Cell Boundaries

Every living cell exists in liquid environment.

There is liquid on the inside and outside of a cell.

One of the most important functions of the cell membrane is to regulate the movement of molecules from one side membrane to the other side.

Semi-Permeable Membrane

Smaller molecules can pass through.

Larger molecules cannot.

Diffusion Movement particles from high to low

concentration. Diffusion will occur until equlibrium is reached. This process does NOT require cellular energy

(ATP).

Osmosis

Diffusion of water across cell membrane from high to low concentration.

Water molecules can very easily pass through cell membranes, because they are small.

Solution Concentrations The cytoplasm of a cell is solution of many

substances dissolved in water. A solution is mixture of two or more

substances. The substances dissolved in a solution are

called solutes. The concentration of solution refers to

amount of solute dissolved in liquid (solvent).

Solution Solute Solvent

Environment of the Cell The solution concentration outside

the cell will determine the direction water moves across the cell membrane.

The terms hypotonic, hypertonic, and isotonic are ADJECTIVES! They describe the environment of the cell!!!

Hypertonic Environments Low concentration of water/High

concentration solutes outside cell. Water diffuses out of the cell and

cell shrinks.

Hypotonic Environments High concentration of water/Low

concentration solutes outside cell. Cells swell with water and may explode.

Isotonic Environment

Equal concentration of water/solutes inside and outside the cell.

Water will move equally in/out cell.

96% Water, 4% salt

98% Water, 2% Salt

97% Water, 3% Salt

95% Water, 5% Salt

98% Water, 2% Salt

98% Water, 2% Salt

Osmotic Pressure

Water pressure that builds up inside a cell due to a hypotonic environment.

If pressure is too high, what could happen? Osmotic pressure in plants = turgor pressure. Cell Wall helps to with stand turgor pressure.

Plasmolysis- loss of water or “wilting” in plants

Facilitated Diffusion Some particles

are too large to pass through the membrane.

They need help from channel proteins.

This process does NOT require energy!

Glucose

ChannelProtein

Passive Transport

Particles moving from high to low concentration.

Doesn’t require energy.

Active Transport

Occasionally, particles need to move “against the concentration gradient.”

Particles moving from low to high concentration.

Requires energy (ATP).

Endocytosis Type of active transport. Process of taking in large amounts of food

or liquid by means of active transport. 1. Phagocytosis (cell eating) – Taking in large

clumps of food.2. Pinocytosis (cell drinking) – Taking in large

amounts of liquid.

Exocytosis Type of active

transport. Forcing contents

out of the cell. Method of removing

large amounts of waste from cell.