Passive and Active Transport

Movement of Material through the Cell Membrane

Each individual cell exists in a environment.

liquid

The presence of a liquid the cell.

environment

makes it easier for materials such as food, oxygen, and water to move into and out of There are several ways in which materials enter and leave the cell.

Two types of Passive Transport: Diffusion and Osmosis

Diffusion

Diffusion is the process by which molecules of a substance move from areas of higher concentration (more particles) of that substance to areas of lower concentration (less particles).

Examples: Food color in water Air freshener in house Dry erase cleaner

What determines whether diffusion occurs through a membrane?

1) If two substances are present at unequal amounts on either side of the membrane, each substance will tend to move towards the area of lower concentration until equilibrium is reached (same amount of particles on both sides).

2) The permeability of the membrane. (allows substances to diffuse across the membrane)

Note

A membrane is said to be impermeable to those things that cannot pass across it. Biological membranes are semi-permeable (cell membrane). They are permeable to some substances and impermeable to others.

Facilitated Diffusion

Many molecules are transported across a membrane in the direction of the lowest concentration by a carrier protein.

For example: In red blood cells, a carrier protein in the cell membrane transports glucose from one side of the membrane to the other.

The glucose transporter protein facilitates, or helps in the diffusion of glucose.

Osmosis

The diffusion of water through a selectively permeable membrane from an area of high concentration of water to an area of low concentration.

For example if you place a concentrated sugar solution on one side of a semi-permeable membrane and a dilute sugar solution on the other side. The result is the net movement of water through the membrane from the side with the

dilute

sugar solution to the side with the concentrated sugar solution.

Note

If, however two solutions contain

exactly

the same amount of dissolved material, there is no

osmotic

pressure across the membrane

separating

them because the concentrations of dissolved

materials

are in equilibrium.

Normal blood

cells will shrink if to much water leaves the cells due to osmosis. If to much water enters the cell during osmosis the red blood cell will swell.

If the amount of water that enters the cell is not

regulated

, then eventually to much water will enter the cell and it will burst.

Osmosis and Diffusion energy

are forms of

passive

transport across the cell membrane because is not needed for these processes.

Active Transport

Active transport

is an

energy

-requiring process that enables materials to move

across

the membrane

against

difference.

the concentration Think of a unicyclist going up hill, requires more energy then going down hill

There are two types of Active Transport

1) Individual membrane-associated pumps in the membrane. Molecules include calcium,

potassium chemical molecules

are carried through the

cell

, and sodium and require energy.

2) Large amount of materials are

transported

through the movement of the cell membrane

Endocytosis

: is the process of taking

material

into the cell by means of of

food

this way.

infoldings

or pockets of the cell membrane. Large molecules, clumps , and even whole cells can be taken up in

Phagocytosis cytoplasm

food.

: large particles taken into the cell by endocytosis. In phagocytosis, extension of surround and engulf

large

particles. Amoebas use this method to take in

Endocytosis

Pinocytosis

: process of taking up

liquid

form the surrounding

environment

by cells. Tiny pockets form along the cell

membrane

, fill with liquid, and pinch off from

vacuoles

within the cell.

Exocytosis: The removal of means of a contractile vacuole, along with removal of

large

material.

water

by

Exocytosis