MOVEMENT THROUGH THE
MEMBRANE
Bubble Lab
Section 7-3

• Function
:
• Regulates what enters and leaves the cell.
Provides protection and support
• Selective permeability
• Some substances can pass across the cell membrane and others can’t

Phospholipid Bilayer (Fluid Mosaic Model): a double-layer sheet that makes up cell membranes.

• Polar Head
– Hydrophilic
“Water Loving”
• Lipid Tails
– Hydrophobic
“Water Fearing”

Why is the lipid bilayer important?
• Tough, flexible structure
• Strong barrier between the cell and its environment

• Allows only certain materials in or out at certain times .
Ex. Ions (electrolytes)
Glucose
Water
Oxygen
Carbon dioxide

• Protein molecules
–Form channels and pumps that help to move material across the membrane

Other Membrane Structures
• Carbohydrate molecules
–Act like ID markers for the cell
–Basis for blood typing: the antigens on the blood cells (A, B, AB) are carbohydrate chains

Definition: The movement of molecules from an area of higher concentration to an area of lower concentration, until equilibrium is reached.
Equilibrium – concentrations of molecules are the same in all areas
Diffusion of Molecules

• Diffusion is caused by the constant movement and collision of molecules .
More molecules = More collision
• The collisions cause the molecules to spread out .

Molecules are able to diffuse through the cell membrane and allow the cell to function .
Facilitated Diffusion – some molecules need help from protein channels to cross the cell membrane.
Animation

Osmosis (A special kind of diffusion)
Osmosis is the diffusion of water molecules through a selectively permeable membrane .
Selectively permeable? only certain substances can pass through the membrane
Selectively Permeable - Osmosis

Isotonic – concentration of solute is the same on both sides of the membrane (equilibrium)
Hypertonic – the solution with a higher concentration of solute
Hypotonic – the solution with a lower concentration of solute

The cytoplasm of Elodea kinds of molecules.
cells is composed of about 70% water molecules and 30% other
What happens when the a liquid that is
Elodea cells are put into a. 50 percent water.
b. 70 percent water.
c. 100 percent water .

Moving down a concentration gradient is like riding a bike down a hill. It doesn’t require energy, goes high to low.
Osmosis, diffusion and facilitated diffusion are examples of passive transport !
ACTIVE TRANSPORT
Moving up a concentration gradient is like riding up a hill.
IT REQUIRES ENERGY .

• Active Transport: is the movement of materials through a cell membrane using energy.
• Molecules move from low concentration to high concentration.
• Protein pumps use ATP to pump ions and small molecules against concentration gradient.

1. Endocytosis – the process of taking material into the cell by means of infoldings of the cell membrane.
– Phagocytosis – extension of the cytoplasm surround and engulf the particle
– Pinocytosis – similar to phagocytosis, but cells take up liquid instead of particles.

2. Exocytosis
– Large molecules move from inside the cell to outside the cell.
– Contractile Vacoule – an organelle that constantly pumps H2O out of the cell.
Animation

• Cells with a specific structure and function and are found in multi-celled organisms.
• We have blood cells, brain cells, bone cells, liver cell, skin cells, etc .

Organ
System
Organs
Tissues
Cells

• Definition: A group of similar cells working together.
• Examples

• Definition: A groups of tissues working together to perform a specific job.

• Definition: Many organs working together to do a specific job.

1. Explain Diffusion
2. Explain Osmosis
3. What does selectively permeable mean?
4. What is facilitated diffusion ?
5. Are phospholipids the only molecules in a cell membrane?
6. What is active transport?
7. What are tissues, organs, and organ systems? Give Examples

= cell
10% salt
10% salt
10% salt
20% salt
20% salt
10% salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?
= cell
10% salt
10% salt
10% salt
20% salt
20% salt
10% salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?

= cell
10% salt
10% salt
10% salt
20% salt
20% salt
10% salt
Label the environment around the cell in each beaker as hypertonic, hypotonic or isotonic.
Label the net flow of water and state what will happen to the cell in each beaker?

1. Compare and contrast integral and peripheral proteins.
Integral proteins span the width of the membrane, some have a hydrophilic channel
(channel protein) to transport hydrophilic substances into or out of the cell.
Peripheral proteins are really appendages bound to the surface of the membrane that tie into the cytoskeleton and provide support.

2. What are the differences between the two types of transport proteins discussed in the article (use figure 7.10 to help you)
One type has a hydrophilic channel selective for a particular solute. The second shuttles a substance from one side to the other by changing shape (carrier proteins and protein pumps) Some use ATP as an energy source

3. Why are proteins so essential to keeping your cells hydrated?
The aquaporin is a channel protein that tremendously increase the rate at which water can enter the cell (3 billion per second)

4. Explain how diffusion relates to a concentration gradient.
Molecules spread out evenly into available space. Each moves randomly, but directional from high to low concentration gradient (“down” the concentration gradient)