Passive Transport (Review)

What is passive transport? (Basics of Passive Transport)

The movement of substances across a cell membrane without using energy (no ATP), from high concentration to low concentration.

Does passive transport require energy from the cell? (Basics of Passive Transport)

No. Passive transport does not require energy/ATP.

In passive transport, substances move down or against the concentration gradient? (Basics of Passive Transport)

They move down the concentration gradient (from high → low concentration).

What are the three main types of passive transport? (Basics of Passive Transport)

1. Diffusion

2. Osmosis

3. Facilitated diffusion

What is diffusion? (Diffusion)

The movement of small molecules from an area of high concentration to low concentration until they are evenly spread out

What was the example of diffusion Ms. Koval showed us one day? (Diffusion)

The air freshner spreading across the room

Which types of molecules can diffuse directly through the cell membrane (simple diffusion)? (Diffusion)

Small, nonpolar, or uncharged molecules, like O₂ (oxygen), CO₂ (carbon dioxide), and some lipids.

What is osmosis? (Osmosis)

The diffusion of water across a selectively permeable membrane from high water concentration to low water concentration.

What does "selectively (semi-)permeable membrane" mean? (Osmosis)

A membrane that allows some substances to pass through but blocks others.

In osmosis, does water move toward the area with more solute or less solute? (Osmosis)

Water moves toward the area with more solute (to dilute it).

What is a hypertonic solution? (Tonicity: Hypotonic, Hypertonic, Isotonic)

A solution with more solute and less water than the cell.

What happens to a cell in a hypertonic solution? (Tonicity: Hypotonic, Hypertonic, Isotonic)

Water moves out of the cell, and the cell shrinks (animal cell shrivels; plant cell membrane pulls away from wall)

What is a hypotonic solution? (Tonicity: Hypotonic, Hypertonic, Isotonic)

A solution with less solute and more water than the cell.

What is an isotonic solution? (Tonicity: Hypotonic, Hypertonic, Isotonic)

A solution that has the same solute concentration as the cell.

What happens to a cell in an isotonic solution?

Water moves in and out equally, and the cell stays the same size.

What is facilitated diffusion? (Facilitated Diffusion)

A type of passive transport where proteins in the cell membrane help bigger or charged molecules move from high to low concentration without energy.

Does facilitated diffusion need energy (ATP)? (Facilitated Diffusion)

No. It is still passive (high → low concentration).

Name two types of proteins used in facilitated diffusion. (Facilitated Diffusion)

1. Channel proteins

2. Carrier proteins

What is an example of a substance that uses facilitated diffusion? (Facilitated Diffusion)

Glucose and ions (like Na, K) use facilitated diffusion.

How is diffusion different from facilitated diffusion? (Comparing Types of Transports)

Diffusion: molecules pass directly through the membrane.

Facilitated diffusion: molecules move through membrane proteins.

How is passive transport different from active transport? (Comparing Types of Transports)

Passive: no energy, moves high → low concentration.

Active: uses energy (ATP), moves low → high concentration.

Is osmosis a type of diffusion? (Comparing Types of Transports)

Yes, osmosis is diffusion of water across a selectively permeable membrane.