Question

In a fish that has an air-breathing organ,

a. there are not likely to be functioning gills.
b. the blood leaving the air-breathing organ mixes with blood leaving the gills.
c. the blood leaving the air-breathing organ mixes with systemic venous blood.
d. the blood enters the air-breathing organ following its exit from the gills.

Answer 1

In a fish that has an air-breathing organ, the blood leaving the air-breathing organ mixes with systemic venous blood.

Step-by-step explanation:

In a fish that has an air-breathing organ, the blood leaving the air-breathing organ mixes with systemic venous blood. (c)

This is because fish have a single circuit for blood flow and a two-chambered heart. The atrium collects blood that has returned from the body and the ventricle pumps the blood to the gills where gas exchange occurs and the blood is re-oxygenated. The blood then continues through the rest of the body before arriving back at the atrium. This unidirectional flow of blood produces a gradient of oxygenated to deoxygenated blood around the fish's systemic circuit.

Therefore, the blood leaving the air-breathing organ mixes with systemic venous blood as it returns to the atrium.