaf as possible to sunlight and air.

Thirdly, the leaf has thin lamina. This reduces the distance across which carbon dioxide diffuses from stomata to photosynthetic cells.

Fourthly, the leaf has network of veins. This provides a good water supply to the photosynthesing mesophyll cells.

Lastly, the leaf has stomata on its surface. These allow carbondioxide to enter the leaf.

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3.Explain five ways in which glucose isused by the plant after photosynthesis. (2004)

Firstly, glucose is used for respiration which produces energy for growth and active transport of substances across membranes.

Secondly, glucose is converted to cellulose which is used to form cell walls that protect the cell from bursting due to osmosis.

Glucose is combined with nitrogen to form proteins which is used to form enzymes.

Fourthly, glucose is converted to fats which are used to form cell membrane that controls substances getting into the cell.

Lastly, glucose is transported to storage organs where it is converted to starch for storage.

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