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Respiration - Lesson Summary

Human body is made up of cells. Cells perform different functions like growth, excretion, reproduction, etc. A cell needs energy to perform all these functions.
  • The digestive system converts the food we eat into glucose. Blood absorbs glucose and transports it to the cells. In the cells, this glucose is broken down to release energy.
  • Respiratory system helps in taking in oxygen by the body. When we inhale air, oxygen enters the lungs. From the lungs, the oxygen is absorbed by the red blood cells and is supplied to all the cells in the body. This oxygen is utilised in breaking down glucose to release energy in the form of ATP.

Respiration is the process of taking in oxygen, using it in oxidation of glucose, releasing energy and eliminating waste products like carbon dioxide and water in the presence of respiratory enzymes. Respiration is brought about in two steps namely external respiration and internal respiration.

a) External respiration is also called as breathing.
  • It involves inhalation and exhalation. Inhalation is the process of taking in air rich in oxygen.
  • Exhalation is the process of releasing out air rich in carbon dioxide.

b) Internal respiration is also called as cellular respiration.
  • Cellular respiration is a chemical reaction which involves oxidation of food.
  • It is the breakdown of glucose in a cell to release energy.
  • Cellular respiration is a slow process which occurs at body temperature.
  • Cellular respiration is observed only in living cells.
  • Cellular respiration involves release of energy at various steps.
  • The energy released will be stored in the form of ATP molecules.

Chemical reaction of respiration

    C 6H 12O 6 + 6O 2  →  6CO 2 + 6H 2O + Energy

Types of respiration

Respiration can be of two types namely, aerobic respiration or anaerobic respiration.  Aerobic and anaerobic respiration are the processes which involve release of energy by exchange of gases. Both these reactions occur inside the cell.

a) Aerobic respiration is the process of breaking up of glucose into carbon dioxide and water in the presence of oxygen with release of energy. Aerobic respiration takes place in almost all the animals.

b) Anaerobic respiration is the breakdown of glucose in the cell in the absence of oxygen. Glucose is converted into alcohol and carbon dioxide with release of little amount of energy.
  • Anaerobic respiration can also be seen in yeast. The breakdown of glucose in the absence of oxygen in yeast forms alcohol, energy and carbon dioxide. Yeasts and other organisms that respire in the absence of oxygen are also known as anaerobes. As yeast is a unicellular organism that respires anaerobically to yield alcohol, it is used in the production of beer and wine. Yeast is used in beverage industries to produce beer and wine by the process of fermentation. Fermentation is the process of breaking down glucose into alcohol and carbon dioxide releasing little amount of energy. Fermentation is otherwise called as anaerobic respiration.

  • Anaerobic respiration is observed in muscle cells. Accumulation of lactic acid inside the cells leads to muscle cramps. Supply of oxygen will break down lactic acid into carbon dioxide and water. Hot water bath relieves muscles from cramps by converting lactic acid into carbon dioxide and water.

Differences between aerobic and anaerobic respiration               AEROBIC RESPIRATION          ANAEROBIC RESPIRATION Glucose is completely oxidised into carbon dioxide and water. Glucose is incompletely oxidised into alcohol and carbon dioxide. This type of respiration takes place in the oxygen rich environment. This reaction takes place in the insufficiency of lack of oxygen. It takes place in the mitochondria of cellular environment. It takes place in the cytoplasm of the cell. It is harmless to the organisms. It shows side-effects and is toxic to plants.

Respiration in plants
During day time, plants utilise carbon dioxide to perform photosynthesis and release out oxygen. During night, plants respire taking in oxygen and releasing carbon dioxide. Exchange of gases in plants takes place through special structures called the stomata.
  • Stomata are the small structures present in the epidermal cells located on the surface of the leaves. Stomata with its guard cells is called as stomatal apparatus.Opening and closing of stomata is brought about by special structures called as guard cells under the influence of amount of moisture and sunlight.  Gases are just exchanged between the leaves and outside environment through stomata.
  • Roots also respire during which they utilise oxygen stored in the air spaces between the soil particles. Over watering of potted plants should be avoided as water molecules displace the air spaces in the soil. In this case, roots cannot breathe affecting the growth of plants. 

Significance of respiration in plants During respiration, plants convert glucose molecules into carbon dioxide and water with release of energy.
  • This energy released is utilised by the plant to sustain its life.
  • The energy released from food is useful for different processes like growth, excretion, reproduction, nutrition etc. 
  • The carbon dioxide released into the environment is again used by the plant in the process of photosynthesis.


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