AP Biology - Quiz 2.4-2.9

Roles of phospholipids

Essential lipids in cell membrane construction, characterized by a hydrophilic head containing a phosphate group and two hydrophobic tails from fatty acids. This unique structure enables them to form a bilayer in water, resulting in a semipermeable membrane that separates internal cellular environments from external surroundings and facilitates selective transport and communication.

Passive transport

A biological process that permits substances to pass through cell membranes without energy input, operating along the concentration gradient as molecules move from areas of higher to lower concentration until equilibrium is reached. Key forms include simple diffusion, facilitated diffusion with protein channels, and osmosis, crucial for maintaining cellular balance and functionality.

Fluid Mosaic Model

A foundational theory describing the plasma membrane's structure as a phospholipid bilayer embedded with mobile proteins, creating a mosaic appearance. The interplay of these proteins, which serve functions such as transport and signaling, is vital for dynamic cellular processes, enabling material translocation and communication.

Membrane permeability

The capacity of a biological membrane to allow substances to pass through. This is influenced by factors such as molecule size and polarity, the presence of transport proteins, and the lipid composition. Highly permeable membranes allow easy passage of various substances, while selectively permeable membranes restrict movement to specific molecules, maintaining internal cellular conditions.

Active transport

A mechanism that moves molecules across a membrane against their concentration gradient, from low to high concentration, requiring energy typically sourced from ATP. This process involves specialized transport proteins called pumps and is crucial for regulating ion and nutrient concentrations within cells, ensuring necessary nutrient uptake and waste elimination.

Osmosis

A specific type of passive transport focused on the movement of water molecules through a selectively permeable membrane. Water moves from areas of lower solute concentration to those of higher solute concentration, striving for equilibrium. This process is essential for maintaining turgor pressure in plant cells and overall hydration in living organisms.

Facilitated diffusion

A form of passive transport that enables larger or polar molecules to cross the cell membrane via protein channels or carriers. This process bypasses the lipid bilayer and does not require energy, allowing cells to effectively absorb nutrients like glucose and regulate ion concentrations.

Endocytosis

A cellular process in which the cell engulfs macromolecules and particulate matter by forming vesicles from the plasma membrane.

Exocytosis

The process where internal vesicles fuse with the plasma membrane to release large macromolecules outside the cell.

Aquaporins

Specialized membrane proteins that facilitate the rapid transport of water molecules across the cell membrane.

Channel proteins

Proteins that form pores in the membrane, allowing specific ions and larger polar molecules to cross without using energy.

Membrane potential

The difference in charge across a cell membrane, created by the distribution of ions; essential for nerve impulse transmission and muscle contraction.

Osmolarity

A measure of the concentration of solute particles in a solution, influencing the movement of water across membranes.

Hypotonic

A solution with a lower concentration of solutes compared to another solution, leading to water movement into the cell.

Hypertonic

A solution with a higher concentration of solutes compared to another solution, resulting in water moving out of the cell.

Isotonic

A solution with an equal concentration of solutes compared to another solution, maintaining equilibrium and preventing net water movement.

Na+/K+ ATPase

An enzyme that pumps sodium out of and potassium into cells, crucial for maintaining the negative membrane potential and cell volume.