Reason for high oxygen requirements in large multicellular organisms
Increased metabolic rate: warm blooded, more active e.g flight
Reason for smaller surface area to volume ratio in large multicellular organisms
They are usually much larger organisms
Adaptations for larger organisms
Specialised gas exchange surface, a ventilation system to maintain diffusion gradients by moving air or water over the exchange surface, a circulatory system to maintain diffusion gradients by transporting gases between respiring cells and the exchange surface. A respiratory pigment (e.g haemoglobin) in the blood to increase its oxygen-carrying capacity
Insects
Gases enter and leave the body through holes called spiracles, gases travel through the tracheal system - a branching system of chitin-lined tubes called tracheae. the ends of the tracheae are known as tracheoles - these are the site of gas exchange
Level of activity in insects
In less active insects, the gases move along the tubes of the tracheal system by diffusion. In more active insects, rhythmical movements of the abdomen help to pump air in and out of the abdomen and ventilate the tracheal system
Insect tracheal system
No need for the circulatory system to transport respiratory gases in insects. The tracheoles deliver oxygen directly to (and remove carbon dioxide from) the body cells. Every cell in the insect's body is in direct contact with, or very close to, the end of the tracheole
Problem and solution with lactic acid
Insects respire anaerobically during times of high activity, this produces lactic acid which reduces the water potential gradient of muscle cells, drawing the fluid into the muscle tissues, so reducing the diffusion pathway