Diffusion and Osmosis

Part A

Which of the following factors does not affect membrane permeability?

	Temperature
	The polarity of membrane phospholipids
	The saturation of hydrocarbon tails in membrane phospholipids
	The amount of cholesterol in the membrane

Correct

Phospholipids contain both a polar head and a nonpolar hydrocarbon tail, both of which are necessary for their ability to form membrane bilayers.

Part B

How can a lipid be distinguished from a sugar?

	Lipids are mostly saturated.
	A lipid dissolves in water.
	Lipids are mostly nonpolar.
	A lipid is made up of only hydrocarbons.

Correct

Lipids are nonpolar molecules, whereas sugars are polar.

Part C

True or false? Osmosis is a type of diffusion.

	True
	False

Correct

Osmosis is the diffusion of water across a selectively permeable membrane.

Part D

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

	Amphipathic nature
	Solubility in water
	Permeability
	Hydrophobic nature

Correct

Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are water-soluble.

Part E

Which of the following particles could diffuse easily through a cell membrane?

	Sodium ion (Na+)
	Oxygen (O2)
	Hydrogen ion (H+)
	Glucose

Correct

Small nonpolar molecules such as oxygen can diffuse across cell membranes.

Part F

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

	True
	False

Correct

The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.

Part G

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

	Hypotonic
	Hypertonic
	Isotonic
	Osmotic

Correct

The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.