Cell Biology: Cell Structure, Organelles, and Evolution

Vocabulary practice flashcards covering cell ultrastructure, differences between prokaryotes and eukaryotes, organelle functions, endosymbiotic theory, and atypical cellular structures.

Plasma Membrane

A fundamental structure common to all living cells that forms an outer boundary and controls what enters and exits the cell.

Lysis

The rupture of the cell membrane, which leads to cell death.

Thrombolysis

The medical process involving the breakdown of a blood clot.

Cytoplasm

The internal fluid present in all cells, composed mostly of water, where metabolic reactions occur.

Prokaryotes

The first cells to evolve, characterized by having one uninterrupted chamber with no compartmentalization, no nucleus, circular naked DNA, and no organelles other than ribosomes.

Naked DNA

Circular genetic material found in prokaryotic cells that is not surrounded by a nuclear membrane and lacks association with histones.

Bacillus and Staphylococcus

The two key bacterial genera specifically designated by the IB syllabus as examples of prokaryotic cells.

Eukaryotic Cell

A complex cell type characterized by compartmentalization with membrane-bound organelles, mitochondria, and a nucleus containing linear DNA organized with histones into chromosomes.

Compartmentalization

The division of the interior of eukaryotic cells into separate membrane-bound functional chambers and organelles.

Homeostasis

The life process by which an organism maintains a stable internal environment.

Metabolism

The total sum of all biochemical reactions carried out within a living organism.

Excretion

The essential life process responsible for the removal of metabolic waste products from an organism.

Response to Stimuli

The life process involving the perception of environmental conditions and generating a response to changes.

Plastids

Double-membrane plant organelles, such as chloroplasts, that are absent in fungal and animal cells.

Cellulose

The carbohydrate material that composes the rigid cell walls of plant cells.

Chitin

The tough substance that makes up the cell walls of fungi.

Undulipodia

Whip-like eukaryotic extensions, specifically cilia and flagella, found on animal cells to aid in cellular movement.

Red Blood Cells (Atypical Eukaryote)

Specialized human blood cells that lack a nucleus at maturity, which makes them smaller and more flexible but shortens their lifespan.

Phloem Sieve Tube Elements

Atypical eukaryotic plant cells that have no dividing walls between adjacent elements and have broken down most internal contents except their membrane.

Endosymbiosis

A symbiotic relationship in which one organism lives inside the body or cell of another organism.

Endosymbiotic Theory

The theory that mitochondria and chloroplasts originated as free-living aerobic prokaryotes that were engulfed by larger cells, avoided digestion, and established a mutualistic existence.

Evidence for Endosymbiotic Theory

Observations supporting organelle prokaryotic ancestry: mitochondria possess a double membrane, circular naked DNA, $70\text{S}$ ribosomes, independent protein synthesis via their own mRNA, and reproduction solely by dividing from preexisting mitochondria.

Cell Differentiation

The developmental process occurring early in embryonic life by which unspecialized cells turn specific genes on and off to form specialized tissues.

Housekeeping Genes

A group of approximately $4{,}000$ genes in humans that remain active across all cells to support fundamental, general cellular functioning.

Advantages of Multicellularity

Evolutionary benefits of being multicellular, including larger body size, increased complexity, and longer lifespans resulting from the ability to repair and replace damaged cells.

Nucleus

A double-membraned organelle perforated by pores that houses chromosomes and functions in DNA replication and mRNA transcription.

Chromatin

Uncoiled chromosomal material located within the nucleus that appears lighter and less dense under an electron microscope.

Rough Endoplasmic Reticulum (RER)

An organelle formed of flattened membrane sacs called cisternae with surface-bound $80\text{S}$ ribosomes, functioning in synthesizing proteins destined for export from the cell.

Cisternae

Flattened sacs of membrane that constitute the structural units of the endoplasmic reticulum and Golgi apparatus.

Smooth Endoplasmic Reticulum (SER)

A system of branching tubular membranes lacking ribosomes that synthesizes lipids, phospholipids, and steroids, and stores calcium in muscle cells.

Golgi Apparatus

An organelle made of short, curved cisternae without ribosomes that modifies proteins received from the rough ER, packages them into vesicles, and secretes them.

Lysosome

A spherical, single-membraned organelle derived from Golgi vesicles that contains digestive enzymes to degrade nutrients, damaged organelles, and pathogens.

Mitochondrion

A spherical or ovoid double-membraned organelle featuring an inner membrane folded into cristae and an internal fluid matrix, responsible for generating ATP through aerobic respiration.

Cristae

Inward folds of the inner mitochondrial membrane that expand surface area for aerobic respiration reactions.

Mitochondrial Matrix

The internal fluid occupying the central compartment of a mitochondrion.

Free Ribosomes

Dark cytoplasmic granules constructed in the nucleolus that synthesize proteins intended for intracellular use.

Nucleolus

A specialized, dense region within the eukaryotic nucleus where ribosomes are assembled.

Chloroplast

A double-membraned plastid containing internal flattened sacs called thylakoids and stroma, which produces glucose via photosynthesis.

Thylakoids

Flattened membrane sacs located inside chloroplasts where the photosynthetic machinery is organized.

Vacuoles

Single-membrane fluid-filled organelles that store water, expel excess fluid, or digest food; typically large and permanent in plant and fungal cells.

Vesicles

Very small, membrane-bound cellular compartments used to transport materials between organelles or to the plasma membrane.

Microtubules

Cylindrical protein fibers that carry out varied functions in the cell, including pulling chromosomes apart during cell division.

Centrioles

Animal cell organelles consisting of two bundles of nine triplet microtubules that serve as anchor points during cell division and for undulipodia.

Cytoskeleton

A dynamic network of protein filaments, including tubulin and actin, that guides intracellular transport, aids plant cell wall construction, and helps animal cells maintain shape.

Cilia

Short, numerous whip-like cell surface projections containing an arrangement of nine double microtubules surrounding two central microtubules, used for movement and creating fluid currents.

Flagella

Long, lash-like appendages featuring a ring of nine double microtubules and two central microtubules, usually occurring singly on a cell to provide propulsion.