Page 153 - Biology Form Two

Biology for Secondary Schools

Temperature which is equal to 3. On the other hand,
Respiration is controlled by enzymes. a smaller organism with the volume of
The functioning of enzymes is affected 4 cm and a surface area of 16 cm , has
3
2
by temperature. The rate of respiration is surface area to volume ratio of 16/4
slow at low temperatures and increases which is equal to 4. Therefore, small
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with the increase in temperature to the organisms need to respire faster than
optimal level. Optimal temperature is larger organisms to replace the energy
the temperature at which the enzymes lost through heat.

function best. At optimum temperature
the rate of respiration reaches its Age
maximum. If the temperature is raised Generally, young organisms respire
above the optimal level, enzymes are faster than older organisms. This is
denatured and the rate of respiration is because they need more energy for
reduced. Similarly, when the temperature growth. In addition, young organisms
is lowered below the optimal level, the are usually more active than older

enzymes become inactive and the rate organisms, hence they need more
energy.
of respiration decreases.

Activity Exercise 6.3
When an organism is involved in a
vigorous activity, it requires more 1. Briefly describe the mechanism of
energy than when it is at rest. For respiration in mammals.
example, a human being requires less 2. Explain clearly adaptations which

energy when sitting than when running. enable the mammalian respiratory
organ to perform its function.
Size
Small organisms lose heat faster than 3. Why is anaerobic respiration
larger organisms. This is because small important to human?
organisms have a larger surface area 4. Differentiate obligate anaerobe
to volume ratio. The ratio of surface from facultative anaerobe.
area to volume in a small organism is
greater than that of a large organism. For 5. The absence of oxygen debt could

example, if an organism has a volume of impair metabolism in human.
8 cm and surface area of 24 cm , its ratio Giving a reason, support this
2
3
statement.
of surface area to volume will be 24/8,

Student’s Book - Form Two 147

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