written portion Topic 2.2 — Osmoregulation & Aquatic Environments

What is osmoregulation?

Osmoregulation is the process of maintaining proper water and solute concentrations inside the body.

What challenge do freshwater fish face?

Freshwater fish are hyperosmotic to their environment, so water enters their bodies while salts leave.

How do freshwater fish solve this problem?

They produce large amounts of dilute urine and actively absorb salts through their gills.

What challenge do saltwater fish face?

Saltwater fish are hypoosmotic to their environment, so water leaves their bodies while salts enter.

How do saltwater fish solve this problem?

They drink seawater and actively excrete excess salts through their gills and kidneys.

Why do sharks retain urea?

Sharks retain urea to increase the osmolarity of their blood, reducing water loss to the surrounding seawater.

Why is carbon dioxide difficult for aquatic plants to obtain?

Carbon dioxide diffuses very slowly through water and can become depleted near plant surfaces.

What is a boundary layer?

A boundary layer is a layer of unstirred water surrounding an organism that slows diffusion of gases and nutrients.

How do aquatic plants obtain carbon for photosynthesis?

Many aquatic plants use dissolved CO₂ and bicarbonate ions as carbon sources.

Why is oxygen acquisition difficult in water?

Oxygen is less abundant and diffuses more slowly in water than in air.

How does countercurrent exchange improve oxygen uptake?

Water and blood flow in opposite directions, maintaining an oxygen concentration gradient across the entire gill surface.

Why is countercurrent exchange better than concurrent flow?

Opposite flow allows oxygen to continue diffusing into the blood along the entire gill, maximizing oxygen uptake.