Respiration in Organisms — Study Notes

1. Introduction

Every living organism needs energy to stay alive, and this energy is released from food inside the body. The process by which the food is broken down in the cells to release energy is called respiration. Respiration is essential for all living beings, from tiny bacteria to large animals and plants. In this chapter we study the process of respiration, the respiratory organs of different organisms, and the differences between breathing and respiration.

The food we eat, mainly glucose, is combined with oxygen in our cells to release energy, carbon dioxide and water. This energy is stored in a molecule called ATP and is used by cells for all their activities. Respiration is the biochemical process that releases energy from food, while breathing is the physical process of taking in oxygen and giving out carbon dioxide. Breathing is only one part of the overall process of respiration.

2. Breathing and Respiration

Breathing is the process of taking in oxygen-rich air (inhalation) and giving out carbon dioxide-rich air (exhalation). In humans, breathing is carried out with the help of the nose, trachea and lungs. During inhalation, the ribs move up and out, and the diaphragm, which is a large dome-shaped muscle below the lungs, moves down. This increases the volume of the chest cavity and reduces the air pressure inside, so air rushes into the lungs. During exhalation, the ribs move down and in, and the diaphragm moves up, decreasing the chest volume and pushing air out.

Respiration is a more complex process that occurs inside the cells. The oxygen we breathe in reaches the blood in the lungs and is carried to all the cells of the body. In the cells, glucose is broken down in the presence of oxygen to release energy. This type of respiration, which requires oxygen, is called aerobic respiration. The equation is given below.

Aerobic respiration releases a large amount of energy. The carbon dioxide produced is carried back to the lungs and breathed out. When we breathe rapidly during exercise, the breathing rate increases to supply more oxygen to the cells and to remove the extra carbon dioxide produced.

3. Aerobic and Anaerobic Respiration

Respiration is of two types based on whether oxygen is used or not. Aerobic respiration takes place in the presence of oxygen and releases a large amount of energy. It occurs in most living organisms, including humans, plants and animals. Anaerobic respiration takes place in the absence of oxygen and releases much less energy. In anaerobic respiration, glucose is partially broken down to form ethyl alcohol and carbon dioxide (as in yeast) or lactic acid (as in our muscles).

Anaerobic respiration in muscles occurs when we exercise heavily and the oxygen supply to the muscles is not enough. In this condition, the muscle cells break down glucose in the absence of adequate oxygen to form lactic acid and release energy. The accumulation of lactic acid in the muscles causes muscle cramps and pain. Yeast, which is a fungus, carries out anaerobic respiration in the absence of oxygen, producing alcohol and carbon dioxide; this process is called fermentation and is used in making bread, beer and wine. Some bacteria can also carry out anaerobic respiration.

4. Breathing in Different Organisms

Different organisms have different organs for breathing, depending on where they live. Terrestrial animals like humans, cats and birds breathe with lungs. Fish breathe underwater with the help of gills, which extract oxygen dissolved in water. Earthworms breathe through their moist skin; oxygen dissolves in the moisture on their skin and enters their body. Insects like cockroaches and grasshoppers breathe through tiny openings on their bodies called spiracles, which are connected to a network of tubes called tracheae that carry air directly to all parts of the body.

The rate of breathing also varies with the organism and its activity. A human being breathes about 15 to 18 times per minute at rest, while a fish breathes much faster. During exercise or heavy work, the breathing rate increases because the cells need more oxygen to release energy. Frogs can breathe through their lungs when on land and through their moist skin when in water. This variety of breathing organs shows how organisms are adapted to their environments.

5. Respiration in Plants

Plants do not have any specific respiratory organs like lungs or gills, but they respire all the time, day and night. Plants take in oxygen and give out carbon dioxide through tiny pores called stomata on their leaves and through lenticels on their stems. The roots of plants take in oxygen from the air present in the spaces between soil particles through their root hairs.

The leaves of plants exchange gases through stomata, while stems exchange gases through lenticels, which are small openings on the bark. It is important to note that plants do photosynthesis only in the presence of sunlight, but respiration goes on in all their cells continuously, day and night. During the day, the oxygen released in photosynthesis is used for respiration, but at night, when photosynthesis stops, plants take in oxygen from the air. This is why people are advised not to sleep under a tree at night, since the plant gives out carbon dioxide.

Quick Revision Tables

Mind Map

Important Diagrams (SVG)

Diagram 1: Human Respiratory System

Diagram 2: Aerobic vs Anaerobic Respiration

Common Mistakes

1. Confusing breathing with respiration; breathing is inhaling and exhaling, respiration is the cellular breakdown of food.
2. Thinking that plants respire only at night; plants respire continuously day and night.
3. Believing that fish breathe air from the surface; they use gills to extract oxygen dissolved in water.
4. Thinking that earthworms breathe through lungs; they breathe through their moist skin.
5. Believing that insects have lungs; they breathe through spiracles and tracheae.
6. Thinking that anaerobic respiration releases more energy than aerobic; it releases much less.
7. Believing that yeast always needs oxygen; yeast can respire anaerobically to produce alcohol.
8. Forgetting that muscles produce lactic acid during heavy exercise, causing cramps.
9. Thinking that the diaphragm moves up during inhalation; it moves down to increase chest volume.
10. Believing that plants have special respiratory organs like lungs; they exchange gases through stomata, lenticels and root hairs.

Exam Tips

1. Define breathing and respiration separately and give the aerobic respiration equation.
2. Describe the mechanism of inhalation and exhalation with the role of the diaphragm and ribs.
3. Compare aerobic and anaerobic respiration in a table with products and energy.
4. Explain the cause of muscle cramps after heavy exercise (lactic acid).
5. List the breathing organs of humans, fish, earthworms, insects and plants.
6. State clearly that plants respire day and night but photosynthesise only in sunlight.
7. Explain why yeast is used in the baking industry (fermentation produces CO2 which makes bread rise).
8. Draw and label the human respiratory system with nose, trachea, lungs and diaphragm.
9. Memorise the normal breathing rate of humans at rest (about 15-18 times per minute).
10. Understand why breathing rate increases during exercise.

Conclusion

Respiration is the fundamental process by which all living organisms release energy from food. Breathing, which involves inhaling oxygen and exhaling carbon dioxide, is just one part of this process, and it is carried out by different organs in different organisms - lungs in humans and animals, gills in fish, moist skin in earthworms, and spiracles in insects. Aerobic respiration releases large amounts of energy in the presence of oxygen, while anaerobic respiration produces less energy and forms alcohol or lactic acid. Plants respire through stomata, lenticels and root hairs continuously. Understanding respiration helps us appreciate how energy sustains all life.