CELL MEMBRANE: Structure and Function

Membrane Function:Supports cell contents by holding the cell together.Maintains cellular homeostasis by regulating what enters (food and nutrients) and leaves (waste).

The fluid mosiac

Membrane Structure:A phospholipid bilayer seperates the cell contents from the environment. Phophate is hydrophilic (water soluble) while lipids are hydrophobic (water insoluble).

Embedded Carbohydrates act as chemical messengers attracting molecules like hormones to the cell.Embedded Proteins regulate the entry and exit of certain substances. Examples: nutrients, wastes, food.

Membrane Permeablility

Cell membranes will allow the passage of some molecules but not others. It is selectively permeable.

Passive Transport

Requires no energy because molecules move with the concentration gradient. High to low.Diffusion- solute molecules move from an area of high concentration to an area of low concentration.

Diffusion

Facilitated Diffusion- protein passageways allow the movement of larger molecules through the cell membrane in accordance with the concentration gradient.

Facilitated diffusion

Osmosis- the movement of water from an area of higher to lower concentration… or the movement of water from an area of low solute concentration to an area of high solute concentration.

Hypertonic vs. Hypotonic vs. Isotonic

Osmosis

Osmosis

Active Transport- requires energyRequires energy because it moves against the concentration gradient from lower to higher concentration. Transport proteins- use energy to pump molecules into and out of the cell. Example: Sodium/Potassium pump

Transport proteins/Molecular pumps

Active vs. Passive transport

Endo and Exocytosis- energy is used to engulf molecules, surrounding them with storage vesicles for later use or expelling them from the cell through the membrane.

Endo/exocytosis

CELL WALLFound around bacteria, fungi and plant cells.Rigid structure made of complex carbohydrates.Protects and supports the cell.