CH 7.2 & The Plasma Membrane, Diffusion & Osmosis “The Basic Unit of Life”

7.2 – The Plasma Membrane How does a cell’s plasma membrane function? What are the roles of proteins, carbohydrates, and cholesterol in the plasma membrane?

The Cell Membrane & Cell Wall The Cell/Plasma Membrane and Cell Wall are the outer boundaries of the cell. Cell Walls are found in plants and some bacteria. It is made of cellulose (a fibrous carbohydrate) and is not easily digested.

The Plasma Membrane

The Cell Membrane & Cell Wall The Plasma/Cell Membrane is made of a phospholipid bi-layer… The phospholipids have protein pores imbedded in them. The pores are selectively permeable – they don’t let everything through! The movement through the membrane is called transport. The structure is also called the Fluid Mosaic Model.

Surface Area to Volume Ratio Cells are limited in how large they can be. This is because the surface area and volume ratio does not stay the same as their size increases. Because of this, it is harder for a large cell to pass materials in and out of the membrane and to move materials through the cell.

Surface Area to Volume Ratio When the cell “length” doubles, the ratio of surface area to volume decreases by HALF! (1 cm = 1:6; 2 cm = 1:3)

Here’s an example…

7.4 – Cellular Transport What are the processes of diffusion, facilitated diffusion, and active transport? What is the effect of a hypotonic, isotonic, or hypertonic solution on a cell? How do large particles enter and exit the cell?

Active and Passive Transport Allows cells to maintain homeostasis (a “stable state”) Also called “dynamic equilibrium” – continuous movement, but no net change. Provides cells with food and oxygen for metabolism Transports waste out of the cell There are 2 types – Active and Passive

Passive Transport Passive Transport (means the cell doesn’t use energy.) Diffusion Osmosis Facilitated Diffusion

Passive Transport - Diffusion Diffusion - is a process by which particles move in a solution. Diffusion happens because of the constant thermal motion of atoms and molecules Materials move from areas of high to low concentration. The difference in the high and low concentration is called the concentration gradient.

Passive Transport - Diffusion Diffusion moves with the gradient – it’s like floating downstream. The end result of diffusion is a constant concentration

Passive Transport - Diffusion The rate of diffusion depends on four main things: 1. temperature, 2. size (mass) of the diffusing particles, 3. viscosity (slipperiness) of the environment 4. charge (+/-) of the particles

Diffusion

Facilitated Diffusion Water can diffuse through the cell membrane (called “osmosis”), but most particles cannot. In facilitated diffusion, ions and other small particles move through transport proteins to get in and out of the cell. There are channel proteins and carrier proteins. It is still passive transport (uses no energy) and goes with the gradient (high to low).

Diffusion Lab – Set Up

Diffusion Lab - Results BEFOREAFTER So what happened here?

Passive Transport - Osmosis Osmosis is the passage of water through a semi- permeable membrane. The water moves from high water concentration to low water concentration. The transport of water across cell membranes is essential for life!! _plant_cells_diagram.svg

Passive Transport - Osmosis If the fluid outside the cell has a higher water concentration (is hypotonic) than the cell, the cell will gain water by osmosis. The cell swells.

Passive Transport - Osmosis If water concentrations are the same inside and outside the cell, there will be no “net” movement of water across the cell membrane. The cell stays the same = isotonic.

Passive Transport - Osmosis If the solution has a lower concentration of water than the cell (is hypertonic), The cell will lose water and shrink.

Plants vs. Animals

Osmosis Quiz… These blood cells have lost fluid… so they are in a ________ solution. HYPERTONIC!

Osmosis Quiz… These blood cells look the same… so they are in a ________ solution. ISOTONIC !

Osmosis Quiz… These blood cells have gained fluid… so they are in a ________ solution HYPOTONIC!

Active Transport Active Transport means that the cell uses energy from ATP to move particles in and out. Endocytosis (taking in materials in vesicles): Pinocytosis (“cell drinking”) - fluids Phagocytosis (“cell eating”) - solids Exocytosis is when materials are released from the cell by vesicles.

Endocytosis and Exocytosis

Here’s a comparison: