Class 7 Biology: Respiration in Organisms
WHY DO WE RESPIRE?
1. What are organisms made of?
Answer: Organisms are made of small microscopic units called cells.
2. What is a cell?
Answer: A cell is the smallest structural and functional unit of an organism.
3. What functions are performed by cells?
Answer: Cells perform functions like nutrition, transport, excretion, and reproduction.
4. Why do cells need energy?
Answer: Cells need energy to perform their functions like digestion, transport, and movement.
5. From where do we get energy?
Answer: We get energy from the food we eat. The energy is released during respiration.
6. What is respiration?
Answer: Respiration is the process by which cells break down food to release energy.
7. Why do we breathe in oxygen?
Answer: We breathe in oxygen because it helps in the breakdown of food in the cells to release energy.
8. What is cellular respiration?
Answer: The breakdown of food in the cells to release energy is called cellular respiration.
9. What is aerobic respiration?
Answer: When food (glucose) is broken down using oxygen, it is called aerobic respiration.
10. Write the equation for aerobic respiration.
Answer:
Glucose + Oxygen → Carbon dioxide + Water + Energy
Glucose + Oxygen → Carbon dioxide + Water + Energy
11. What is anaerobic respiration?
Answer: When food is broken down without using oxygen, it is called anaerobic respiration.
12. Name one organism that respires anaerobically.
Answer: Yeast respires anaerobically.
13. What is produced during anaerobic respiration in yeast?
Answer: In yeast, anaerobic respiration produces alcohol, carbon dioxide, and energy.
14. Where is yeast used? Why?
Answer: Yeast is used to make wine and beer because it produces alcohol during anaerobic respiration.
15. Can our muscle cells do anaerobic respiration? explain why?
Answer: Yes, Our muscle cells can also do anaerobic respiration, but only for a short time when there is temporary deficiency of oxygen. During heavy activities like fast running, cycling, walking for many hours, or lifting heavy weights, the body needs more energy. But oxygen supply is limited. So, muscle cells use anaerobic respiration to produce energy without oxygen.
16. When does anaerobic respiration happen in muscles?
Answer: It happens during heavy exercise like running, cycling, or weight lifting when oxygen is less.
17. What are the products of anaerobic respiration in human muscles?
Answer: In muscles, anaerobic respiration produces lactic acid and energy.
Why do we get muscle cramps after heavy exercise?
Answer: We get muscle cramps because muscle cells respire anaerobically during heavy exercise, which produces lactic acid. The buildup of lactic acid causes cramps.
How can we get relief from muscle cramps?
Answer: We can get relief by taking a hot water bath or a massage.
How does a hot water bath or massage help in muscle cramps after heavy exercise?
Answer: A hot water bath or massage improves blood circulation, which increases the oxygen supply to the muscles. When more oxygen reaches the muscles, the lactic acid breaks down completely into carbon dioxide and water, and the cramps go away.
what produce more energy anaerobic or aerobic respiration?
Answer: Aerobic respiration produces more energy than anaerobic respiration.
List the similarities and differences between aerobic and anaerobic respiration.
✅ Similarities:
| Feature | Description |
|---|---|
| 1. Energy Production | Both release energy from food (glucose). |
| 2. Takes place in cells | Both occur inside the cells of organisms. |
🔄 Differences:
| Feature | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Oxygen | Uses oxygen | Does not use oxygen |
| Products | Carbon dioxide, water, and energy | Lactic acid (in muscles) or alcohol + CO₂ (yeast) |
| Energy released | More energy | Less energy |
| Example organisms | Humans, animals, plants | Yeast, some bacteria, human muscles (temporarily) |
BREATHING
What is breathing?
Answer:
Breathing is the process of taking in air rich in oxygen (called inhalation) and giving out air rich in carbon dioxide (called exhalation) with the help of respiratory organs.
Breathing is the process of taking in air rich in oxygen (called inhalation) and giving out air rich in carbon dioxide (called exhalation) with the help of respiratory organs.
What are inhalation and exhalation?
Answer:
Inhalation: Taking in oxygen-rich air into the body.
Exhalation: Releasing carbon dioxide-rich air from the body.
Inhalation: Taking in oxygen-rich air into the body.
Exhalation: Releasing carbon dioxide-rich air from the body.
What is breathing rate?
Answer:
The number of times a person breathes in one minute is called the breathing rate.
The number of times a person breathes in one minute is called the breathing rate.
What is the average breathing rate of an adult at rest?
Answer:
An adult breathes 15 to 18 times per minute at rest.
An adult breathes 15 to 18 times per minute at rest.
What happens to our breathing rate during heavy exercise?
Answer:
During heavy exercise, the breathing rate increases up to 25 times per minute, and we breathe more deeply to take in more oxygen.
During heavy exercise, the breathing rate increases up to 25 times per minute, and we breathe more deeply to take in more oxygen.
Why do we breathe faster after running or exercise?
Answer:
We breathe faster because the body needs more energy, so it takes in more oxygen to break down food quickly and release more energy.
We breathe faster because the body needs more energy, so it takes in more oxygen to break down food quickly and release more energy.
What did you feel when you closed your nose and mouth tightly?
Answer:
After some time, it becomes difficult to hold the breath, and we feel the need to breathe heavily to take in oxygen.
After some time, it becomes difficult to hold the breath, and we feel the need to breathe heavily to take in oxygen.
Why do we feel hungry after physical activity?
Answer:
During physical activity, our body uses more energy, so after the activity, we feel hungry to replace the used-up energy.
During physical activity, our body uses more energy, so after the activity, we feel hungry to replace the used-up energy.
In which activity will the breathing rate be fastest and slowest?
Answer:
Fastest: After running or heavy exercise.
Slowest: While resting or sleeping.
Fastest: After running or heavy exercise.
Slowest: While resting or sleeping.
What happens to the breathing rate when we feel sleepy or drowsy? Why?
Answer:
When we feel sleepy or drowsy, our body becomes relaxed, and the breathing rate becomes slow. This happens because the body is using less energy and doesn't need as much oxygen as during active times.
When we feel sleepy or drowsy, our body becomes relaxed, and the breathing rate becomes slow. This happens because the body is using less energy and doesn't need as much oxygen as during active times.
Why does our body get less oxygen when we feel sleepy?
Answer:
When we feel sleepy, our body and brain start to slow down. We breathe more slowly and shallowly, which means less air goes into our lungs. As a result, less oxygen reaches the blood and the brain. This is why the body gets less oxygen when we are sleepy.
When we feel sleepy, our body and brain start to slow down. We breathe more slowly and shallowly, which means less air goes into our lungs. As a result, less oxygen reaches the blood and the brain. This is why the body gets less oxygen when we are sleepy.
Why do we yawn when we are sleepy?
Answer:
We yawn because the body gets less oxygen when we feel sleepy, as our body and brain slow down. Yawning helps to take in more oxygen quickly and keeps us alert.
We yawn because the body gets less oxygen when we feel sleepy, as our body and brain slow down. Yawning helps to take in more oxygen quickly and keeps us alert.
Why does an athlete breathe faster and deeper than usual after finishing the race?
Answer:
After a race, the athlete's body needs more energy to recover. So, to produce more energy, the athlete breathes faster and deeper. This brings in more oxygen, which helps in the complete breakdown of food in the cells and releases extra energy.
After a race, the athlete's body needs more energy to recover. So, to produce more energy, the athlete breathes faster and deeper. This brings in more oxygen, which helps in the complete breakdown of food in the cells and releases extra energy.
HOW DO WE BREATHE
How does the air reach our lungs during breathing?
Answer:
Air enters through the nostrils, passes into the nasal cavity, then goes through the windpipe, and finally reaches the lungs.
Air enters through the nostrils, passes into the nasal cavity, then goes through the windpipe, and finally reaches the lungs.
What are lungs?
Answer:
Lungs are spongy, balloon-like organs in our chest that help us breathe.
Lungs are spongy, balloon-like organs in our chest that help us breathe.
Where are the lungs located?
Answer:
The lungs are located inside the chest cavity, which is surrounded by ribs and has a muscular sheet called the diaphragm at the bottom.
The lungs are located inside the chest cavity, which is surrounded by ribs and has a muscular sheet called the diaphragm at the bottom.
What is the diaphragm?
Answer:
The diaphragm is a large muscular sheet that forms the floor of the chest cavity and helps in breathing.
The diaphragm is a large muscular sheet that forms the floor of the chest cavity and helps in breathing.
What happens during inhalation (breathing in)?
Answer:
When we breathe in, the ribs move up and outwards, while the diaphragm moves down.
This increases the space in the chest cavity, and air rushes into the lungs.
When we breathe in, the ribs move up and outwards, while the diaphragm moves down.
This increases the space in the chest cavity, and air rushes into the lungs.
What happens during exhalation (breathing out)?
Answer:
When we breathe out, the ribs move down and inwards, while the diaphragm moves up.
This decreases the space in the chest cavity, and air is pushed out of the lungs.
When we breathe out, the ribs move down and inwards, while the diaphragm moves up.
This decreases the space in the chest cavity, and air is pushed out of the lungs.
What is the role of ribs and diaphragm in breathing?
Answer:
The ribs and diaphragm help in changing the size of the chest cavity to allow air to move in and out of the lungs.
The ribs and diaphragm help in changing the size of the chest cavity to allow air to move in and out of the lungs.
What is the effect of smoking on our lungs?
Answer:
Smoking damages the lungs and is also linked to cancer, so it must be avoided.
Smoking damages the lungs and is also linked to cancer, so it must be avoided.
What is sneezing? Why does it happen?
Answer:
Sneezing is a way the body removes unwanted particles from the nose. It happens when dust or other particles irritate the nasal lining.
Sneezing is a way the body removes unwanted particles from the nose. It happens when dust or other particles irritate the nasal lining.
What happens when we inhale dusty or polluted air?
Answer:
Dust, smoke, or pollen in the air gets trapped by tiny hairs in the nasal cavity. If they enter deeper, they can irritate the lining and cause sneezing.
Dust, smoke, or pollen in the air gets trapped by tiny hairs in the nasal cavity. If they enter deeper, they can irritate the lining and cause sneezing.
Why should we cover our nose while sneezing?
Answer:
To stop foreign particles from spreading and being inhaled by others, we must cover our nose when sneezing.
To stop foreign particles from spreading and being inhaled by others, we must cover our nose when sneezing.
WHAT DO WE BREATHE OUT?
What happens when you blow air into lime water using a straw? Why?
Answer:
Lime water turns milky when we blow air into it.
Because the air we blow out contains carbon dioxide, which reacts with lime water and makes it look milky.
Lime water turns milky when we blow air into it.
Because the air we blow out contains carbon dioxide, which reacts with lime water and makes it look milky.
Do we exhale only carbon dioxide?
Answer:
No, we exhale a mixture of gases, not just carbon dioxide. It also includes some oxygen, water vapour, and other gases like nitrogen.
No, we exhale a mixture of gases, not just carbon dioxide. It also includes some oxygen, water vapour, and other gases like nitrogen.
What do we mainly inhale and exhale?
Answer:
We inhale a mixture of gases — mostly nitrogen (78%), oxygen (21%), and a little carbon dioxide and water vapour.
We exhale less oxygen, more carbon dioxide, water vapour, and still a lot of nitrogen.
We inhale a mixture of gases — mostly nitrogen (78%), oxygen (21%), and a little carbon dioxide and water vapour.
We exhale less oxygen, more carbon dioxide, water vapour, and still a lot of nitrogen.
What is the percentage of oxygen in inhaled and exhaled air?
Answer:
Inhaled air has about 21% oxygen.
Exhaled air has about 16.4% oxygen.
Inhaled air has about 21% oxygen.
Exhaled air has about 16.4% oxygen.
What is the percentage of carbon dioxide in inhaled and exhaled air?
Answer:
Inhaled air has about 0.04% carbon dioxide.
Exhaled air has about 4.4% carbon dioxide.
Inhaled air has about 0.04% carbon dioxide.
Exhaled air has about 4.4% carbon dioxide.
Take three test-tubes. Fill each with water. Label them A, B, and C.
Put a snail in test-tube A
Put a water plant in test-tube B
Put both snail and plant in test-tube C
Which test-tube would have the highest concentration of carbon dioxide (CO₂)?
Put a snail in test-tube A
Put a water plant in test-tube B
Put both snail and plant in test-tube C
Which test-tube would have the highest concentration of carbon dioxide (CO₂)?
Answer:
Test-tube A will have the highest concentration of carbon dioxide.
Explanation:
The snail in test-tube A respires and gives out carbon dioxide.
There is no plant in A to use up the CO₂ exhaled by the snail.
In test-tube B, the plant uses CO₂ for photosynthesis, so CO₂ is low.
In test-tube C, the snail gives CO₂ and the plant uses it, so the CO₂ stays balanced.
Test-tube A will have the highest concentration of carbon dioxide.
Explanation:
The snail in test-tube A respires and gives out carbon dioxide.
There is no plant in A to use up the CO₂ exhaled by the snail.
In test-tube B, the plant uses CO₂ for photosynthesis, so CO₂ is low.
In test-tube C, the snail gives CO₂ and the plant uses it, so the CO₂ stays balanced.
BREATHING IN OTHER ANIMALS
🌬️ Breathing Organs in Different Organisms
| Organism | Breathing Organ/Method | Extra Information |
|---|---|---|
| Human | Lungs | Located in chest cavity |
| Elephant | Lungs | Same as humans |
| Lion | Lungs | Same as humans |
| Cow | Lungs | Same as humans |
| Goat | Lungs | Same as humans |
| Bird | Lungs | Birds also have air sacs to help in breathing |
| Frog | Lungs and moist skin | Uses lungs on land and skin in water |
| Lizard | Lungs | Reptile – breathes through lungs |
| Snake | Lungs | Has one functional lung |
| Cockroach | Spiracles and Tracheae (air tubes) | Air enters spiracles and travels through tracheal tubes |
| Other Insects | Spiracles and Tracheae | Similar to cockroach |
| Earthworm | Moist Skin | Gases pass through skin directly; needs moisture |
How does a cockroach breathe?
Answer: A cockroach breathes through tiny openings on its body called spiracles. Air enters through these and passes into air tubes called tracheae, which carry oxygen to all body parts and remove carbon dioxide.
How does an earthworm breathe?
Answer: An earthworm breathes through its moist and slimy skin. Oxygen passes through the skin into the body, and carbon dioxide comes out the same way.
How does a frog breathe?
Answer: A frog breathes through its lungs as well as its moist skin. It uses lungs on land and can also absorb oxygen through its skin, especially in water.
BREATHING UNDER WATER
How do fish breathe?
Answer: Fish breathe through gills, which are special organs that take in oxygen dissolved in water. Gills have many blood vessels that help in the exchange of gases. Oxygen from water enters the blood, and carbon dioxide is removed.
What are gills?
Answer: Gills are special organs found in fish and some other water animals. They help the animal take in oxygen from water and remove carbon dioxide.
DO PLANTS ALSO RESPIRE?
1. Do plants breathe like animals?
✅ Answer: Yes, plants also breathe. They take in oxygen and give out carbon dioxide.
2. How do leaves help in plant breathing?
✅ Answer: Leaves have tiny pores called stomata. They help in the exchange of gases.
3. Do roots also need oxygen?
✅ Answer: Yes, roots also need oxygen to make energy.
4. How do roots get oxygen if they are underground?
✅ Answer: Roots take oxygen from the air present between the soil particles.
5. What happens if we give too much water to a plant?
✅ Answer: Too much water fills air spaces in the soil. Roots can't get oxygen and the plant may get damaged.
Did you know? For us oxygen is essential, but for those organisms which do not use it, oxygen is toxic. In fact, for humans and other organisms it may be dangerous to breathe pure oxygen for long.
🌬️ Breathing Rate (at rest):
| Group | Breathing Rate (breaths per minute) |
|---|---|
| 👨🦰 Adult Male | 12 – 16 breaths/min |
| 👩 Adult Female | 16 – 20 breaths/min |
| 🧒 Children | 20 – 30 breaths/min |
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