I.The Cell Membrane

A. Controls what enters and leaves the cell

B. Provides structure and support

C. Most cell membranes are made of a double layered sheet called a phospholipid bilayer.

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel

Lipid bilayer

Carbohydratechains

Section 7-3

Figure 7-15 The Structure of the Cell Membrane

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The Cell Membrane

A semi permeable membrane means that some substance can pass across the membrane and others cannot. The cell membrane is a semi-permeable membrane

Solution vs. Solutes• A solution is a liquid mixture of two or

more substances and are evenly mixed.

• The dissolved substance is called the solute.

• A solvent dissolves the solute• Solvent + Solute = Solution

Examples: Salt water, sugar water,

Passive Transport

• Transport across the cell membrane that does not require energy.

Diffusion

• Diffusion is the tendency of molecules to move from an area of high concentration to an area of low concentration.

Diffusion

• Molecules move from an area of high concentration to an area of low concentration.

Diffusion

• A semi permeable membrane means that some substance can pass across the membrane and others cannot.

• The cell membrane is made up of a semi-permeable membrane

Diffusion• Some molecules, such as water, can cross the

cell membrane by diffusion.

Diffusion• When the concentration of a solute is the

same through out a solution, the system has met equilibrium.

Diffusion

• Cells constantly maintain equilibrium in any system they are in and molecules are always passing in and out of the lipid bilayer even when equilibrium is met.

• Equilibrium- When the concentration of a solute is the same through out a solution, the system has met equilibrium.

Example of Diffusion

Osmosis

• Osmosis is the diffusion of water through a selectively permeable membrane.

Review Osmotic Pressure video

Effect when cell is placed in…

HYPO TONIC HYPERTONIC ISOTONIC

Hypertonic: The solution the cell is has a LOWER concentration of water than the concentration of the water inside the cell therefore water would MOVE OUT the cell and the cell would shrink

Hypotonic: The solution has a HIGHER concentration of water than the concentration of water inside the cell therefore water will GO INTO the cell and the cell increases in size.

Isotonic: The solution has an EQUAL concentration compared to the inside of the cell therefore no water would move in or out and the cell would remain the SAME size and shape.

Active Transport

Active Transport

• Material moves from an area of lower concentration to an area of higher concentration in a process called active transport.

• Active transport is the movement across the cell membrane that requires energy in the form of ATP.

How is this different than passive transport?

Forms of Active Transport

• Endocytosis- the process of taking in material into the cell by means of infoldings, or pockets, of the cell membrane.

Forms of Active Transport

• Exocytosis- is the removal of large amounts of material from the cell.

Two Methods of Transport

Passive Transport Active transport

With EnergyWithout Energy

1. Diffusion2. Osmosis

1. Endocytosis2. Exocytosis