LAB QUIZ 1

1. Plasma membrane structure & function

It's the barrier around every cell. Structure: a phospholipid bilayer (two layers of fat molecules) with proteins stuck in it, plus some cholesterol and carb chains. Function: keeps the inside of the cell separate from the outside, controls what gets in and out, and lets the cell "sense" its environment via those proteins.

Remember it as: the cell's skin with security guards (proteins) posted in it.

2. Phospholipid bilayer components + why the arrangement matters

Each phospholipid has a head (phosphate, loves water = hydrophilic) and two tails (fatty acids, hate water = hydrophobic). In water, they auto-arrange into two layers with heads facing out (toward watery fluid inside and outside the cell) and tails facing each other in the middle, hiding from water.

Why it matters: this creates a natural barrier — water-soluble stuff can't just pass through the greasy middle, so the cell controls what crosses.

Memory trick: "heads out, tails hiding" — like a sandwich with the water-scared parts in the middle.

3. Selectively permeable (NOT semipermeable)

Semipermeable just means "some things pass, some don't" — like a coffee filter, it's static/dumb.

Selectively permeable means the membrane actively chooses what crosses, based on size, charge, and what transport proteins are present. It's not just physics — the cell is picky on purpose.

Memory trick: "selective" = the membrane has standards, not just holes.

4. Active vs passive transport

• Passive = no energy needed, moves with the gradient (high → low concentration). Examples: diffusion, osmosis, facilitated diffusion.

• Active = requires energy (ATP), moves against the gradient (low → high). Example: sodium-potassium pump.

Memory trick: Passive = "going downhill" (easy, free). Active = "pushing uphill" (needs gas/ATP).

5. Solution components: solvent vs solute

• Solvent = the thing doing the dissolving, usually the liquid (in the body, that's water).

• Solute = the thing being dissolved (salt, sugar, proteins, etc.)

Memory trick: solVENT = the venture/big liquid; solUTE = the little guy dissolved in it.

6. Concentration gradient & equilibrium

• Concentration gradient = a difference in concentration between two areas (more particles here, fewer there).

• Equilibrium = when particles spread out evenly and there's no more net movement (gradient = gone).

Memory trick: gradient = a hill of particles; equilibrium = the hill flattens out.

7. Factors affecting rate of diffusion

• Temperature (higher temp = faster particle movement)

• Concentration gradient size (bigger difference = faster diffusion)

• Molecule size (smaller = faster)

• Distance (shorter distance = faster)

• Surface area (more area = faster)

Memory trick: "Big gradient, small molecule, short trip, hot day, wide door" = fast diffusion.

8. Diffusion vs osmosis

• Diffusion = movement of any particles (solutes or gases) from high to low concentration.

• Osmosis = specifically the movement of water across a selectively permeable membrane, from low solute concentration to high solute concentration (water follows the solute).

Memory trick: Osmosis is just diffusion, but only for water.

9. Hypertonic, isotonic, hypotonic — effect on cells

Think about it from water's perspective — water always moves toward more solute.

• Hypertonic (more solute outside) → water leaves the cell → cell shrinks

• Isotonic (equal solute in/out) → no net water movement → cell stays normal

• Hypotonic (less solute outside, more inside) → water rushes into the cell → cell swells

Memory trick: "Hyper" = cell shrinks and shrivels. "Hypo" = cell fills up like a balloon.

10. Effect on red blood cells: crenate vs lyse

• In a hypertonic solution: water leaves the RBC, cell shrivels up with little spikes → this is called crenation.

• In a hypotonic solution: water rushes in, cell swells until it bursts → this is called lysis (cell lyses).

• In isotonic, the RBC stays normal (this is why IV saline is isotonic).

Memory trick: Crenate = "crinkle" (shrink). Lyse = "lightbulb popping"