Cell Membranes

Cell Membrane

I. Why must cells control materials? Cells must maintain homeostasis: or balance of its internal environment.

II. Structure of Plasma Membrane: A. Bilayer of phospholipids (which have a

phosphate “head” and fatty “acid tails”) and proteins.

B. Phospholipids can move around sideways through their layer. This makes it act like a liquid. It is called a fluid mosaic model.

III. Proteins

1. Determine which particles (water, ions) will pass into the cell.

2. Act as markers that recognize chemicals from both inside and outside the cell.

A. Experiences:

The goal is to understand how particles or molecules spread with kinetic energy…then we can apply this to the cell.

III. Diffusion

III. DiffusionB. Kinetic Energy.

1. Particles are in constant motion

2. They move from areas of HIGH

concentrations to areas of LOW

concentration. 3. Particles spread until they are evenly distributed (spread out) (called dynamic equilibrium).

They are still moving, but have EQUAL concentrations.

I. Osmosis

A. Osmosis is the DIFFUSION of WATER across a membrane from areas of high water concentration to areas of low water concentration.

1. Isotonic Solution: concentration of dissolved substances is the same as the concentration inside the cell.

Effect on cell:

Result:

2. Hypotonic Solution: concentration of dissolved substances is ______________ than that in the cell.

Effect on cell:

Result:

3. Hypertonic Solution: concentration of dissolved substances is ___________ than inside the cell.

Effect on cell:

Result:

B. Dynamic Equilibrium:

Particles are continually moving but there is no overall change.

C. Diffusion depends on random movement of particles.

D. Diffusion continues until there is no overall change in concentration. At this point dynamic equilibrium occurs.