Phospholipid bilayers and simple diffusion

What is the primary molecule that makes up cell membranes?

Phospholipids.

What class of molecules are phospholipids?

A class of lipids (fats).

Where are phospholipids synthesized?

In the smooth endoplasmic reticulum.

How are phospholipids transported to the cell membrane?

As vesicles.

What does amphipathic mean?

Having both hydrophobic and hydrophilic parts.

Which part of a phospholipid is hydrophilic?

The phosphate head.

Which part of a phospholipid is hydrophobic?

The hydrocarbon tails.

Why do phospholipids form bilayers in water?

Hydrophilic heads face water and hydrophobic tails face inward away from water.

Where is water found relative to the cell membrane?

On both sides: cytoplasm inside and extracellular fluid outside.

Define diffusion.

The net movement of molecules from an area of high concentration to an area of low concentration without energy input.

Why is diffusion considered passive transport?

Because it does not require energy.

Give one example of simple diffusion in cells.

Gas exchange of O₂ and CO₂ in lung alveoli.

Why can oxygen and carbon dioxide diffuse across membranes?

They are small and non-polar molecules.