Environmental biology examines the impact of human activities on ecosystems, one of the many Biology Topics.
How Do Animals and Plants Breathe?
We have just studied that the breathing organs of human beings are lungs. Just like human beings, the animals such as cows, buffaloes, dogs, cats, lions, goats, deer, elephants, frogs, lizards, snakes and birds also have lungs for breathing. So, the process of breathing and respiration in these animals is similar to that in humans. There are, however, a large number of animals which do not have lungs for breathing.
Some of the animals which do not have lungs for breathing are earthworm, fish, cockroach, grasshopper, mosquitoes, houseflies and ants. The animals such as cockroach, grasshopper, mosquito, housefly and ant are called insects. So, we can also say that insects do not have lungs for breathing. We will now describe the process of breathing and respiration in earthworm, fish and insects (such as cockroach and grasshopper, etc.), which do not have lungs.
1. Breathing in Earthworm
The earthworm breathes through its skin (see Figure). The skin of earthworm is quite thin and moist. Gases can easily pass through the skin of earthworm. The skin of earthworm has a good blood
supply. So, the earthworm absorbs the oxygen (of air) needed for respiration through its thin and moist skin. This oxygen is then transported to all the cells of the earthworm by its blood where it is used in respiration (production of energy). The carbon dioxide produced during respiration is carried back by the blood. This carbon dioxide is expelled from the body of the earthworm through its skin. Thus, in earthworm the exchange of gases takes place through the thin and moist skin. Frogs live on land as well as in water. Though frogs have lungs for breathing, they can also breathe through their moist skin. Thus, frog is an animal which can breathe through lungs as well as its moist skin (see Figure).
2. Breathing in Fish
There are many animals which live in water. The animals living under water have ‘gills’ for breathing. Gills are the organs which help the animals living in water to use oxygen dissolved in water for breathing. Gills are projections of the skin. Gills have blood vessels for the exchange of respiratory gases (oxygen and carbon dioxide).
Fish lives in water. The fish has special organs of breathing called ‘gills’. The gills help the fish to use oxygen which is dissolved in water (in which it lives). The fish has gills on both the sides of its head (see Figure). The gills are covered by gill covers so they are not visible from outside.
For breathing, the fish uses the oxygen which is dissolved in water. This happens as follows : The fish breathes by taking in water through its mouth and sending it over the gills (see Figure). When water passes over the gills, the gills extract dissolved oxygen from this water. The extracted oxygen is absorbed by the blood and carried to all the parts of the fish for respiration (release of energy). The carbon dioxide produced during respiration is brought back by the blood into the gills for expelling into the surrounding water. The fish has no lungs like us, the exchange of gases in fish takes place in the gills. Some other aquatic animals like prawn, crab and fresh water mussel also respire through gills or similar structures.
Most of the snails live in water and have gills for breathing. They use gills to extract oxygen dissolved in water. Some of the snails who live on land have developed a kind of lung. So, the land snails breathe by using the lung. There are, however, some sea-animals like dolphins and whales which live in water but do not have gills. Dolphins and whales breathe in air through their nostrils (called blowholes) which are located on the upper parts of their heads. Dolphins and whales come to the surface of sea-water from time to time to breathe in air. We (human beings) cannot survive under water because we have no gills to make use of oxygen dissolved in water for breathing. We have to take along oxygen gas cylinder for breathing under water.
3. Breathing in Insects
All the insects have tiny holes on the sides of their body which are called ‘spiracles’ (see Figure).
The spiracles on the body of insects are connected to a network of thin air-tubes called ‘tracheae’ which spread into the whole body of the insect (The singular of tracheae is trachea). The breathing in all the insects takes place through tiny holes (called spiracles) and thin air-tubes (called tracheae). This happens as follows : Air (rich in oxygen) enters into the insect through spiracles by the up and down movements of its body. This air goes into the network of thin air-tubes called tracheae.
From the tracheae, oxygen of air diffuses into the body tissues of insect and reaches each and every cell of its body where it is utilised in respiration (production of energy). Carbon dioxide produced during respiration in the cells diffuses into tracheae and carried to the spiracles where it is expelled in the process of breathing. Thus, in insects the exchange of gases occurs through tracheae.
The spiracles (tiny holes) and tracheae (air-tubes) are found only in insects and not in any other group of animals. For example, cockroach is an insect, so a cockroach has spiracles (tiny holes) on the sides of its body and tracheae (air-tubes) throughout inside its body for the process of breathing and respiration. The insects such as grasshoppers, mosquitoes, houseflies, bees and wasps also have spiracles and tracheae for breathing and respiration.
Please note that insects have blood in their body but it is not red because it does not contain haemoglobin. Since the blood of insects does not contain haemoglobin, so it cannot carry oxygen to all the parts of the body. Every part of the body of an insect gets oxygen through a network of big and small air-tubes.
Respiration in Plants
Like animals, plants also need energy. The plants get energy by the process of respiration in which glucose food (prepared by them) breaks down in the presence of oxygen (of air) to form carbon dioxide and water with the release of energy. This energy is used by the plant for carrying out its various life processes. Thus, like other living organisms, plants also respire for their survival. Plants take oxygen from air for respiration and give out carbon dioxide. So, just like animals, respiration in plants also involves the exchange of gases : oxygen and carbon dioxide. The respiration in plants differs from that of animals in that in plants, each part (like leaves, roots, etc.) can carry out respiration independently. In other words, in plants, each part can independently take in oxygen from air, utilise it to obtain energy, and give out carbon dioxide. We will now describe the respiration in the leaves and roots of a plant, one by one.
1. Respiration in Leaves
The leaves of plants have tiny pores on their surface which are called stomata (see Figure). The exchange of gases (oxygen and carbon dioxide) in the leaves during respiration takes place through stomata. This happens as follows : Oxygen from air enters into a leaf through stomata and reaches all the cells by the process of diffusion. This oxygen is used in respiration in the cells of the leaf. The carbon dioxide produced during respiration diffuses out from the leaf into air through the same stomata. So, we can also say that the plants breathe through the tiny pores in their leaves called stomata.
2. Respiration in Roots
The roots of a plant are under the ground but root cells also need oxygen to carry out respiration and release energy for their own use. The roots obtain oxygen for breathing and respiration from the soil as follows : Air is present in-between the particles of soil (see Figure). The roots of a plant take up air from the spaces between the soil particles. Actually, the roots of a plant have a very large number of tiny hair on them which are called ‘root hair’.
The root hair are in contact with the air in the soil particles (see Figure). Oxygen from air in soil particles diffuses into root hair and reaches all the cells of the root where it is utilised in respiration. Carbon dioxide produced in the cells of the root during respiration goes out through the same root hair by the process of diffusion.
Thus, the respiration in roots occurs by the exchange of gases (oxygen and carbon dioxide) through the root hair. If a potted plant is over-watered for a long time, then the plant may ultimately die. This is because too much water expels all the air from in-between the soil particles. Due to this, oxygen is not available to the roots for aerobic respiration. Under these conditions, the roots of plant respire anaerobically producing alcohol. This may kill the plant.
Please note that plants carry out photosynthesis (for making food) only during the day time when sunlight is available. On the other hand, plants carry out respiration (to obtain energy) during the day time as well as at night (because they require energy all the time). We will now answer a question based on respiration taken from the NCERT book.
Three test-tubes are taken and labelled A, B and C. Each test-tube is half filled with water.
(a) In test-tube A, a snail is kept,
(b) In test-tube B, a water plant is kept, and
(c) In test-tube C, a snail and a water plant, both are kept.
The three test-tubes are then placed in sunlight. Which test-tube would have the highest concentration of carbon dioxide ? Why?
(a) Test-tube A contains a snail in water. The snail will use up oxygen for respiration and produce carbon dioxide.
(b) Test-tube B contains a ‘water plant’ in water. The water plant will do photosynthesis by using carbon dioxide and water, and produce oxygen. The water plant will use some of this oxygen for respiration and produce carbon dioxide. This carbon dioxide will then be used by the plant in photosynthesis.
(c) Test-tube C contains both, a snail and a water plant. The carbon dioxide produced by the respiration in snail will be all used up by the water plant in photosynthesis.
From the above discussion we conclude that the test-tube A containing only snail will have the highest concentration of carbon dioxide because there is no plant to use up the carbon dioxide produced during the respiration in snail.