BOTANY Higher Secondary Second Year - Textbooks Online

5.2.1. Significance of photosynthesis
Photosynthesis is a source of all our food and fuel. It is the only
biological process that acts as the driving vital force for the whole
animal kingdom and for the non-photosynthetic organism.
It drives all other processes of biological and abiological world. It is
responsible for the growth and sustenance of our biosphere.
It provides organic substances, which are used in the production of
fats, proteins, nucleoproteins, pigments, enzymes, vitamins, cellulose,
organic acids, etc. Some of them become structural parts of the
organisms.
It makes use of simple raw materials such as CO 2, H 2 O and inexhaustible
light energy for the synthesis of energetic organic compounds.
It is significant because it provides energy in terms of fossil fuels like
coal and petrol obtained from plants, which lived millions and millions
of years ago.
Plants, from great trees to microscopic algae, are engaged in converting
light energy into chemical energy, while man with all his knowledge
in chemistry and physics cannot imitate them.
5.2.2. Site of photosynthesis
Chloroplasts are the actual sites for photosynthesis. All green parts
of a plant are involved in photosynthesis. Leaves are the most important
organs of photosynthesis. In xerophytes like Opuntia, the stem is green
and it performs photosynthesis. Over half a million chloroplasts are present
in one square millimetre of a leaf. It measures about 4 to 6 micron. A
Fig. 5.6 Structure of chloroplast
typical chloroplast of higher plants is discoid shaped. It is a double
membrane bound organelle containing chlorophyll, carotenoid, xanthophyll,
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