Chapter 3: Cell Structures and Their Functions

A comprehensive set of question-and-answer flashcards covering key definitions, structures, processes, and functions from Chapter 3 on cell structures and their functions.

What are organelles?

Specialized structures within cells that perform specific functions, such as the nucleus, mitochondria, and ribosomes.

What is the cytoplasm?

A jelly-like substance that surrounds and supports the organelles inside a cell.

What primary role does the cell (plasma) membrane play?

It forms a selective barrier that separates intracellular from extracellular material and controls the movement of substances in and out of the cell.

Which model describes the structure of the cell membrane?

The fluid-mosaic model.

Name the four major components of the cell membrane.

Phospholipids, cholesterol, proteins, and carbohydrates.

Describe the two regions of a phospholipid.

A hydrophilic polar head and a hydrophobic non-polar tail.

Which substances are in higher concentration INSIDE a typical cell?

Enzymes, glycogen, and potassium (K⁺).

Which substances are in higher concentration OUTSIDE a typical cell?

Sodium (Na⁺), calcium (Ca²⁺), and chloride (Cl⁻).

How do O₂ and CO₂ cross the cell membrane?

They diffuse directly through the phospholipid bilayer.

How do sodium ions (Na⁺) typically cross the membrane?

Through specific transmembrane protein channels.

What molecule transports glucose across the membrane?

A carrier protein (carrier-mediated transport).

What is vesicular transport?

Transport that uses membrane-bound vesicles which fuse with the cell membrane to move substances in or out.

Define passive membrane transport.

Movement of substances across the membrane without cellular energy expenditure (no ATP).

Define active membrane transport.

Movement of substances across the membrane that requires cellular energy, usually ATP.

List three passive transport mechanisms.

Diffusion, osmosis, and facilitated diffusion.

List four active transport mechanisms.

Primary active transport, secondary active transport, endocytosis, and exocytosis.

What is diffusion?

Movement of solute molecules from an area of higher concentration to an area of lower concentration down a concentration gradient.

Define concentration gradient.

The difference in solute concentration between two points divided by the distance separating them.

How do lipid-soluble substances move across the membrane?

They diffuse directly through the phospholipid bilayer.

Differentiate leak and gated channels.

Leak channels are always open; gated channels open or close to regulate ion movement.

What is osmosis?

Diffusion of water across a selectively permeable membrane from higher to lower water concentration.

What is osmotic pressure?

The force required to prevent water movement across a selectively permeable membrane.

What happens to a cell in an isotonic solution?

No net water movement; the cell neither swells nor shrinks.

What happens to a cell in a hypotonic solution?

Water enters the cell, causing swelling and possible lysis.

What happens to a cell in a hypertonic solution?

Water leaves the cell, causing shrinkage (crenation).

What is carrier-mediated transport?

Transport in which membrane proteins bind specific molecules and move them across the membrane.

Does facilitated diffusion require ATP?

No; substances move down their concentration gradient with the help of a carrier protein.

Define active transport.

Carrier-mediated movement of substances against their concentration gradient using ATP.

What does the sodium-potassium pump do?

Pumps 3 Na⁺ out of the cell and 2 K⁺ into the cell using ATP.

What is secondary active transport?

Transport that uses the energy of an ion gradient created by primary active transport to move another substance.

Differentiate cotransport and countertransport.

In cotransport, both substances move in the same direction; in countertransport, they move in opposite directions.

Define endocytosis.

Process of bringing materials into the cell via vesicles that bud from the plasma membrane.

What is receptor-mediated endocytosis?

Endocytosis triggered when a specific ligand binds to its membrane receptor.

What is phagocytosis?

‘Cell eating’—ingestion of solid particles by a cell via large vesicles.

What is pinocytosis?

‘Cell drinking’—ingestion of extracellular fluid and small solutes via small vesicles.

Define exocytosis.

Fusion of secretory vesicles with the plasma membrane to release their contents outside the cell.

What is the cytoplasm?

Cytosol plus all organelles between the nucleus and the plasma membrane.

List at least five major organelles.

Nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria (others include peroxisomes, cytoskeleton, centrioles, cilia, flagella, microvilli).

What surrounds and protects the nucleus?

A double-layered nuclear envelope containing nuclear pores.

What are chromosomes composed of?

DNA and proteins.

When loosely coiled, chromosomes are called .

Chromatin.

What is the nucleolus?

A nuclear structure where ribosomal subunits are assembled; it lacks a surrounding membrane.

Function of ribosomes?

Sites of protein synthesis.

Difference between free and attached ribosomes?

Free ribosomes float in cytosol; attached ribosomes bind to rough endoplasmic reticulum.

Roles of rough ER versus smooth ER?

Rough ER synthesizes proteins (has ribosomes); smooth ER synthesizes lipids, detoxifies, and stores Ca²⁺ in muscle.

Primary function of the Golgi apparatus?

Collects, modifies, packages, and distributes proteins and lipids from the ER.

What are lysosomes?

Membrane-bound vesicles containing digestive enzymes that break down materials within the cell.

Purpose of peroxisomes?

Break down fatty acids, amino acids, and hydrogen peroxide via oxidative enzymes.

Why are mitochondria called the cell’s powerhouses?

They produce ATP through aerobic respiration; their matrix contains enzymes and mtDNA.

Name the three main components of the cytoskeleton.

Microtubules, microfilaments, and intermediate filaments.

Two key roles of microtubules?

Support cytoplasm and form structures like cilia, flagella, and the mitotic spindle.

Function of microfilaments?

Support cell shape and enable movement or contraction (especially in muscle cells).

What do intermediate filaments provide?

Mechanical strength and structural support (e.g., keratin in skin).

Role of centrioles?

Organize microtubules during cell division (mitotic spindle formation).

Function of cilia?

Move materials (e.g., mucus) across the cell surface.

Function of flagella?

Propel the cell itself; in humans, found on sperm cells.

Why are microvilli important?

Increase cell surface area to enhance absorption (e.g., in intestine and kidney).

What is gene expression?

The process by which information in DNA directs protein synthesis (transcription and translation).

Describe a nucleotide.

A 5-carbon sugar, a phosphate group, and a nitrogenous base (A, T, C, or G in DNA).

Define gene.

A sequence of DNA nucleotides that codes for a specific protein.

Where does transcription occur?

In the nucleus.

Base-pairing rule for DNA → mRNA during transcription?

DNA A→RNA U, DNA T→RNA A, DNA C→RNA G, DNA G→RNA C.

What is translation?

Process at the ribosome where mRNA codons specify amino acids delivered by tRNA to build a polypeptide chain.

Name the two major phases of the cell cycle.

Interphase (non-dividing) and mitosis (cell division).

What happens during interphase?

Cell performs normal functions and DNA is replicated to form identical chromatids.

How many chromosome pairs do human somatic cells contain?

23 pairs (46 total chromosomes).

List the four phases of mitosis in order.

Prophase, metaphase, anaphase, telophase.

Key event of prophase?

Chromatin condenses into visible chromosomes; spindle fibers form; nuclear membrane breaks down.

Key event of metaphase?

Chromosomes align at the cell’s equatorial plane.

Key event of anaphase?

Sister chromatids separate and move toward opposite poles.

Key event of telophase?

Chromosomes unravel; nuclear membranes reform; followed by cytokinesis to produce two daughter cells.

What is differentiation?

Process by which cells become specialized in structure and function by selectively activating portions of DNA.

Define apoptosis.

Programmed cell death that removes unneeded or damaged cells.

List two possible causes of cellular aging.

DNA damage and accumulation of free radicals (other causes: cellular clock, death genes, mitochondrial damage).

Differentiate benign and malignant tumors.

Benign tumors do not invade or metastasize; malignant tumors invade surrounding tissues and can spread (metastasize).