Bio Adv: Unit 3 Study Guide 4

lipid bilayer

two-sided layer

What is a lipid bilayer?

A two-sided layer of phospholipids that forms the basic structure of the cell membrane.

What is the primary function of the cell membrane?

It controls what enters and exits the cell.

What three main phrases describe the structure and function of the cell membrane?

It is composed of a phospholipid bilayer, described as a fluid mosaic, and is selectively permeable.

What are the two main parts that make up a phospholipid molecule?

Two hydrophobic fatty acid tails and one hydrophilic phosphate group.

Which part of a phospholipid is hydrophobic and which part is hydrophilic?

The fatty acid tails are hydrophobic, and the phosphate group is hydrophilic.

How are the phosphate groups positioned in the lipid bilayer?

The polar phosphate groups face the cytoplasm inside the cell and the extracellular environment outside.

Why do phospholipids form a lipid bilayer in water?

To keep the hydrophobic fatty acid tails away from water.

Why is the cell membrane described as "fluid"?

Because phospholipid molecules are able to move throughout the layer.

Why is the cell membrane described as a "mosaic"?

Because it is made of a variety of phospholipid types, embedded molecules, and large proteins.

What does it mean for a membrane to be semipermeable (selectively permeable)?

It means only certain substances can pass through the cell membrane.

Which types of molecules can easily pass through the cell membrane without help?

Small molecules and nonpolar molecules.

Which types of molecules need help to pass through the cell membrane?

Large molecules, polar molecules, and charged ions.

What are the two primary ways molecules can cross the cell membrane?

Passive transport and active transport.