NCERT Book Class 7 Science Chapter 6 Respiration in Organisms

6 Respiration in
Organisms

O
ne day Boojho was eagerly Therefore, all living organisms respire
waiting to meet his to get energy from food. During
grandparents who were coming breathing, we breathe in air. You know
to the town after a year. He was in a real that air contains oxygen. We breathe out
hurry as he wanted to receive them at the air which is rich in carbon dioxide. The
bus-stop. He ran fast and reached the air we breathe in is transported to all
bus-stop in a few minutes. He was parts of the body and ultimately to each
breathing rapidly. His grandmother asked cell. In the cells, oxygen in the air helps
him why he was breathing so fast. Boojho in the breakdown of food. The process
told her that he came running all the way. of breakdown of food in the cell with the
But the question got stuck in his mind. release of energy is called cellular
He wondered why running makes a respiration. Cellular respiration takes
person breathe faster. The answer to place in the cells of all organisms.
Boojho’s question lies in understanding In the cell, the food (glucose) is broken
why we breathe. Breathing is a part of down into carbon dioxide and water using
respiration. Let us learn about respiration. oxygen. When breakdown of glucose
occurs with the use of oxygen it is called
6.1 WHY DO WE RESPIRE? aerobic respiration. Food can also be
In Chapter 2 you learnt that all broken down, without using oxygen. This
organisms are made of small is called anaerobic respiration.
microscopic units called cells. A cell is Breakdown of food releases energy.
the smallest structural and functional
unit of an organism. Each cell of an
organism performs certain functions You should know that there are some
such as nutrition, transport, excretion organisms such as yeast that can survive
and reproduction. To perform these in the absence of air. They are called
functions, the cell needs energy. Even anaerobes. They get energy through
when we are eating, sleeping or reading anaerobic respiration. In the absence of
we require energy. But, where does this oxygen, glucose breaks down into alcohol
energy come from? Can you say why and carbon dioxide, as given below:
your parents insist that you should eat
regularly? The food has stored energy,
which is released during respiration.