Respiration Class 7 Science — Revision Notes
Every living cell breaks down food to release the energy it needs, and that process is respiration. This chapter separates breathing from respiration, foll
TL;DR: Every living cell breaks down food to release the energy it needs, and that process is respiration. This chapter separates breathing from respiration,…
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Every living cell breaks down food to release the energy it needs, and that process is respiration. This chapter separates breathing from respiration, foll
Key Points to Remember
- Respiration is the breakdown of food inside the cells of the body to release energy; it goes on in every living cell, all the time
- Breathing is only one part of it — taking in oxygen-rich air and giving out carbon dioxide-rich air. Breathing is not the same as respiration
- One breath means one inhalation plus one exhalation, and the breathing rate is the number of breaths taken in a minute
- An adult at rest breathes about 15 to 18 times a minute; during heavy exercise this can rise to about 25 times a minute
- Aerobic respiration uses oxygen; organisms that respire this way are called aerobes
- Anaerobic respiration takes place without oxygen; yeast is the standard example of an anaerobe, and it is used to make alcohol and wine
- During heavy exercise the muscles do not get enough oxygen, so glucose breaks down into lactic acid, and the build-up causes muscle cramps
- A hot water bath or a massage relieves cramps because it improves blood circulation, so more oxygen reaches the muscle and the lactic acid is broken down
- In inhalation the ribs move up and outwards and the diaphragm moves down, making the chest cavity larger; in exhalation both move back and it becomes smaller
- Exhaled air turns lime water milky, which is the test showing it contains more carbon dioxide
- Cockroaches breathe through small openings called spiracles and a network of air tubes called tracheae; earthworms breathe through their moist skin
- Fish take in oxygen dissolved in water using gills; frogs can breathe through their skin as well as their lungs
- Plants respire too — leaves exchange gases through stomata, and roots take in air from the spaces between soil particles
Important Word Equations
- Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy
- Anaerobic respiration in yeast: Glucose → Alcohol + Carbon dioxide + Energy
- In our muscles when oxygen runs short: Glucose → Lactic acid + Energy
- Note that anaerobic respiration releases much less energy than aerobic respiration from the same amount of glucose
Key Terms
- Respiration: The breakdown of food inside the cells of the body to release energy
- Breathing: Taking in oxygen-rich air into the body and giving out air rich in carbon dioxide
- Breathing rate: The number of breaths taken in one minute; about 15 to 18 for an adult at rest
- Aerobic respiration: Respiration that takes place using oxygen; organisms doing this are called aerobes
- Anaerobic respiration: Respiration that takes place without oxygen, as in yeast, releasing much less energy
- Diaphragm: The sheet of muscle below the chest cavity that moves down during inhalation and up during exhalation
- Spiracles: Small openings on the sides of a cockroach's body through which air enters the tracheae
- Gills: Organs that allow fish to take in oxygen dissolved in water
Frequently Asked Questions
What is the difference between breathing and respiration?
Breathing is the physical act of taking in oxygen-rich air and giving out carbon dioxide-rich air, and it involves the nose, windpipe and lungs. Respiration is the breakdown of food inside the cells to release energy. Breathing supplies the oxygen that respiration uses, so breathing is one step that supports respiration, not the same thing as it
Why do we get muscle cramps after heavy exercise?
During heavy exercise the muscle cells need more energy than the oxygen reaching them can supply. The cells then break down glucose without oxygen, producing lactic acid, and the build-up of lactic acid causes cramps. A hot water bath or a massage improves blood circulation so more oxygen reaches the muscle, the lactic acid is broken down and the cramp is relieved
How do we know that exhaled air contains more carbon dioxide?
Blow exhaled air through lime water using a straw and the lime water turns milky. Lime water turns milky in the presence of carbon dioxide, so the change shows that the air we breathe out is richer in carbon dioxide than the air around us
How do earthworms and fish breathe?
An earthworm breathes through its skin, which feels moist and slimy; gases pass through the moist skin into the blood. A fish takes in water through its mouth and passes it over the gills, which extract the oxygen dissolved in the water. Both are solving the same problem as our lungs do, but in the medium each animal lives in
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