Cell Membrane Structure Quiz

Cell Membrane Structure

• The cell membrane is a phospholipid bilayer
• Proteins are embedded in the bilayer, acting as channels for transporting materials
• Glycoproteins, glycolipids, and cholesterol are components of the cell membrane
• Peripheral proteins and filaments of the cytoskeleton are also present

Cell Membrane Orientation

• Hydrophilic heads of phospholipids face the aqueous environments (inside and outside the cell)
• Hydrophobic tails of phospholipids face inwards, away from the aqueous environments

Cholesterol and Fluidity

• Cholesterol maintains membrane fluidity at high and low temperatures.
• High temperatures: reduces membrane fluidity
• Low temperatures: reduces tight packing of phospholipids, improving fluidity

Selective Permeability

• Some substances cross the membrane more easily than others.
• Small, nonpolar, hydrophobic molecules pass easily (e.g., hydrocarbons, CO2, O2, N2)
• Hydrophilic molecules, large molecules, and ions have difficulty crossing and often need protein assistance

Cell Size and Function

• Cellular metabolism depends on cell size.
• Cells need a high surface area-to-volume ratio to effectively exchange materials across the plasma membrane.
• Large cells have less surface area compared to volume, leading to inefficient material exchange
• Small cells have a higher surface area-to-volume ratio that facilitates effective material exchange

Formulas

• Cuboidal Cells: Total surface area (SA)= height × width × number of sides × number of boxes; Total volume (V)= height × width × length × number of boxes
• Spherical Cells: SA= 4πr²; V= 4/3 πr³ ; SA:V ratio= SA/V

Practice Examples

• Cells with higher SA:V ratios are more efficient for material exchange.

Concentration Gradient

• A difference in the amount of substance between two areas.
• Example: water with food coloring (food coloring is most concentrated at place of addition)

Diffusion

• Movement of particles from an area of high concentration to low concentration.
• This process continues until dynamic equilibrium (constant concentration) is reached
• Movement is driven by kinetic energy of particles

Facilitated Diffusion

• Passive transport process where specific proteins assist larger or non-lipid soluble molecules across the cell membrane
• Carrier and channel proteins help in moving these molecules.
• Examples: Glucose

Diffusion Through Ion Channels

• Membrane proteins transport ions such as Na+, K+, Ca2+, and Cl-.
• Ion channels are specific for a given ion and can be controlled using concentration gradients or other signals

Osmosis

• Net movement of water across a semi-permeable membrane (from high to low water concentration)
• Water moves down the concentration gradient
• An example of diffusion and passive transport.

Solutions

• Solvent: A substance that dissolves a solute
• Solute: A substance that is dissolved in a solvent(e.g., sugar, salt dissolved in water)
• Water is the common solvent in living organisms

Direction of Osmosis

• Isotonic: Equal solute concentration inside and outside the cell (water moves in and out at equal rates)
• Hypotonic: Lower solute concentration outside the cell (water moves into the cell)
• Hypertonic: Higher solute concentration outside the cell (water moves out of the cell).

Dealing with Osmosis

• Contractile Vacuoles (protozoa): Pump out excess water
• Plasmolysis (plant cells): Water loss, turgor pressure decreases, wilting
• Cytolysis (animal cells): High turgor pressure, cell explodes

Active Transport

• Movement of substances against the concentration gradient (from low to high concentration)
• Requires energy (ATP)
• Examples: Sodium-Potassium Pump, Endocytosis, Exocytosis

Endocytosis

• Cell membrane engulfs substances, forming vesicles to bring substance into the cell.
• Includes Phagocytosis (solids) and Pinocytosis (liquids)

Exocytosis

• Vesicles carrying substances fuse with the cell membrane, releasing their contents outside the cell.
• It's involved in the release of hormones and neurotransmitters

Dialysis

• A process that utilizes diffusion to filter waste materials from blood in a damaged kidney
• A machine filters out wastes from the blood by diffusion while healthy blood is returned to the body.

Fish Gill Function

• Water and blood flow in opposite directions (countercurrent exchange) across the gill surface.
• Oxygen moves from the water to the blood.