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| Gaseous Exchange in Grasshopper |
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| The respiratory system in insects is called the tracheal system. It involves the diffusion of oxygen directly from the atmosphere into the air-filled tubes. Thus, the diffusion is through air and hence, is more efficient than the diffusion through water (300,000 times more) or tissues (1,000,000 times more). |
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| Grasshopper - Respiratory System |
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| In grasshopper, the tracheal system consists of 10 pairs of spiracles, located laterally on the body surface. Of these, 2 pairs are thoracic and 8 pairs are abdominal. The spiracles are guarded by fine hairs to keep the foreign particles out and by valves that function to open or close the spiracles as required. The spiracles open into small spaces called the atria that continue as air tubes called the tracheae. The tracheae are fine tubes that have a wall of single layered epithelial cells. The cells secrete spiral cuticular thickenings around the tube that gives support to the tubes. |
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| Tracheal System of Insects |
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| The tracheal tubes branch further into finer tracheoles that enter all the tissues and sometimes, even the cells of the insect. The ends of the tracheoles that are in the tissue are filled with fluid and lack the cuticular thickenings. |
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| The main tracheal tubes join together to form three main tracheal trunks- dorsal, ventral and lateral. At some places, the trachea enlarge to form air sacs which are devoid of cuticle and serve to store air. |
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| Air Sac |
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| The first four pairs of spiracles are involved in inspiration or drawing in of air that is oxygen-rich. This air passes through the trachea and the air sacs to reach the tracheoles. |
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| The Functioning of Tracheoles |
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| Conditions in Resting and Active Insect Tissues |
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| The ends of the tracheoles are filled with fluid. This end enters into the tissue. The ends of the tracheoles are also devoid of cuticle and therefore the respiratory surface is very thin making the diffusion of oxygen into the cells easy. As respiration occurs in the cell, the products of respiration accumulate in the cell and this forces the fluid in the tracheoles to enter the tissue. The exit of fluid creates low pressure in the tubes and draws in more oxygen to the tissues where it is needed. |
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| The carbon dioxide produced is detected by the chemoreceptors which make the muscles near the spiracles contract. This pushes the air out. The last six pairs of spiracles are involved in expiration of air. |
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| Thus, in grasshopper there is ventilation or circulation of air as the oxygen-rich air is inhaled through the first four spiracles and the carbon dioxide-rich air is exhaled through the remaining six pairs of spiracles. |
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| In insects, therefore, the respiratory system is independent of the circulatory system. |
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