1. Unit G: Membrane Transport
Unit G: Membrane Transport

2. Standards Unit G: Membrane Transport
I can recognize the fluid mosaic model and accurately identify and describe the function of the components.
I can compare and contrast the various ways substances cross the cell membrane.
I can recognize the various ways substances cross the membrane and provide examples from the human body for each.
I can predict changes to a cell mass and size placed in solutions of differing concentrations
I can use data to create a graph to show the relationship between concentration and mass.
I can use a graph to extrapolate the concentration that is isotonic to a cell.

3. Crash Course: Membranes and Transport

4. MEMBRANE STRUCTURE AND FUNCTION
Membranes organize the chemical activities of cells
Membranes provide structural order for metabolism
The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell
Cytoplasm
Outside of cell
TEM 200,000 

5. Membrane phospholipids form a bilayer
CH2
CH3 CH N + O O– P C
Phosphate group
Symbol
Hydrophilic head
Hydrophobic tails
Membrane phospholipids form a bilayer
Phospholipids have a hydrophilic head and two hydrophobic tails and are the main structural components of membranes
Phospholipids form a two-layer sheet called a phospholipid bilayer, with the heads facing outward and the tails facing inward
Water
Hydrophilic heads
Hydrophobic tails

6. The membrane is a fluid mosaic of phospholipids and proteins
A membrane is a fluid mosaic with proteins and other molecules embedded in a phospholipid bilayer where the phospholipids are constantly moving and shifting (FLUID)
Membrane proteins are located studded within the membrane giving it a mosaic appearance (MOSAIC)
Fibers of the extracellular matrix
Carbohydrate (of glycoprotein)
Glycoprotein
Microfilaments of cytoskeleton
Phospholipid
Cholesterol
Proteins
Plasma membrane
Glycolipid
Cytoplasm

7. Proteins make the membrane a mosaic of functions
Many membrane proteins function as enzymes
Other membrane proteins function as receptors for chemical messages from other cells
Membrane proteins also function in transport moving substances across the membrane
ATP
Messenger molecule
Receptor
Activated molecule

8. Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work (energy) by the cell spreading from areas of high concentration to areas of low concentration
Small nonpolar molecules such as O2 and CO2 diffuse easily across the phospholipid bilayer of a membrane
Equilibrium
Membrane
Molecules of dye

9. Transport proteins may facilitate diffusion across membranes
Many kinds of molecules do not diffuse freely across membranes
For these molecules, transport proteins provide passage across membranes through a process called facilitated diffusion
Solute molecule
Transport protein

10. Osmosis is the diffusion of water across a membrane
In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration
Why would water move in this direction?
Lower concentration of solute
Higher concentration of solute
Equal concentration of solute
H2O
Solute molecule
Selectively permeable membrane
Water molecule
Solute molecule with
cluster of water molecules
Net flow of water

11. Water balance between cells and their surroundings is crucial to organisms
The control of water balance is called osmoregulation
Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions
In hypertonic solutions animals cells are shriveled and plants cells are plasmolyzed – why does this happen?
In hypotonic solutions animal cells burst/lysis and plant cells are in turgid (their ideal state) – why does this happen?
In isotonic solutions animal cells are normal, but plant cells are limp – why??
Plant cell
H2O
Plasma membrane
(1) Normal
(2) Lysed
(3) Shriveled
(4) Flaccid
(5) Turgid
(6) Shriveled (plasmolyzed)
Isotonic solution
Hypotonic solution
Hypertonic solution
Animal cell

12. Cells expend energy for active transport
Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP P
Protein changes shape
Phosphate detaches
ATP
ADP
Solute
Transport protein
Solute binding 1
Phosphorylation 2
Transport 3
Protein reversion 4

13. Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
A vesicle may fuse with the membrane and expel its contents (exocytosis)
Fluid outside cell
Cytoplasm
Protein
Vesicle

14. Membranes may fold inward enclosing material from the outside (endocytosis)
Vesicle forming

15. Endocytosis can occur in three ways Phagocytosis Pinocytosis
Receptor-mediated endocytosis
Pseudopodium of amoeba
Food being ingested
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
Material bound to receptor proteins
PIT
Cytoplasm
Plasma membrane
TEM 54,000
TEM 96,500 
LM 230

16. CONNECTION Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
LDL particle
Protein
Phospholipid outer layer
Cytoplasm
Receptor protein
Plasma membrane
Vesicle
Cholesterol

17. Salt Shakedown
/the-great-salt-shakedown