Step into my elevator!• When the elevator was

crowded, what did all the people in the elevator want to do? WHY?

• When one more person was forced into the already crowded elevator did they find it was easy or difficult to get in? WHY?

Just like people entering or exiting an elevator, molecules move into or out of cells. Sometimes easily, sometimes with great effort.

Cell TransportPages 80-85

• There are two ways that molecules can move through a cell membrane

1. Passive Transportex. Osmosisex. Diffusion

2.Active Transportex. Transport Proteinsex. Engulfing

• Diffusion is the main method that small molecules move across a membrane

• It’s the process by which molecules move from an area of higher concentration to an area of lower concentration.

• Example – perfume bottle

What Does Concentration Mean?

• Taste the liquid in the three cups.• Which cup has a lower concentration of water in

it? (higher concentration of lemonade mix)?• Which cup has a higher concentration of water

molecules in it (lower concentration of lemonade mix)?

More mix, less water molecules

Less mix, more water molecules

Diffusion Across A Cell Membrane

Cell Membrane

OUTSIDE OF CELL

INSIDE OF CELL

How do most small molecules move across the cell

membrane?• The cell membrane that

surrounds the cell is selectively permeable.– Some substances can

pass through the membrane while others cannot Ex. the balloon with vanilla

• Cells must get needed molecules in and expel wasteSubstances move in and

out through pores.

What causes Diffusion?• Molecules are always

moving and bumping into each other.

• The more molecules there are the more collisions there will be.

• Collisions will cause the molecules to push away from each other until, over time, they will spread out evenly.– They meet a point of

equilibrium.

OSMOSIS• Like oxygen, water passes easily

into and out of cells.• Osmosis is the diffusion of water

molecule.– Water moves from an area of higher

concentration to an area of lower concentration.

• Cells cannot function without water, so most cell processes depend on osmosis.

Effects of Osmosis

Normal blood cell at

equilibrium. Concentration of water inside the cell is the

same as outside.

Hypertonic blood cell.

Concentration of water inside

the cell is higher than the outside.Water

flows out of the cell, shrinking

it.

Hypotonic blood cell.

Concentration of water inside the cell is lower

than the outside. Water flows in the cell,

swelling it.

ACTIVE TRANSPORT• Diffusion and osmosis are forms of

passive transport.– Movement of molecules without using

cellular energy

• What if cells need to take in molecules that are found in a higher concentration?– The cell has to move molecules in the

opposite direction.– Cells can do this, but they need to use their

own energy

• Active transport is the movement of molecules using cellular energy.

Methods of Active Transport

1. Transport proteins – proteins that pick up molecules outside the cell and carry them in using energy. (ex. calcium, potassium, sodium)

2. Engulfing – Cell membrane surrounds the particle and forms a vacuole around it. The cell uses energy in this process.

In PASSIVE transport molecules (in this case, sugar) will move from a more concentrated area and will spread out to a less concentrated area throughout the beaker filled with water. Molecules NATURALLY want to move this way, so it does NOT require energy to happen.

In ACTIVE transport molecules will move from a less concentrated area and will be taken into a more concentrated area. The cells need lots of energy in order to do this.