Cell Membrane Structure & Transport

All cells need to exchange substances like food, water, and nutrients with their environment Cell membranes accomplish this exchange through cell transport!

Cell Membrane is composed of –Phospholipid bilayer: forms the basic unit of the cell membrane –Proteins: help transport large molecules through the membrane –Carbohydrates: help cells send and receive chemical messages

Lipid tails repel water: Hydrophobic ( water–fearing) Phosphate heads interact with water: Hydrophilic (water–loving)

Why is the membrane’s structure described as a “fluid mosaic”? Membranes are fluid and have the consistency of vegetable oil Membranes are fluid and have the consistency of vegetable oil The lipids & proteins are always in motion The lipids & proteins are always in motion Proteins form patterns or mosaics Proteins form patterns or mosaics

2 M ain Types of Cell Transport Active Transport: NEEDS energy Active Transport: NEEDS energy Passive Transport: NO energy required Passive Transport: NO energy required

Active transport requires energy moves substances against the concentration gradient Low concentration to high concentration!! Low conc.. High conc.

Like facilitated diffusion, ACTIVE TRANSPORT uses proteins to transport a substance across the membrane. Active transport, however, requires energy!

Types of Active Transport Bulk Transport moves LARGE MATERIALS in and out of the cell

Moving large substances into the cell by infolding of the cell membrane Endocytosis: Moving large substances into the cell by infolding of the cell membrane Pinocytosis: engulfs liquids Phagocytosis: engulfs solids

Amoebas take in food and nutrients through phagoctosis…...

Phagocytosis of Streptococcus pyogenes. White blood cells engulf many types of pathogenic bacteria

Large substances are shipped out of the cell by outfolding of the cell membrane Exocytosis: Large substances are shipped out of the cell by outfolding of the cell membrane Think “exit”

Passive Transport: Movement of materials across the membrane that does not require energy 3 Types: Diffusion Osmosis Facilitated Diffusion

Diffusion is the movement of molecules from an area of high concentration to an area of lower concentration until they are evenly spread out Hi to the Low YO!

Concentration Gradient and Permeability affect whether diffusion occurs across a membrane

Concentration Gradient: the difference between the amount of a particular substance in one area and the amount in an adjacent area

Permeability is the ability of a substance to pass through the membrane Permeability is the ability of a substance to pass through the membrane Impermeable: Cannot pass Impermeable: Cannot pass and only allow certain molecules to pass Selectively permeable or Semi-permeable and only allow certain molecules to pass

Some things like glucose and proteins are too large to pass though the membrane by diffusion or osmosis Carrier proteins transport (diffuse) large substances across the membrane from high to low concentration

29 Osmosis is the diffusion of water molecules through a selectively permeable membrane Water will continue to diffuse/move until there is an equal concentration of molecules inside and outside the cell.

31 60% H 2 O 90% H 2 O Which way will the water move? On the left side, more of the space is occupied by solutes than by water

Hypertonic Solutions Solute concentration outside of the cell is higher than the solute concentration inside the cell Water moves OUT of the cell 32

75% H 2 O 90% H 2 O Which way will the water move?

75% H 2 O 90% H 2 O What type of solution is this cell in?

Hypotonic Solutions Solute concentration outside of the cell is lower than the solute concentration inside the cell Water moves INTO the cell 35

100% H 2 O 80% H 2 O Which way will the water move?

100% H 2 O 80% H 2 O What type of solution is this cell in?

Isotonic Solution Solute concentration in the solution is equal to the solute concentration in the cell Water moves equally in and out of the cell 38

90% H 2 O Which way will the water move?

90% H 2 O What type of solution is this cell in?