Respiration in Animals and Plants | CBSE Class 7 Science

What is Respiration?

Respiration is a vital chemical process that occurs in all living cells. Its main purpose is to break down food molecules, like glucose, to release energy. This energy is then stored in a special molecule called ATP (Adenosine Triphosphate), which acts like the energy currency of the cell.

There are two main types of respiration:

1. Aerobic Respiration: This process happens in the presence of oxygen. Glucose is completely broken down into carbon dioxide, water, and a large amount of energy. Most animals and plants, including humans, use aerobic respiration.

The chemical equation is: Glucose (in the presence of Oxygen) → Carbon Dioxide + Water + Energy.

1. Anaerobic Respiration: This process occurs without oxygen. Glucose is only partially broken down, releasing much less energy compared to aerobic respiration. Yeast is a common example of an organism that performs anaerobic respiration, producing alcohol and carbon dioxide. This process is also called fermentation. In humans, our muscle cells can respire anaerobically for a short time during intense exercise, producing lactic acid.

Key Terms in Respiration

Breathing

The mechanical process of taking air rich in oxygen into the body (inhalation) and giving out air rich in carbon dioxide (exhalation).

Cellular Respiration

The process that takes place inside the cells of an organism to break down food and release energy.

Aerobic Respiration

The breakdown of glucose to release energy in the presence of oxygen. It produces carbon dioxide, water, and a large amount of energy.

Anaerobic Respiration

The breakdown of glucose to release energy in the absence of oxygen. It produces alcohol (in yeast) or lactic acid (in muscles) and a small amount of energy.

Spiracles

Small openings found on the sides of an insect's body through which air enters the respiratory system.

How Do We Breathe? The Human Respiratory System

1. Step 1: Inhalation through the Nasal Cavity — We take in air through our nostrils. The air passes into the nasal cavity, where it is filtered by fine hairs, warmed, and moistened.
2. Step 2: Air travels to the Lungs — From the nasal cavity, the air passes through the throat (pharynx) and into the windpipe (trachea). The trachea then splits into two smaller tubes called bronchi, with one bronchus going to each lung.
3. Step 3: Reaching the Alveoli — Inside the lungs, the bronchi divide into smaller and smaller branches called bronchioles. At the end of these bronchioles are tiny, balloon-like air sacs called alveoli. The lungs are filled with millions of alveoli!
4. Step 4: Gaseous Exchange — The alveoli are surrounded by a network of tiny blood vessels (capillaries). Here, oxygen from the inhaled air passes from the alveoli into the blood, and carbon dioxide from the blood passes into the alveoli to be exhaled.
5. Step 5: Exhalation — The diaphragm (a large muscle below the lungs) and rib cage relax, pushing the air rich in carbon dioxide out from the lungs, through the same pathway, and out of our nostrils.

Breathing Mechanisms in Different Animals

Different animals have evolved different organs for respiration based on their habitat and body structure.

• Earthworms: These creatures breathe through their skin! Their skin is moist and slimy, which allows gases like oxygen and carbon dioxide to diffuse directly in and out of their body. For this to work, their skin must always be kept moist.
• Insects (like cockroaches): Insects have a network of air tubes called tracheae. Air enters this system through small openings on the sides of their body called spiracles. The tracheae branch out and deliver oxygen directly to all the cells in the body.
• Fish: Fish live in water and use special organs called gills for breathing. As water flows over the gills, the gills, which are rich in blood vessels, extract dissolved oxygen from the water and release carbon dioxide into it.
• Frogs: Frogs have a dual system! As tadpoles, they live in water and breathe through gills. As adult frogs, they can breathe through their moist skin when in water and through their lungs when on land.

How Do Plants Respire?

Yes, plants respire too! Just like animals, they need energy for their life processes. Plants take in oxygen and release carbon dioxide during respiration. This happens 24 hours a day.

How do they exchange gases?

• Leaves: The surfaces of leaves are covered with tiny pores called stomata. Each stoma is a small opening that allows for the exchange of oxygen and carbon dioxide.
• Stems and Roots: Even the roots and stems respire. Roots take up oxygen from the air spaces present in the soil. Woody stems have special pores called lenticels on their surface for gaseous exchange.

It's important to remember that respiration is different from photosynthesis. Photosynthesis uses carbon dioxide, water, and sunlight to make food (glucose) and releases oxygen. Respiration uses glucose and oxygen to release energy, water, and carbon dioxide.

Key Difference: Breathing vs. Respiration

• Breathing is Physical, Respiration is Chemical: Breathing is the mechanical act of inhaling and exhaling. Cellular respiration is a chemical reaction inside cells to produce energy.
• Location: Breathing involves organs like the lungs or gills. Respiration happens inside every single living cell.
• Energy: Breathing itself uses a small amount of energy. Respiration's main goal is to release a large amount of energy from food.
• Process: Think of breathing as just the first step – getting the oxygen needed for the main event, which is cellular respiration.

Practice Questions with Solutions

• Q: Differentiate between aerobic and anaerobic respiration. A: Step 1: Aerobic respiration occurs in the presence of oxygen, producing more energy, carbon dioxide, and water. Step 2: Anaerobic respiration occurs without oxygen, producing less energy, carbon dioxide, and alcohol (in yeast) or lactic acid (in muscles). Final answer: Aerobic needs O2, yields more energy, CO2, H2O. Anaerobic doesn't need O2, yields less energy, CO2, alcohol/lactic acid.
• Q: How do earthworms and fish respire? A: Step 1: Earthworms breathe through their moist skin. Gases diffuse directly through the skin into and out of their blood. Step 2: Fish respire using gills. Gills have blood vessels that absorb oxygen dissolved in water and release carbon dioxide. Final answer: Earthworms use moist skin, fish use gills to absorb dissolved O2 from water.
• Q: Explain how plants respire. A: Step 1: Plants respire through small pores called stomata on leaves and lenticels on stems. Roots respire through root hair cells. Step 2: They take in oxygen and release carbon dioxide, breaking down glucose to release energy for their life processes. Final answer: Plants respire via stomata, lenticels, and root hairs, taking in O2 and releasing CO2 to produce energy.
• Q: Describe the role of the diaphragm during inhalation in humans. A: Step 1: During inhalation, the diaphragm contracts and moves downwards. Step 2: This increases the volume of the chest cavity, reducing air pressure inside, causing air to rush into the lungs. Final answer: Diaphragm contracts and moves down, increasing chest cavity volume, which draws air into lungs.

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