Questions: Comparative Circulation and Gas Exchange in Animals
4 questions to test your understanding
Score: 0 / 4
Question 1 Multiple Choice
Why can an insect be active with a circulatory system that does not transport much oxygen?
AInsects do not need oxygen
BBranching air tubes (tracheae) carry oxygen from openings in the body wall directly to the tissues
CInsect blood contains more hemoglobin than human blood
DInsects absorb oxygen through their wings only
Air enters through spiracles and travels through tracheae that branch into fine tubes reaching nearly every cell. Gas exchange happens at the tube ends, so the circulatory fluid has little role in oxygen delivery.
Question 2 True / False
In fish gills, water flows over the gill surfaces in the same direction as blood flows through the gill capillaries.
TTrue
FFalse
Answer: False
Water and blood flow in opposite directions, an arrangement called countercurrent exchange. Along the whole length of the capillary, the water next to the blood has more oxygen than the blood, so oxygen keeps diffusing in, and the fish extracts a large fraction of the oxygen in the water.
Question 3 Short Answer
Why does a four-chambered heart with fully separate circuits suit birds and mammals?
Think about your answer, then reveal below.
Model answer: Birds and mammals are endotherms with high metabolic rates, so their cells need a large, steady oxygen supply. Keeping oxygen-rich and oxygen-poor blood fully separate sends only oxygen-rich blood to the body, and a separate systemic circuit can run at high pressure without damaging the delicate lung capillaries.
Double circulation lets the pulmonary circuit stay at low pressure while the systemic circuit runs at high pressure. Birds and mammals evolved four-chambered hearts independently, in separate lineages, which is an example of convergent evolution.
Question 4 Multiple Choice
In a fish, blood leaves the heart, passes through the gills and then goes to the body before returning. What limitation does this single circuit have?
ABlood never picks up oxygen
BBlood pressure drops in the gill capillaries, so blood flows to the body at low pressure
CThe heart has four chambers that compete with each other
DOxygen-poor blood goes directly to the brain
Passing through the narrow gill capillaries uses up much of the pressure the heart produced. Blood then reaches the body tissues slowly. Swimming movements help push it along. Double circulation in land vertebrates solves this by returning blood to the heart for a second push.