Page 86 - NCERT Science Class 10 English Medium

design in multi-cellular organisms are followed, a specialised tissue for
excretion will be developed, which means that the transportation system
will need to transport waste away from cells to this excretory tissue.
Let us consider these various processes, so essential to maintain
life, one by one.

Q U E S T I O N S

1. Why is diffusion insufficient to meet the oxygen requirements of multi-
cellular organisms like humans?
2. What criteria do we use to decide whether something is alive? ?
3. What are outside raw materials used for by an organism?
4. What processes would you consider essential for maintaining life?

5.2
5.2
5.2 NUTRITION
5.2 NUTRITIONNUTRITION
5.2 NUTRITION
NUTRITION
When we walk or ride a bicycle, we are using up energy. Even when we
are not doing any apparent activity, energy is needed to maintain a
state of order in our body. We also need materials from outside in order
to grow, develop, synthesise protein and other substances needed in
the body. This source of energy and materials is the food we eat.

How do living things get their food?
The general requirement for energy and materials is common in all
organisms, but it is fulfilled in different ways. Some organisms use simple
food material obtained from inorganic sources in the form of carbon
dioxide and water. These organisms, the autotrophs, include green
plants and some bacteria. Other organisms utilise complex substances.
These complex substances have to be broken down into simpler ones
before they can be used for the upkeep and growth of the body. To
achieve this, organisms use bio-catalysts called enzymes. Thus, the
heterotrophs survival depends directly or indirectly on autotrophs.
Heterotrophic organisms include animals and fungi.

5.2.1 Autotrophic Nutrition

Carbon and energy requirements of the autotrophic organism are
fulfilled by photosynthesis. It is the process by which autotrophs take
in substances from the outside and convert them into stored forms of
energy. This material is taken in the form of carbon dioxide and water
which is converted into carbohydrates in the presence of sunlight and
chlorophyll. Carbohydrates are utilised for providing energy to the plant.
We will study how this takes place in the next section. The carbohydrates
which are not used immediately are stored in the form of starch, which
serves as the internal energy reserve to be used as and when required
by the plant. A somewhat similar situation is seen in us where some of
the energy derived from the food we eat is stored in our body in the form
of glycogen.

Life Processes 81

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