Cell Membrane and Transport Mechanisms

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Questions and Answers

What is the definition of a concentration gradient?

A concentration gradient is the difference in concentration of a solute across a region, specifically the high and low concentration sides.

Which type of transport requires energy input for movement of solute across the membrane?

Active transport (correct)

Passive transport

Simple diffusion requires energy to move molecules across the membrane.

False

What is the role of channel proteins in facilitated diffusion?

They act as small pores in the membrane, facilitating the movement of specific molecules. Signup and view all the answers

What is the primary function of ligand-gated channels?

Ligand-gated channels open or close in response to the binding of a specific molecule, called a ligand. This binding triggers a change in the protein's shape, opening or closing the channel to allow or prevent the passage of molecules. Signup and view all the answers

Voltage-gated channels are activated by changes in the concentration of ions across the membrane.

False Signup and view all the answers

Which of the following is NOT a characteristic of a hypotonic solution?

The solute concentration outside the cell is higher than that inside the cell. Signup and view all the answers

What is the primary function of aquaporins?

They act as channels that allow the movement of water across the cell membrane. Signup and view all the answers

What is the main role of primary active transport in the cell?

To move solutes against their concentration gradient, using energy derived from ATP hydrolysis. Signup and view all the answers

Describe the role of the Na+/K+ pump in active transport.

The Na+/K+ pump uses energy from ATP hydrolysis to move sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, both against their concentration gradients. This creates and maintains the electrochemical gradient across the membrane, which is essential for nerve impulse transmission, muscle contraction, and many other vital processes. Signup and view all the answers

Secondary active transport relies on the movement of one substance down its concentration gradient to power the movement of another substance against its concentration gradient.

True Signup and view all the answers

Which of the following best describes the function of an antiporter?

It moves two different substances in opposite directions across the membrane. Signup and view all the answers

Explain how the proton pump is used in secondary active transport.

The proton pump uses energy to move protons (H+) against their concentration gradient, creating a proton gradient across the membrane. This gradient is then used to power the movement of other substances, such as sugars, against their concentration gradient, through a cotransporter protein. Signup and view all the answers

Study Notes

Cell Membrane

Regulates substance movement
Concentration gradient: difference in solute concentrations across a region. High and low concentration sides.

Passive Transport

Diffusion of solutes depends on concentration.
Typically moves from high to low concentration.
No energy required.
Exergonic.

Diffusion

Simple diffusion: small, nonpolar molecules (e.g., O2) can diffuse directly across the lipid bilayer.
Facilitated diffusion: polar or charged molecules still cross the lipid bilayer with the help of integral membrane proteins.
- These proteins move molecules down the concentration gradient.
Channel proteins: act as small pores in the membrane.

Active Transport

Movement against the concentration gradient, requiring ATP.
Endergonic.
Pumps (transport proteins) facilitate active transport using ATP.
Two types:
- ATP hydrolysis (primary active transport): example is Na+/K+ pump (moving Na+ and K+ against their concentration gradients).
- Co-transport (secondary active transport): one substance moves down its concentration gradient, providing energy to move another substance against its gradient. Example: sucrose movement against gradient using H+ diffusion.
Antiporters: move two different substances in different directions. The diffusion of H+ powers sucrose movement against its concentration gradient.

Osmosis

Diffusion of water.
Water moves from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
Selectively permeable membrane allows water to move but not solutes.
Aquaporins: channel proteins in cell membranes that allow water to diffuse across. These are crucial for water balance in cells, as they regulate and are gated and found in kidney cells.

Tonicity

Isotonic solution: solute concentration is the same inside and outside the cell, no water movement.
Hypotonic solution: solute concentration outside the cell is lower than inside the cell. Water moves into the cell. Animal cells can lyse (burst) in a hypotonic solution; good for plant cells.
Hypertonic solution: solute concentration outside the cell is higher than inside the cell. Water moves out of the cell. Animal cells shrivel in a hypertonic solution; good for plant cells.

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Description

Explore the functions of the cell membrane and the various transport mechanisms involved in substance movement. This quiz covers passive transport processes like diffusion, as well as active transport that requires energy. Test your knowledge on how different molecules cross the lipid bilayer.