What are the three specific parts of a phospholipid?

Glycerol backbone, two fatty acid tails (hydrophobic), and a phosphate group (hydrophilic).

Why do phospholipids naturally form a bilayer in water?

Amphipathic nature. Hydrophilic heads face water; hydrophobic tails hide inside.

Besides phospholipids, what other macromolecule is major in membranes?

Proteins (integral and peripheral).

How does cholesterol maintain membrane health?

It acts as a “fluidity buffer,” preventing membranes from becoming too fluid or too rigid.

Why do membranes become less permeable at low temperatures?

Tighter packing of phospholipids reduces movement and permeability

Define “selective permeability” and list two molecules that pass through easily.

plasma membrane ability to regulate what can enter and exit like Oxygen (O2​) and Carbon Dioxide (CO2​).

Why do ions (like Na+) rarely cross without help?

The hydrophobic core repels charged particles.

Define “gradient” in biology.

A difference in concentration or charge across a distance.

Contrast a concentration gradient with an electrical gradient.

Concentration = amount of substance; Electrical = difference in charge.

What is it, and why is losing it considered “cellular death”?

It drives ATP production and homeostasis. Loss = energy failure.

Define diffusion and explain its energy source.

Movement from high to low concentration. Energy source: Kinetic energy (thermal motion).

What is the state of equilibrium?

Uniform concentration; no net movement, though molecules still move randomly.

How does diffusion in 90°C water compare to 4°C water? Why?

Faster at 90°C due to higher kinetic energy.

Define osmosis and “water potential.”

Water moves from high water potential (dilute) to low water potential (concentrated).

How does salt water relieve a sore throat?

Draws water out of swollen tissues via osmosis.