Respiration in Organisms

"The process of releasing energy from food is called respiration."

1.0Introduction

All organisms are made of small, microscopic units called cells. A cell is the smallest structural and functional unit of an organism. Each cell of an organism performs certain functions such as nutrition, transportation, excretion and reproduction. To perform these functions, the cell needs energy. Even when we are eating, sleeping or reading we require energy. The food has stored energy, which is released during respiration. Therefore, all living organisms respire to get energy from food.

2.0Respiration

The metabolic process by which organisms obtain energy from oxidation of food (organic molecules). During breathing, we breath in air. You know that air contains oxygen. We breathe out air which is rich in carbon dioxide. The air we breathe in is transported to all parts of the body and ultimately to each cell. In the cells, oxygen helps in the breakdown of food.

Cellular respiration

Cellular respiration takes place in the cells of all organisms. It is an intracellular process in which glucose is oxidized and the energy is used to make ATP (adenosine triphosphate). It consists of many separate enzymatic reactions.

Types of cellular respiration

Cellular respiration is of two types - (i) Aerobic respiration (ii) Anaerobic respiration. (i) Aerobic respiration: The glucose and oxygen react together in the cells to produce carbon dioxide, water and energy is released. The reaction is called aerobic espiration because oxygen from the air is needed for it to work. Here is the word equation for aerobic respiration: $\text{ Glucose }+\text{ oxygen }⟶\text{ Carbon dioxide }+\text{ Water }+\text{ Energy }$ (ii) Anaerobic respiration: When the food is broken down without using oxygen it is known as anaerobic respiration. In this type of respiration incomplete oxidation of food takes place and in comparison to aerobic respiration, much less amount of energy is produced.

• (a) Anaerobic respiration in yeast cell: Yeast can survive in the absence of air. They are called anaerobes. They get energy through anaerobic respiration. The glucose breaks down into alcohol and carbon dioxide in the absence of oxygen. The reaction is called anaerobic respiration or fermentation. Here is the word equation for anaerobic respiration: Glu cose (without the use of oxygen) $⟶$ Alcohol + Carbon dioxide + Energy
• (b) Anaerobic respiration in muscle cells: Our muscle cells can also respire anaerobically but only for a short time when there is a temporary deficiency of oxygen. During heavy exercise, fast running, cycling, walking for many hours or heavy weightlifting, the demand for energy is high but the supply of oxygen to produce the energy is limited. Then anaerobic respiration takes places in the muscle cells to fulfil the demand of energy. Glucose (without the use of oxygen) $⟶$ Alcohol + Carbon dioxide + Energy We get relief from cramps after a hot water bath or a massage. Hot water bath or massage improves circulation of blood. As a result, the supply of oxygen to the muscle cells increases. The increase in the supply of oxygen results in the complete breakdown of lactic acid into carbon dioxide and water.
  

Breathing

We require oxygen for oxidation of food and breathing is essential for this purpose. Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. It is a continuous process which goes on all the time and throughout the life of an organism.

Breathing includes inhalation and exhalation. On an average, an adult human being at rest breathes in and out 15-18 times in a minute. During heavy exercise, the breathing rate can increase upto 25 times per minute. While we exercise, not only do we breathe fast, but we also take deep breaths and thus inhale more oxygen.

Inhalation:

The process of taking in air rich in oxygen into the body is called inhalation.

Exhalation:

The process of giving out of air rich in carbon dioxide is known as exhalation.

Breathing rate:

The number of times a person breathes in a minute is termed as the breathing rate. A breath means one inhalation and one exhalation. During breathing, inhalation and exhalation take place alternately.

3.0Respiratory organs in animals

Most animals use specialized organs or organ system such as lungs, trachea, or gills for external respiration. In all cases, exchange of gases between the environment and an animal occurs by diffusion through a surface which is permeable to oxygen and carbon dioxide.

Skin:

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 pair of lungs like human beings, they can also breathe through their skin which is moist and slippery.

Trachea:

Cockroach, grasshopper and other insects have small openings on the sides of its body. These openings are 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.

Gills:

Gills are projections of the skin and they help in breathing in fishes. Gills are well supplied with blood vessels for exchange of gases.

• Animals with gills or lungs take up oxygen and transport oxygen-rich blood throughout the body. They transport carbon dioxide-rich blood from the body back into the respiratory organs where it is expelled.

Lungs:

Animals such as frogs, lizards, snakes, birds, elephants, lions, cows, goats have lungs in their chest cavities like the human beings.

4.0Human respiratory system

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 diaphragm forms the floor of the chest cavity. Breathing involves the movement of the diaphragm and the rib cage.

Mechanism of breathing

During inhalation, ribs move up and outwards and 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 diaphragm moves up to its former position. This reduces the size of the chest cavity and air is pushed out of the lungs. These movements in our body can be felt easily.

5.0Gaseous exchange in plants

The process of respiration is similar in all organisms, whether plants or animals. Carbon dioxide is given out and oxygen is used up, and a lot of energy is produced.

In plants, specific organs for breathing are absent. The exchange of gases, however, occurs by the process of diffusion. Diffusion of gases (oxygen and carbon dioxide) occurs through following:

Through stomata (singular stoma), the minute openings on the surface of leaves.

During day, ${\mathrm{CO}}_2$ generated during respiration is used up for photosynthesis hence there is no ${\mathrm{CO}}_2$ release instead oxygen release in the atmosphere is the major event. Rate of photosynthesis is more as compared to respiration during day time. During night, stomata is closed and photosynthesis does not occur. ${\mathrm{CO}}_2$ elimination is the major exchange activity going on because ${\mathrm{CO}}_2$ is liberated during respiration is not used in photosynthesis.

Through general surface of the roots.

The roots take up oxygen from the air spaces present between the soil particles. In aquatic plants, gases diffuse through the body surface.

Through lenticels of stem.

The living cells are organised in a thin layer inside and beneath the bark. They also have opening called lenticels.

6.0Building Concepts

Can cell survive in the absence of oxygen?

• Yes, some cells can survive in the absence of oxygen. For example, yeast and most of bacteria can survive in anaerobic conditions. Thus, all the cells do not use oxygen to produce energy.

Why we get muscle cramps after heavy exercise?

• The cramps occur when muscle cells respire anaerobically. The partial breakdown of glucose produces lactic acid. The accumulation of lactic acid causes muscle cramps.

Why do fishes die when taken out of water?

• Fishes have gills as respiratory structures which can take in only dissolved oxygen from water. So, outside water they cannot respire and therefore die.

Why we should cover our nose while sneezing?

• The air around us has various types of unwanted particles, such as smoke, dust, pollens etc. When we inhale, the particles get trapped in the hair present in our nasal cavity. However, sometimes these particles may get past the hairs in the nasal cavity. Then they irritate the lining of the cavity, as a result of which we sneeze. Sneezing expels these foreign particles from the inhaled air and a dust-free, clean air enters our body.

7.0Biology Diagrams made Easy

8.0Chapter at a Glance

9.0SOME BASIC TERMS

• Aerobic respiration: The glucose and oxygen react together in the cells to produce carbon dioxide, water and energy is released.
• Anaerobic respiration: When the food is broken down without using oxygen, it is known as anaerobic respiration.
• Cellular respiration: It is an intracellular process in which glucose is oxidized and the energy is used to make ATP.
• Diaphragm: A large, muscular sheet forming the floor of the chest cavity called diaphragm.
• Gills: Gills are projections of the skin and they help in exchange of gases in fishes.
• Ribs: Curved bones present in the chest.
• Inhalation : The process of taking in air rich in oxygen into the body is called inhalation.
• Exhalation : The process of giving out of air rich in carbon dioxide is known as exhalation.
• Spiracles: Insects have small openings on the sides of its body known as spiracles.
• Tracheae: Insects have a network of air tubes called tracheae for gas exchange.