What is the advantage of counter-current flow in a fish gill?

It maintains an oxygen gradient along the whole length of the lamella

Why does a large mammal need specialised gas exchange surfaces?

It has a small surface-area-to-volume ratio and long diffusion distances

Ventricular pressure rises above atrial pressure

It shifts right, lowering oxygen affinity so more is unloaded

The afferent arteriole being wider than the efferent

It makes the collecting duct more permeable to water, so more is reabsorbed

The action potential jumps between nodes of Ranvier (saltatory conduction)

Calcium ions entering the presynaptic neurone

12questions. Pick an answer and you'll see why right away.

What is the advantage of counter-current flow in a fish gill?
Why does a large mammal need specialised gas exchange surfaces?
During ventricular systole, why do the atrioventricular valves close?
What happens to the oxygen dissociation curve during the Bohr effect?
Which secretion emulsifies fats in the small intestine (but is not itself an enzyme)?
Which adaptation of the small intestine epithelial cells provides ATP for active transport?
In the renal capsule, what creates the high pressure needed for ultrafiltration?
When the blood water potential falls too low, how does ADH help restore it?
What approximately is the resting potential of a neurone?
During depolarisation in an action potential, which ions move into the neurone?
Why does conduction occur faster in a myelinated neurone?
What triggers the release of neurotransmitter from the presynaptic neurone?