CellsDiffusion and

Osmosis

Cells have to control what leaves and what enters the cytoplasm.

Concentration Gradient

Water and solutes move according to their concentration gradient Everything naturally moves away from where it is concentrated and towards where it is less concentrated

This natural movement is called diffusion.

Concentration gradients

Concentration gradients form when there is a difference in concentration between two places

Diffusion takes place until the concentration reaches equilibrium

Diffusion naturally tries to equalize concentration of water and solutes

Carbon dioxide naturally diffuses out of animal cells because animal cells produce CO2 as they make energy from food.The concentration inside is higher, so the net movement of CO2 is outward.

Movement of CO2 and O2

Oxygen naturally diffuses into animal cells because they use up oxygen as they turn food into energy

Carbon dioxide builds up as cells use the oxygen

The concentration of oxygen outside is higher, so the net movement of O2 is inward.

The concentration of CO2 is higher inside the cell and has a net movement outside the cell.

The cell membrane does not stop the diffusion of CO2, O2, or water molecules

CO2, O2, and H2O are small molecules

they each move down their individual concentration gradients until equilibrium is reached.

Salts and sugars cannot get through the bilayer, but water can

This makes the cell membrane semipermeable.

The movement of water through a semipermeable membrane that blocks solutes from moving is called osmosis.

Osmosis is the diffusion of water through a semipermeable membrane

Osmosis

Osmosis is used by plants to lift water upward. All the plants cells must do is maintain a higher solute concentration inside their cells.

Osmosis can pull water into of a cell if the cell is placed in an environment with a lower solute concentration

Hypotonic Solutions

Hypotonic means lower solute concentrationanimal cells can rupture in hypotonic environments

plant cells are protected from rupture by their strong cell walls

Osmosis can also pull water out of a cell if the cell is placed in an environment with a higher solute concentration

Hypertonic Solutions

Hypertonic means higher concentration of solutes A cell placed in a hypertonic

environment will lose water and shrink.

Plant cells plasmolyze when placed in very salty water.

Isotonic Solutions

Isotonic means balanced Cells in an isotonic environment

experience no net flow of water due to osmosis.

The water flowing in is balanced by the water flowing out

Red Blood Cells in a Range of

Solutions

Summary

Hypertonic = higher = dehydrating environment, cells shrink

Hypotonic = lower = bloating environment, cells swell

Isotonic = equal =homeostatic environment, cells “happy”

Hypertonic, Hypotonic, and Isotonic Examples

Solution Examples

Quick Osmosis Movie

Experiment Videos

Iodine Ziplock Experiment

Lettuce Experiment

Egg Experiment