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The Cell Membrane

Moretz

Biology

Outline

Structure of the membrane

Phospholipids

Proteins

Movement across the membrane

Homeostasis

Passive transport – diffusion & osmosis

Active transport – endocytosis & exocytosis

Location

Surrounds the cell.

Present in ALL cells.

Functions

Regulates what materials enter & exit the cell.

Communicates with other cells.

Uses receptor proteins to communicate.

Structure

Made up of:

Phospholipids

Proteins

Phospholipids

Two fatty acids

Nonpolar.

Hydrophobic

Phosphate group

Polar

Hydrophilic

Phospholipids

Hydrophilic

head (water

loving)

Two

hydrophobic

tails (water

fearing)

Lipid Bilayer

Two layers of

phospholipids

make up the

cell membrane.

1

2

Proteins

Embedded throughout the cell

membrane.

Transport materials across the

membrane (carrier proteins)

Act as chemical signals to help

cells communicate (receptor

proteins)

Move around the membrane.

Fluid Mosaic Model

FLUID- proteins &

phospholipids can

move.

MOSAIC- proteins

form patterns.

Modeling the Membrane

Create a model of the cell membrane

Label each component.

On the phospholipid, label the following: hydrophobic,

hydrophilic, polar, nonpolar, phosphate heads, lipid tails.

Describe how the structure of each part of the

membrane helps it do its specific job.

Describe the function of the cell membrane.

Explain how the structure of the membrane allows it

to perform its function.

Selectively Permeable

The cell membrane controls what enters &

exits the cell.

It selects which molecules may pass through

the membrane and which ones are blocked.

Homeostasis

The cell membrane helps the cell maintain

homeostasis.

Properly balances the amount of water and

nutrients in the cell.

Concentration Gradient

Difference in concentration in two parts of a

system.

Types of movement across the membrane are

determined by the concentration gradient.

Types of movement:

Passive transport – with gradient

Active Transport – against gradient

Concentration GradientHIGH

CONCENTRATION

LOW

CONCENTRATION

Concentration

Sort the following from least concentrated to

most concentrated.

12 g of salt in 3 L of water.

12 g of salt in 12 L of water.

12 g of salt in 8 L of water.

12 g of salt in 2 L of water.

Concentration

Sort the following from least concentrated to

most concentrated.

12 g of salt in 2 L of water.

12 g of salt in 3 L of water.

12 g of salt in 8 L of water.

12 g of salt in 12 L of water.

Concentration

Which is more concentrated?

12 g of salt in 3 L water or 12 g salt in 6 L of

water?

Concentration

Which is more concentrated?

12 g of salt in 3 L water or 12 g salt in 6 L of

water?

12 g/3L vs. 12 g/6 L

4 g/L vs. 2 g / L

4 g/L is twice as concentrated.

Passive Transport

Movement WITH the concentration gradient.

Does NOT require energy.

Types:

Diffusion

Osmosis

Diffusion

Molecules move from areas of high

concentration to low concentration.

OSMOSIS – diffusion of water molecules across

the membrane.

Equilibrium

Concentration

of molecules

throughout

the solution is

equal.

Effects of Osmosis

Isotonic

Concentration outside the cell is EQUAL to the

concentration in the cell.

Effects of Osmosis

Hypertonic

Concentration outside

the cell is GREATER

than the concentration

inside of the cell.

Plasmolysis – cell

shrinks

Effects of Osmosis

Hypotonic

Concentration outside

the cell is LESS than

the concentration in

the cell.