Page 283 - Biology_F5

Biology for Advanced Level Secondary Schools

intensity brings no effect on the rate Wind velocity
of photosynthesis, if other factors are Wind moving at high speed reduces the
not limiting. However, unless the plant rate of photosynthesis because strong
is adapted to high light intensity, the wind usually facilitates transpiration and
chlorophyll might undergo bleaching. hence it affects the availability of water.
Leaf adaptation to very high light intensity Therefore, speedy wind reduces the amount
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includes presence of thick cuticle and of water available as the raw material for
hairs. Light intensity varies with location photosynthesis, and consequently reduces
and seasons of the year. In the tropical and the rate of photosynthesis.
subtropical areas, light intensity is higher
than in the temperate areas. Light intensity Exercise 5.4
also decreases during rainy seasons due to 1. Describe photosystem I and
cloud cover. photosystem II in green plants and

show how they are involved in
During photosynthesis, the plant producing NADPH and ATP during
consumes carbon dioxide via respiration light reaction of photosynthesis.
as it eliminates oxygen, which is
important for respiration. A point is 2. Explain how plants such as sugarcane
reached when light intensity causes the and sorghum are adapted to overcome
rate of photosynthesis to balance with photorespiration.
that of respiration. This means that the 3. Explain how the light quality
rate of carbon dioxide production from and intensity affect the rate of
respiration equals to that of carbon dioxide photosynthesis.
consumption in photosynthesis. This is
called a compensation point of a plant, 5.3 Heterotrophic nutrition
which refers to the point at which net gain
of atmospheric air is zero (Figure 5.9). Task 5.9
Read about heterotrophic nutrition
Higher CO
Light saturation concentration from different internet sources and
2
other biology books, and then make
short notes about your search.
Low CO
2
concentration Heterotrophic nutrition is the mode of
Carbondioxide taken up Rate of photosynthesis nutrition in which an organism feeds by

taking in organic substances made by other
Net gas exchange zero organisms. Organisms that obtain organic
Carbondioxide 0 Compasation point CO released food substances from other organisms
Light intensity
are termed as heterotrophs. Examples of
given out
2
during respiration equals that taken
up during photosynthesis
protoctists and most monerans.
Figure 5.9: The light intensity and compensation heterotrophs include animals, fungi, some
point
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