Gaseous Exchange in Animals and Plants

1.0Gaseous Exchange in Terrestrial Animals

Different land animals have different organs for gaseous exchange like skin or general body surface as in earthworm, air tubes or trachea as in insects (grasshopper, cockroach, housefly) and lungs as in frogs, lizards, birds, rats and humans.

Earthworms

Earthworms breathe through their skin. The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. 

Insects  

Insects like cockroache, grasshopper etc. have small openings on the sides of their body. These openings are called spiracles. Insects have a network of air tubes called tracheae for gaseous 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. 

2.0Gaseous Exchange in Aquatic Animals

Fish

In fish, there is a hard flap called gill cover or operculum on either side of the head. Underneath the operculum, respiratory organs are located called gills. The fish gulps water through the mouth and forces it out through the sides of the throat through gill-slits under the operculum. 

In this way, the blood capillaries in the gills are brought in close contact with the current of water. The blood in the gills absorbs dissolved oxygen from water and gives out carbon dioxide. 

3.0Gaseous Exchange in Amphibians

The frog respires through three body parts:

(i) Skin

(ii) Lining of the mouth 

(iii) Lungs

(i) Respiration by skin : The skin is richly supplied with blood vessels and is always kept moist. When the frog is in water, the air dissolved in it provides oxygen to the blood in the skin. When the frog is on land, the oxygen of the air diffuses into the mucus of the skin and then into the blood. The carbon dioxide is also given out the same way. Skin respiration is the sole method of respiration when the frog is hibernating (undergoing winter sleep in the ground pits).

(ii) Respiration by mouth: In mouth respiration, the frog draws air into the mouth cavity through the nostrils and without taking it into the lungs, forces it back to the outside. The lining of mouth absorbs some oxygen from this air and the carbon dioxide is given out. A sitting or floating frog constantly keeps lowering and raising the lower part of its mouth to carry out respiration by this way.

(iii) Respiration by lungs: When the frog needs more oxygen, as during and after active jumping on land, it breathes through the lungs. It takes the air into the mouth cavity through the nostrils and keeping the nostrils and the mouth closed, it forces this air into the lungs. After serving for respiration in the lungs, the air is drawn back into the mouth cavity and from there, it is forced out into the atmosphere by opening the nostrils.   

4.0Gaseous Exchange in Plants

The plants do not have any special respiratory system so they have to respire through all of their individual parts like leaf, stem and root.

The plants also have to exchange gases with the atmosphere by simple diffusion process. Direction of diffusion depends upon the environmental condition and the requirement of the plant.

Aquatic plants can carry out gaseous exchange by diffusion over their whole surfaces. In terrestrial plants gaseous exchange occurs through stomata, lenticels and root hairs.

Gaseous Exchange Through Stomata

Oxygen enters into the plant body through stomata by the process of diffusion and then goes into other cells of the leaf. The intercellular spaces which are present throughout the plant ensure that all the cells are in contact with air. These intercellular spaces reduce the distance of diffusion between cells and air.

During the day, CO₂ generated during respiration is used up for photosynthesis hence there is no CO₂ release instead oxygen release in the atmosphere is the major event. Rate of photosynthesis is high as compared to respiration during day time. 

During the night, stomata is closed and photosynthesis does not occur. CO₂ elimination is the major exchange activity going on because CO₂ liberated during respiration is not used in photosynthesis.

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