Respiration in Organisms - Class 7 Notes & Olympiad Questions

What is Respiration?

Respiration is a metabolic process that happens inside the cells of living organisms. It helps cells get the energy they need to function properly. During respiration, cells take in oxygen and break down complex substances in the body to release energy. As a result of this process, carbon dioxide is produced and released from the body.

Types of Respiration

There are two types of respiration: external respiration and internal respiration.

1. External Respiration

a) External respiration is the process of breathing. It involves inhaling air that is rich in oxygen and exhaling air that is rich in carbon dioxide.
b) This exchange of gases happens in the tiny air sacs called alveoli in our lungs.
c) So, when we breathe in, oxygen enters our lungs, and when we breathe out, carbon dioxide is released.

2. Internal Respiration

a) Internal respiration, also known as cellular respiration, happens inside our body cells. It's like the cells' way of breathing.
b) During this process, the cells break down glucose (a type of sugar) to produce energy, carbon dioxide, and water.
c) The energy generated is used by the cells to carry out various functions in our bodies. The equation for cellular respiration is:

Internal Respiration is Classified into two categories:

Internal respiration can be further classified into two categories: aerobic respiration and anaerobic respiration.

1. Aerobic Respiration

a) Aerobic respiration is a type of internal respiration that occurs in the presence of oxygen.
b) It takes place in the mitochondria, which are tiny structures within our cells. During aerobic respiration, glucose (sugar) is broken down with the help of oxygen to produce carbon dioxide, water, and energy.
c) The end products of aerobic respiration are carbon dioxide and water. This process is commonly observed in organisms like humans, lions, tigers, cats, dogs, and many others.
d) The equation for the aerobic reaction is:

2. Anaerobic Respiration

a) On the other hand, anaerobic respiration is a type of internal respiration that occurs without the use of oxygen.
b) In this process, glucose is only partially broken down, and the end products differ depending on the organism.
c) For example, in yeast, the end products of anaerobic respiration are carbon dioxide and alcohol (specifically ethanol).
d) In certain situations, even human beings can undergo anaerobic respiration. During intense exercise, when our muscle cells don't receive enough oxygen, glucose is partially broken down without oxygen, resulting in the production of lactic acid. The end products of anaerobic respiration in humans are lactic acid.
e) The equation for the anaerobic reaction that occurs in human muscle cells is:

Respiration in Plants

a) Plants also undergo respiration, just like animals. They take in oxygen and release carbon dioxide as part of the respiration process.
b) In plants, respiration occurs through small openings called stomata, which are present on the surface of leaves and young stems. These stomata allow for the exchange of oxygen and carbon dioxide with the external environment. Each stoma is protected by two guard cells, which control the opening and closing of the stomata to regulate the exchange of gases.
c) Apart from stomata, the bark of plant stems contains small openings called lenticels. These lenticels also play a role in the exchange of gases through diffusion, allowing oxygen to enter the plant and carbon dioxide to be released.
d) Even the cells in plant roots participate in respiration. Roots have hair-like structures that assist in absorbing oxygen from the air present in the soil. This oxygen is used in respiration by the plant's root cells.
e) So, plants respire by taking in oxygen through stomata and lenticels, while carbon dioxide is released as a byproduct. Additionally, the roots of plants absorb oxygen from the air in the soil to support respiration in root cells.

Respiration in Animals

Animals have various respiratory adaptations depending on their requirements. These adaptations enable them to obtain oxygen and release carbon dioxide effectively, ensuring their cells receive the necessary oxygen for respiration and removing waste carbon dioxide.

Some examples of respiration in different animals are:

Lower organisms: Lower organisms such as yeast and most bacteria respire anaerobically, meaning they do not require oxygen for respiration.

Hydra and earthworm: These organisms have a moist outer surface through which gas exchange occurs by diffusion. This type of respiration is called cutaneous respiration. In some animals like frogs, cutaneous respiration is complemented by other respiratory methods. For example, when frogs are underwater, they respire through their skin, and when on land, they primarily respire through their lungs.

Insects: Insects like cockroaches and grasshoppers have small openings called spiracles on the sides of their bodies. These spiracles are connected to tubes called tracheae. Insects respire through a system called tracheal respiration. Air enters the body through the spiracles and then diffuses into the cells via the tracheae, allowing for gas exchange.

Aquatic organisms: Fish respire through gills. Gills are specialized respiratory organs that allow them to extract oxygen from water and release carbon dioxide.

Reptiles, birds, and mammals: These animals respire through lungs located in their chest cavities, similar to humans. Lungs are highly efficient respiratory organs that enable the exchange of gases between the air and the bloodstream.

Respiration in Humans

Respiration in humans is the process by which our bodies take in oxygen from the air and release carbon dioxide. It's an essential process that allows us to get the oxygen we need to survive and remove waste carbon dioxide from our bodies.

Human Respiratory System

a) The human respiratory system includes several parts: the nostrils, nasal cavity, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs. When we breathe in, air enters through our nostrils and flows into the nasal cavity. From there, it passes through the throat, voice box, and windpipe, eventually reaching the lungs.
b) The lungs are situated in the chest cavity and are protected by the rib cage. They are responsible for the exchange of gases and play a vital role in respiration.
c) Below the lungs lies the diaphragm, a large muscle shaped like a dome. The diaphragm contracts and relaxes rhythmically to help in the process of breathing.

Difference Between Respiration and Breathing

Respiration should not be confused with breathing. Respiration is a broader process that includes the exchange of gases (oxygen and carbon dioxide) at the cellular level. Breathing, on the other hand, refers specifically to the act of inhaling oxygen and exhaling carbon dioxide.

Mechanism of Breathing

The mechanism of breathing involves the movement of the ribs and diaphragm, which helps the lungs expand and contract.
When we inhale, the diaphragm contracts and moves downward, while the rib cage expands, allowing the lungs to expand and fill with air. During exhalation, the diaphragm relaxes, and the rib cage contracts, pushing the air out of the lungs.

Inhalation (Breathing In)

a) When we inhale, the muscles between our ribs, contract.
b) This causes the ribcage to move upward and outward, expanding the chest cavity.
c) At the same time, the diaphragm, which is a dome-shaped muscle below the lungs, contracts and moves downward.
d) These movements of the ribs and diaphragm create more space in the chest cavity, allowing the lungs to expand.
e) As the lungs expand, the air is drawn in through the nostrils or mouth, and it travels down the windpipe (trachea) into the lungs.

Exhalation (Breathing Out)

a) When we exhale, the muscles and diaphragm relax.
b) This allows the ribcage to move downward and inward, and the diaphragm moves back up to its relaxed position.
c) As the chest cavity decreases in size, the lungs also deflate.
d) The decrease in lung volume increases the pressure inside the lungs, causing air rich in carbon dioxide to be pushed out.
e) The carbon dioxide-rich air is then expelled through the nostrils or mouth during exhalation.

This process of the ribs and diaphragm moving during inhalation and exhalation helps create changes in the chest cavity, allowing the lungs to expand and contract, and air to flow in and out. It's the mechanism that enables us to breathe and exchange oxygen and carbon dioxide with the external environment.