Respiration in Organisms | Most IMP Bits for NMMS 2024-25 from Class 7 Science
Why do we Respire?
All living organisms are made up of small microscopic units called cells.
The process of breakdown of food in the cell with the release of energy is called cellular respiration.
Cellular respiration takes place in the cells of all organisms. Cellular respiration takes place in a cell organelle called mitochondria.
The process of respiration could be shown as follows:
Glucose + oxygen
The breakdown of glucose food occurs with the use of oxygen it is called aerobic respiration. All living organisms like birds, lizards, snakes, earthworms, insects, and most plants carry out this respiration.
Aerobic Respiration in Animals
Glucose + Oxygen
C6H12O6 + 6O2 +
The breakdown of glucose food occurs without the use of oxygen it is called anaerobic respiration.
Anaerobic Respiration in Yeast
Glucose
C6H12O6
| Aerobic Respiration | Anaerobic Respiration |
| This kind of respiration takes place in the presence of oxygen. | This type of respiration happens in the cells in the absence of oxygen. |
| It leads to the release of a high amount of energy in living organisms. | It results in a low amount of energy. |
| Human beings and many other animals undergo aerobic respiration. | Yeast and sometimes human beings undergo anaerobic respiration. |
| Carbon dioxide and water are also in aerobic respiration. | Animal muscle cells release lactic acid and Yeasts release ethanol and carbon dioxide in anaerobic respiration. |
Breathing
Breathing: It is the process in which air rich in oxygen is taken inside and air rich in CO2 is given out, with the help of respiratory organs.
Inhalation: Taking air rich in oxygen into our body is called inhalation.
Exhalation: Giving out air rich in carbon dioxide from our body to the external environment is called exhalation.
Breathing Rate: The number of times a person breathes in a minute is termed as breathing rate.
An adult human being can inhale and exhale 15-18 times in a minute. It is the average breathing rate of an adult human being.
During heavy exercise, the breathing rate can increase to 25 times per minute. Because of this, food gets broken down at a faster rate and thus makes us feel hungry.
The mountaineers carry oxygen cylinders with them for breathing because at high altitudes the amount of air available to a person for breathing is much less than at ground level.
How do we Breathe?
The mechanism of breathing can be understood by the following points:
- Normally, we take in air through our nostrils. When we inhale air, it passes through our nostrils into the nasal cavity.
- From the nasal cavity, the air reaches our lungs through the windpipe.
- Lungs are present in the chest cavity. This cavity is surrounded by ribs on the sides.
- A large, muscular sheet called a diaphragm forms the floor of the chest cavity.
Human respiratory system
When we inhale air, it passes through our nostrils into the nasal cavity. From the nasal cavity, the air reaches our lungs through the windpipe.
Lungs are present in the chest cavity. This cavity is surrounded by ribs on the sides.
A large, muscular sheet called a diaphragm forms the floor of the chest cavity.
Breathing involves the movement of the diaphragm and the rib cage.
During inhalation, ribs move up and outwards and the diaphragm moves down. This movement increases space in our chest cavity and air rushes into the lungs. The lungs get filled with air. The muscles between the ribs contract causing the rib cage to move upward and outward.
During exhalation, ribs move down and inwards, while the diaphragm moves up to its former position. This reduces the size of the chest cavity and the air is pushed out of the lungs. As the chest cavity becomes smaller air is pushed out from the lungs. Take a deep breath. Keep your palm on the abdomen, and feel the movement of the abdomen.
Sneeze
- As we inhale the air present in the surroundings sometimes various unwanted elements such as smoke and dust are also included in it.
- However, they get stuck in the hair in our nostrils but some of them can get through the nasal cavity.
- They thus irritate the nasal cavity which makes us sneeze.
- This helps in getting rid of unwanted particles out of the nasal cavity.
What do we Breathe Out?
| Inhaled air | Exhaled air | |
| Oxygen | Contains 21% oxygen (more oxygen than exhaled air) | Contain 16% oxygen (less oxygen than inhaled air) |
| Carbon dioxide | Contain 0.03% carbon dioxide (less carbon dioxide than exhaled air) | Contains about 4% carbon dioxide (more carbon dioxide than inhaled air) |
| Water vapour | Contain less water vapour | Contain more water vapour |
Effect of exhaled air on lime water
Model to show the mechanism of breathing
Breathing in other Animals
Breathing in cockroach:
- Many insects like Cockroaches have small openings called spiracles present on the sides of their bodies.
- Also, they have an air tube-like structure called the trachea that allows the exchange of gases in these insects.
- The air enters the body through the spiracles and diffuses in the cells via the trachea.
- Similarly, the air from the cells enters the trachea and moves out of the body through spiracles.
Breathing in earthworms:
- Earthworms have soft, slimming, and moist skin.
- Hence the gases can easily pass in and out of the earthworm through its skin.
Breathing in Frog:
A frog-like human possesses a pair of lungs but when they are in the water, they breathe through their moist and slippery skin. When they are on land they breathe through their nostrils and a pair of lungs.
Do Plants also Respire?
All the parts of the plants can independently respire that is they can take in the carbon dioxide and release oxygen on their own.
The leaves of the plants have stomata present upon them which are small pore-like structures. They allow gas exchange in leaves.
The woody stems of the plants also respire. This is because of the presence of special tissue called Lenticels. The cells of this tissue have large intercellular spaces. They exist as dead cells on woody plants and roots and allow the exchange of gases. The bark of trees although impermeable to gases hence these tissues serves an important purpose of respiration in the stems. As the name suggests, lenticels have a lens-like shape.
The roots of the plants have hair-like structures on them. Hence they can absorb the air present in the soil.
- Plant roots have a large number of tiny hairs on them which are called root hairs.
- Oxygen from the air present in soil particles diffuses into root hair and reaches the cells of the root where it is utilized for respiration.
Breathing under Water
- Animals that live underwater have special respiratory organs called gills.
- They are a comb-like structure present on the skin of these animals.
- Gills allow the exchange of gases between animals and the water easily.
Amphibians: Some animals called amphibians can breathe on land by lungs and through moist skin underwater. For example frogs and toads.
Fishes are aquatic animals that live in water. These have a special organ for breathing called gills. The oxygen dissolved in water enters through the gills.
Dolphins and Whales: Sea animals like dolphins and whales live in water but unlike fishes, they do not possess gills for respiration. These possess nostrils which are called blowholes.
Humans cannot survive underwater because they do not possess any gills to make use of oxygen dissolved in water for breathing. When we go underwater we have to take oxygen gas cylinders for breathing.
