5.1-5.5: cell structure & transport

A set of 40 practice flashcards reviewing plasma membrane structure, passive and active transport mechanisms, tonicity, and organelle functions based on AP Biology Unit 2 study material.

what is the main function of the plasma membrane?

separates internal cell contents from the external environment and regulates what enters and exits.

how does the fluid mosaic model describe the plasma membrane?

as a flexible phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates.

what are the two regions of a phospholipid?

hydrophilic (water-attracting) phosphate heads and hydrophobic (water-repelling) fatty acid tails.

how are phospholipids arranged in the plasma membrane?

as a bilayer where hydrophilic heads face aqueous solutions and hydrophobic tails face inward.

what does selective permeability mean?

the membrane allows only certain substances to cross more easily than others.

which types of molecules cross the lipid bilayer most easily?

small nonpolar molecules, such as oxygen and carbon dioxide, cross easily without transport proteins.

why do ions require membrane transport proteins to cross the lipid bilayer?

the hydrophobic interior of the phospholipid bilayer repels charged particles.

what is the role of cholesterol in animal cell membranes?

it buffers membrane fluidity across varying temperatures, keeping it stable.

what role do glycoproteins and glycolipids play in the plasma membrane?

they act as identification markers for cell-to-cell recognition and communication.

what five functional roles can membrane proteins serve?

channels, carriers, receptors, enzymes, and structural attachment anchors.

what defines passive transport across a biological membrane?

movement of substances down a concentration or electrochemical gradient without cellular energy input.

what is a concentration gradient?

a difference in solute concentration between two distinct regions.

what is simple diffusion?

unassisted net movement of solute molecules directly through the membrane from high to low concentration.

what is facilitated diffusion?

passive transport of substances down their gradient through specific channel or carrier proteins without atp.

does facilitated diffusion require direct energy from atp?

no, it is driven solely by the concentration gradient without using cellular energy.

what is a channel protein?

a membrane protein forming a hydrophilic tunnel that lets specific ions or polar molecules cross.

what is a carrier protein?

a membrane protein that binds a specific solute and changes shape to move it across.

which change most directly reduces the rate of facilitated diffusion for a specific solute?

removing or blocking the specific transport proteins used by that solute.

what is osmosis?

the net movement of water across a selectively permeable membrane toward a higher solute concentration.

in which direction does water move during osmosis relative to solute concentration?

water moves toward the side with the higher effective solute concentration.

what happens to an animal cell placed in a hypotonic solution?

water enters the cell, causing it to swell and potentially lyse.

what happens to an animal cell placed in a hypertonic solution?

water leaves the cell, causing it to shrivel and shrink.

what occurs when a cell is in an isotonic solution?

water moves into and out of the cell at equal rates, resulting in no net change.

what happens to a plant cell in hypotonic conditions?

water enters until the internal pressure against the rigid cell wall makes the cell turgid.

what happens to a plant cell in hypertonic conditions?

water leaves the cell, causing the plasma membrane to pull away from the cell wall in plasmolysis.

what is active transport?

the movement of substances against their concentration gradient requiring cellular energy, usually from atp.

what does the sodium-potassium pump transport per cycle and what energy source does it use?

it uses one atp molecule to export three sodium ions and import two potassium ions.

what is cotransport?

a process that couples the downhill diffusion of one solute to the uphill transport of another.

what is endocytosis?

the process of taking materials into a cell by forming vesicles from the plasma membrane.

what is phagocytosis?

a form of endocytosis where the cell engulfs large particles or food items into a vesicle.

what is pinocytosis?

a form of endocytosis where the cell takes in droplets of extracellular fluid and dissolved solutes.

what is receptor-mediated endocytosis?

selective uptake where specific extracellular molecules bind membrane receptors and trigger vesicle formation.

what is exocytosis?

the process where intracellular vesicles fuse with the plasma membrane to release substances outside the cell.

do vesicular transport processes like endocytosis and exocytosis require cellular energy?

yes, both processes require energy from atp for vesicle movement and membrane fusion.

what is the function of the nucleolus?

it synthesizes ribosomal rna and combines it with proteins to assemble ribosome subunits.

what are the destinations of proteins made on bound versus free ribosomes?

bound ribosomes make proteins for membranes, secretion, or lysosomes, while free ribosomes make cytosolic proteins.

what are the primary metabolic functions of the smooth endoplasmic reticulum?

synthesizing lipids, metabolizing carbohydrates, and detoxifying drugs and poisons.

what is the role of the golgi apparatus?

it modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum.

what are lysosomes and what internal environment do their enzymes require?

membrane-enclosed sacs containing hydrolytic enzymes that digest macromolecules in an acidic environment.

what is the structural advantage of cristae in mitochondria?

they increase the inner-membrane surface area to accommodate more proteins for atp production.