What exactly does it mean to say that insects have no transport system? Watch

anactualmess
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What replaces the transport systems (such as the circulatory system) in insects? My textbook states that due to the fact that insects do not have transport system they necessarily have an exchange system. So why do other organisms need both transport and exchange systems?
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OxFossil
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(Original post by anactualmess)
What replaces the transport systems (such as the circulatory system) in insects? My textbook states that due to the fact that insects do not have transport system they necessarily have an exchange system. So why do other organisms need both transport and exchange systems?
The main explanation is size. Insects are small enough that adequate gas and nutrient exchange can take place (mainly) by diffusion. For gas exchange, insects have a system of highly branching tubes (the trachea) that run from the exterior of the body (where there are little holes called spiracles) into the deeper tissues. Similarly, nutrients are directly diffused from the gut into the tissues.

However, it isn't quite true to say that no insect has any kind of transport system. The interior of the insect body is bathed in a solution of haemolymph, which acts as an exchange medium where nutrients, oxygen, and waste products are dissolved. Larger insects have simple pumping systems to help move the haemolymph around the body cavity.

The limitations of a diffusion-based transport/exchange system is the reason why larger animals have evolved circulatory systems. That's why no insect is larger than a mouse, and also why in periods during prehistory when the atmospheric O2 level was higher than it is today, some insects grew much larger.
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anactualmess
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(Original post by OxFossil)
The main explanation is size. Insects are small enough that adequate gas and nutrient exchange can take place (mainly) by diffusion. For gas exchange, insects have a system of highly branching tubes (the trachea) that run from the exterior of the body (where there are little holes called spiracles) into the deeper tissues. Similarly, nutrients are directly diffused from the gut into the tissues.

However, it isn't quite true to say that no insect has any kind of transport system. The interior of the insect body is bathed in a solution of haemolymph, which acts as an exchange medium where nutrients, oxygen, and waste products are dissolved. Larger insects have simple pumping systems to help move the haemolymph around the body cavity.

The limitations of a diffusion-based transport/exchange system is the reason why larger animals have evolved circulatory systems. That's why no insect is larger than a mouse, and also why in periods during prehistory when the atmospheric O2 level was higher than it is today, some insects grew much larger.
Thank you!
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