Multiple Choice
In passive transport by simple diffusion, how does increasing molecular weight generally affect the rate of diffusion across a membrane (all else being equal)?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
In the context of passive transport, how is osmosis different from diffusion?
A
Osmosis can occur only for nonpolar molecules, whereas diffusion can occur only for water.
B
Osmosis moves solutes from low concentration to high concentration, whereas diffusion moves solutes from high concentration to low concentration.
C
Osmosis is the diffusion of water across a selectively permeable membrane, whereas diffusion is the net movement of any particles down their concentration gradient (and may occur without a membrane).
D
Osmosis requires cellular energy (ATP), whereas diffusion is always energy-independent.
Verified step by step guidance1
Step 1: Understand the general concept of diffusion. Diffusion is the passive movement of particles (solutes or solvents) from an area of higher concentration to an area of lower concentration, driven by the concentration gradient, and it does not require energy.
Step 2: Define osmosis specifically. Osmosis is a special type of diffusion that involves the movement of water molecules across a selectively permeable membrane from a region of lower solute concentration (higher water concentration) to a region of higher solute concentration (lower water concentration).
Step 3: Highlight the key difference in what moves during each process. In diffusion, any type of particle (solutes or solvents) can move, whereas in osmosis, only water molecules move.
Step 4: Emphasize the role of the membrane. Osmosis requires a selectively permeable membrane that allows water to pass but restricts solutes, while diffusion can occur with or without a membrane.
Step 5: Clarify the energy requirement. Both diffusion and osmosis are passive processes and do not require cellular energy (ATP).
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