Compare and contrast three types of passive transport across a cell membrane.

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1. Identify the three types of passive transport: simple diffusion, facilitated diffusion, and osmosis.
2. Explain simple diffusion: Molecules move from an area of higher concentration to an area of lower concentration directly through the phospholipid bilayer without the need for energy or transport proteins.
3. Describe facilitated diffusion: Molecules also move from an area of higher concentration to an area of lower concentration, but they require the assistance of specific transport proteins embedded in the cell membrane, such as channel proteins or carrier proteins.
4. Discuss osmosis: A special case of diffusion where water molecules move across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration, aiming to equalize solute concentrations on both sides of the membrane.
5. Compare and contrast: All three processes are passive, meaning they do not require cellular energy (ATP). Simple diffusion and osmosis do not require transport proteins, whereas facilitated diffusion does. Osmosis specifically involves water movement, while the other two can involve various molecules.

Key Concepts

Passive Transport

Passive transport is a biological process that allows substances to cross cell membranes without the need for energy input. This movement occurs along the concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration. It is essential for maintaining cellular homeostasis and allows for the efficient exchange of materials.

Diffusion

Diffusion is a type of passive transport where molecules spread from an area of high concentration to an area of low concentration until equilibrium is reached. This process is driven by the kinetic energy of the molecules and does not require cellular energy. An example of diffusion is the movement of oxygen and carbon dioxide across the cell membrane.

Facilitated Diffusion

Facilitated diffusion is a specific form of passive transport that utilizes membrane proteins to help larger or polar molecules cross the cell membrane. Unlike simple diffusion, which occurs directly through the lipid bilayer, facilitated diffusion requires specific carrier or channel proteins. This process is crucial for the transport of substances like glucose and ions that cannot easily pass through the lipid bilayer.