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Questions and Answers
What is the primary requirement for active transport to occur?
What is the primary requirement for active transport to occur?
Passive transport requires energy expenditure for molecules to move across a membrane.
Passive transport requires energy expenditure for molecules to move across a membrane.
False
What is the osmotic pressure of pure water?
What is the osmotic pressure of pure water?
Name one type of passive transport.
Name one type of passive transport.
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Osmosis is the diffusion of water from a region of high ______ concentration to a region of low concentration.
Osmosis is the diffusion of water from a region of high ______ concentration to a region of low concentration.
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A hypertonic solution has a lower concentration of solutes than the extracellular fluid.
A hypertonic solution has a lower concentration of solutes than the extracellular fluid.
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Which type of transport requires specific carrier proteins?
Which type of transport requires specific carrier proteins?
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What is the normal osmolarity of body fluids?
What is the normal osmolarity of body fluids?
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Active transport occurs against the ______, requiring energy.
Active transport occurs against the ______, requiring energy.
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Match the following types of transport with their definitions:
Match the following types of transport with their definitions:
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Match the terms related to osmosis with their definitions:
Match the terms related to osmosis with their definitions:
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All types of active transport involve movement against a concentration gradient.
All types of active transport involve movement against a concentration gradient.
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Which type of active transport directly uses ATP for energy?
Which type of active transport directly uses ATP for energy?
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Give an example of a bulk transport mechanism.
Give an example of a bulk transport mechanism.
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In secondary active transport, the transporter directly hydrolyzes ATP.
In secondary active transport, the transporter directly hydrolyzes ATP.
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What does the cotransport of Na+ and glucose require?
What does the cotransport of Na+ and glucose require?
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Study Notes
Transport across Cell Membranes
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Learning Objectives:
- Differentiate between passive and active transport.
- Identify types of passive transport and provide examples for each.
- Describe the mechanisms of water transport across membranes.
- Identify types of active transport and provide examples.
- Explain the transport of large molecules across membranes (bulk transport).
Plasma Membrane Structure
- The plasma membrane is a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins/glycolipids.
- Phospholipids have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.
- Proteins are embedded within the membrane and have various functions, including transport.
- Cholesterol provides structural support and fluidity to the membrane.
- Glycoproteins and glycolipids are involved in cell recognition and signaling.
Types of Transport
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Passive Transport: Movement of molecules down a concentration gradient (high to low). No energy required.
- Simple Diffusion: Movement of nonpolar molecules (e.g., oxygen, carbon dioxide) directly through the lipid bilayer.
- Facilitated Diffusion: Movement of polar or charged molecules (e.g., glucose, ions) through channel or carrier proteins.
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Active Transport: Movement of molecules against a concentration gradient (low to high). Energy (ATP) is required.
- Primary Active Transport: Directly uses ATP to move molecules against the gradient (e.g., Na+/K+ pump, Ca2+ pump).
- Secondary Active Transport: Uses the energy stored in an ion concentration gradient (e.g., Na+-glucose symport).
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Bulk Transport: Transport of large molecules or large volumes of substances across the membrane.
- Endocytosis: Movement of substances into the cell by invagination of the plasma membrane (e.g. pinocytosis, phagocytosis).
- Exocytosis: Movement of substances out of the cell by fusion of vesicles with the plasma membrane.
Passive Transport Details
- Simple Diffusion: Movement of molecules without protein assistance. Rate depends on concentration gradient, membrane permeability, and surface area.
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Facilitated Diffusion: Needs membrane proteins (channels or carriers).
- Channels: Provide a pathway through the membrane for specific molecules.
- Carriers: Bind to molecules, change shape, and facilitate their movement across the membrane. This is important for larger molecules or charged substances.
Osmosis
- Osmosis is the specific diffusion of water across a selectively permeable membrane, from a region of high water concentration to low water concentration.
- Osmotic Pressure: The pressure required to prevent water movement across a semipermeable membrane. Higher solute concentration means higher osmotic pressure.
Active Transport Details
- Primary Active Transport: Direct use of ATP for transport. (e.g., Sodium-Potassium Pump). This is crucial for maintaining osmotic balance and concentration gradients.
- Secondary Active Transport: Takes advantage of electrochemical gradient created by primary active transport. The movement of one substance down its gradient provides the energy to move a second substance against its gradient (symport or antiport).
Bulk Transport Details
- Endocytosis: Invagination of the membrane forms a vesicle around the substances to be moved into the cell. Phagocytosis (cell eating) and pinocytosis (cell drinking).
- Exocytosis: Vesicles carrying molecules fuse with the plasma membrane, releasing their contents into the extracellular fluid. This is crucial for secretion and waste removal.
Concentration Gradients and Active Transport
- The Na+-K+ pump is a crucial example of primary active transport, maintaining a low intracellular Na+ concentration and a high intracellular K+ concentration, which are essential for nerve impulse transmission and other cellular processes.
- The Na+ concentration gradient is crucial for many secondary active transport mechanisms.
- Different types of molecules traverse the plasma membrane through one of these various routes that maintain proper concentration and transport crucial substances for the upkeep of the cell.
Other Key Concepts
- Isotonic: A solution has the same solute concentration as the inside of the cell.
- Hypotonic: A solution has a lower solute concentration than the inside of the cell.
- Hypertonic: A solution has a higher solute concentration than the inside of the cell.
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Description
This quiz focuses on the mechanisms of transport across cell membranes, including the differentiation between passive and active transport. You'll explore the structure of the plasma membrane and the types of transport processes that occur, such as diffusion, osmosis, and bulk transport. Test your knowledge on the various components that facilitate transport in and out of cells.
