CH. 3 ~ CELLS

Cell Membrane1. Surrounds ALL cells

2. Has a “Phospholipid bilayer” which makes it “flexible and “fluid”

Cell Membrane“Phospholipid bilayer”

- Phosphate ‘head’ (polar- hydrophillic)

-2 Lipid ‘tails’ (nonpolar- hydrophobic)

-What is “Polar” vs “Nonpolar”?

Water Molecule2 Hydrogen Atoms + 1 Oxygen Atom

A water molecule is a ‘polar’ molecule because it has a partial negative charge on one side and a partial positive charge on the other side.

When the Hydrogen atom of one water molecule is attracted to the oxygen atoms of another water molecule a hydrogen bond is formed.

Lipids are Nonpolar molecules

Cell Membrane3. Semi-permeable – only allows certain

substances to pass through

4. Contains proteins- some used for identification and some for transport (that help to pass materials through).

Transport of materials into and out of the cell

• Passive Transport – movement of molecules that does not require energy.– Usually from high concentration to lower

concentration

ex. Diffusion, Osmosis, Facilitated diffusion

• Active Transport – movement of molecules that requires energy. – Usually from low concentration to high

concentration (against the concentration gradient)

ex. Pumps, endocytosis, exocytosis

Passive Active • Diffusion

• Osmosis

• Facilitated Diffusion

• Pumps

• Endocytosis

• Exocytosis

Terms:• Equilibrium – when 2 given areas have the same

concentration of molecules.

• Concentration Gradient – the difference in concentration of molecules in 2 given areas.

(Ocean- swimming with the tide or against it- which requires energy?)

• Defines HOW molecules will move, if going WITH the concentration gradient (from high to low = passive transport) or AGAINST it (from low to high = requires energy = active transport

Passive Transport:

1. Diffusion – movement of molecules from an area of high concentration to an area of lower concentration.

Passive Transport:

2. Osmosis – diffusion of water

3. Facilitated diffusion – passive transport of materials across a cell membrane using protein channels.

Facilitated Diffusion(complete on back of the notes)

Protein Channels Carrier Proteins

Facilitated DiffusionIncreases the rate of diffusion

• Similar to simple diffusion in the sense that it is diffusion (across a membrane) from a high concentration to a lower concentration.

• However, this time the rate of diffusion is greatly accelerated by the action of membrane proteins that act as carrier molecules and aid in diffusion.

http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

Passive vs. Active Transport

• Passive Transport - Transport processes that happen "passively" without the cell needing to expend any energy to make them happen.

• Active Transport - transport processes that require energy from the cell's reserves to "power" them.

Pictures of Passive and Active Transport(complete on back of the notes)

Using a Protein Pump

Using a Protein Channel

Energy Added

Pumps

• Type of active transport

• Move molecules from an area of LOW concentration to an area of HIGH concentration

ACTIVENa-K (sodium-potassium) Pump

ACTIVEEndocytosis

• Intake of material (food) using the cell membrane

• Cell membrane surrounds material and encloses it – forming a vesicle/vacuole.

Amoeba Eating

ACTIVEExocytosis

• Removal of material (waste) from a cell.

• Golgi Apparatus “packages” the material into a vesicle and sends it to the cell membrane

• The vesicle fuses with the membrane

• The material is deposited outside the cell

Exocytosis

Endocytosis and Exocytosis(complete on back of the notes)

http://www.northland.cc.mn.us/biology/Biology1111/animations/transport1.html

PASSIVE ACTIVENO ENERGY• Diffusion of

perfume, food coloring

• Osmosis• Facilitated diffusion

– Protein channels– Carrier proteins

ENERGY• Exocytosis

– GA packages and secretes wastes

• Endocytosis– Membrane

surrounds and engulfs food, etc. (Amoeba)

• Pumps– Sodium-Potassium

Electron Micrograph of Exocytosis

• This figure was taken from Alberts et al, Molecular Biology of the Cell, Garland Publishing Third Edition, 1994

DIALYSIS DEMO

• The small molecules of water and iodine moved from an area of high concentration, outside the cell, to an area of low concentration inside the cell in order to try to reach equilibrium. The large molecules of starch were not able to diffuse and reach equilibrium because they were too large to pass through the semi-permeable membrane.

Solute vs. SolventOsmosis and Tonicity

• Solution – a homogenous (same throughout) mixture

• Solvent – the substance in a solution that dissolves other substances (solutes)

• Solute – the substance in a solution that is dissolved.

Another way to think about it:

a solute is dissolved in another substance, known as a solvent. Usually, the substance present in a greater amount is considered as the solvent.

Which is the solute? Solvent? Explain your

rationale

water and kool-aid.

WATER IS THE UNIVERSAL SOLVENT

Osmosis

• A type of diffusion• The movement of

WATER from an area of ______ concentration to an area of ____ concentration

There are 3 types of osmotic solutions

• Hypotonic – there is a greater concentration of solute (ie, salt, the ‘stuff’) in the cell then in the fluid around the cell

• Hypertonic – there is a greater concentration of solute (ie, salt, the ‘stuff’) in the solution than in the cell

• Isotonic - equilibrium

Another way to think about it

• Hypotonic – more water outside the cell, therefore water rushes into the cell

• Hypertonic – more water inside the cell, therefore water rushes out of the cell

• Isotonic – same amount of water inside and outside the cell so nothing changes

Whenever solutes (dissolves substances) are added to water, they decrease the number of free water molecules; more solute molecules, fewer free water molecules

Osmosis inRed Blood Cells

Osmosis inRed Blood Cells

Hypo Iso Hyper

Osmosis in a Plant Cell

Hypo

Iso

Hyper

Osmosis in a Plant Cell

Comparison of Plant and Animal Cells in Osmotic Solutions

What is the major differences between what happens in plant and animal cells when placed in a hypotonic solution?

PASSIVE ACTIVE• Material only

moves DOWN the concentration gradient (from HIGH to LOW concentration).

• Material can move up OR down the concentration gradient since energy is used to move the material.

• http://www.nclark.net/BioChapter8

Animation

• www.biologycorner.com/bio1/diffusion.html

• http://www.nclark.net/BioChapter8