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Questions and Answers
What is the primary requirement for passive transport to occur?
Which of the following processes do NOT involve the expenditure of energy?
How is concentration mathematically defined in a solution?
In diffusion, which statement best describes the movement of solute particles?
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Which of the following processes is an example of active transport?
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What is the primary role of carrier proteins in facilitated diffusion?
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Under which circumstances would diffusion occur the slowest?
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In a hypertonic solution, which of the following occurs?
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Which type of molecules diffuse easily across the phospholipid bilayer?
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What characterizes facilitated diffusion as compared to simple diffusion?
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Study Notes
Cell Membrane Transport
- Cells need to move substances across their membrane to maintain homeostasis.
- The cell membrane acts as a barrier, controlling the movement of molecules from one side to the other.
- Concentration is the amount of solute in a solvent. Higher concentration means more solute.
- To calculate concentration, divide the mass of the solute by the volume of the solvent.
Transport Methods
- Passive transport does not require energy.
- Active transport requires energy.
Passive Transport: Diffusion
- Molecules move from a region of high concentration to an area of low concentration.
- This movement continues until equilibrium is reached, where the concentration of solutes is equal on both sides of the membrane.
- Solutes move down their concentration gradient, moving from high to low concentration.
- The rate of diffusion is affected by:
- Concentration: Higher concentration leads to faster diffusion.
- Temperature: Higher temperature leads to faster diffusion.
- Pressure: Higher pressure leads to faster diffusion.
Diffusion: Non-Polar Molecules
- Small, non-polar molecules diffuse easily across the phospholipid bilayer of a cell membrane.
- Example: Oxygen enters red blood cells and carbon dioxide leaves them in the lungs through passive transport.
Facilitated Diffusion
- Large, polar, or charged molecules cannot cross the lipid bilayer on their own.
- These molecules require the assistance of transport proteins.
- Each protein is specific to a particular molecule.
- Channel proteins open and close to allow substances to cross the membrane.
- Carrier proteins change shape to move particles across the membrane.
Osmosis
- Water diffuses across a selectively permeable membrane from an area of high water concentration to an area of low water concentration.
- Hypertonic solution: Has a higher solute concentration and lower water concentration than the cell. Water moves out of the cell.
- Hypotonic solution: Has a lower solute concentration and higher water concentration than the cell. Water moves into the cell.
- Isotonic solution: Has the same solute concentration as the cell. No net movement of water.
Osmoregulation
- Animals need to control water balance to survive in hypotonic or hypertonic environments.
- This process is called osmoregulation.
- Example: Freshwater fish have kidneys and gills to prevent water buildup.
- In a hypertonic solution, an animal cell shrivels.
- In a hypotonic solution, an animal cell swells or lyses (bursts).
Water Balance in Plants
- Plant cells have rigid cell walls.
- Isotonic solution: Plant cell is flaccid and wilts.
- Hypotonic solution: Plant cell is turgid and healthy. The cell wall prevents the cell from bursting.
- Hypertonic solution: Plant cell loses water, and the plasma membrane pulls away from the cell wall, called plasmolysis.
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Description
Test your knowledge on cell membrane transport mechanisms, including passive and active transport. Understand how molecules move across membranes and the role of concentration gradients in diffusion. This quiz will help reinforce concepts of homeostasis in cells.
