HOMEOSTASIS and the PLASMA MEMBRANE Chapter 7-3

Maintaining a Balance All organisms are subject to changes in their environment; temperature, pressure, gas levels, sunlight, chemicals, etc.

Cells must be able to control what enters and what leaves while at the same time maintaining concentrations of water, salts, glucose, etc. as they eliminate wastes and other unnecessary materials.

STRUCTURE of the PLASMA MEMBRANE The plasma membrane – which is “selectively permeable” – is responsible for this regulation.

2 layers of phospholipids (phosphate heads with lipid tails) Plasma Membrane 2 layers of phospholipids (phosphate heads with lipid tails)

“hydrophilic” heads facing watery environments “hydrophobic” tails facing away from the watery environments “hydrophilic” heads facing watery environments

The lipid layer is periodically embedded with two kinds of proteins: integral proteins peripheral proteins

Integral Proteins Proteins that span the width of the cell membrane – from surface to surface act as channels to help ferry non-lipid soluble materials into the cell (glucose, amino acids, large molecules, etc.)

Proteins that are on one surface of the membrane only Peripheral Proteins Proteins that are on one surface of the membrane only act as markers (“flags”) or as docking sites for other chemicals such as hormones and enzymes.

Fluid-Mosaic Model Because the lipids are not bound together, they can move side-to-side in a fluid fashion.

peripheral protein integral protein peripheral protein

Cellular Transport

Molecules are constantly in motion and are always colliding with each other.

Movement of Materials Through a Cell Membrane Passive Transport Active Transport

PASSIVE TRANSPORT Does NOT require energy from the cell - from HIGH to LOW concentration

Active Transport A process that requires energy that enables material to move across the cell membrane AGAINST a concentration gradient

Passive Transport Diffusion: Diffusion Simulation

The process by which molecules of a substance move from areas of high concentration to areas of low concentration.

Diffusion Gizmo | ExploreLearning

Osmosis Diffusion of water molecules through a selectively permeable membrane.

The diffusion of water molecules. OSMOSIS The diffusion of water molecules. Diffusion across a membrane (osmosis)

Effects of Osmosis on Cells Isotonic – concentration of solutes is the SAME inside and outside cell membrane

Effects of Osmosis on Cells Hypertonic – solution has HIGHER solute concentration than the cell

Effects of Osmosis on Cells Hypotonic – solution has a LOWER solute concentration than the cell

Hypertonic, Hypotonic, Isotonic Passive Transport

Facilitated diffusion Movement of specific molecules through a cell membrane through protein channels

ACTIVE TRANSPORT Requires ENERGY by the cell. From LOW to HIGH concentration

Individual molecules are carried through the membranes via proteins in the cell membrane.

Active transport

Endocytosis (Type 1) the process of taking the material INTO the cell by infoldings of the cell membrane.

Two Types: Phagocytosis: engulfing of large particles into the cell.

Two Types: Pinocytosis: cell takes in fluid from the surrounding environment

Types of Endocytosis with sound

Exocytosis (Type 2) Molecules are taken up by the cell forming pockets along the membranes to REMOVE molecules from the cell.

Exocytosis

Quiz

If you start with A, do you end up with B or C?

1. Define diffusion. 2. Define osmosis. 3. Define active transport. 4. What is endocytosis and exocytosis?