Questions and Answers
What is the primary mechanism through which water moves across cell membranes?
What characteristic of facilitated diffusion indicates that the transport rate cannot increase indefinitely?
In what direction do molecules move during passive diffusion?
What is the main requirement for active transport to occur?
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Which term describes a solution with a lower solute concentration compared to another?
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What do carrier proteins in facilitated transport exhibit?
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What type of solution has an equal solute concentration on both sides of a membrane?
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How do cells absorb large molecules that cannot pass through the membrane?
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Study Notes
Passive Diffusion
- Molecules and ions move randomly, creating a net movement from high to low concentration.
- Diffusion continues until equilibrium is reached across regions.
Facilitated Transport
- Requires specific channels for polar molecules like glucose since they cannot freely cross the plasma membrane.
- Channels exhibit selective permeability, permitting only particular molecules to pass.
Facilitated Diffusion
- Involves carrier proteins that bind solutes such as sugars and amino acids for transport across the membrane.
- Movement occurs from high to low solute concentration and can be saturated when all carriers are occupied.
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Key Characteristics:
- Specificity: Each carrier is designed to transport specific molecules or ions.
- Passivity: Movement direction is dictated by concentration gradients.
- Saturation: Limited transport rate occurs when all carriers are utilized.
Osmosis Overview
- Cytoplasm consists of an aqueous solution where water is the solvent, and substances like ions and sugars act as solutes.
- Water moves through cell membranes via aquaporins, as it cannot easily pass through the lipid bilayer.
Diffusion of Water
- Water diffuses from low solute concentration (high water concentration) to high solute concentration (low water concentration) to maintain equilibrium.
- Movement of water is influenced by solute concentration and is driven by osmotic pressure.
Osmotic Concentration
- Solutions categorized by solute concentration:
- Hyperosmotic: Contains a higher solute concentration.
- Hypoosmotic: Contains a lower solute concentration.
- Isosmotic: Displays equal solute concentration across compartments.
Active Transport
- Active transport moves substances against their concentration gradient, from low to high concentration.
- This energy-dependent process utilizes ATP.
- Involves protein carriers similar to those in facilitated diffusion but requires energy input.
Endocytosis
- Endocytosis enables cells to absorb large molecules by engulfing them, as these cannot traverse the hydrophobic cell membrane.
- Two main types:
- Phagocytosis (Cell-eating): Engages in nutrient ingestion and immune defense against pathogens.
- Pinocytosis (Cell-drinking): Involves the intake of fluids and dissolved substances, later processed by lysosomes.
Exocytosis
- Exocytosis is a method of expelling materials via secretory vesicles from the cell.
- Serves to release soluble proteins and incorporate membrane proteins and lipids into the cell membrane.
Filtration
- Filtration drives the movement of water and dissolved substances from high pressure areas to low pressure areas.
- This process relies on mechanical pressure rather than ATP energy for transport.
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Description
Test your understanding of the key concepts of diffusion, including passive diffusion and facilitated transport. This quiz covers the mechanisms by which molecules move across plasma membranes and the principles of selective permeability. Enhance your knowledge of these essential biological processes.
