Transport through

the

Cell Membrane

Review of the Types of

Membranes:

1. Permeable

2. Impermeable

3. Semi-permeable

1. Permeable

• ALL types of molecules can get

through, regardless of size or charge.

2. Impermeable

(non-permeable) • NO molecules can get through

3. SEMI-PERMEABLE !!!:

• SOME

MOLECULES CAN

GET THROUGH

– Very small or

– Non-charged

Fluid Mosaic Model

Example: • If you had glucose molecules and starch

molecules, which ones do you think could get through after 24 hours and why? The membrane is permeable to both.

4%

C6H12O6

in H2O

15% NaCl

2% C6H12O6

15 % NaCl

2% C6H12O6

30% NaCl

in H2O

Review of Definitions • Solute:

– what gets dissolved

• Solvent: – What does the dissolving, more plentiful than solute

• Solution: – the mixture of solutes and solvent

• Example: H2O and NaCl

Solute: NaCl

Solvent: H2O

Solution: H2O and NaCl

Passive Transport

The movement of

molecules across a

cell membrane

without energy input

from the cell.

http://www.tokresource.org/tok_classes/biobiobio/biome

nu/membranes/index.htm

It is made possible by the diffusion of molecules down a concentration gradient.

Diffusion: movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.

Concentration gradient: difference in the concentration of a substance from one location to another.

In diffusion, molecules generally move… …until equal distribution of concentrations

reached in all areas (EQUILIBRIUM)

…due to the random movement of molecules

Two types of passive

transport.

1. Osmosis

2. Facilitated Diffusion

OSMOSIS: Definition:

• Diffusion (movement) of H2O – from area of higher concentration to

area of low concentration

– THROUGH A MEMBRANE

– until equilibrium

OSMOSIS:

U-tube Osmosis

Three ways to describe solutions

in relation to other solutions,

based on their concentrations

1. Hypertonic

2. Hypotonic

3. Isotonic

1.Hypertonic: • Solution outside of the cell is hypertonic

when it has a higher concentration of

solutes than the solution inside of the cell.

90% water

80% water

The cells is said

to be in a

hypertonic

environment.

2. Hypotonic:

• Solution outside of the cell is hypotonic when it

has a lower concentration of solutes than the

solution inside of the cell.

This causes water

to move INTO the

cell.

3. Isotonic:

• Solution outside of the

cell is isotonic when its

concentration is equal

to the concentration

inside the cell

There are three consequences of osmosis:

• PLASMOLYSIS (cell shrinking): cell shrivels when placed in hypertonic environment – Examples:

• Drinking out of ocean when you are dying of thirst or

• Placing a fresh water fish in salt water…

(a) Isotonic

Water concentration inside the

cells is equal to the water

concentration in the fluid

surrounding the cell. Therefore,

there is no net movement of

water either into or out of the

cell.

(b) Hypertonic

Water concentration in the

surrounding medium is lower

than it is in the cell. Water

moves out of the cells and the

cells shrivel (crenate).

(c) Hypotonic

Water concentration outside

the cell is greater than it is

inside the cell. Water moves

into the cell, which swell and

sometimes burst – a process

called lysis.

Consequences: • Cytolysis (cell bursting): cell

balloons and bursts when placed in a hypotonic environment. – Examples:

• Place a salt water fish in fresh water

• Red Blood Cells in pure water

(a) Isotonic

Water concentration inside the

cells is equal to the water

concentration in the fluid

surrounding the cell. Therefore,

there is no net movement of

water either into or out of the

cell.

(b) Hypertonic

Water concentration in the

surrounding medium is lower

than it is in the cell. Water

moves out of the cells and the

cells shrivel (crenate).

(c) Hypotonic

Water concentration outside

the cell is greater than it is

inside the cell. Water moves

into the cell, which swell and

sometimes burst – a process

called lysis.

Turgor Pressure = Osmotic Pressure • In plants, turgor pressure forms as a result of

water pushing up against the CELL WALL

** This is what causes plants to grow upright.

Example:

http://homeschoolersresources.blogsp

ot.com/p/general-science.html

http://www.rpdp.net/sciencetips_v3/L8B2.htm

FACILITATIVE DIFFUSION:

• Protein Channels aid in the movement of

molecules across the cell membrane

FACILITATIVE DIFFUSION:

• Many of these protein channels are “two-way” and are

called PORES.

• Sometimes, a protein acts like a revolving door to allow

across only certain molecules. (Carrier proteins)

• These transport molecules ions or molecules (solutes)

through membranes in either direction until equilibrium is

reached

http://imcurious.wikispaces.com/Period+2+Midterm+Review+2009

FACILITATIVE DIFFUSION:

• Different solute particles fit different pores

• This depends on –Size –Polarity –Shape of molecule

• Ex. Glucose

• DON’T FORGET,

– THESE WERE ALL

•PASSIVE TRANSPORT

–SO THE CELL DID NOT NEED

TO EXPEND ANY NRG TO MAKE IT HAPPEN!!!!!