insects
INSECTS
Insects, being larger and having a hard, chitinous and therefore impermeable exoskeleton, have a more specialised gas exchange system.
Insects have no transport system so gases need to be transported directly to the respiring tissues.
There are tiny holes called spiracles along the side of the insect.
The spiracles are openings of small tubes running into the insect's body, the larger ones being called tracheae and the smaller ones being called tracheoles.
The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles.
Ventilation movements of the body during exercise may help this diffusion.
The spiracles can be closed by valves and may be surrounded by tiny hairs. These help keep humidity around the opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation.
FISH
Fish use gills for gas exchange. Gills have numerous folds that give them a very large surface area.
The rows of gill filaments have many protrusions called gill lamellae. The folds are kept supported and moist by the water that is continually pumped through the mouth and over the gills.
Fish also have an efficient transport system within the lamellae which maintains the concentration gradient across the lamellae.
The arrangement of water flowing past the gills in the opposite direction to the blood (called counter current flow) means that they can extract oxygen at 3 times the rate a human can.
Countercurrent flow
As the blood flows in the opposite direction to the water, it always flows next to water that has given up less of its oxygen.
This way, the blood is absorbing more and more oxygen as it moves along. Even as the blood reaches the
Insects, being larger and having a hard, chitinous and therefore impermeable exoskeleton, have a more specialised gas exchange system.
Insects have no transport system so gases need to be transported directly to the respiring tissues.
There are tiny holes called spiracles along the side of the insect.
The spiracles are openings of small tubes running into the insect's body, the larger ones being called tracheae and the smaller ones being called tracheoles.
The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles.
Ventilation movements of the body during exercise may help this diffusion.
The spiracles can be closed by valves and may be surrounded by tiny hairs. These help keep humidity around the opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation.
FISH
Fish use gills for gas exchange. Gills have numerous folds that give them a very large surface area.
The rows of gill filaments have many protrusions called gill lamellae. The folds are kept supported and moist by the water that is continually pumped through the mouth and over the gills.
Fish also have an efficient transport system within the lamellae which maintains the concentration gradient across the lamellae.
The arrangement of water flowing past the gills in the opposite direction to the blood (called counter current flow) means that they can extract oxygen at 3 times the rate a human can.
Countercurrent flow
As the blood flows in the opposite direction to the water, it always flows next to water that has given up less of its oxygen.
This way, the blood is absorbing more and more oxygen as it moves along. Even as the blood reaches the