Passive Transport

What does it mean that atoms and molecules are in constant motion?

They vibrate and move randomly in all directions.

Why is the random motion of molecules important?

It allows many biological principles, like diffusion and osmosis, to occur.

What is passive transport?

The movement of molecules into or out of a cell without the cell expending any energy.

What are the three main types of passive transport?

Simple diffusion, osmosis, and facilitated diffusion.

Does passive transport require energy?

No, it requires no energy from the cell.

What is diffusion?

The movement of molecules from an area of high concentration to an area of low concentration.

What does diffusion cause molecules to do?

Spread out across their medium as much as possible.

What is a concentration gradient?

The difference in concentration of a substance between two areas.

What happens when there is a higher concentration gradient?

There is a higher density of molecules and more parts per billion.

In what direction does diffusion always occur?

Down a concentration gradient, from high to low concentration.

What happens to molecules in diffusion over time?

They reach equilibrium, where the concentration is uniform throughout the mixture.

Which molecules can diffuse across the plasma membrane?

Small molecules like water, oxygen, and nitrogen.

What happens when the concentration of a molecule is higher outside the cell?

Molecules flow into the cell.

What happens when the concentration of a molecule is lower outside the cell?

Molecules flow out of the cell.

What are the two components of a solution?

The solvent (does the dissolving) and the solute (is dissolved).

What is osmosis?

The diffusion of water molecules across a membrane from an area of higher water concentration to lower water concentration.

Does osmosis require energy?

No, it is a passive process.

What determines the direction of osmosis?

The concentration of solutes inside and outside the cell.

What are the three types of solutions affecting osmosis?

Hypotonic, hypertonic, and isotonic.

What is a hypertonic solution?

A solution with a higher solute concentration outside the cell than inside.

What happens to a cell in a hypertonic solution?

Water flows out of the cell, causing a net decrease in cell water.

What is a hypotonic solution?

A solution with a lower solute concentration outside the cell than inside.

What happens to a cell in a hypotonic solution?

Water flows into the cell, causing a net increase in water inside the cell.

What is an isotonic solution?

A solution where solute concentrations inside and outside the cell are equal.

What happens to a cell in an isotonic solution?

Water moves in and out equally, with no net change in water content.

What is facilitated diffusion?

A type of passive transport for larger molecules that cannot pass directly through the plasma membrane.

What helps larger molecules cross the membrane in facilitated diffusion?

Carrier proteins.

Does facilitated diffusion require energy?

No, it moves molecules from high to low concentration without using energy.

What is an example of a molecule that uses facilitated diffusion?

Glucose, which passes through a carrier protein to enter the cell.