bio

Cell

The smallest unit with the capacity to live and reproduce independently or as part of a multicellular organism.

Robert Hooke

The scientist who in 1665 observed plant cells in a bottle cork using an early compound microscope and coined the word "Cella" meaning little room.

Cell Theory

A biological principle stating that every organism is composed of one or more cells, the cell is the smallest unit of life, and new cells arise from the division of existing cells.

Surface Area to Volume Ratio

A physical relationship where as a cell increases in volume, its relative surface area decreases, limiting its ability to absorb sufficient water, oxygen, and nutrients.

Prokaryotic Cell

A tiny cell type lacking a nucleus and internal membrane-bound organization, belonging to the domains Bacteria and Archaea.

Eukaryotic Cell

A cell containing a nucleus and membrane-bound organelles with internal compartmentalization, belonging to the domain Eukarya.

Organelle

A specialized compartment within the cell cytoplasm that is enclosed by its own plasma membrane.

Nucleus

The administrative center of a eukaryotic cell that houses DNA, coordinates cellular functions, and instructs protein production.

Chromatin

The combination of DNA and its associated proteins located inside the nucleus.

Nucleolus

The dense region inside the nucleus where ribosomes are assembled.

Nuclear Envelope

A double-layered membrane equipped with pores that controls the movement of substances into and out of the nucleus.

Rough Endoplasmic Reticulum (Rough ER)

An organelle surrounding the nucleus studded with ribosomes that folds newly assembled polypeptide chains into their functional shapes.

Ribosome

A small, membrane-less, granular organelle where polypeptide chains are assembled during the translation of RNA into protein.

Smooth Endoplasmic Reticulum (Smooth ER)

An organelle without ribosomes that synthesizes lipids (fats, phospholipids, sterols) and detoxifies harmful molecules like drugs, alcohol, and metabolic waste.

Golgi Body

An organelle that modifies and packages lipids and proteins, synthesizes carbohydrates, produces lysosomes and vesicles, and ships products within or outside the cell.

Lysosomes

Membrane-bound organelles produced by the Golgi body that act as cellular garbage disposals, digesting food and recycling unwanted waste products.

Endomembrane System

A functional group of membrane-bound organelles working together, consisting of the rough ER, smooth ER, Golgi body, lysosomes, and vesicles.

Mitochondria

The power plants of eukaryotic cells that contain their own DNA and feature two membranes (a smooth outer membrane and a convoluted inner membrane).

Chloroplasts

Plant cell organelles containing their own DNA, two outer membranes, and thylakoid disks filled with chlorophyll that convert sunlight into chemical energy.

Cytoskeleton

A cellular framework responsible for cell movement, comprised of actin filaments, microtubules, and intermediate filaments.

Monomer

A single molecular subunit that serves as a building block for larger polymers.

Polymer

A long molecular chain formed by repeating monomer subunits connected by covalent bonds.

Monosaccharide

A simple single-subunit sugar monomer with the formula $\text{C}_6\text{H}_{12}\text{O}_6$, such as glucose, fructose, or galactose.

Disaccharide

A complex carbohydrate formed by joining two simple monosaccharides together, such as sucrose or lactose.

Polysaccharide

A complex carbohydrate consisting of many linked simple sugar monomers, such as starch, cellulose, or chitin.

Cellulose

An indigestible structural polysaccharide in plants that provides rigidity to trees and plants.

Chitin

An indigestible structural polysaccharide that forms the protective exoskeletons of invertebrates.

Fiber

Indigestible plant carbohydrates (including cellulose) that aid in human digestion, offer health benefits, and reduce colon cancer risk.

Triglyceride

A fat molecule composed of a glycerol head attached to three fatty acid tails, used for long-term energy storage and insulation.

Saturated Fat

A fat containing straight hydrocarbon chains with single-bonded carbon atoms bound to two hydrogens, allowing the molecules to pack tightly as solids at room temperature.

Unsaturated Fat

A fat containing crooked or kinked hydrocarbon chains with double-bonded carbon atoms, preventing tight packing and making them liquid at room temperature.

Sterols

Non-fat lipids built on a four-carbon ring structure, including cholesterol and steroid hormones like estrogen and testosterone.

Phospholipid

A lipid containing a hydrophilic polar head and two hydrophobic nonpolar fatty acid tails, forming the cell membrane bilayer.

Collagen and Elastin

Structural proteins found in skin that maintain its flexibility and elasticity, whose declining production with age leads to wrinkles.

Antibodies

Protective proteins produced by the immune system that bind to invading microorganisms and viruses to stop infection.

Actin and Myosin

Contractile proteins that slide past one another to produce muscle contractions.

Hemoglobin

A transport protein packed in red blood cells that can bind and carry up to four oxygen molecules across the body.

Primary Structure of Protein

The linear sequence of amino acids in a polypeptide chain connected by peptide bonds.

Secondary Structure of Protein

The corkscrew-like twists (helices) or pleated folds (sheets) stabilized by hydrogen bonds between amino acids in a polypeptide chain.

Tertiary Structure of Protein

The complex three-dimensional folding of a polypeptide chain driven by interactions among the amino acid side chains.

Quaternary Structure of Protein

A protein structure formed by two or more polypeptide chains bonded together.

Denaturation

The disruption of a protein's three-dimensional shape and function caused by extreme environmental factors like heat or extreme pH.

Nucleotide

The monomer building block of nucleic acids, consisting of a phosphate group, a sugar molecule, and a nitrogen-containing base.

Ribonucleic Acid (RNA)

A nucleic acid that acts as a middleman molecule, taking genetic instructions from DNA to direct the assembly of proteins.

Evolution

A change in allele frequency within a population over time.

Gametes

Reproductive cells (sperm, egg, pollen) containing half of the parent's DNA that unite during reproduction; mutations must occur here to be inherited.

Mutation

A heritable change in the nucleotide sequence of DNA.

Adaptive Trait

A specific heritable trait that increases an individual's ability to survive and reproduce in a given environment.

Natural Selection

An evolutionary process where environmental pressures favor individuals with adaptive traits, leading to differential survival, higher reproductive success, and the spread of the trait over generations.

Sexual Selection

An evolutionary mechanism favoring traits that assist individuals in attracting or competing for mates, increasing offspring count even if the traits lower overall survival.

Artificial Selection

A process where humans selectively breed individuals with desired traits to cause rapid evolutionary change over time.

Homeostasis

Maintaining a relatively stable internal environment.

Metabolism / Energy Use

The process where living things acquire and use energy to carry out life processes.

Reproduction

The process where living things produce new organisms or cells.

Evolution

The process where populations change over generations.

Emergent Property

A property that arises from interactions among smaller parts as components become organized into larger systems, which individual pieces do not possess by themselves.

Hierarchy of Life

The levels of biological organization moving from atoms to molecules, organelles, cells, tissues, organs, organ systems, and organisms.

Producer / Autotroph

An organism that produces its own food, generally using sunlight (e.g., plants). Auto means self.

Consumer / Heterotroph

An organism that gets food by consuming other organisms (e.g., animals). Hetero means other.

Decomposer / Saprotroph

An organism that breaks down dead organisms or tissues and obtains nutrients from them (e.g., bacteria, fungi).

Binomial Nomenclature

A classification system that gives organisms a two-part scientific name consisting of a genus and a species (e.g., Homo sapiens).

Genus

The important part of a scientific name when determining relatedness; sharing a genus (e.g., Canis in Canis familiaris and Canis lupus) indicates organisms are closely related.

Eight Categories of Classification

The taxonomic ranks ordered from broadest to most specific: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Morphology

The physical form or structure of an organism.

Morphological Classification

Classifying organisms by comparing physical structures such as the number of limbs, number of toes, or other physical characteristics. It works for living organisms and fossils, but not well for single-celled organisms.

Genetic Classification

Modern classification comparing DNA sequences, RNA sequences, and genes to reveal relationships not obvious from appearance; requires living organisms and cannot be used in the same way for ancient fossils.

Prokaryotes

Organisms that have no nucleus ('Pro = no'), no membrane-bound internal organelles, less internal organization, and a capsule outside the plasma membrane; includes Bacteria and Archaea.

Eukaryotes

Organisms that have a nucleus ('Eu = nucleus'), membrane-bound internal organelles, and more internal organization; includes Animals, Plants, Fungi, and Protists.

Three Domains of Life

The major domains consisting of Bacteria (prokaryotes), Archaea (prokaryotes), and Eukarya (eukaryotic).

Protista

A eukaryotic kingdom containing single-celled or multicellular organisms with no tissues and no division of labor, which can be producers, consumers, or decomposers (e.g., Amoeba, Paramecium, Diatoms, Slime molds, Kelp, and Foraminifera).

Fungi

A eukaryotic kingdom of single-celled or multicellular decomposers that have no tissues but possess division of labor.

Animalia

A eukaryotic kingdom consisting of multicellular consumers.

Plantae

A eukaryotic kingdom consisting of multicellular producers.