Class 7 Respiration in Organisms

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Respiration in Organisms

What is Respiration?

Respiration is a fundamental process by which energy is released/obtained by the breakdown of digested food. Respiration occurs in all the living cells. The process of respiration involves taking in oxygen (of air) into the cells, using it for releasing energy by burning food, and then eliminating the waste products (carbon dioxide and water) from the body. Most living things need oxygen to obtain energy from food. This oxygen reacts with the food (like glucose) present in the body cells and burns them slowly to release energy. This energy is used by the living things. The process of respiration can be written in the form of a word equation as follows:


During respiration, the energy-rich foodstuff such as glucose and fructose (called respiratory substrates) are changed to water and carbon dioxide, accompanied by the release of usable energy (ATP or adenosine

triphosphate).  In fact, respiration is a kind of slow-burning (or slow combustion) of food at ordinary temperature to produce energy. During Respiration, oxygen is taken in and carbon dioxide is given out. Thus, the process of
respiration involves the exchange of gases: Oxygen and Carbon dioxide. The process of respiration is the reverse of photosynthesis. This is because, photosynthesis is the making of food (like glucose) by absorbing sunlight energy, whereas respiration is the breaking down of food (like glucose) to release energy.

There are two main parts in the process of respiration :
• Breathing (taking in oxygen from air and releasing carbon dioxide).
• Using oxygen in the cells of the organism for releasing energy from food (like glucose)
The air which we ‘breathe in’ is transported to all the parts of the body and ultimately to each cell of the body. In the cells, oxygen (or air) brings about the breakdown of glucose (food). Since the process of respiration releases energy from food, takes place inside the cells of the body, it is also called cellular respiration. The process of cellular respiration is common to all the living organisms (humans, other animals as well as plants). It takes place in all the cells of an organism.

What is Aerobic and Anaerobic Respiration? 

Respiration usually takes place in the presence of oxygen. Respiration can, however, also take place in the absence of oxygen, though it is very rare. Based on whether oxygen is used up or not, there are two types of respiration: Aerobic respiration and anaerobic respiration. These two types of respiration are discussed below:
Aerobic respiration: Breakdown of food (glucose) into carbon dioxide and water to release energy using oxygen
is called aerobic respiration. It is called aerobic respiration because it uses ‘air’ which contains oxygen (aerobic means with air). In aerobic respiration, the glucose food is completely broken down into carbon dioxide and water with the use of oxygen, to release energy. It can be represented by the word equation as follows:


The energy released during aerobic respiration is used by the organisms. Most of the living organisms carry out aerobic respiration (by using oxygen of air), and such organisms are called aerobes. For example, humans, dogs,

cats, lions, elephants, cows, buffaloes, goats, deer, birds, Lizards, snakes, earthworms, frogs, fish and insects (such as cockroach, grasshopper, house flies, mosquitoes. Humans and most of the plants carry out aerobic respiration by using oxygen of air (to obtain energy). Aerobic respiration produces much more energy because the complete breakdown of glucose (food) occurs during aerobic respiration by the use of oxygen.

Anaerobic respiration:

Some organisms like yeast and some bacteria do not require oxygen during their respiration.  Energy through anaerobic respiration Breakdown of food (glucose) into alcohol and carbon dioxide with the release of energy without the use of oxygen is called anaerobic respiration. It is called anaerobic respiration because it takes place without air which contains oxygen (‘anaerobic’ means ‘without air’). The microscopic organisms like yeast (and certain bacteria) obtain energy by anaerobic respiration. In anaerobic respiration, the microorganisms like yeast break down glucose (food) in the absence of oxygen to form alcohol and carbon dioxide and release energy. The breaking down of glucose (food) during anaerobic respiration carried out by yeast can be represented by writing a word equation as follows :


The organisms which obtain energy by the process of anaerobic respiration (without using oxygen) are called anaerobes. Thus, yeast is an anaerobe. Hence, yeast can survive in the absence of oxygen.

Similarities between aerobic and anaerobic respiration.

What are differences between Aerobic and Anaerobic respiration?



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 Summative Assessment – II