Moving Substances Across Cell Membrane

• cell membrane is semi–permeable

• Some molecules pass through easily, some need help• Some molecules pass through without the expenditure of

energy (spontaneous) and some require an input of energy (ATP)

What molecules move IN and OUT of a cell:

• Small nonpolar molecules (CO2, O2)• Small polar molecules such as water • Ions and charged molecules• Large polar molecules (eg. Glucose)• Macromolecules

Movement IN and OUT can Be PASSIVE or

ACTIVE

Passive Transport• cell uses no energy • molecules move randomly• Molecules spread out from an area of high

concentration to an area of low concentration.

[High][Low]Three types: 1. Diffusion 2. Facilitative Diffusion3. Osmosis

high

low

Weeee!!!

Passive Transport:

1. Diffusion: random movement of particles from an area of [high] to an area of [low].

• diffusion continues until all molecules are evenly spaced (equilibrium is reached)-

Note: molecules will still move around but stay spread out.

http://bio.winona.edu/berg/Free.htm

Simple Diffusion Animation

2. Facilitated diffusion: diffusion of particles from [H L] through transport proteins found in the membrane

Transport Proteins arespecific – they “select” onlycertain molecules to crossthe membrane

Facilitated diffusion (Channel Protein)

Diffusion (Lipid

Bilayer)

Passive Transport:

Carrier Protein

A B

• http://bio.winona.edu/berg/Free.htm

3.Osmosis: diffusion of water through a selectively permeable membrane from an area of [H L]

•Water moves freely through pores.

•Solute (green) too large to move across.

Osmosis animation

Passive Transport:

Effects of Osmosis on Life

• Water molecules are so small and so numerous that cells can’t control movement of water through the cell membrane.

So what determines the direction of water movement?The environment around the cell,

…specifically,the concentration of water molecules inside the cell

compared to outside

Environment around the cell is either:

HYPOTONIC, ISOTONIC, HYPERTONIC

But first - Don’t confuse Volume of water with Concentration

Equal Volumes, Different Concentration

Hypotonic Solution

Hypotonic: The external environment (ECF) has a lower concentration of solutes and a higher concentration of water than inside the cell.

Result: Water moves from the ECF to inside the cell

- Cell Swells and bursts open (cytolysis)!

• Osmosis Animations for isotonic,

hypertonic, and hypotonic solutions

Compare a blood cell in an isotonic environment with one in a hypotonic

environment

Isotonic SolutionIsotonic: The concentration of solutes in the ECF is equal to the concentration of solutes inside the cell.

Result: Water moves equally in both directions and the cell remains same size. (Dynamic Equilibrium)

• Osmosis Animations for isotonic,

hypertonic, and hypotonic solutions

Water on the way out

Hypertonic Solution

Hypertonic: The ECF has a higher concentration of solutes and a lower concentration of water than inside the cell.

Result: Water moves from inside the cell into the solution: Cell shrinks. Plasmolysis (plant cell) Crenation (animal cell)

• Osmosis Animations for isotonic,

hypertonic, and hypotonic solutions

shrinks

In what type of solution are these cells?

A CB

Hypertonic Isotonic Hypotonic

Plant cells resist bursting. Why?

Active Transport•cell uses energy

•actively moves molecules to where they are needed

•Movement of molecules from an area of [low] to

an area of [high]Three Types1. Protein Pumps2. Endocytosis3. Exocytosis

high

low

This is gonna be

hard work!!

•Animations of Active Transport & Passive

Transport

Types of Active Transport

1. Protein Pumps –are special transport proteins that help move molecules IN/OUT - require energy to do work

example: Na+/K+

Potassium Pumps are important in nerve responses.

Sodium Potassium Pumps (Active Transport using proteins)

Protein changes shape to move molecules: this requires energy!

Types of Active Transport

• 2. Endocytosis: taking bulky material into a cell • Uses energy• Cell membrane folds itself

around food particle• “cell eating”• forms food vacuole &

digests food• This is how white blood

cells eat bacteria!

Types of Active Transport

3. Exocytosis: Forces material out of cell in bulk• membrane surrounding

the material fuses with cell membrane

• Cell changes shape – requires energy

• EX: Hormones or wastes released from cell

Endocytosis & Exocytosis animations

• Endocytosis_[www.keepvid.com].mp4

• Active_Transport_~~_[www.keepvid.com].mp4