Cell Transport Mechanisms Quiz

Module Information

• Module: HUMAN BODY FUNCTION (HBF-102)
• Academic Year: 2024/2025
• Year: 1
• Semester: 1

Transport Across the Cell Membrane

• The transport across cell membranes can be passive or active.
• Passive transport doesn't require energy, while active transport does.
• Passive transport includes simple diffusion and facilitated diffusion.
• Active transport can be primary or secondary.

Objectives

• Differentiate between the types of transport across cell membranes
• List different types of channels
• Identify different types of carriers
• Explain how macromolecules cross cell membranes
• Define osmosis and osmotic pressure

Active vs Passive Transport

• Active transport moves molecules against the concentration gradient. It requires energy.
• Passive transport moves molecules with the concentration gradient. It doesn't require energy.

Simple Diffusion

• Simple diffusion is a passive transport.
• It doesn't require energy or carriers.
• Molecules move from an area of high concentration to an area of low concentration.
• It's affected by Fick's law of diffusion.

Fick's Law of Diffusion

• Diffusion rate is directly proportional to the permeability coefficient, concentration gradient, and surface area.
• Diffusion rate is inversely proportional to the thickness of the membrane.
• Increasing temperature increases the rate of diffusion.

Demonstration of Diffusion in Fluids

• Place methylene blue crystals in beakers with different temperatures (cold, room temperature, hot) of water.
• Observe and record the time it takes for the dye to disperse evenly in each beaker.

Charged Molecules and Cell Membranes

• Charged molecules diffuse across cell membranes at an extremely low rate.
• This is due to the formation of large hydrated ions with water, and the interaction between charges on the molecules and membrane.

Ion Channels

• Ion channels are important for ion diffusion.
• Ions move through these channels by simple diffusion, following their electrochemical gradient.
• Types include leakage, voltage-gated, and ligand-gated channels.

Leakage Channels

• Leakage channels are water pathways through integral proteins in the cell membrane.
• They are tubular and extend from the extracellular fluid (ECF) to the intracellular fluid (ICF).
• These channels are highly selective.
• Examples include Na+ and K+ leakage channels.

Gated Channels

• Gated channels have gates that open or close in response to specific signals.
• Ligand-gated channels open or close when a specific molecule (ligand) binds to them, like neurotransmitters.
• Voltage-gated channels open or close in response to changes in membrane potential.
• Examples of voltage-gated channels include Na+ and K+ voltage-gated channels.

Role of Sodium Channels in Local Anesthesia

• Local anesthetics bind to voltage-gated sodium channels.
• Binding blocks sodium entry into the cell.
• This prevents the generation and conduction of action potentials (no pain sensation).

Facilitated Diffusion

• Facilitated diffusion is a passive transport that requires a carrier protein.
• Molecules move from high to low concentration.
• It has a transport maximum.
• An example is the transport of glucose.

Transport Maximum

• Transport maximum is the maximal rate at which a substance can be transported by facilitated diffusion.
• It depends on the number of carriers in the membrane.
• Affected by hormones (e.g., insulin). An increase in Insulin increases the rate of glucose carrier.

Active Transport

• Active transport is uphill/against the concentration gradient, and thus requires energy from ATP.
• It involves carrier proteins.
• Types are primary active transport and secondary active transport

Primary Active Transport

• Carriers have ATPase activity.
• This type of transport moves molecules 'uphill' against their concentration gradient.
• Includes Na+-K+ pump, Ca2+ pump, and H+-K+ pump.

Secondary Active Transport

• This type of transport depends on the sodium gradient created by the sodium-potassium pump.
• It is either cotransport (symport) or countertransport (antiport).

Exocytosis

• Transports material to outside the cell.
• An active transport process that requires energy.
• Example: Transport of acetylcholine at the motor end plate.

Endocytosis

• Transport of materials into the cell.
• Active process that requires energy.
• Example: Phagocytosis of bacteria and dead tissue.

Osmosis

• Passive transport of water across a semi-permeable membrane.
• Water moves from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).

Osmotic Pressure

• Pressure required to prevent osmosis.

Isotonic, Hypotonic, Hypertonic Solutions

• Isotonic: Solute concentration inside the cell equals the solution outside the cell.
• Hypotonic: Solute concentration inside the cell is higher than outside. Water moves into the cell.
• Hypertonic: Solute concentration inside the cell is lower than outside. Water moves out of the cell.