Cell (Plasma) Membrane
Phospholipids have a hydrophilic (water-loving) phosphate molecule and two hydrophobic (water-hating) fatty acid tails that helps the cell membrane function.
The head of the phospholipid is made of alcohol and ______group.

1- A bilayer of phospholipid molecules with hydrophilic heads facing out towards the water environment that lies in/out the cell, and their hydrophobic tails facing inward towards each other
2- Cholesterol makes the membrane more fluid.
3- There’re proteins that aid in diffusion. Integral proteins (bound to hydrophobic interior of the membrane, AKA channel proteins) go all the way through the bilayer, while peripheral proteins (not bound this way) serve four functions. Large glucose molecules/carbs use proteins to move across cell membrane, some with carb chains that help cells recognize each other and molecules
a) Support structure when attached to cytoskeleton
b) Recognition, binding sites on some proteins to identify other cells

c) Communication. Receptor proteins that stick out of the membrane are Transport. Every time a msg is received from outside of the membrane, the membrane forms a keyhole to recognize the key on other organisms. Proteins serve as channels where materials can pass through in/out of the cell
d) E) The glycocalyx. Sugar chains attach to communication/recognition proteins serving as their binding sites.

Integral or intrinsic proteins—special carriers/transport channels for molecules that are either too large/hydrophilic to pass through the phospholipid bilayer. Other membrane proteins have sugar chains attached to them (carbohydrate and protein combos called glycoproteins) are attachment sites for molecules that need to enter or carry a message to the cell. They help the cells of the immune system to recognize body cells and destroy foreign cells.

Cholesterol in cell membranes help keep the membrane fluid. Low temp=fluid, high temp= attracts phospholipids and stabilizes membrane

Diffusion—movement of particles along/with the concentration gradient (passive transport) from a high (more collisions) to low (fewer collisions) concentrated area. When there’s equal concentration of particles in all areas, there’s equilibrium.

Factors Affecting Diffusion—Size; large molecules can’t squeeze through. Lipid Solubility; If a molecule can’t dissolve in the oily mixture created by fatty acids, it can’t diffuse through membrane. Size of the concentration difference and the distance the molecule have to travel affect diffusion.

Lungs rely on diffusion to get oxygen. Alveoli and the capillaries speed up to slow diffusion. Capillaries increase SA for diffusion. Since more oxygen is in inhaled air of the alveoli than in the