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taken up in the form of inorganic nitrates or nitrites. Or it is taken up as
organic compounds which have been prepared by bacteria from
atmospheric nitrogen.

5.2.2 Heterotrophic Nutrition

Each organism is adapted to its environment. The form of nutrition
differs depending on the type and availability of food material as well
as how it is obtained by the organism. For example, whether the food
source is stationary (such as grass) or mobile (such as a deer), would
allow for differences in how the food is accessed and what is the nutritive
apparatus used by a cow and a lion. There is a range of strategies by
which the food is taken in and used by the organism. Some organisms
break-down the food material outside the body and then absorb it.
Examples are fungi like bread moulds, yeast and mushrooms. Others
take in whole material and break it down inside their bodies. What can
be taken in and broken down depends on the body design and
functioning. Some other organisms derive nutrition from plants or
animals without killing them. This parasitic nutritive strategy is used
by a wide variety of organisms like cuscuta (amar-bel), ticks, lice,
leeches and tape-worms.

5.2.3 How do Organisms obtain their Nutrition?

Since the food and the way it is obtained differ, the digestive system is
different in various organisms. In single-celled organisms, the food
may be taken in by the entire surface. But as the complexity of the
organism increases, different parts become specialised to perform
different functions. For example, Amoeba takes in food using
temporary finger-like extensions of the cell surface which fuse over
the food particle forming a food-vacuole (Fig. 5.5). Inside the food-
vacuole, complex substances are broken down into simpler ones
which then diffuse into the cytoplasm. The remaining undigested
material is moved to the surface of the cell and thrown out. In
Paramoecium, which is also a unicellular organism, the cell has a
definite shape and food is taken in at a specific spot. Food is moved
to this spot by the movement of cilia which cover the entire surface
of the cell.

Figure 5.5
Figure
Figure 5.5 5.2.4 Nutrition in Human Beings
Figure 5.55.5
Figure 5.5
Nutrition in Amoeba
The alimentary canal is basically a long tube extending from the mouth
to the anus. In Fig. 5.6, we can see that the tube has different parts.
Various regions are specialised to perform different functions. What
happens to the food once it enters our body? We shall discuss this
process here.

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