Cell membrane & Transportation

What do cell membranes do?

They hold the cell together and also allow things to move in and out of the cell. They are SELECTIVELY PERMEABLE - meaning they have very small holes in them which only allow very small molecules through.

What can and cant pass through

Glucose, amino acids, water, oxygen, carbon dioxide can all pass through.

Starch and proteins cannot pass through.

What 3 ways to substances move in and out of cells?

Diffusion

Osmosis

Active transport

What is diffusion?

Diffusion is the movement of particles from a region o high concentration to a region of low concentration this allows substances to move across the cell membrane.

Information on diffusion

It is a movement down the concentration gradient.
It happens in fluids (liquids/gases) because the particles in these substances are free to move about randomly.
It is a passive process - does not require energy.

What is osmosis?

Osmosis is the diffusion of water molecules, from a region of higher concentration to a region of lower concentration, through a selectively permeable membrane.

A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.

Information on osmosis

The water molecules pass both ways through the membrane during osmosis, because the water molecules move about randomly.
BUT because theres more water molecules on one side than the other, theres a steady net flow of water into the region with fewer water molecules.
The solute solution becomes more dilute - evening up the concentration until it is the same.

What is active transport?

Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. The particles move against the concentration gradient, using energy released during respiration.

Information on active transport

The energy used is released during respiration and is in the form of ATP.
It moves up the concentration gradient.

COMPARING - Down a concentration gradient

Diffusion - Yes

Osmosis - Yes

Active transport - No

COMPARING - Agains a concentration gradient

Diffusion - No

Osmosis - No

Active transport - Yes

COMPARING - Energy needed

Diffusion - No

Osmosis - No

Active transport - Yes

COMPARING - Substance moved

Diffusion - Dissolved solutes

Osmosis - Water

Active transport - Dissolved solutes

COMPARING - Notes

Diffusion - Gases and dissolved gases also diffuse

Osmosis - Partially permeable membrane needed

Active transport - Carrier protein needed

3 factors that affect diffusion

1. Larger concentration gradient = the steeper the concentration , the faster the rate

2. Higher temperature

3. Larger surface area

4. Pressure = molecules move quickly from area of higher to lower pressure

How do solutions become in equilibrium?

Mixing the solutes and solvents until the concentration of solute is equal throughout

Examples of osmosis in living things

• helps plant cells absorb water from the soil then moves the water throughout the plant carrying minerals to support the plants growth.

• helps the intenstines absorb water from food then circulates throughout the body transporting nutrients to maintain cell function.

Examples of diffusion in the body

• Gases within lungs

• Oxygen in our blood

examples of active transport in living things

• uptake of glucose in the intestines of human body

• uptake of minerals / ions into root hair cel