Lesson 8 - Plasma Membrane

What is selective permeability?

The plasma membrane allows some substances to cross more easily than others.

What is a concentration gradient?

The difference in a solute’s concentration across a membrane—each solute has its own gradient.

What are the two main types of membrane transport?

Passive transport and active transport.

What characterizes passive transport?

Molecules move down their concentration gradient —from high to low concentration — without energy input.

What are the three kinds of passive transport?

Diffusion, osmosis, and facilitated diffusion.

What is diffusion?

Random movement of molecules from high → low concentration until evenly spread out.

What is osmosis?

Movement of water across a selectively permeable membrane to balance concentrations.

Define tonicity.

The relative solute concentration of the solution surrounding a cell.

What happens to a cell in a hypertonic solution?

Water diffuses out; the cell shrivels.

What happens in a hypotonic solution?

Water diffuses in; the cell swells and may burst

What happens in an isotonic solution?

Water moves equally in both directions—no net change in cell size.

Which condition do animal cells prefer?

Isotonic

Which condition do plant cells prefer?

Hypotonic (creates healthy turgor pressure).

What is osmoregulation?

The control of solute concentrations and water balance by a cell or organism

What is facilitated diffusion?

Passive movement of molecules down their gradient with help from transport proteins.

What are the two types of transport proteins?

Carrier proteins (change shape to move molecules) and channel proteins (form hydrophilic tunnels).

What are aquaporins?

Channel proteins that allow billions of water molecules to cross the membrane per second.

How does active transport differ from passive transport?

It moves molecules against their gradient (low → high) and requires ATP.

What is the sodium–potassium pump?

An active transport system that pumps 3 Na⁺ out and 2 K⁺ into the cell, using ATP

What does the sodium–potassium pump create?

A charge difference (positive outside, negative inside) known as the membrane potential

What is membrane potential?

The voltage across a membrane due to unequal ion distribution.

What is an electrochemical gradient?

The combined effect of a concentration gradient and electrical forces on ion movement.

What are electrogenic pumps?

Transport proteins that generate voltage across membranes (e.g., Na⁺/K⁺ pump, proton pump).

What is cotransport?

When one substance moves down its gradient, driving another substance up its gradient.

What is exocytosis?

Vesicles fuse with the membrane to release materials outside the cell.

What is endocytosis?

The membrane engulfs material to bring it into the cell.

What are the three types of endocytosis?

Phagocytosis (“cell eating”), pinocytosis (“cell drinking”), and receptor-mediated endocytosis (specific uptake