High School Biology Class Cell Transport High School Biology Class

I. Cell (Plasma) Membrane The cell membrane is composed of lipids (because they can separate substances.)

Cell Membrane (cont’d) The membrane is made of many phospholipids which have two parts: hydrophilic (water loving) heads and hydrophobic (water fearing) tails.

Cell Membrane (cont’d) Notice also that the membrane is made of two layers of lipids called a lipid bilayer.

Cell Membrane (cont’d) Also found in the cell membrane are certain proteins, which play an important part in the cell by: 1) Coordinating cell-to-cell behaviors. 2) Adjusting the cells metabolism rates. 3) Initiating growth & division times.

Cell Membrane (cont’d)

A. Marker Proteins Helps cells recognize similar cells. This is helpful for when our defensive cells encounter bacteria with unknown marker proteins, they can then destroy them.

B. Receptor Proteins Helps cells receive materials/signals outside of the cell. When cells need stored energy from the pancreas, they release signal molecules, which find and bind with the pancreas cells to let them know to release some energy.

C. Channel/Carrier Proteins Helps substances move across the cell membrane. If substances are too large to get through the lipid bilayer channel proteins (doughnut shaped) act as passage ways.

II. How Substances Move There are 2 types of transport across cell membranes: Passive – transport that does not need any energy. Active – transport that requires energy.

Passive Transport Chapter 4 Section 1 Passive transport (no energy required) can occur in 4 different ways: i) Simple Diffusion ii) Osmosis iii) Diffusion through Ion Channels iv) Facilitated Diffusion (Carrier Proteins)

Passive Transport (cont’d) During passive transport substances always move from high concentration to low concentration (this is known as a concentration gradient). After passive transport when the concentration of molecules is the same we say equilibrium exists.

i) Diffusion Diffusion is the movement of molecules down a concentration gradient, from high to low concentrations. Examples: food coloring in water, perfume spreading throughout a room, etc.

ii) Osmosis Osmosis is the diffusion of water across a semipermeable (cell) membrane. It is the same process as diffusion except it specifically means water movement.

a) Solutions A solution is a mixture of solutes (things being dissolved) and a solvent (things doing the dissolving). Water is typically the solvent. (i.e. sugar cube in water, the sugar is the solute)

b) Types of Solutions 1. Hypertonic: solution with a higher concentration of dissolved particles than its surroundings. 2. Hypotonic: solution with a lower concentration of dissolved particles than its surroundings. 3. Isotonic: solution with an equal concentration of dissolved particles to its surroundings.

c) Water Balance in a Cell 1. Cells placed in a hypertonic environment (salt water) will plasmolysis. – SHRINK!

c) Water Balance in a Cell 2. Cells placed in a hypotonic environment (fresh water) will cytolysis. – BURST!

c) Water Balance in a Cell 3. Cells placed in a isotonic environment will be balanced.

Water Movement Problems

iii) Diffusion through Ion Channels An ion channel is a doughnut shaped channel protein that is hydrophilic (polar) inside. Ions can pass through the channels without contacting the hydrophobic (nonpolar) part of the cell membrane.

Ion Channel (B)

iv) Facilitated Diffusion Facilitated diffusion is a passive form of transport caused by carrier proteins specific for the molecules they transport. Remember movement is always down the concentration gradient. (i.e. high to low) Also facilitated diffusion needs no energy.

a) Steps in Facilitated Diffusion 1. A molecule outside the cell binds to the carrier protein. 2. The carrier protein transports the molecule across the cell membrane. 3. The molecules are released inside the cell.

B) Active Transport Chapter 4 Section 2 There are many types of active transport, but the 2 we will learn are: i) The Sodium-Potassium (Na-K) Pump ii) Movement by Vesicles

Active Transport (cont’d) Active transport is the movement of molecules up (against) the concentration gradient, from low to high. Remember this time the cell must use its own energy (ATP) to move substances.

i) Sodium Potassium Pump It takes 3 sodium ions out for every 2 potassium ions put in the cell. There is more sodium inside the cell and more potassium outside the cell so the cell is working against the concentration gradient. Energy for the pump comes from ATP made by the mitochondria.

ii) Movement by Vesicles There are 2 types of vesicles: Endocytosis – into the cell. Exocytosis – out of the cell.

1) Endocytosis Process by which a cell engulfs a substance that is much too large to enter the cell by passing through the membrane. 2 types of Endocytosis: a) pinocytosis - liquids b) phagocytosis - solids

a) Pinocytosis Process where the liquids are taken into the cell.

b) Phagocytosis Process where a vacuole is formed around solid particles before they are taken into the cell.

2) Exocytosis Process by which large molecules are passed out of the cell without going through the membrane.

Any Questions? “Knowledge is not simply another commodity. On the contrary. Knowledge is never used up. It increases by diffusion and grows by dispersion.” --Daniel J. Boorstin