NCERT Explained: Class VII Science, Chapter 10 - Respiration in Organisms

Introduction to Respiration in Organisms

Have you ever wondered why we breathe faster after a brisk walk or a high-energy game of football? Why does our body require a constant supply of air, even when we are sleeping? The answer lies in a fundamental biological process called respiration. In Class VII Science, Chapter 10, we delve into the fascinating world of how living organisms—from tiny insects to giant whales and even the plants in your garden—obtain the energy they need to stay alive.

Many people often confuse 'breathing' with 'respiration'. While they are related, they are not the same thing. Breathing is simply the physical act of inhaling and exhaling air. Respiration, on the other hand, is a complex chemical process that happens inside our cells. It is the method by which food (glucose) is broken down with the help of oxygen to release energy. This energy is what powers every single action in our body, from the beating of our heart to the thinking processes in our brain. In this post, we will break down the NCERT curriculum for this chapter into simple, easy-to-understand concepts to help students master the topic of respiration.

Key Concepts Explained

1. Why do we Respire?

Every living organism is made up of tiny microscopic units called cells. A cell is the smallest structural and functional unit of an organism. Each cell performs various functions such as nutrition, transport, excretion, and reproduction. To perform these functions, the cell needs energy. Even when we are eating, sleeping, or reading, we require energy. But where does this energy come from? The food we eat has stored energy, which is released during respiration.

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. It is the reason why we must breathe; we breathe to provide the oxygen required by the cells to break down food and release the energy stored within.

2. Types of Respiration

Depending on whether oxygen is used or not, respiration can be classified into two main types: Aerobic and Anaerobic.

• Aerobic Respiration: When the breakdown of glucose occurs with the use of oxygen, it is called aerobic respiration. Most living organisms, including humans, plants, and animals, undergo aerobic respiration. The chemical reaction can be summarized as: Glucose + Oxygen → Carbon dioxide + Water + Energy.
• Anaerobic Respiration: Sometimes, food can also be broken down without using oxygen. This is called anaerobic respiration. Organisms that can survive in the absence of air are called anaerobes. A common example is Yeast. Yeasts are single-celled organisms that respire anaerobically and, in the process, yield alcohol. This is why they are used to make wine and beer. The reaction is: Glucose → Alcohol + Carbon dioxide + Energy.

Interestingly, our own bodies can also undergo anaerobic respiration for short periods. During heavy exercise, fast running, cycling, or heavy weight lifting, the demand for energy is high but the supply of oxygen to the cells is limited. To meet this extra demand for energy, anaerobic respiration takes place in our muscle cells. In this case, glucose is broken down into lactic acid instead of carbon dioxide and water. The accumulation of lactic acid is what causes muscle cramps after intense physical activity. This is why a hot water bath or a massage helps—it improves blood circulation, increasing the oxygen supply to the muscles and helping break down lactic acid into carbon dioxide and water.

3. The Process of Breathing

Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. This is a continuous process which goes on all the time and throughout the life of an organism.

• Inhalation: The taking in of air rich in oxygen into the body is called inhalation.
• Exhalation: The giving out of air rich in carbon dioxide is called exhalation.
• Breathing Rate: The number of times a person breathes in a minute is termed the breathing rate. On average, an adult human being at rest breathes in and out 15–18 times per minute. During heavy exercise, the breathing rate can increase up to 25 times per minute.

4. How do we Breathe? (Human Respiratory System)

To understand how we breathe, we need to look at the organs involved. 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 the 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.
• 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 air is pushed out of the lungs.

Did you know? We sneeze when we inhale air containing dust, pollen, or smoke. These foreign particles irritate the lining of the nasal cavity, and a sneeze expels these particles so that only clean air enters our lungs.

5. Breathing in Other Animals

Not all animals have lungs like humans. Different organisms have evolved different ways to exchange gases:

• Cockroaches and Insects: A cockroach has small openings on the sides of its body called spiracles. Insects have a network of air tubes called tracheae for gas exchange. Oxygen-rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissue, and reaches every cell of the body. Similarly, carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles.
• Earthworms: Earthworms breathe through their skins. The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. Though frogs have a pair of lungs like human beings, they can also breathe through their skin, which is moist and slippery.
• Fish (Breathing Underwater): Fish have gills that help them to use oxygen dissolved in water. Gills are projections of the skin and are well-supplied with blood vessels for the exchange of gases.

6. Respiration in Plants

Like other living organisms, plants also respire for their survival. They take in oxygen from the air and give out carbon dioxide. In the cells, glucose is broken down into carbon dioxide and water using oxygen, just like in other organisms. In plants, each part can independently take in oxygen from the air and give out carbon dioxide.

• Leaves: The leaves of the plants have tiny pores called stomata for the exchange of oxygen and carbon dioxide.
• Roots: Like all other living cells of the plant, the root cells also need oxygen to generate energy. Roots take up air from the air spaces present between the soil particles. This is why overwatering a plant can kill it—the water fills up the air spaces in the soil, preventing the roots from 'breathing' or respiring, leading to root rot.

Summary & Key Takeaways

• Respiration is vital for the survival of all living organisms as it releases energy from food.
• Cellular respiration occurs in the cells; aerobic uses oxygen, while anaerobic occurs without oxygen.
• Breathing is the physical part of respiration involving inhalation (taking in O2) and exhalation (releasing CO2).
• The diaphragm and rib cage movements are responsible for the expansion and contraction of the lungs in humans.
• Different animals use different organs: lungs (humans, birds, frogs), spiracles/tracheae (insects), moist skin (earthworms), and gills (fish).
• Plants respire through stomata in leaves and through root cells that absorb air from soil spaces.
• Respiration is a continuous process that happens day and night in all living beings to ensure energy availability for biological functions.