B2 Simple

Why are lipid bilayers critical for eukaryotic cells?

They maintain compartmentalization within the cells.

What is the role of the lipid bilayer in a cell?

It defines the boundary between a cell and its environment and controls the passage of substances in and out.

What is the orientation of hydrophilic heads and hydrophobic tails in the lipid bilayer?

Hydrophilic heads face outward toward water

What is a phospholipid?

A molecule with a hydrophilic head (polar phosphate group) and two hydrophobic tails (nonpolar hydrocarbon chains).

What does amphipathic mean?

A molecule that has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

What drives the formation of the lipid bilayer?

Hydrophobic interactions (tails clustering together) and hydrophilic interactions (heads forming hydrogen bonds with water).

Why is the lipid bilayer considered selectively permeable?

Its hydrophobic core allows small nonpolar molecules to diffuse freely

What types of molecules can diffuse freely through the lipid bilayer?

Small nonpolar molecules

What is the significance of fluidity in the lipid bilayer?

Fluidity allows phospholipids to move laterally

What role does cholesterol play in the lipid bilayer?

Cholesterol modulates membrane fluidity and stability by fitting between phospholipids.

What are glycolipids?

Glycolipids are lipids with attached carbohydrate groups that play roles in cell recognition and signaling.

What happens to the lipid bilayer if it is disrupted?

It will spontaneously reassemble

What interactions stabilize the bilayer structure?

Hydrophilic interactions

What are the two main components of the lipid bilayer?

Two layers of phospholipids and other amphipathic molecules.

What is the hydrophobic effect?

The tendency of hydrophobic tails to cluster together

How do phospholipids arrange themselves in an aqueous environment?

They spontaneously arrange to shield their hydrophobic tails while exposing their hydrophilic heads to water.

What is the hydrophilic part of a phospholipid?

The phosphate group

What are the hydrophobic parts of a phospholipid?

The two non-polar hydrocarbon tails that repel water.

What is the hydrophobic core of a phospholipid bilayer?

The region formed by the clustered hydrophobic tails that repels water and limits permeability.

Which substances cannot easily cross the phospholipid bilayer?

Hydrophilic particles (ions and polar molecules) and large molecules (like glycogen and proteins).

Give an analogy for the hydrophobic core of a membrane.

The hydrophobic core is like a security gate: only small

What is the interaction of cell membranes with aqueous solutions?

Cell membranes are surrounded by aqueous solutions on both sides

How do water and small solutes move in relation to the membrane?

They move randomly.

What happens to solutes that attempt to penetrate the hydrophilic phosphate heads?

They are repelled back into the surrounding aqueous solution upon encountering the hydrophobic core.

Can water pass through the membrane easily? Why or why not?

Yes

What about larger molecules like glucose?

Larger molecules like glucose need transport proteins to cross the membrane.

Why is the phospholipid bilayer effective as a barrier?

The hydrophobic core limits permeability to ions

What is the external solution surrounding a cell membrane?

The external solution contains water and dissolved solutes.

What role do transport proteins play in membrane permeability?

Transport proteins act as 'keys' that allow larger or polar molecules to cross the membrane.

What is the internal solution of a cell called?

The cytoplasm

How does the amphipathic nature of phospholipids contribute to membrane function?

It allows for the formation of a bilayer that creates a selective barrier

What is diffusion?

Diffusion is the passive movement of particles in liquids and gases due to their continuous random motion.

What is the direction of molecular movement during diffusion?

Molecules move from an area of higher concentration to an area of lower concentration

Do living organisms require energy for diffusion?

No

What is simple diffusion?

Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration

How do particles move in simple diffusion?

Particles pass through the phospholipid bilayer of membranes.

Which types of molecules can easily diffuse through the membrane?

Non-polar molecules (e.g.

What is the hydrophobic nature of the phospholipid bilayer?

The center of the membrane is hydrophobic

What is the effect of the hydrophobic core on polar molecules?

Polar molecules with partial charges diffuse at lower rates

Give an example of diffusion in action.

If oxygen concentration inside a cell decreases

What are the key features of simple diffusion?

No energy required; selective permeability; dependence on concentration gradient.

What does selective permeability mean in the context of diffusion?

Only certain molecules can pass directly through the membrane; hydrophobic molecules cross easily

What happens to molecules during diffusion when equilibrium is reached?

Molecules stop moving from high to low concentration and distribute evenly.