Page 84 - NCERT Science Class 10 English Medium

5
CHAPTER

Life Processes

ow do we tell the difference between what is alive and what is not
Halive? 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.

5.1
5.1 WHAWHAT ARE LIFE PROCESSES?T ARE LIFE PROCESSES?
WHAT ARE LIFE PROCESSES?
5.1 WHAT ARE LIFE PROCESSES?T ARE LIFE PROCESSES?
5.1 WHA
5.1
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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