Chapter 3: Cells as Units of Life

Vocabulary practice flashcards covering cell structure, organelles, membrane transport, and cell division based on Chapter 3 of Integrated Principles of Zoology.

Robert Hooke

English scientist and inventor who viewed slices of cork and leaves using a compound microscope and called the box-like cavities he observed "cells."

Antonie van Leeuwenhoek

Dutch microscopist whose numerous detailed descriptions of various cells laid the foundation for the cell theory.

Cell Theory

The core biological principle stating that all living organisms are made of cells, life cannot exist without cells, and cells are the basic structural and functional units of life.

Prokaryotic Cell

An early-evolving cell type (mostly $1\text{--}10\text{ }\boldsymbol{\rm \mu m}$ in size) that lacks a nucleus and membrane-bound organelles, containing simple circular DNA inside an un-enclosed nucleoid.

Eukaryotic Cell

A cell type (mostly $10\text{--}100\text{ }\boldsymbol{\rm \mu m}$ in size) found in animals and plants that contains membrane-bound organelles and complex linear chromosomes enclosed by a membranous nuclear envelope.

Nucleoid

The non-membrane-bound region in a prokaryotic cell where its simple, circular DNA molecule is located.

Plasma Membrane

The dynamic phospholipid bilayer boundary that maintains cellular integrity, acts as a gatekeeper, and selectively regulates what enters and leaves the cell.

Phospholipid Bilayer

A double-layered membrane structure consisting of hydrophilic ("water-loving") heads and hydrophobic ("water-fearing") tails.

Cholesterol (Cell Membrane)

A lipid component within the plasma membrane that acts like a "stiffener," where higher cholesterol content results in reduced membrane flexibility.

Nucleus

The control center of a eukaryotic cell enclosed by a double membrane nuclear envelope that stores and processes genetic information.

Nuclear Envelope

A double membrane equipped with complex protein pores that separates nuclear contents from the cytoplasm and regulates molecular exchange between them.

Nucleolus

A specialized structure inside the nucleus responsible for the synthesis of ribosomal RNA (rRNA).

Chromatin

The loose, uncoiled form of DNA complexed with DNA-binding proteins used for everyday cellular instructions.

Chromosomes

Tightly packed, highly condensed structures of DNA and binding proteins formed during cell division.

Rough Endoplasmic Reticulum

A network of cellular membranes studded with ribosomes that functions primarily in protein synthesis.

Smooth Endoplasmic Reticulum

A network of cellular membranes lacking ribosomes that functions primarily in lipid (fat) synthesis.

Ribosomes

Tiny cellular protein factories that are either attached to the ER to synthesize export proteins or free in cytoplasm to synthesize internal proteins.

Golgi Complex

Stacks of flattened membranes functioning as the cell's "post office" by modifying, packaging, and storing proteins and lipids from the ER.

Vesicles

Tiny membranous sacs that transport and store materials within the cell.

Lysosomes

Specialized vesicles containing hydrolytic (digestive) enzymes that function as the cell's cleanup crew to break down damaged organelles and destroy pathogens.

Endomembrane System

An assembly network comprising the outer nuclear membrane, ER, Golgi complex, vesicles, lysosomes, and plasma membrane that work together to synthesize, package, transport, and recycle cellular components.

Mitochondria

Self-replicating, double-membrane powerhouses of the eukaryotic cell whose inner membrane is folded into cristae to produce most of the cell's ATP.

Cristae

The folds of the inner mitochondrial membrane that increase surface area for ATP energy production.

Cytoskeleton

A network of microfilaments, intermediate filaments, and microtubules that maintains cell shape and facilitates intracellular movement.

Diffusion

The passive movement of particles or molecules along a concentration gradient from an area of higher concentration to lower concentration.

Chemically Gated Ion Channel

A transmembrane channel protein that opens or closes in response to binding specific chemical signals (ligands).

Voltage-Gated Ion Channel

A transmembrane channel protein that opens or closes in response to changes in electrical charge across the plasma membrane.

Mechanically Gated Ion Channel

A transmembrane channel protein that opens or closes in response to physical forces such as stretch or pressure.

Aquaporins

Specialized transmembrane protein channels through which water diffuses across the plasma membrane.

Osmosis

The movement of water molecules across a selectively permeable membrane from higher water concentration to lower water concentration.

Hypotonic Solution

An osmotic solution where water enters the cell, causing red blood cells to swell and potentially lyse (burst).

Isotonic Solution

An osmotic solution with balanced water and solute levels causing no net movement of water, allowing cells to stay the same size.

Hypertonic Solution

An osmotic solution where water moves out of the cell, causing red blood cells to shrink (crenate).

Facilitated Diffusion

Passive transport down a concentration gradient (high to low) that requires no ATP energy and relies on specific transmembrane transporter proteins.

Active Transport

Energy-dependent transport moving solutes against a concentration gradient (low to high) using transporters and ATP energy.

Sodium–Potassium Pump

An active transporter complex powered by ATP that maintains normal ion gradients by expelling $3\text{ Na}^+$ ions out of the cell and importing $2\text{ K}^+$ ions inside.

Endocytosis

An ATP-requiring bulk transport process where cells engulf external material into vesicles formed from the plasma membrane.

Phagocytosis

"Cell eating"; an endocytic process where the plasma membrane engulfs solid material or microbes into a vesicle that fuses with lysosomes for enzyme digestion.

Pinocytosis

"Cell drinking"; an endocytic process where tiny membrane pits called caveolae invaginate to take in extracellular fluids and small solutes.

Caveolae

Invaginated membrane pits rich in caveolin proteins and concentrated receptors that form tiny vesicles during pinocytosis.

Receptor-Mediated Endocytosis

A highly specific bulk transport mechanism where extracellular ligands bind to membrane receptors located in clathrin-coated pits, triggering vesicle internalization.

Exocytosis

"Cell secretion"; an energy-requiring process where intracellular vesicles fuse with the plasma membrane to release waste or products outside the cell.

Mitosis

Nuclear division in somatic cells that produces two daughter cells genetically identical to the original parent cell.

Meiosis

A reductional nuclear division process in sexually reproducing animals that cuts chromosome numbers in half to create four genetically unique gametes.

Prophase

The first mitotic phase where chromatin condenses into chromosomes, centrosomes replicate and migrate to opposite poles, nucleolus disappears, and the nuclear membrane breaks down.

Metaphase

The mitotic phase where chromosomes line up on the metaphase plate and kinetochores connect to centrosomes via kinetochore microtubules.

Kinetochore

A specialized protein complex at the centromere region of each chromosome equipped to attach to kinetochore microtubules during mitosis.

Anaphase

The mitotic phase where cohesin proteins at centromeres are removed, allowing sister chromatids to separate and move to opposite cell poles as independent chromosomes.

Telophase

The final stage of nuclear division where chromosomes complete migration to poles, spindle fibers disappear, chromosomes decondense into chromatin, and nuclear membranes reappear.

Cytokinesis

The cytoplasmic division process following nuclear division, in which actin and myosin interactions tighten a cleavage furrow to split the cell into two.