Cell Boundaries MIAMI BEACH SENIOR HIGH MRS DIAZ

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. The heads are made of Glycerol (alcohol) and a phosphate group and the tails are chains of fatty acids.

Phospholipids Phospholipids can move side to side and allow water and other non-polar molecules to pass into and out of the cell. This is known as simple diffusion because it does not require any energy and the water or molecules are moving with/down the concentration gradient. (high to low concentration)

Cell Membrane (cont’d) Notice also that the membrane is made of two layers of lipids, thus we call it a phospholipid 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)

Cholesterol Another type of lipid in the cell membrane is cholesterol which makes the membrane stronger.. Embedded in the phospholipid bilayer are glycoproteins that aid in identification and in cell recognition.

Proteins Proteins called integral proteins go all the way through the bilayer, while peripheral proteins only stay on one side. Integral proteins are also called a protein channel. Large molecules like lipids or carbohydrates use protein channels to move across membranes.

Carbohydrates Some of the membrane proteins called glycoproteins have carbohydrate chains attached to help cells recognize each other and certain molecules. Carbohydrate chains attached directly to phospholipids are called glycolipids

4 Functions of the cell membrane 1.Cell to Cell recognition 2.Regulates what enters the cell 3.Cell signaling 4.Separates the cell from the environment

Passive Transport Chapter 4 Section 1 Passive transport (no energy required) can occur in 4 different ways: i) Simple Diffusion ii) Osmosis 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.

ii) Osmosis Osmosis is the diffusion of water across a semipermeable (cell) membrane. Water will move down the concentration gradient

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! 2. Cells placed in a hypotonic environment (fresh water) will cytolysis. – BURST! Cells placed in a isotonic environment will be balanced

Water Movement Problems explain what will happen in each example

Active Transport (cont’d) Active transport is the movement of molecules up (against) the concentration gradient, from low to high. This type of transport requires energy in the form of ATP.

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.

Levels of Organization Atoms Molecules Cells Tissues Organs Organ Systems Organism

Final Thought “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