Before starting with Class 7 Science Chapter 6 i.e. ‘Respiration in Organisms’, I am hoping that you have completed Chapter 5 of the 7th class. If not, then you can go through its Notes and NCERT Exercise Solutions whose links have been provided below. ⤵️
Table of Content
Introduction
Sometimes we confuse the term respiration with breathing. But actually, these two terminologies are different from each other.
Breathing simply is the inhalation (taking in) of air or oxygen and exhalation (giving out) of air or carbon dioxide.
Whereas, respiration is the breakdown of food or glucose with the help of oxygen to gain energy.
Why do we respire?
In the first chapter, we learnt that the ‘cells’ being the structural and fundamental unit(s) of an organism.
Each living cell performs various functions i.e. nutrition, respiration, transport, excretion, reproduction, etc. and to perform these functions our cells need energy, which they acquire from the food via respiration.
All living organisms respire to fulfil their energy needs.
When we breathe in we take in oxygen and then this oxygen reaches to our organs and then to all our cells.
The process of breakdown of food in the cell with the release of energy is called cellular respiration and it takes place in the cells of all living organisms.
In the cells, the breakdown of glucose into carbon dioxide, water and energy in the presence of oxygen is called aerobic respiration.
The breakdown of glucose in the absence of oxygen is called anaerobic respiration. There are some organisms like yeast, etc. that undergo this kind of respiration and they are called anaerobes. In the absence of oxygen, the glucose is broken down into water, carbon dioxide and alcohol. This process is also called fermentation.
Did you know?
Yeast are single-celled organisms and they are used in the fermentation industry to make wine and alcohol.
Our muscles can also respire anaerobically but for a short time period. They respire anaerobically when there is a temporary deficiency of oxygen mainly during running or heavy workouts, because during these tasks our demand for energy is quite high and the available oxygen in our blood isn’t able to meet this increased demand.
Have you ever gotten any muscle cramps after doing a heavy workout or running?
Well, this is due to the accumulation of lactic acid in our muscles. Our muscles undergo anaerobic respiration and produce lactic acid as a byproduct.
You can get relief from the cramps by taking a hot shower or by getting a massage because these practices increase the blood flow in your muscles, more blood flow means more oxygen being supplied to the muscles for the lactic acid to completely break down into water and carbon dioxide.
Breathing
It means taking in air rich in oxygen (inhalation) and giving out air rich in carbon dioxide (exhalation) with the help of respiratory organs.
Breathing is a continuous process that goes on all the time and throughout the life of an organism.
The number of times a person breathes in a minute is called the breathing rate.
During breathing the inhalation and exhalation takes place alternately. A breath means one inhalation and one exhalation.
Whenever we need extra energy like while running, playing, working out, etc. we breathe faster so that more oxygen can be supplied to our cells and as a result, the rate of respiration can be sped up.
On average a normal human being breathes 15-18 times per minute but this breathing rate can also be as high as 25 times per minute while we are running. During running and working out not only do we breathe faster but we also take deep breaths to inhale more oxygen.
When we feel drowsy or asleep our breathing rate drops down.
How do we breathe?
Our breathing mechanism is quite fascinating.
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 to our lungs through windpipe. Then from lungs it reaches to our bloodstream.
Lungs are present in our chest cavity which is surrounded by the rib cage. A large muscular sheet known as diaphragm is present at the base of the chest cavity.
Breathing involves the movement of the rib cage and the diaphragm.
DURING INHALATION:
- Ribs move up and outwards
- The diaphragm moves down.
These movements increase space in our chest cavity and air rushes into our lungs. The lungs get filled with air.
DURING EXHALATION:
- Ribs move down and inwards.
- The diaphragm moves up to its original position.
This reduces the size of the chest cavity and air pushed out of the lungs.
Activity to understand the working of the diaphragm and lungs
- Take a wide plastic bottle and remove its bottom.
- Get a Y-shaped plastic or glass tube.
- Make a hole in the lid/cap of the bottle so that the tube may pass through it, fix the tube in the cap of the bottle and then cap it tightly.
- At the forked end of the tube fix two deflated balloons.
- To the open base of the bottle tie a thin rubber sheet with a rubber band.
- To understand the expansion/inhalation: pull the rubber sheet from the base downwards and watch the balloons as they inflate.
- To understand the contraction/exhalation: release the rubber sheet slowly to its original resting position and watch the balloons as they deflate.
What do we breathe out?
We all know that we breathe out carbon dioxide mainly, along with other non-usable gases (nitrogen, arogon, etc.), water vapors, etc.
So, to test the presence of carbon dioxide in the air we exhale we are going to perform a simple activity:
- Take a test tube or glass bottle and fill it half with lime water.
- Take a straw and dip it in the test tube.
- Now breathe in with your nose and breathe out slowly with your mouth through the straw that is dipped in the lime water.
- Repeat this process 4-5 times and observe the change in the colour of lime water.
The lime water turns turbid or milky with the content of our exhalation.
The percentage of oxygen and carbon dioxide in the air we inhale and exhale is:
INHALED AIR:
- Oxygen: 21%
- Carbon dioxide: 0.04%
EXHALED AIR:
- Oxygen: 16.4%
- Carbon dioxide: 4.4%
Did you know?
Lung capacity or total lung capacity (TLC) is the volume of air in the lungs upon the maximum effort of inspiration/inhalation. Among healthy adults, the average lung capacity is about 6 litres.
Breathing in Other Animals
Not all animals have lungs to breathe with. Different animals have different organs and methods of breathing.
Animals like tigers, lions, cows, deer, elephants, frogs, snakes, birds, etc. have lungs in their cavities just like us.
Let’s find out the different modes of breathing in various organisms:
1. Cockroach and Other Insects
It is an insect and almost all insects have a very similar mode of breathing.
They have small openings on the sides of their body called spiracles. And along with the spiracles they have a complex network of air tubes called tracheae for the exchange of gases.
Oxygen-rich air rushes into the body via these spiracles into the tracheal tubes, then it diffuses into the body tissues and reaches every single cell of the body.
Similarly, carbon dioxide-rich air from the cells goes into the tracheal tubes and moves out through spiracles.
Tracheas are only found in insects, not in any other group of animals.
2. Earthworm
In the 6th chapter of class 6, we have already learned that earthworms live in soil and breathe through the skin.
The skin of an earthworm is moist and slimy in touch.
Gases can easily pass through their skin.
Did you know?
Frogs are amphibians means they can live both on Earth and underwater. On the surface, they breathe with their lungs and underwater they breathe through their skin which is moist and slippery.
Breathing under Water
In the 6th chapter of class 6, we have already learned about the special organs that fishes have to breathe underwater i.e. gills.
Gills are the projection of the skin. Gills are well supplied with blood vessels for the exchange of gases.
Did You Know?
Dolphins and whales are not fish but they are mammals and they don’t have gills to breathe underwater but instead have a blowhole present at the top of their head through which they breathe.
Respiration in Plants
Just like any other living being, plants also need energy and for that they also respire.
Unlike photosynthesis, the process of respiration takes place throughout the day.
Plants have pores on their surface called stomata and through these pores the exchange of gases takes place. Plants take in oxygen for respiration and give out carbon dioxide. Then they undergo cellular respiration.
Plant roots take up air from the air spaces present between the soil particles
As plant roots depend mainly on the oxygen present in the soil. So, when we overwater the plants this oxygen is replaced by the water and the plant can die.
Conclusion
The quality of air is degrading day by day with new pollutants being released in the air every single day. Common air pollutants other than harmful gases are smoke, smog, dust, pollens, etc. Our nasal hairs act as a filter for these pollutants, they trap these particles not letting them go further in our respiratory system. Because these particles can cause various health issues like sneezing, hay fever, allergic reactions, asthma etc.
Sneezing is our normal body response meant to expel these particles out of our respiratory system. We should always cover our nostrils while sneezing to prevent contaminating others with these pollutants.
Indian Yogic practices like ‘Anulom Vilom, Kapalbhati, Bhastrika‘, etc. can increase the capacity of the lungs to take in more air and keep us healthy.
Credits & References
- Class 7th Science NCERT Textbook
- https://www.canva.com/
- Image by alba1970 from Pixabay
- Image by freepik
- Image by vectorpouch on Freepik
- Image by brgfx on Freepik
- https://www.britannica.com/animal/insect/Circulatory-system#/media/1/289001/47792
- https://www.britannica.com/animal/insect/Circulatory-system
- Image by brgfx on Freepik
- Image by brgfx on Freepik
- Image by brgfx on Freepik
- Image by PublicDomainImages from Pixabay
- Image by Natfot from Pixabay
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