Class 7 Science Respiration in Plants and Animals Exam Notes

Class 7 Science Respiration in Plants and Animals Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Covers following topics

Respiration in plants and animals is the process of taking in oxygen, using it to release energy from food and giving out carbon dioxide and water. This Class 7 Science exam notes page covers respiration, breathing and its steps, the difference between breathing and respiration, aerobic and anaerobic respiration, respiration in plants and animals, the human respiratory system and the mechanism of breathing.

Topics Covered

1. Respiration
2. Breathing
3. Types of Respiration
4. Anaerobic Respiration in Human
5. Respiration in Plants
6. Respiration in Animals
7. Respiratory System of Human
8. Mechanism of Breathing

RESPIRATION

The process of taking oxygen into the cells, using it for energy release and then eliminating the waste products like CO₂ and H₂O is known as respiration. It is a very slow process. A number of enzymes help in the process of respiration.

BREATHING

The process of taking in O₂ rich air into the lungs and giving out carbon dioxide rich air is known as breathing.

Breathing process includes 2 steps -
1. Inhalation: The process of taking in air is called inhalation.
2. Exhalation: Giving out of air is called exhalation.

Breathing involves only exchange of gases.

DIFFERENCE BETWEEN BREATHING AND RESPIRATION

TYPE OF RESPIRATION

There are 2 types of respiration.

Aerobic respiration

In this type of respiration, complete oxidation of glucose takes place and CO₂, H₂O and energy are released. Aerobic respiration takes place in the presence of oxygen and is carried out in the bodies of almost all living animals and plants.

Glucose + O₂ → CO₂ + H₂O + Energy (Aerobic respiration)

Anaerobic respiration

In anaerobic respiration, there is incomplete oxidation of glucose. CO₂, ethyl alcohol and energy are the end products. Anaerobic respiration takes place in the absence of oxygen.

Glucose (absence of O₂) → Alcohol + CO₂ + Energy (Anaerobic respiration)

Yeast and some bacteria show anaerobic respiration. Anaerobic respiration in microorganisms present in food and alcohol causes fermentation.

ANAEROBIC RESPIRATION IN HUMAN

During excessive physical exercise, anaerobic respiration takes place in muscles to produce lactic acid. The accumulation of lactic acid in the muscle causes fatigue and pain.

Glucose (absence of O₂) → Lactic acid + Energy

RESPIRATION IN PLANTS

Like all other living organisms, plants also respire for their survival. They take in oxygen from the air and give out carbon dioxide. During this process most plants use atmospheric oxygen to break down glucose into carbon dioxide and water with the release of energy.

In plants, breathing takes place through tiny holes or openings called stomata, present under the leaves. Stomata trap air and the exchange of gases takes place inside the plant cells.

Stomatal Apparatus

A stomatal opening surrounded with two guard cells and several subsidiary cells is called stomatal apparatus. The opening and closing of the stomata is brought about by the expansion and contraction of the guard cells. Guard cells expand and contract due to the flow of water in and out of the cells. The exchange of gases in plants is not as fast as in animals.

[Figure: Stomatal apparatus showing two guard cells around a stomatal opening, with the labels Guard cells, Stoma Open, Stomatal Openings and Stoma Open]

Plant roots also respire. Roots take in oxygen from the air present between the soil particles.

[Figure: Root hair growing from the root in soil, with the labels Soil particles, Root hair and Air space]

Some of the woody stems take in air through openings called lenticels.

RESPIRATION IN ANIMALS

Respiration through moist skin - Eg. Frog and Earthworm
Respiration through cell membrane - Eg. Amoeba
Respiration through spiracles - Eg. Cockroach
Respiration through gills - Eg. Fishes

RESPIRATORY SYSTEM OF HUMAN

The respiratory system in human beings consists of the following organs.

Nasal Cavity
Air enters the nose through the nostrils and reaches the nasal cavity.

Larynx
The nasal cavity leads into the pharynx. From the pharynx, air passes into a rectangular chamber called larynx.

Trachea
The trachea or wind pipe is a delicate muscular tube situated in the front of the neck. It is 12 cm in length and 2.5 cm in diameter. The trachea divides into two bronchi.

Bronchi
Each bronchus leads to the lungs of its own side. Each bronchus then branches into smaller tubes known as bronchioles. They end in tiny globules called air sacs or alveoli, where exchange of gases takes place.

Lungs
Lungs are two in number and are present in the chest cavity of the body. Air sacs are richly supplied with blood vessels. When air enters the lungs, the blood takes in oxygen and gives out carbon dioxide and water.

Blood carries oxygen to all parts of the body from the lungs.

When we exhale, the carbon dioxide rich air follows the reverse route and finally moves out through the nose, as shown below.

[Figure: Path of air in the human respiratory system from top to bottom for inhalation with Oxygen: Nose, Nasal cavity, Larynx, Trachea, Bronchi, Lungs, Bronchioles, Alveoli; and from bottom to top for exhalation with Carbon dioxide, with arrows between each organ]

MECHANISM OF BREATHING

Breathing takes place with the help of the intercostal muscles between the ribs and the diaphragm. When we breathe in, the intercostal muscles contract and the ribs are pushed outwards. The chest cavity becomes larger and the air rushes into the lungs.

During breathing out, the intercostal muscles relax and the ribs move inwards. The chest cavity shrinks and the air containing carbon dioxide is pushed out of the lungs.

[Figure: Mechanism of breathing. Inhalation: Diaphragm contracts and flattens, lungs expand, air drawn into lungs. Exhalation: Diaphragm relaxes and moves up, lungs contract, air forced out of lungs]

Breathing rate: The number of times a person breathes in a minute is termed as the breathing rate. The normal breathing rate in an adult at rest ranges from 12 to 20.

Breathing process include 2 steps -

• Anaerobic respiration takes place in the absece of oxyen.