molecular movement & cell signaling

What is diffusion?

Net movement of particles from high → low concentration

What drives diffusion?

A concentration gradient

What is osmosis?

Diffusion of water across a selectively permeable membrane

Which way does water move during osmosis?

Toward the side with higher solute concentration

What is bulk flow?

Movement of fluid & dissolved substances together due to pressure differences

What drives bulk flow?

A pressure gradient

Diffusion vs. Osmosis?

Diffusion moves particles & osmosis moves water

Diffusion vs. Bulk flow

Diffusion follows a concentration gradient & bulk flow follows a pressure gradient

What is a concentration gradient?

Difference in concentration between two areas

What happens when diffusion reaches equilibrium?

Particles continue moving but there's no net movement

What is hydrostatic pressure?

Pressure exerted by a fluid against the surface

What is osmotic pressure?

Pressure caused by dissolved solutes pulling water toward them

What is oncotic pressure?

Osmotic pressure created specifically by proteins in a fluid

What many creates plasma oncotic pressure?

Plasma proteins especially albumin

What drives fluid movement by bulk flow

Differences in hydrostatic and / or oncotic pressure

Hydrostatic vs. Osmosis pressure?

Hydrostatic pushes fluid and osmotic pressure draws water toward higher solute concentration

Osmotic vs. Oncotic pressure?

Oncotic pressure is a type of osmotic pressure caused by proteins

What is an isotonic solution?

Same effective solute concentration as the cell & the cell stays the same size

What is a hypotonic solution?

Lower effective solute concentration outside + water enters & the cells swell

What is a hypertonic solution?

Higher effective solute concentration outside + water leaves the cell & the cell swells

In which direction does water move by osmosis?

Toward the side with higher effective solute concentration

Now does water cross the cell membrane?

Directly through the membrane slowly / through water channels called aquaporins

What happens to a cell in an isotonic solution?

Water enters & leaves at equal rates + no net water movement

What happens to a cell in a hypotonic solution?

It gains water & swells (animal cell may burst)

What happens to a cell in a hypertonic solution?

It loses water & shrinks