115 terms in biology
In genetics, "2n" denotes the diploid number of chromosomes in a cell. The symbol n represents a single set of chromosomes (the haploid numb…
"2n = 46" is the notation indicating that an organism's diploid number is 46. In humans, this means each somatic cell has 46 chromosomes (23…
Acetylcholine (ACh) is a neurotransmitter released by certain nerve cells in both the central and peripheral nervous system. It is notably t…
Active transport is the energy-requiring process of moving substances across a cell membrane against their concentration (or electrochemical…
Adaptation in biology refers to a heritable trait or characteristic that improves an organism's ability to survive and reproduce in a partic…
An allele is one of the different forms of a particular gene. For any given gene, an individual normally has two alleles (one inherited from…
Allopatric speciation is the formation of a new species from populations that are geographically isolated from one another. Physical separat…
Aquaporins are integral membrane proteins that serve as channels for water transport in and out of cells. Each aquaporin forms a pore in the…
Artificial selection is the process by which humans intentionally breed plants or animals for specific traits. By choosing which individuals…
ATP synthase is a large protein complex in the inner mitochondrial membrane (and similar membranes of bacteria and chloroplasts) that synthe…
Autosomal refers to the non-sex chromosomes (chromosomes 1-22 in humans). A gene or trait described as autosomal is located on one of these …
A bacterial ribosome is the ribosome found in prokaryotic cells, responsible for protein synthesis in bacteria. It is a 70S ribosome, compos…
A capsid is the protein shell of a virus that encloses its genetic material (DNA or RNA). It is built from protein subunits called capsomere…
In biology, a cell is the basic unit of life - a membrane-bound structure containing the fundamental molecules and organelles needed for lif…
The cell cycle is the ordered series of phases that a cell goes through to grow and divide into two daughter cells. In eukaryotes, the cell …
The cell membrane (plasma membrane) is a thin, flexible barrier that surrounds the cell-s cytoplasm, separating the cell interior from the e…
The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord. It serves as the body's main con…
Centrioles are paired barrel-shaped organelles in the cytoplasm of animal cells near the nuclear envelope. They play a role in organizing mi…
The centromere is a constricted region of a chromosome where spindle fibers attach during cell division. After spindle attachment, sister ch…
A centrosome is a cellular structure involved in cell division. Before division, the centrosome duplicates; as division begins, the two cent…
A channel protein is an integral membrane protein that spans a cell membrane and contains a hydrophilic pore through which specific ions or …
Chiasmata (singular: chiasma) are the physical X-shaped junctions where homologous chromosomes have exchanged genetic material during crossi…
Chromatin is a mixture of DNA and proteins that forms the chromosomes in humans and other higher organisms. Histone proteins help package DN…
A chromosome is a threadlike structure made of protein and a single DNA molecule that carries genomic information. In plants and animals, ch…
The circulatory system (cardiovascular system) is the organ system that circulates blood throughout the body via the heart and blood vessels…
In biology, cloning is the process of creating a genetically identical copy of a biological entity. This could mean copying a gene or DNA se…
Co-dominance is an inheritance pattern in which two different alleles of a gene are both fully expressed in a heterozygote. Instead of one a…
Connective tissue is a broad category of tissue that supports, connects, or separates different types of tissues and organs in the body. It …
Crossing over is the process during meiosis in which two homologous chromosomes exchange genetic material. It occurs in prophase I when non-…
Cytochrome c (Cyt c) is a small, soluble heme protein associated with the inner mitochondrial membrane. In the electron transport chain, cyt…
In genetics, a deletion is a type of mutation where one or more nucleotides (bases) are removed from a DNA sequence. Deletions can be as sma…
Diploid describes a cell or organism that has two complete sets of chromosomes. In a diploid cell, chromosomes are in pairs - one set inheri…
DNA is the hereditary material in nearly all living organisms. It is a double-stranded helix of nucleotides (with the bases A, T, C, and G) …
A dominant allele is one that will determine the phenotype even if only one copy is present. In other words, a trait is called dominant if a…
The endocrine system is the body's hormone network - a collection of ductless glands that secrete hormones (chemical messengers) directly in…
Epithelial tissue (epithelium) consists of sheets of tightly packed cells that cover the exterior surfaces of the body, line internal caviti…
Evolution is the change in the heritable characteristics of a population over successive generations. In other words, it describes how popul…
FAD (flavin adenine dinucleotide) is a redox coenzyme that can accept electrons and protons. In its oxidized state (often notated just as FA…
FADH2 is the reduced form of FAD (flavin adenine dinucleotide), a coenzyme that carries electrons in metabolic reactions. FADH2 contains two…
Fermentation is an anaerobic metabolic process by which cells break down sugars to generate energy without using oxygen. In fermentation, gl…
Fructose is a six-carbon monosaccharide sugar (C₆H₁₂O₆) commonly known as "fruit sugar." It is an isomer of glucose with a slightly differen…
A G protein-coupled receptor (GPCR) is a cell surface receptor protein that traverses the cell membrane 7 times and, when a ligand (signalin…
G1 phase (Gap 1) is the first stage of interphase in the cell cycle, occurring right after cell division (mitosis). During G1, the cell grow…
G2 phase (Gap 2) is the third and final stage of interphase in the cell cycle, following S phase. During G2, the cell continues to grow and …
Genetic drift is a mechanism of evolution in which allele frequencies in a population change over generations due to chance events. Unlike n…
Glucose is a six-carbon monosaccharide sugar (formula C₆H₁₂O₆) that serves as a primary energy source for cells. It is a key product of phot…
Glycolysis is the anaerobic breakdown of glucose (a 6-carbon sugar) into two 3-carbon pyruvate molecules. This process occurs in the cytopla…
Gregor Mendel (1822-1884) was an Austrian monk and scientist whose experiments with pea plants established the basic laws of inheritance. By…
Haploid describes a cell or organism that has only one set of chromosomes. In humans, the haploid number (n) is 23. Only gametes (sperm and …
The heart is a muscular organ that pumps blood through the circulatory system. In humans, the heart has four chambers - two upper atria and …
Heme is an iron-containing molecular component (a prosthetic group) found in hemoglobin and certain other proteins. It consists of a large r…
Homeostasis is the process by which living organisms maintain a stable internal environment despite changes in external conditions. It invol…
A hormone is a chemical messenger produced by an endocrine gland and released into the bloodstream to regulate the activity of specific targ…
The immune system is a complex network of cells, tissues, and organs that helps the body fight infections and other diseases. It includes ba…
Incomplete dominance is a pattern of inheritance in which a heterozygote's phenotype is intermediate between the phenotypes of the two homoz…
An insertion is a mutation in which one or more nucleotides are added into a DNA sequence. Like deletions, insertions can vary in size - fro…
An inversion is a chromosome mutation in which a segment of DNA breaks off and reattaches in the opposite orientation. In an inversion, the …
A kidney is one of two bean-shaped organs that filter the blood to remove waste products and excess water, forming urine. The kidneys also p…
A kinetochore is a protein structure assembled on the centromere of a chromosome that serves as the attachment point for spindle fibers (mic…
The Krebs cycle (citric acid cycle) is a series of enzyme-driven reactions in the mitochondrial matrix that fully oxidize acetyl-CoA into ca…
The law of independent assortment states that genes for different traits are sorted into gametes independently of one another. In other word…
The law of segregation is Mendel's principle that the two alleles for a single trait separate (segregate) during gamete formation. This mean…
A ligand-gated channel is a type of ion channel that opens or closes in response to the binding of a specific chemical messenger (the ligand…
A lipid bilayer is a double-layered sheet of phospholipid molecules that forms the core structure of cell membranes. The phospholipids are a…
The liver is the largest internal organ of the body and a vital metabolic center. Located in the upper right abdomen, the liver has hundreds…
The lungs are a pair of spongy, air-filled organs in the chest that serve as the primary organs of respiration. Their main function is gas e…
A lysosome is a membrane-bound organelle in eukaryotic cells that contains digestive enzymes. It functions as the cell's "recycling center",…
Mitochondria are double-membraned organelles known as the "powerhouses" of the cell. They generate most of the cell's ATP via aerobic respir…
Mitochondrial ribosomes are the protein synthesis machinery inside mitochondria. They are similar to bacterial ribosomes in structure and or…
Messenger RNA is a single-stranded RNA copy of a gene that serves as a template for protein synthesis. mRNA is transcribed from DNA in the n…
Muscle tissue is a type of tissue composed of cells (muscle fibers) that have the ability to contract, generating force and movement. There …
A mutation is a change or error in the DNA sequence of an organism. Mutations can range from a single nucleotide change to large segments of…
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in all living cells that acts as an electron acceptor. It is the oxidized form …
NADH is the reduced form of the coenzyme NAD- (nicotinamide adenine dinucleotide). It carries high-energy electrons and a proton, which can …
Natural selection is the process by which individuals with traits that confer an advantage in a given environment tend to survive and reprod…
A nephron is the microscopic functional unit of the kidney responsible for filtering blood and forming urine. Each nephron consists of a ren…
Nervous tissue is the tissue type that makes up the nervous system, composed of nerve cells (neurons) and supporting glial cells. It is spec…
A neuron is a nerve cell - the basic functional unit of the nervous system specialized to receive and transmit signals. Neurons typically ha…
A non-coding RNA (ncRNA) is an RNA molecule that is transcribed from DNA but not translated into a protein. These RNAs are functional in the…
Nuclear pores are large protein-lined channels in the nuclear envelope that regulate exchange of materials between the nucleus and cytoplasm…
Osmosis is the passive movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a …
The parasympathetic nervous system is one of the two divisions of the autonomic nervous system, responsible for the body's "rest and digest"…
Peripatric speciation is a specific type of allopatric speciation that happens when a small population becomes isolated on the periphery of …
The peripheral nervous system (PNS) is the part of the nervous system outside the brain and spinal cord. It consists of nerves and ganglia t…
A peroxisome is a small, single-membrane organelle containing enzymes that catalyze oxidative reactions. Peroxisomes break down fatty acids …
A phospholipid is a lipid molecule composed of a glycerol backbone attached to two fatty acid tails and a phosphate group head. Phospholipid…
Photosynthesis is the process by which certain organisms (plants, algae, and cyanobacteria) convert light energy into chemical energy. Using…
A plasmid is a small, circular DNA molecule found in bacteria (and some other microorganisms) that is separate from the bacterial chromosoma…
Polymerase Chain Reaction (PCR) is a laboratory technique used to rapidly make millions of copies of a specific DNA sequence in vitro (in a …
The pyruvate shunt is the transitional step that converts pyruvate (the end product of glycolysis) into acetyl-CoA, CO2, and NADH, effective…
In genetics, "recessive" describes an allele or trait that is only expressed when an individual has two identical copies of that allele (no …
Recombinant DNA is DNA that has been artificially created by combining genetic material from multiple sources, often different species. This…
A ribosome is a cellular structure composed of RNA and proteins that serves as the site of protein synthesis. Ribosomes -read- the sequence …
RNA is a nucleic acid similar to DNA but usually single-stranded. It contains ribose sugar (instead of deoxyribose) and uses uracil (U) in p…
The rough endoplasmic reticulum (rough ER) is a series of flattened membrane sacs studded with ribosomes, usually located near the nucleus. …
S phase (Synthesis phase) is the part of the cell cycle during which DNA replication occurs. In S phase, each chromosome's DNA is copied to …
A sarcomere is the fundamental contractile unit of striated muscle fibers. It is the segment of a myofibril between two adjacent Z lines (Z …
Secondary active transport is a form of active transport in which one substance is moved against its concentration gradient by coupling it t…
A sex-linked trait results from a gene located on a sex chromosome (in humans, either the X or Y chromosome). In practice, most often "sex-l…
The smooth endoplasmic reticulum (smooth ER) is a network of membranous tubules in the cell, continuous with the rough ER but lacking riboso…
Speciation is the evolutionary process by which one ancestral species splits into two or more new species. It occurs when a population diver…
The sympathetic nervous system is the division of the autonomic nervous system that triggers the "fight or flight" response, preparing the b…
Sympatric speciation occurs when new species arise from a single ancestral species while inhabiting the same geographic region. No physical …
A synapse is the junction between two nerve cells (neurons), or between a neuron and another target cell (such as a muscle cell), where nerv…
T-tubules (transverse tubules) are deep invaginations of a muscle fiber's plasma membrane (sarcolemma) that tunnel into the cell's interior.…
A tendon is a tough, fibrous connective tissue band that attaches a muscle to a bone. Tendons transmit the force generated by muscle contrac…
Transcription is the process of making an RNA copy of a gene's DNA sequence. In transcription, an enzyme (RNA polymerase) reads one strand o…
Translation is the process by which the information encoded in messenger RNA (mRNA) directs the assembly of amino acids into a protein. It t…
Transfer RNA is a small RNA molecule that helps build proteins by carrying amino acids to the ribosome. Each tRNA has an anticodon region th…
A vaccine is a biological preparation that teaches the immune system to recognize and fight a specific disease without causing the disease i…
A vacuole is a membrane-bound sac within a cell that functions in storage and transport of substances. Vacuoles often contain water, nutrien…
A virus is a tiny infectious particle consisting of genetic material (DNA or RNA) enclosed in a protein coat (capsid). Viruses are not livin…
A voltage-gated channel is an ion channel that opens or closes in response to changes in the electric potential (voltage) across a cell memb…
X-linked describes genes or traits located on the X chromosome. Because females have two X chromosomes (XX) and males have one (XY), X-linke…
Y-linked traits are determined by genes on the Y chromosome. These traits are passed exclusively from father to son, since only males carry …