Form 1:
Nutrition in Plants and Animals

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Factors affecting the rate of photosynthesis.

a) Carbon (IV) oxide concentration

While the concentration of carbon (IV) oxide in the atmosphere is fairly constant at 0.03%, an increase in carbon (IV) oxide concentration translates into an increase in the rate of photosynthesis upto a certain point when the rate of photosynthesis becomes constant. At this point, other factors such as light intensity, water and temperature become limiting factors.

b) Light intensity

The rate  of photosynthesis increases with an increase in light intensity up to a certain level. Beyond the optimum light intensity, the rate of photosynthesis becomes constant.To this effect, plants photosynthesize faster on bright and sunny days than on dull cloudy days.

Light quality/wavelength also affects the rate of photosynthesis. Most plants require red and blue wavelengths of light for photosynthesis. Light duration also affects photosynthesis rate.

c) Temperature

Photosynthesis is an enzyme controlled process. At very low temperatures the rate of photosynthesis is slow because the enzymes are inactive. As temperature increases, the rate of photosynthesis increases because the enzymes become more active. Rate of photosynthesis is optimum at (35-40) °C. Beyond 40°C the rate of photosynthesis decreases and eventually stops since the enzymes become denatured.

d) Water

Water is a raw material for photosynthesis. At extreme level of water shortage, rate of photosynthesis will be severely affected.

In this experiment, sodium hydrogen carbonate is added to the water to boost the amount of carbon (IV) oxide in the water since water has a low concentration of carbon (IV)oxide.

A water plant is also selected because water plants are adapted to photosynthesis under the low light intensity in water where terrestrial plants cannot easily photosynthesize.

This experiment can also be used to investigate the factors affecting the rate of photosynthesis:

1) Carbon (IV) oxide concentration: Carry out the experiment using different amounts of dissolved sodium hydrogen carbonate e.g 5g, 10g, 15g, 20g and examine the rate at which the gas collects.

2) Light intensity: An artificial light source can be used. Illuminate the plant and vary the distance between the set up and the light source while recording the time it takes for the gas jar to fill or counting the number of bubbles per unit time

3) Temperature: carry out the experiment at varying temperatures and record the rate at which the gas collects.

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