Topic 2.2 Osmoregulation

Osmosis

Movement of water across a semipermeable membrane from low solute concentration to high solute concentration

Osmoregulation

Maintaining proper water and solute balance

Passive transport

Movement down a concentration gradient without energy

Active transport

Movement against a concentration gradient using energy

Freshwater fish are hyperosmotic or hypoosmotic?

Hyperosmotic

What happens to water in freshwater fish?

Water enters the body

What happens to salts in freshwater fish?

Salts leave the body

How do freshwater fish solve this problem?

Produce lots of dilute urine and actively absorb salts through gills

Saltwater fish are hyperosmotic or hypoosmotic?

Hypoosmotic

What happens to water in saltwater fish?

Water leaves the body

What happens to salts in saltwater fish?

Salts enter the body

How do saltwater fish solve this problem?

Drink seawater and excrete excess salts

Why do sharks retain urea?

To increase osmolarity and reduce water loss

What protects shark proteins from urea?

Trimethylamine oxide (TMAO)

Why is CO₂ acquisition difficult in water?

CO₂ diffuses very slowly through water

Boundary layer

Layer of unstirred water surrounding an organism

Why does a boundary layer reduce photosynthesis?

It slows replacement of CO₂ near the surface

Countercurrent exchange

Water and blood flow in opposite directions

Why is countercurrent exchange beneficial?

Maximizes oxygen diffusion into blood