MovinMovin’ On Out

Molecules in Motion

The Gatekeeper• Cell membrane

• Selectively permeable

Permeable• Oxygen

• Water

• Carbon dioxide

Not Permeable• Some large molecules

• Salts

Methods of Movement

• Diffusion

• Osmosis

• Active transport

Diffusion• Molecules are ALWAYS

moving.• Molecules bump into each

other.• Collisions cause molecules to

push away from one another• Molecules continue to spread

out evenly throughout the area.

Osmosis• the diffusion of water

molecules• Water moves from an area of

higher concentration to an area of lower concentration through the cell membrane.

• See Fig.5

Passive Transport• Moving materials through

the cell membrane through osmosis or diffusion does not require much energy—this is passive.

Active Transport• Cell uses energy to move

materials through a cell membrane.

• Transport Proteins “pick up” molecules outside the cell and carry them in, using energy. They also take molecules out by the same method.

Active Transport (cont’d)

• Another form: Engulfing-cell membrane surrounds particle and cell membrane pinches off to form a vacuole using energy.

Why are cells so small??

• Cytoplasm carries materials throughout the cell.

• If a cell is too large, it take a longer time for a molecule to reach its center.

• It would also take a long time for wastes to be removed.

Why are cells so small? (cont’d)

• So… a cell that is too large could not function well enough to survive.

• When a cell reaches a certain size, it divides into two cells.

Answers to the Study Guide

Pages 58-59

1. Define osmosis.

• Diffusion of water molecules through a selectively permeable membrane.

2. What happens to a red blood cell when there is no longer a lower concentration of water outside the

cell than inside the cell?• If there is too much salt in the cell, the

water moves out of the cell by osmosis. The cell shrinks.

3. What happens to a red blood cell when there is a higher

concentration of water outside the cell than inside the cell?

• The water moves into the cell causing the cell to swell.

4. Define passive transport.

• The movement of materials through a cell membrane WITHOUT USING ENERGY!

5. Name 2 examples of passive transport.

• Diffusion and osmosis.

6. Define active transport.

• USES ENERGY to move substances through a cell membrane.

7. An example of active transport is when the cell moves molecules

in the __________ direction.

• Opposite (lower to higher)

8. What is the difference between active and passive transport?

• Active transport uses energy to move substances, and passive transport does not require energy.

9. What are transport proteins?

• Transport proteins pick up molecules outside the cell and carry them in or out.

10. Name 3 substances transport proteins move in and out of cells.

• calcium, potassium, sodium

11. Describe the steps in transport by engulfing.

• The cell membrane surrounds a particle. The cell membrane pinches off to form a vacuole within the cell.

12. How is a molecule moved through a cell?

• It is carried by a stream of moving cytoplasm.

13. What would happen if a cell became too large???

• The cell would not function well enough to survive. It would divide into 2 cells.