Chapter 3

Section 2 Moving Cellular Materials

Passive Transport

• Why do we have screens on our windows at home?

• A cell has a membrane that works just like your window screen– It takes in food, oxygen, & other substances– Releases wastes– It is SELECTIVELY PERMEABLEWhat if the holes in your window screen were 1 inch

by 1 inch???

Passive Transport Continuted..

• Which was things move depend on the size of molecules or particles

• The path they take through the membrane• Whether or not energy is used

• THE MOVEMENT OF SUBSTANCES THROUGH THE CELL MEMBRANE WITHOUT ENERGY IS PASSIVE TRANSPORT

Diffusion

• Molecules moving from one area where there are more of them to an area where there are fewer of them– Ex: perfume– This is still a type of passive transport– The molecules will continue to move from one

area to another until they are equal in both areas

Equilibrium

• When the molecules are balanced out, we call this equilibrium

• After equilibrium is reached it is maintained because molecule continue to move

Osmosis- The Diffusion of Water

• The diffusion of water through the cell membrane is referred to as osmosis

Osmosis

Where does osmosis occur?

• In plant cells- for example the carrot experiment-losing water from a plant cell causes its cell membrane to come away from its cell wall. This reduces pressure against the cell wal and a plant cell become limp- like the carrot

In animal cells- if too much water enters the cell it will burst!

Swollen- Normal- Shrivelled

Facilitated Diffusion

• Molecules are SO large they can only enter the cell with the help of molecules in the cell membrane called transport proteins

• Think of it like a fast-food restaurant- if you hand money in the drive through window they hand back your change and food. Without giving them money- you wouldn’t get food

Without the protein opening up to let the molecule in- there is not a

way in because it is too large.

Active Transport

• When a substance is needed inside a cell even though the amount of that substance inside the cell is already greater than the amount outside the cell

• For ex- You leave the football game and get outside of the gates when you realize your forgot your jacket in the bleachers. You have to squeeze back throught the crowd at the gates to get your jacket. You will have to push and squeeze (use energy) to get back through everyone.

Getting through the crowd takes effort

Active Transport uses energy!

Endocytosis

• The process of taking a substance into a cell by surrounding it with the cell membrane – Usually these molecules and particles are too

large to move by diffusion or to use the cell membrane transport proteins.

– The cell membrane actually folds in on itself, enclosing the item in a sphere called a vesicle

Exocytosis

• When the contents of a vesicle are RELEASED by a cell (moved out)

• A vesicles membrane fuses with the cell’s membrane and the vesicles contents are released