1. Protect cell
2. Control incoming and outgoing substances
3. Maintain ion concentrations of various substances
4. Selectively permeable - allows some molecules in, others are kept out
Allows some substances into the brain, but screens out toxins and bacteria
Substances allowed to cross include:
water, CO2, Glucose, O2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.
Solutions are made of solute and a solvent
Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today.
Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.
3. Facilitated Diffusion
4. Active Transport
1. Diffusion -passive transport - no energy expended
2. Osmosis - Passive transport of water across membrane
3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across
4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP
Movement of molecules from an area of high concentration to an area of low concentration.
Movement from one side of a membrane to another, un-facilitated
Hypotonic Solution - One solution has a lower concentration of solute than another.
Hypertonic Solution - one solution has a higher concentration of solute than another.