Westside High School 9th Grade Biology

Crossing the Plasma Membrane

Questions• What is the job of the plasma membrane?

• What is semi-permeable?

• What is the difference between active transport and passive transport?

• What is osmosis?

• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?

• What are examples of each type of transport?

The plasma membrane maintains homeostasis for the cell

It is selectively permeable:

It controls what goes into and out of the cell

Plasma Membrane Structure

Two key components of the membrane:

Phospholipids – form the membrane

Proteins – act as “gates”

Two forms of transport across the membrane:

Passive TransportNo energy needed

• Examples:– Diffusion– Osmosis

Active Transport• ENERGY used

• Examples:– Endocytosis– Exocytosis

Two forms of transport:

Passive Transport

Diffusion Osmosis

* Does not use energy

Active Transport

Endocytosis Exocytosis

* Uses energy

Endocytosis

Figure 3.8

Active transport

Exocytosis

Figure 3.8

Active transport

Active Transport• Endocytosis

– Pino-

– Phago-

• Exocytosis

Figure 3.9

Ion pumps: Thru a protein, but using energy

Active Transport:

Energy Used?

Examples?

Passive Transport: Diffusion

• Small, uncharged particles are able to pass right between the phospholipids

• This is called simple diffusion

Passive Transport: Diffusion

• There are also proteins embedded between the phospholipids.

• These proteins function as gates, allowing larger or charged molecules to get in/out of the cell

• Only molecules which are “recognized” are allowed thru these proteins

• This is facilitated diffusion

Passive transport: Diffusion

Lower Concentration

Higher Concentration

Molecules collide – pass thru membrane

Concentration gradient:

Osmosis is the movement of water

• Water moves TOWARDS the molecules

• Think of it as “water wants to dissolve stuff”

Passive Transport: Osmosis

HYPERtonic ISOtonic HYPOtonic

Which way will water move in each case?

Passive Transport: Osmosis

• HYPERtonic ISOtonic HYPOtonic

What do plant cells have outside of the cell membrane

that animal cells do not have?

What difference will this make with osmosis?

Effect of osmosis on plant cells

Flaccid - Turgiddue to plasmolysis - cell shrinks from cell wall

Passive transport: osmosis

Osmosis

Which way will water move?

Passive Transport

Energy?Examples?

Hypertonic or Hypotonic?

Crossing the Plasma Membrane

Passive Transport Active Transport

Crossing the Plasma Membrane

Passive Transport

• No energy needed

• Diffusion

• Osmosis

Active Transport

• ENERGY used

• Endocytosis

• Exocytosis

Post test• What is the job of the plasma membrane?

• What is semi-permeable?

• What is the difference between active transport and passive transport?

• What is osmosis?

• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?

• What are examples of each type of transport?