Gas Exchange in Insects
Environment
Insects live on land. This means the gas exchange surface is at risk of desiccation. Because of this, an insect's gas exchange system is internal to keep in as much moisture as possible. Because they live on land, insects get oxygen from the air, which has a relatively high oxygen concentration. Air is also easy to ventilate across the gas exchange surface.
Structures and Adaptations
Insects have air tubes called tracheae and tracheoles throughout their body. The tubes are held open by hard rings of chitin. Insects don't have a circulatory system, so the tracheoles must reach every cell in the body as they rely on diffusion to take in oxygen. At the end of each tracheole is a small amount of liquid which allows gasses to dissolve and then diffuse into the cells. The places where the tubes leave the body are called spiracles, and these can open and close to control water loss. When they need lots of oxygen, or the environment is moist, the spiracles will be open. When they don't need as much oxygen or the environment is dry, the spiracles will be closed or only slightly open to reduce water loss. Insects ventilate their gas exchange system by opening and closing their spiracles in a certain order and compressing the trachea to pump air in one end of the insect and out the other end. This keeps fresh air flowing into the body and old air flowing out. There are bristles in the spiracles which filter unwanted particles out of the air so they don't damage the gas exchange surface. Insects also have air sacs which can store extra air until it is needed. This means the insect can keep its spiracles closed in a dry environment and use the oxygen it has stored inside. The air sacs are also used when the insect has a high energy demand. An example of this is when the insect is flying. The air sacs allow the insect to take in more air and therefore more oxygen that can be used for respiration. The gas exchange system is inside the insect's body where it is humid to help to prevent desiccation.
Advantages and Limitations
An advantage of the insect gas exchange system is that they have air sacs which can store extra air for when it is needed. This is useful when an insect has a high energy demand (e.g. while flying), or when it is in a dry environment and needs to close it's spiracles to keep moisture in. They allow the insect to get enough oxygen without loosing to much moisture.
Another advantage is that the spiracles can open and close. This controls how much moisture is lost, while still making sure the insect gets enough oxygen. This helps the gas exchange surface to stay moist and allow for more efficient diffusion of oxygen. It is important that the gas exchange doesn't dry out, because oxygen must dissolve in water before it can diffuse into the cells.
A limitation is that insects rely on diffusion to get oxygen to every cell. Insects don't have a circulatory system to carry oxygen around their bodies. Instead the tracheoles reach each individual cell so oxygen can diffuse straight into the cells. Because insects rely on diffusion for oxygen, their size is limited and they don't get very big. As insects get bigger, it is harder for oxygen to diffuse to every cell. If the insect got too big, oxygen wouldn't be able to reach every cell, so some cells would die.
Another limitation is tidal ventilation. Because the air goes in and out of the tracheoles the same way, not all of the oxygen is absorbed from the air that is taken in. Some air taken in never reaches the gas exchange surface, and not all of the air that has been to the gas exchange surface and lost its oxygen to the cells makes it out of the body. This means only some of the oxygen that comes into the body makes it into the cells.
Insects live on land. This means the gas exchange surface is at risk of desiccation. Because of this, an insect's gas exchange system is internal to keep in as much moisture as possible. Because they live on land, insects get oxygen from the air, which has a relatively high oxygen concentration. Air is also easy to ventilate across the gas exchange surface.
Structures and Adaptations
Insects have air tubes called tracheae and tracheoles throughout their body. The tubes are held open by hard rings of chitin. Insects don't have a circulatory system, so the tracheoles must reach every cell in the body as they rely on diffusion to take in oxygen. At the end of each tracheole is a small amount of liquid which allows gasses to dissolve and then diffuse into the cells. The places where the tubes leave the body are called spiracles, and these can open and close to control water loss. When they need lots of oxygen, or the environment is moist, the spiracles will be open. When they don't need as much oxygen or the environment is dry, the spiracles will be closed or only slightly open to reduce water loss. Insects ventilate their gas exchange system by opening and closing their spiracles in a certain order and compressing the trachea to pump air in one end of the insect and out the other end. This keeps fresh air flowing into the body and old air flowing out. There are bristles in the spiracles which filter unwanted particles out of the air so they don't damage the gas exchange surface. Insects also have air sacs which can store extra air until it is needed. This means the insect can keep its spiracles closed in a dry environment and use the oxygen it has stored inside. The air sacs are also used when the insect has a high energy demand. An example of this is when the insect is flying. The air sacs allow the insect to take in more air and therefore more oxygen that can be used for respiration. The gas exchange system is inside the insect's body where it is humid to help to prevent desiccation.
Advantages and Limitations
An advantage of the insect gas exchange system is that they have air sacs which can store extra air for when it is needed. This is useful when an insect has a high energy demand (e.g. while flying), or when it is in a dry environment and needs to close it's spiracles to keep moisture in. They allow the insect to get enough oxygen without loosing to much moisture.
Another advantage is that the spiracles can open and close. This controls how much moisture is lost, while still making sure the insect gets enough oxygen. This helps the gas exchange surface to stay moist and allow for more efficient diffusion of oxygen. It is important that the gas exchange doesn't dry out, because oxygen must dissolve in water before it can diffuse into the cells.
A limitation is that insects rely on diffusion to get oxygen to every cell. Insects don't have a circulatory system to carry oxygen around their bodies. Instead the tracheoles reach each individual cell so oxygen can diffuse straight into the cells. Because insects rely on diffusion for oxygen, their size is limited and they don't get very big. As insects get bigger, it is harder for oxygen to diffuse to every cell. If the insect got too big, oxygen wouldn't be able to reach every cell, so some cells would die.
Another limitation is tidal ventilation. Because the air goes in and out of the tracheoles the same way, not all of the oxygen is absorbed from the air that is taken in. Some air taken in never reaches the gas exchange surface, and not all of the air that has been to the gas exchange surface and lost its oxygen to the cells makes it out of the body. This means only some of the oxygen that comes into the body makes it into the cells.
Header photo taken by myself