Chapter 3: Cell Structures and Their Functions

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

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77 Terms

1
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What are organelles?

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

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What is the cytoplasm?

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

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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.

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Which model describes the structure of the cell membrane?

The fluid-mosaic model.

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Name the four major components of the cell membrane.

Phospholipids, cholesterol, proteins, and carbohydrates.

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Describe the two regions of a phospholipid.

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

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Which substances are in higher concentration INSIDE a typical cell?

Enzymes, glycogen, and potassium (K⁺).

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Which substances are in higher concentration OUTSIDE a typical cell?

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

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How do O₂ and CO₂ cross the cell membrane?

They diffuse directly through the phospholipid bilayer.

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

Through specific transmembrane protein channels.

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What molecule transports glucose across the membrane?

A carrier protein (carrier-mediated transport).

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What is vesicular transport?

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

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Define passive membrane transport.

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

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Define active membrane transport.

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

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List three passive transport mechanisms.

Diffusion, osmosis, and facilitated diffusion.

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List four active transport mechanisms.

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

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What is diffusion?

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

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Define concentration gradient.

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

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How do lipid-soluble substances move across the membrane?

They diffuse directly through the phospholipid bilayer.

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Differentiate leak and gated channels.

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

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What is osmosis?

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

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What is osmotic pressure?

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

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What happens to a cell in an isotonic solution?

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

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What happens to a cell in a hypotonic solution?

Water enters the cell, causing swelling and possible lysis.

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What happens to a cell in a hypertonic solution?

Water leaves the cell, causing shrinkage (crenation).

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What is carrier-mediated transport?

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

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Does facilitated diffusion require ATP?

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

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Define active transport.

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

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What does the sodium-potassium pump do?

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

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What is secondary active transport?

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

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Differentiate cotransport and countertransport.

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

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Define endocytosis.

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

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What is receptor-mediated endocytosis?

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

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What is phagocytosis?

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

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What is pinocytosis?

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

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Define exocytosis.

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

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What is the cytoplasm?

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

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List at least five major organelles.

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

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What surrounds and protects the nucleus?

A double-layered nuclear envelope containing nuclear pores.

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What are chromosomes composed of?

DNA and proteins.

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When loosely coiled, chromosomes are called .

Chromatin.

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What is the nucleolus?

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

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Function of ribosomes?

Sites of protein synthesis.

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Difference between free and attached ribosomes?

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

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Roles of rough ER versus smooth ER?

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

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Primary function of the Golgi apparatus?

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

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What are lysosomes?

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

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Purpose of peroxisomes?

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

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Why are mitochondria called the cell’s powerhouses?

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

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Name the three main components of the cytoskeleton.

Microtubules, microfilaments, and intermediate filaments.

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Two key roles of microtubules?

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

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Function of microfilaments?

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

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What do intermediate filaments provide?

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

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Role of centrioles?

Organize microtubules during cell division (mitotic spindle formation).

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Function of cilia?

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

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Function of flagella?

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

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Why are microvilli important?

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

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What is gene expression?

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

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Describe a nucleotide.

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

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Define gene.

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

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Where does transcription occur?

In the nucleus.

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Base-pairing rule for DNA → mRNA during transcription?

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

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What is translation?

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

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Name the two major phases of the cell cycle.

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

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What happens during interphase?

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

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How many chromosome pairs do human somatic cells contain?

23 pairs (46 total chromosomes).

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List the four phases of mitosis in order.

Prophase, metaphase, anaphase, telophase.

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Key event of prophase?

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

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Key event of metaphase?

Chromosomes align at the cell’s equatorial plane.

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Key event of anaphase?

Sister chromatids separate and move toward opposite poles.

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Key event of telophase?

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

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What is differentiation?

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

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Define apoptosis.

Programmed cell death that removes unneeded or damaged cells.

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List two possible causes of cellular aging.

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

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Differentiate benign and malignant tumors.

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