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Chapter 5 Life Processes
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These are the notes for the students of class 10th for biology Chapter 5th Life Processes.
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CHAPTER 5Life Processes
H ow do we tell the difference between what is alive and what is not
alive? If we see a dog running, or a cow chewing cud, or a man
shouting loudly on the street, we know that these are living beings. What
if the dog or the cow or the man were asleep? We would still think that
they were alive, but how did we know that? We see them breathing, and
we know that they are alive. What about plants? How do we know that
they are alive? We see them green, some of us will say. But what about
plants that have leaves of colours other than green? They grow over
time, so we know that they are alive, some will say. In other words, we
tend to think of some sort of movement, either growth-related or not, as
common evidence for being alive. But a plant that is not visibly growing is
still alive, and some animals can breathe without visible movement. So
using visible movement as the defining characteristic of life is not enough.
Movements over very small scales will be invisible to the naked eye –
movements of molecules, for example. Is this invisible molecular
movement necessary for life? If we ask this question to professional
biologists, they will say yes. In fact, viruses do not show any molecular
movement in them (until they infect some cell), and that is partly why
there is a controversy about whether they are truly alive or not.
Why are molecular movements needed for life? We have seen in earlier
classes that living organisms are well-organised structures; they can
have tissues, tissues have cells, cells have smaller components in them,
and so on. Because of the effects of the environment, this organised,
ordered nature of living structures is very likely to keep breaking down
over time. If order breaks down, the organism will no longer be alive. So
living creatures must keep repairing and maintaining their structures.
Since all these structures are made up of molecules, they must move
molecules around all the time.
What are the maintenance processes in living organisms?
Let us explore.
WHATT ARE LIFE PROCESSES?
5.1 WHA
The maintenance functions of living organisms must go on even when
they are not doing anything particular. Even when we are just sitting in
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, class, even if we are just asleep, this maintenance job has to go on.
The processes which together perform this maintenance job are
life processes.
Since these maintenance processes are needed to prevent damage
and break-down, energy is needed for them. This energy comes from
outside the body of the individual organism. So there must be a process
to transfer a source of energy from outside the body of the organism,
which we call food, to the inside, a process we commonly call nutrition.
If the body size of the organisms is to grow, additional raw material will
also be needed from outside. Since life on earth depends on carbon-
based molecules, most of these food sources are also carbon-based.
Depending on the complexity of these carbon sources, different
organisms can then use different kinds of nutritional processes.
The outside sources of energy could be quite varied, since the
environment is not under the control of the individual organism. These
sources of energy, therefore, need to be broken down or built up in the
body, and must be finally converted to a uniform source of energy that
can be used for the various molecular movements needed for
maintaining living structures, as well as to the kind of molecules the
body needs to grow. For this, a series of chemical reactions in the
body are necessary. Oxidising-reducing reactions are some of the most
common chemical means to break-down molecules. For this, many
organisms use oxygen sourced from outside the body. The process
of acquiring oxygen from outside the body, and to use it in the process
of break-down of food sources for cellular needs, is what we call
respiration.
In the case of a single-celled organism, no specific organs for taking
in food, exchange of gases or removal of wastes may be needed because
the entire surface of the organism is in contact with the environment.
But what happens when the body size of the organism increases and
the body design becomes more complex? In multi-cellular organisms,
all the cells may not be in direct contact with the surrounding
environment. Thus, simple diffusion will not meet the requirements of
all the cells.
We have seen previously how, in multi-cellular organisms, various
body parts have specialised in the functions they perform. We are familiar
with the idea of these specialised tissues, and with their organisation in
the body of the organism. It is therefore not surprising that the uptake
of food and of oxygen will also be the function of specialised tissues.
However, this poses a problem, since the food and oxygen are now taken
up at one place in the body of the organisms, while all parts of the body
need them. This situation creates a need for a transportation system for
carrying food and oxygen from one place to another in the body.
When chemical reactions use the carbon source and the oxygen for
energy generation, they create by-products that are not only useless
for the cells of the body, but could even be harmful. These waste by-
products are therefore needed to be removed from the body and discarded
outside by a process called excretion. Again, if the basic rules for body
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, 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 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.
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