All organisms are made of cellsCells are mostly liquid. Surrounding the cells is also liquid.

Movement through Cells

Inside Cell

Cell membrane

The cell membrane separates the cell from the liquid it is bathed in.

a) It allows only certain particles to enters and leave the cell. Therefore the cell membrane is considered

____________________

Role of the Cell Membrane

Selectively Permeable

lipid bilayerprotein channels

b) The cell membrane is made up of two parts:

___________________________

____________________________

Large particles can only enter and exit the cell through the protein channels BUT

Small particles can enter and exit straight through the lipid bilayer!!

Role of the Cell Membrane

All particles of matter--atoms or molecules are constantly in motion. In liquids, the molecules randomly move.*A solution is made when particles of sugar,

salt, or oxygen, etc. are dissolved in liquids

Particles of liquids

= solution+

What is a solution? Liquid mixture of 2 or

more substances. Water - solventThe substance dissolved

in the water - soluteConcentration =

mass of solute/volume of solvent

Concentration is similar to density.

Imagine you have a beaker filled with sugar water.

Problem: Imagine you add double the amount of sugar to the water.

Which beaker

contains a more

concentrated sugar

solution?

Sugar

Concentration of SolutionsMolarity (M) = unit of concentration used in

biochemistryThe greater the molarity of a solution the

greater the concentration. 0.25M sucrose solution (read as 0.25 molar)

has half of the concentration of a 0.50M sucrose solution.

Particles within an organism must continuously enter and exit the cell through the cell membrane using one of four processes:• Diffusion• Osmosis• Facilitated diffusion• Active transport

Particles in solution cross the cell membrane

The movement of a substance (liquid or gas) from areas of high concentration to areas of low concentration.

The motion is random --eventually all particles spread out evenly throughout the solution = equilibrium.

Diffusion

Food coloring (solute)+ water (solvent). What do you think will happen over time in

the solution? Discuss at table and draw on white board.

Diffusion Demonstration

Once equilibrium is reached, the movement of particles continues, but it is equal in all directions.

Solution remains in equilibrium. Particles remain equally spaced out.*See molecular workbench and answer

questions. (p1-6)

Diffusion

The cell membrane allows many types of particles (ions, atoms, molecules) to move in and out of the cell by diffusion.

But some types of molecules are not able to cross the membrane.

What determines whether a particle can cross the cell membrane?

Diffusion Across a Cell Membrane

Complete Worksheet to find out!

Design an experiment to test the effect of the size of a particle on its ability to diffuse. Your materials:

Diffusion Across a Cell Membrane

Small particles diffuse __________ than large particles across a cell membrane

• Only substances that can permeate the cell membrane can diffuse across it.

• Diffusion occurs from areas of ________concentration of solute particles to areas of ________ concentration.

• The movement of particles is always taking place.

Conclusions for Diffusion: faster

The cell expends NO ENERGY on the process of diffusion

high low

Particles dissolved in water cross the cell membrane

•Diffusion•Osmosis

Diffusion of water through a selectively permeable membrane. Water diffuses from where there is less solute (sugar, salt, etc.) to where there is more solute.

Osmotic pressure is the force that is placed on a selectively permeable membrane due to the flow of water into one side more than the other.

 See molecular workbench and answer questions

Osmosis: A special type of diffusion

OSMOTIC PRESSURE-placed on semipermeable membrane

Osmosis:Osmosis results in equilibrium when the

concentration of the solutions is equal on both sides of the membrane. A solution in equilibrium is also referred to as isotonic.

When solutions on both sides of the cell membrane do not have equal concentration they are described as hypotonic or hypertonic.

Hypotonic = lower concentration of soluteHypertonic = higher concentration of solute

Osmosis

Overall Direction of Water flow

Inside cell

Outside cell

Osmosis in AnimalsAt your table: Draw a picture illustrating #1 and

#2 below and answer the questions! Use arrows to show the movement of water.

1. What happens if blood cells are placed in a hypertonic (more concentrated) solution? (saltwater)*

2. What happens if blood cells are placed in a hypotonic (less concentrated) solution?(distilled water)*

Osmosis in Animals

Osmosis in AnimalsUnder normal bodily conditions, blood is the

liquid that surround the cells. Blood has the same concentration of solutes as

those inside the cell. This means that blood and cytoplasm are ______________________ to each other.

isotonic

Osmosis in Plants

1) What happens if plant cells are placed in a hypertonic solution (example: salt water)?

2) What happens if plant cells are placed in a hypotonic solution (example: distilled water)?

3) What happens if plant cells are placed in an isotonic solution (example: water with minerals)?

Healthy Plant

A plant cell is filled with proteins, sugars, salts.

The cytoplasm of plant cells is more concentrated than fresh water

The plant cell is hypertonic relative to freshwater

Since freshwater is used to water plants (not blood), the plant cells fill up with water.

Osmotic Pressure = Pressure created by water moving into a hypertonic cell.

With your table answer the following question:

Why doesn’t a plant cell burst (like a blood cell) when placed in freshwater? (Hint: What is a MAJOR difference between plant and animal cells?)

Osmotic Pressure = Pressure created by water moving into a hypertonic cell.

Cell Wall is RIGID

In one-celled organisms the cell does not burst when in a hypotonic solution (for example pond water).

One-celled organisms have mini-pumps called contractile vacuoles. As water enters the cell, it is pumped out by this organelle.

Osmosis in one-celled organisms

Osmosis and Contractile Vacuoles*

Because osmosis is a special type of diffusion

Osmosis:

The cell expends NO ENERGY on osmosis

Now: Complete Worksheet on OSMOSIS

Particles cross the cell membrane

•Diffusion•Osmosis•Facilitated diffusion•Active transport

Movement of specific molecules through protein channels in the cell membrane

The protein channels are specific to a type of particle. Example: glucose moves through a protein channel that is specific to glucose.

 

Facilitated Diffusion

The movement of particles is two ways but always from areas of high concentration (hypertonic) to areas of low concentration (hypotonic).

Cells use facilitated diffusion for substances such as salt, sugars and starches*.

 

Facilitated Diffusion

The cell expends no energy on facilitated diffusion.

Particles cross the cell membrane

•Diffusion•Osmosis•Facilitated diffusion•Active transport

Active Transport: Movement of material across the cell membrane in the OPPOSITE direction of diffusion.

During diffusion particles always moves in the direction of high concentration to low concentration (=concentration gradient).

During active transport particles move against the concentration gradient from low concentration to high concentration.

Active Transport

Because the flow of solute is from an area of LESS concentration to an area of MORE concentration the solute must be pumped by the cell*.  

See molecular workbench.

Complete Packet on Transport through a Cell Membrane

Active Transport

The cell EXPENDS ENERGY (found in molecules of ATP) on Active Transport

You will be assigned an article on a topic with a group of students. Read and discuss the article with your group and present the information to the class…as a poster, as a play, as a song, etc.

Topics Facilitated diffusion, insulin and diabetesDiffusion of oxygen into our lungs and emphysema Diffusion and alcoholPregnancy and diffusion of nutrients between

mother and fetus.

Connections to Daily Life