Page 84 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

v Cellular respiration is the result of a series of reactions that are controlled by different

enzymes. No enzymes are involved in the process of breathing.
v Based on whether the respiration is taking place in the presence or absence of oxygen,

respiration is classified into two types–aerobic respiration and anaerobic respiration.
v Aerobic respiration refers to the breakdown of glucose completely with the release of
carbon dioxide, water and energy in the presence of oxygen.

C H O + 6O 2  6CO + 6H O + 38 ATP
6
12
6
2
2
Glucose Oxygen Carbon dioxide Water Energy
(food)
v Anaerobic respiration refers to the breakdown of glucose to release energy in the absence
of oxygen. In this type of respiration, less energy is released.

C H O  2C H OH + 2CO + 2ATP
6 12 6 2 5 2
Glucose Ethanol Carbon dioxide Energy

The above reaction shows anaerobic respiration in yeasts. Yeasts convert glucose into
alcohol and hence they are used to make wine and beer. This process is called alcoholic

fermentation.
v Anaerobic respiration in humans occurs during running, cycling, walking, etc. At these times,

inhaled air is unable to fulfil the oxygen requirements of the muscles, so the muscle cells
perform anaerobic respiration forming lactic acid along with the release of less amount of
energy.

C H O  Lactic acid + 2ATP
12
6
6
Glucose Energy
v Lactic acid produces during anarobic repiration while doing heavy exercises causes cramps.
Hot water bath or massage of muscles is very effective to get relief from cramps. These help

in blood circulation due to which oxygen reaches the cells and breaks down lactic acid into
carbon dioxide and water.

v The path of air inside the respiratory system after inhalation from the nose is shown as
follows:
Nostrils  Pharynx  Trachea  Bronchi  Lungs  Bronchioles  Alveoli

(a) Oxygen is inhaled through the nostrils, where the tiny hair filter out dust & other
foreign particles. Also, the air is warmed and humidified by the mucous.

(b) Nasal cavity is divided into two halves by a wall of thin bone called central septum.
(c) Now, the air passes from the trachea (windpipe), which is further divided into smaller

tubes called bronchi (singular- bronchus) for each lung.
(d) Bronchi carry the inhaled air from the trachea to the lungs.

(e) Lungs are a pair of organs of the repiratory system where oxygen is expelled taken in
and carbon dioxide is expelled.

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