Biology Dictionary
Our Biology Dictionary is the largest dictionary of Biology terms and definitions in the world. Learn various topics, concepts, and principles in Biology by searching the definitions and essential details of 70,000+ Biology terms.
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A
- A Band
- Abdomen
- Abiogenesis
- Abiotic
- Abiotic factor
- Abscission
- Absolute fitness
- Absorption
- Accessory pigment
- Acellular
- Acid
- Acidophile
- Acoelomate
- Action potential
- Active immunity
- Active transport
- Adaptation
- Adaptive evolution
- Adaptive radiation
- Adaptive trait
- Adaptive zone
- Adenine
- Adenosine diphosphate
- Adenosine triphosphate
- Adhesion
- Adventitious root
- Aerial root
- Aerobic
- Aerobic bacteria
- Aerotolerant
- Afferent nerve
- Agar
- Agglutination
- Agonist muscle
- Agriculture
- Akinetes
- Alcoholic fermentation
- Algae
- Algal bloom
- Alkaliphile
- Allele
- Alloimmunity
- Allopatric speciation
- Allopolyploidy
- Alternation of generations
- Amino acid
- Amino acid sequence
- Amino group
- Ammonification
- Amnion
- Amniote
- Amoeboid movement
- Amoebozoa
- Amphimixis
- Amylase
- Amyloplast
- Anabolic pathway
- Anabolism
- Anaerobic
- Anaerobic organism
- Anaerobic process
- Anaerobic respiration
- Anagenesis
- Analogous
- Analogous structures
- Analogy
- Anaphase
- Anaphase I
- Anaphase II
- Anastomosis
- Anatomy
- Ancestral
- Anemia
- Angiosperm
- Animal
- Animal Kingdom
- Animal testing
- Antagonism
- Antagonistic Muscle
- Anther
- Antibiotic
- Antibody
- Anticodon
- Antigen
- Anucleate
- Apical bud
- Apical Dominance
- Apical Growth
- Apical meristem
- Apicomplexa
- Apoenzyme
- Apomixis
- Apomorphy
- Apoptosis
- Apparent competition
- Appendage
- Appositional growth
- Archaea
- Archaebacteria
- Archaeplastida
- Arterioles
- Arthropod
- Artificial Selection
- Asexual reproduction
- Assay
- Assimilation
- Aster
- Atom
- ATP synthase
- ATPase
- Atria
- Atrium
- Atrophy
- Autecology
- Autocrine signaling
- Autophagy
- Autopolyploidy
- Autosome
- Autotroph
- Aves
- Axon
- Axon hillock
B
- B lymphocyte
- Bacillus
- Backbone
- Bacteria
- Bacterial conjugation
- Bacteriophage
- Balanced diet
- Barophile
- Basal metabolic rate
- Base pair
- Base pair substitution
- Base pairing
- Bear
- Benign
- Betaproteobacteria
- Bicoid
- Bidirectional replication
- Bilateral symmetry
- Bile
- Binary fission
- Binomial nomenclature
- BIOACCUMULATION
- Biochemistry
- Biodiversity
- Biogenesis
- Biogeochemical cycle
- Biogeography
- Biological system
- Biology
- Biomass
- Biome
- Biomolecule
- Biosphere
- Biosynthesis
- Biota
- Biotic
- Biotic factor
- Biotic potential
- Bipennate muscle
- Birth Rate
- Bivalent
- Blade
- Blastopore
- Blastula
- Blastulation
- Blood
- Blood vessel
- Blunt end
- Body cavity
- Bone matrix
- Bone tissue
- Botany
- Branches of Biology
- Branches of biology
- Branching tree
- Buccal cavity
- Budding
- Buffer
C
- C3 plant
- C4 plant
- Caecum
- Calvin cycle
- CAM
- CAM plant
- Camouflage
- Canaliculus
- Cancer
- Capillaries
- Capillary action
- Capping
- Capsid
- Capsule
- Carbohydrate
- Carbon
- Carbon cycle
- Carbon dioxide
- Carbon fixation
- Cardiovascular system
- Carnivore
- Carotenoid
- Carrier
- Carrier protein
- Carrying capacity
- Cartilage
- Cartilage cell
- Cartilaginous joint
- Catabolic pathway
- Catabolism
- Cell
- Cell adhesion
- Cell culture
- Cell cycle
- Cell death
- Cell determination
- Cell differentiation
- Cell division
- Cell growth
- Cell junction
- Cell line
- Cell locomotion
- Cell matrix
- Cell membrane
- Cell membrane permeability
- Cell morphology
- Cell plate
- Cell recognition
- Cell sap
- Cell theory
- Cell wall
- Cellular
- Cellular respiration
- Cellulose
- Centriole
- Centromere
- Centrosome
- Chamber
- Channel
- Character
- Chemical synapse
- Chemiosmosis
- Chemiosmotic theory
- Chemoautotroph
- Chemoheterotroph
- Chemolithotroph
- Chemoreceptor
- Chemosynthesis
- Chemotaxis
- Chemotroph
- Chemotropism
- Chiasma
- Chimera
- Chitin
- Chlorophyll
- Chlorophyll a
- Chlorophyta
- Chloroplast
- Cholesterol
- Chondrichthyes
- Chondroblast
- Chordata
- Chromatid
- Chromatids
- Chromatin
- Chromoplast
- Chromosomal crossover
- Chromosomal mutation
- Chromosome
- Chyme
- Cilia
- Ciliate
- Cilium
- Circular muscles
- Circulation
- Circulatory system
- Cisterna
- Citric Acid Cycle
- Clade
- Cladogram
- Class
- Classification
- Cleavage
- Cleavage furrow
- Climax
- Clone
- Cloning
- Closed circulatory system
- Cnidocyte
- CNS
- Coated pits
- Codominance
- Codominant trait
- Codon
- Coelom
- Coelomate
- Coenzyme
- Coevolution
- Cofactor
- Cohesion Tension Theory
- Colcemid
- Coleoptile
- Collagen fiber
- Colony
- Colony morphology
- Commensal
- Commensalism
- Compact bone
- Competent cell
- Competition
- Complementary base pairing
- Complementary strands
- Complete dominance
- Compound
- Concentration
- Concentration gradient
- Condyloid joint
- Cone
- Conjugation
- Connective tissue
- Conservation
- Conserved sequence
- Conspecific
- Consumer
- Consumption
- Contamination
- Contractile proteins
- Contractile vacuole
- Control
- Control group
- Convergence
- Convergent evolution
- Convergent muscles
- Copulation
- Cork
- Cornification
- Cotransport
- Cotyledon
- Covalent bond
- Coxal bone
- Crenation
- Cristae
- Crop
- Cross
- Cross linking
- Crossbreeding
- Crossover
- Cuticle
- Cyanobacteria
- Cyclic adenosine monophosphate
- Cyclins
- Cytochrome
- Cytokinesis
- Cytolysis
- Cytoplasm
- Cytoplasmic matrix
- Cytosine
- Cytosol
D
- Dark reaction
- Dark respiration
- Darwinian fitness
- Daughter cell
- De novo
- Death
- Decatenation
- Decomposer
- Decomposition
- Dedifferentiation
- Definitive host
- Deforestation
- Degradation
- Deletion
- Deletion mutation
- Deltaproteobacteria
- Denitrification
- Dense connective tissue
- Dense irregular connective tissue
- Dense regular connective tissue
- Density
- Density dependent limiting factor
- Deoxyribonucleic acid
- Deoxyribose
- Depolarization
- Descent
- Desert
- Desiccation
- Desmotubule
- Detritivore
- Development
- Diarthrodial joint
- Diatom
- Dichotomous
- Dichotomous key
- Dicot
- Differentiation
- Diffusion
- Diffusion equilibrium
- Digestion
- Digestive system
- Dihybrid
- Dihybrid cross
- Dimorphism
- Dioecious
- Diploblastic
- Diploid
- Diploidy
- Disaccharide
- Discoidal cleavage
- Disease
- Disjunction
- Dithecous
- Diurnal rhythm
- Divergence
- Divergent evolution
- Diversity
- Division
- Dizygotic twins
- DNA
- Dna methylation
- DNA polymerase
- DNA polymerase II
- DNA replication
- Dna synthesis
- Docking protein
- Dogma
- Domain
- Dominance
- Dominant
- Dominant species
- Dominant trait
- Dormancy
- Dorsal spine
- Double circulation
- Double stranded DNA virus
- Dried yeast
- Drupe
- Duplication mutation
- Dyad
E
- Ecological pyramid
- Ecological succession
- Ecology
- Ecosystem
- Ecosystem diversity
- Ectoparasite
- Ectoplasm
- Ectotherm
- Egestion
- Egg
- Ejaculation
- Elastic cartilage
- Elastic tissue
- Electron acceptor
- Electron carrier
- Electron carriers
- Electron transport chain
- Electron transport phosphorylation
- Electron transport system
- Element
- Elongation
- Embryo
- Embryology
- Emigration
- Endangered species
- Endemic
- Endocrine system
- Endocytosis
- Endomembrane system
- Endoparasite
- Endoplasmic reticulum
- Endosome
- Endospore
- Endosymbiosis
- Endosymbiotic theory
- Endothelial cells
- Energy
- Energy Flow
- Enteric bacteria
- Enterobacteriaceae
- Entomology
- Entropy
- Environment
- Enzyme
- Enzyme activation
- Enzymes
- Epidermis
- Epimastigote
- Epistasis
- Epithelium
- Epoch
- Equilibrium
- Equilibrium potential
- Erythrocyte
- Ethical
- Ethics
- Eubacteria
- Euchromatin
- Eucoelomate
- Eukarya
- Eukaryota
- Eukaryote
- Eukaryotic
- Eukaryotic cells
- Euploidy
- Eutrophication
- Evolution
- Ex vivo
- Excretion
- Exocytosis
- Exon
- Exotic species
- Exploitation competition
- Expression
- Extinction
- Extirpation
- Extracellular
- Extracellular digestion
- Extracellular fluid
- Extracellular matrix
- Extrinsic muscles
- Exudate
F
- F-factor
- Facilitated diffusion
- Facultative anaerobe
- Facultative mutualism
- Facultative parasite
- Fad
- Family
- Family traits
- Fastidious organism
- Fat
- Fatty acid
- Fecundity
- Feedback inhibition
- Feedback mechanism
- Feedback regulation
- Female
- Fermentation
- Fertilization
- Fertilization membrane
- Fetus
- Fiber
- Fibre
- Fibrinous exudate
- Fibrocartilage
- Fibrous tissue
- Fight or flight reaction
- Filament
- Filial generation
- Filtration
- Fimbria
- First filial generation
- Flaccid
- Flagellate
- Flagellum
- Flatworm
- Flavin adenine dinucleotide
- Flower
- Fluid
- Fluid mosaic model
- Fluorescence
- Flux
- Follicle cell
- Food
- Food chain
- Food web
- Fossil
- Fossil fuel
- Fossil record
- Fossilization
- Fragmentation
- Frameshift mutation
- Fructose
- Fruit
- Fundamental niche
- Fungus
- Fusiform muscle
- Fusion
G
- Gamete
- Gametogenesis
- Gametophyte
- Ganglia
- Gap 1 phase
- Gap 2 phase
- Gap junction
- Gap junctions
- Gastric juice
- Gastrulation
- Gated channel
- Gdp
- Gene
- Gene expression
- Gene flow
- Gene pool
- Gene regulation
- Gene transfer
- Genera
- Generation
- Generation time
- Generic name
- Genetic code
- Genetic disorder
- Genetic diversity
- Genetic drift
- Genetic equilibrium
- Genetic linkage
- Genetic locus
- Genetic material
- Genetic model
- Genetic mutations
- Genetic recombination
- Genetic screening
- Genetic variation
- Genetically modified organism
- Genetics
- Genome
- Genomic dna
- Genomic imprinting
- Genotype
- Genotypic ratio
- Genus
- GERL
- Germination
- Giemsa stain
- Glabrous skin
- Global warming
- Gluconeogenesis
- Glucose
- Glycerol
- Glycogen
- Glycogenesis
- Glycogenolysis
- Glycolipid
- Glycolysis
- Glycoprotein
- GMO
- Golgi apparatus
- Gonad
- Gram staining
- Gram-positive
- Grana
- Granum
- Grass
- Gravitaxis
- Gravitropism
- Greenhouse effect
- Gross photosynthesis
- Ground meristem
- Ground substance
- Growth
- Growth factor
- Growth rate
- Gtp
- Guanine
- Gullet
- Gut
- Gymnosperm
H
- H antigen
- Habitat
- Haemocoel
- Haemolysis
- Halophile
- Haploid
- Hardy-Weinberg equilibrium
- Hatch
- Head
- Heart
- Heart valve
- Heat
- Heat-labile
- Helicase
- Hemidesmosome
- Hemizygosity
- Hemizygote
- Hemizygous
- Hemoglobin
- Hemolysis
- Hepatocyte
- Heptose
- Herbivore
- Heredity
- Heritage
- Hermaphrodite
- Heterochromatin
- Heterogeneity
- Heterospecific
- Heterotroph
- Heterotrophic
- Heterozygosity
- Heterozygote
- Heterozygous
- Hierarchy
- Histone
- HnRNA
- Holoblastic cleavage
- Holocrine gland
- Homeostasis
- Homeostatic equilibrium
- Hominid
- Hominin
- Homo
- Homo sapiens
- Homo sapiens sapiens
- Homogenate
- Homolog
- Homologous chromosome
- Homologous structures
- Homologue
- Homology
- Homoplasy
- Homozygous
- Hormone
- Host
- Host cell
- Host range
- Housekeeping gene
- Hox gene
- Human
- Humor
- Humoral immunity
- Hyaline cartilage
- Hyaloplasm
- Hybrid
- Hybrid Sterility
- Hybridization
- Hydrogen
- Hydrolysis
- Hydrolytic cleavage
- Hydrolytic enzyme
- Hydrophilic
- Hydrophobic
- Hydrostatic pressure
- Hydrotropism
- Hyperosmotic
- Hyperpolarization
- Hyperthermophile
- Hypertonic
- Hypertonic solution
- Hyphae
- Hypomorphic mutation
- Hyposmotic
- Hypothesis
- Hypotonic solution
I
- Ichthyology
- Immovable joint
- Immune system
- Immunity
- Immunoglobulin
- Imperfect flower
- Imprinting
- In situ
- In vitro
- In vivo
- Inbreeding
- Incipient Species
- Incomplete dominance
- Incomplete penetrance
- Incubation
- Independent assortment
- Independent variable
- Indeterminate cleavage
- Indirect life cycle
- Induced fit model
- Infection
- Inflammatory response
- Ingestion
- Inheritance
- Inherited trait
- Initiation
- Inner cell mass
- Inoculating loop
- Inoculation
- Inoculum
- Inorganic Phosphate
- Inorganic salt
- Inspiration
- Insulin
- Integral membrane protein
- Integral protein
- Integrin
- Integument
- Interbreed
- Intercalary meristem
- Intercalated discs
- Intercellular
- Interference competition
- Interkinesis
- Intermediate host
- INTERMEDIATE PHENOTYPE
- Internal environment
- Internal naris
- Interneuron
- Interphase
- Interspecific competition
- Interspecific hybridization
- Interstitial fluid
- Intracellular
- Intracellular digestion
- Intraspecific competition
- Intraspecific Competition
- Intron
- Invagination
- Invasive species
- Inversion
- Invertebrate
- Involuntary muscle
- Involuntary Response
- Involution
- Ion
- Ion channel
- Ion Pump
- Ions
- Irritability
- Isoenzyme
- Isopeptide bond
- Isotonic
- Isotonicity
L
- Lacrimation
- Lactate
- Lactic acid
- Lactic acid fermentation
- Lactose
- Lacuna
- Lagging strand
- Lamellae
- Lanugo
- Latency
- Latent Infection
- Law of Dominance
- Law of Independent Assortment
- Law of Segregation
- Law of the minimum
- Leading strand
- Legumes
- Lenticel
- Leucoplast
- Leukocytosis
- Lichen
- Life
- Life cycle
- Ligand
- Ligase
- Light
- Light dependent reaction
- Light reactions
- Lignin
- Liliopsida
- Lineage
- Linkage
- Linkage map
- Linked genes
- Lipid
- Lipid bilayer
- Lithotroph
- Liver
- Liver cell
- Living thing
- Loci
- Lock-and-key model
- Locomotion
- Longitudinal section
- Loose connective tissue
- Lumen
- Lung capacity
- Lymph
- Lymph nodes
- Lymphocyte
- Lymphoid cell
- Lysate
- Lysis
- Lysogenic conversion
- Lysogenic cycle
- Lysosome
- Lytic cycle
M
- Macroevolution
- Macromolecule
- Macroorganism
- Magnification
- Male
- Malic acid
- Maltose
- Mammal
- Mantle
- Mass
- Mass extinction
- Maternal inheritance
- Matrix
- Maturation
- Mature mRNA
- Mechanoreceptors
- Medicinal plant
- Medusa
- Meiosis
- Meiosis I
- Meiosis II
- Meiotic spindle
- Membrane
- Membrane protein
- Membrane Transport Protein
- Memory cell
- Mendelian Genetics
- Mendelian inheritance
- Menstruation
- Meristem
- Meroblastic cleavage
- Mesophile
- Mesophyll
- Messenger RNA
- Metabolic pathway
- Metabolic Process
- Metabolic rate
- Metabolic Water
- Metabolism
- Metabolite
- Metachromatic granules
- Metamerism
- Metamorphosis
- Metaphase
- Metaphase I
- Metaphase II
- Metaphase plate
- Metastasis
- Microaerophile
- Microbe
- Microbiology
- Microevolution
- Microfibril
- Microfilament
- Microhabitat
- Micrometer
- Micromolecule
- Microorganism
- Microscope
- Microsphere
- Microspore
- Microtubule
- Microtubule organizing center
- Microvilli
- Migration
- Milk
- Mimicry
- Missense mutation
- Mitochondrial inheritance
- Mitochondrion
- Mitogen
- Mitosis
- Mitotic phase
- Mitotic spindle
- Mixotroph
- Modification
- Moiety
- Mole
- Molecule
- Mollusca
- Monera
- Monocot
- Monogenic inheritance
- Monogenic trait
- Monohybrid
- Monohybrid cross
- Monomer
- Monophyletic
- Monoploid
- Monosaccharide
- Monozygotic twins
- Morphology
- Mortality
- Mosaic
- Motif
- Motility
- Mouth
- MRNA
- Mucus
- Multicellular
- Multicellularity
- Multipennate muscle
- Multiple alleles
- Multipotent
- Murine
- Muscle
- Muscle cell
- Muscle contraction
- Muscle fatigue
- Muscle tone
- Muscle tonus
- Muscular system
- Muscular Tissue
- Mutagen
- Mutagens
- Mutant
- Mutation
- Mutualism
- Mutualistic symbiosis
- Mycelium
- Mycorrhiza
- Myelinated neuron
- Myoblast
- Myocardium
- Myofibril
N
- NAD
- NADH
- Nadp
- Natural active immunity
- Natural environment
- Natural passive immunity
- Natural selection
- Naturally acquired passive immunity
- Nature
- Negative feedback
- Nematocyte
- Neoplasm
- Nephron
- Nerve
- Nerve cell
- Nerve impulse
- Nervous system
- Nervous tissue
- Net photosynthesis
- Net primary productivity
- Neurilemma
- Neuroglia
- Neutral mutation
- Nicotinamide adenine dinucleotide phosphate
- Nitrates
- Nitrification
- Nitrogen Cycle
- Nitrogen fixation
- Nitrogenous base
- Non Random Mating
- Non-Mendelian inheritance
- Nondisjunction
- Nonpolar
- Nonpolar molecule
- Nonsense mutation
- Nuclear division
- Nuclear envelope
- Nuclear membrane
- Nuclear pore
- Nuclear pore complex
- Nuclease
- Nucleic acid
- Nucleoid
- Nucleolus
- Nucleotide
- Nucleus
- Null hypothesis
- Nullisomy
- Nutrient
O
- O antigen
- Obligate aerobe
- Obligate anaerobe
- Obligate mutualism
- Obligate parasite
- Offspring
- Oil
- Okazaki fragment
- Oligopeptide
- Oligosaccharide
- Omnivore
- Oncogene
- Ontogeny
- Oocyte
- Open circulatory system
- Operator
- Operon
- Opportunistic pathogen
- Orbits
- Order
- Organ
- Organelle
- Organic catalyst
- Organic compound
- Organic molecule
- Organism
- Origin
- Osmoregulation
- Osmosis
- Osmotic lysis
- Osmotic Potential
- Osmotic pressure
- Osmotrophy
- Osteoblast
- Osteocyte
- Outbreeding
- Ovum
- Oxaloacetate
- Oxidation
- Oxidative phosphorylation
- Oxygen
- Oxyhemoglobin
P
- P680
- P700
- Pancreatic juice
- Paracrine
- Paracrine signaling
- Parallel evolution
- Parapatric speciation
- Paraphyletic
- Parasite
- Parasitism
- Paratenic host
- Paravertebral ganglia
- Parent cell
- Parental generation
- Parthenogenesis
- Particulate inheritance
- Passive immunity
- Passive transport
- Pathogen
- Pathogenicity
- Pathology
- Pedigree
- Penetrate
- Pentadactyl Limb
- Pentose
- PEP carboxylase
- Pepsin
- Peptidoglycan
- Perception
- Perfect flower
- Pericardial Membrane
- Perinuclear space
- Peripatric speciation
- Peristalsis
- Peritoneum
- Permeability
- Perpendicular
- Perturbation
- PGA
- PH
- PH scale
- Phagocyte
- Phagocytosis
- Phagotrophy
- Phelloderm
- Phenotype
- Phenotype frequency
- Phenotypic ratio
- Pheomelanin
- Pheromones
- Phloem
- Phosphate
- Phosphate group
- Phospholipid
- Phospholipid bilayer
- Phosphorylation
- Photoautotroph
- Photoheterotroph
- Photophosphorylation
- Photorespiration
- Photosynthesis
- Photosystem
- Photosystem I
- Photosystem II
- Phototaxis
- Phototroph
- Phototropism
- Phyletic gradualism
- Phyllode
- Phylogeny
- Phylum
- Physiological processes
- Physiology
- Phytochrome
- Phytoplankton
- Pili
- Pilus
- Pinocytosis
- Pit
- Placebo
- Plankton
- Plant
- Plant leaves
- Plantae
- Plaque assay
- Plasma
- Plasma B cell
- Plasmid
- Plasmid vector
- Plasmodesmata
- Plasmolysis
- Plastid
- Pleiotropy
- Ploidy
- Plumule
- Pluripotent
- Pneumatophore
- Point mutation
- Polar cell
- Polar compound
- Polar molecule
- Polarity
- Polarization
- Pollen
- Pollen Grain
- Pollination
- Poly a tail
- Polycythemia
- Polygene
- Polygenic inheritance
- Polygenic trait
- Polymer
- Polymerization
- Polymorphism
- Polynucleotide
- Polypeptide
- Polyphyletic
- Polyploid
- Polyploidy
- Polyprotein
- Polysaccharide
- Population density
- Population growth
- Porin
- Positive feedback
- Postsynaptic cell
- Potency
- Precursor
- Predation
- Predator
- Predator-prey relationship
- Presynaptic cell
- Presynaptic terminals
- Prevertebral ganglia
- Prey
- Primary cell wall
- Primary consumer
- Primary meristem
- Primary oocyte
- Primary phloem
- Primary productivity
- Primary succession
- Primary xylem
- Primate
- Primer
- Prion
- Producer
- Progeny
- Prokaryote
- Prokaryotic
- Prokaryotic cell
- Proliferation
- Promastigote
- Prometaphase
- Promoter
- Promoter gene
- Propagation
- Prophase
- Prophase I
- Prophase II
- Proplastid
- Proprioceptor
- Protease
- Protein
- Protein domain
- Protein pump
- Protein synthesis
- Proteoglycan
- Proteome
- Protist
- Protista
- Proto-oncogene
- Protobiont
- Protocell
- Protoderm
- Proton donor
- Proton gradient
- Proton pump
- Proton-motive force
- Protons
- Protoplasm
- Protozoa
- Pseudodominance
- Pseudopodia
- Pseudostratified columnar epithelium
- Pulmonary ventilation
- Pulse
- Punctuated equilibrium
- Punnett Square
- Purebred
- Purine
- Purines
- Pyramid of Productivity
- Pyrimidine
- Pyruvate
R
- R plasmid
- Race
- Radial symmetry
- Reading frame
- Realized niche
- Reannealing
- Receptor
- Recessive
- Recessive Allele
- Recessive gene
- Recessive trait
- Recombinant DNA
- Recombination
- Reduction Division
- Reflex
- Regeneration
- Regulation
- Relative fitness
- Relay neuron
- Replication
- Replication fork
- Repolarization
- Reproduction
- Reproductive isolation
- Reservoir host
- Residual air
- Respiration
- Respiratory system
- Resting potential
- Restriction enzyme
- Reticular connective tissue
- Reticular fiber
- Retrovirus
- Reverse transcription
- Rhizoids
- Rhizome
- Ribonucleic acid
- Ribose
- Ribosomal RNA
- Ribosome
- Ribosomes
- Ribozyme
- Rivet Hypothesis
- RNA polymerase
- RNA virus
- Root
- Root cap
- Root Hair
- Rostrum
- Rough endoplasmic reticulum
- Roughage
- Rubisco
- Rule of nines
- Runner
S
- Saccharide
- Salt
- Sample
- Saprophyte
- Saprophytic
- Sarcolemma
- Sarcomere
- Sarcoplasmic reticulum
- Saturated fat
- Scavenger
- Schizogony
- Schwann cell
- Science
- Scientific method
- Scientific name
- Scion
- Secondary cell wall
- Secondary meristem
- Secondary oocyte
- Secondary succession
- Secondary xylem
- Secretion
- Secretory vesicle
- Seed
- Segmentation
- Segregation
- Selective breeding
- Selective permeability
- Selectively-permeable membrane
- Self
- Self antigen
- Semipermeable membrane
- Sensory neuron
- Sensu lato
- Septa
- Septum
- Sex
- Sex chromosome
- Sex hormone
- Sex linkage
- Sex pili
- Sex-linked
- Sex-linked gene
- Sex-linked trait
- Sexual reproduction
- Sexual selection
- Sieve plate
- Signal peptide
- Signal sequence
- Signal transduction
- Silent mutation
- Simple columnar epithelium
- Simple cuboidal epithelium
- Simple diffusion
- Simple epithelium
- Simple fruit
- Sinew
- Single stranded dna
- Single stranded DNA virus
- Siphonophore
- Sister chromatids
- Sister chromosomes
- Slime layer
- Smooth endoplasmic reticulum
- Smooth muscle
- Solute
- Solution
- Somatic cells
- Somatosensation
- Somite
- Speciation
- Speciation event
- Species
- Species Richness
- Specific epithet
- Specific heat
- Specificity
- Spectrophotometer
- Sperm
- Sperm cell
- Spermatogenesis
- Spermatophyta
- Spermiogenesis
- Sphenopalatine ganglioneuralgia
- Spindle
- Spindle apparatus
- Spindle fiber
- Splicing
- Spongy bone
- Spontaneous generation
- Spontaneous Mutation
- Spore
- Sporophyte
- Sporozoa
- Sporozoan
- Staining
- Standard deviation
- Starch
- Starlings law
- Statistics
- Statolith
- Stem
- Stem cell
- Sterile
- Steroid
- Sterol
- Sticky end
- Stigma
- Stimulus
- Stock
- Stoma
- Stomate
- Stop codon
- Storage
- Strain
- Strata
- Stratified
- Stratified columnar epithelium
- Stratified epithelium
- Stratified squamous epithelium
- Stratum germinativum
- Striated muscle
- Stroma
- Style
- Subcellular
- Submetacentric chromosome
- Subspecies
- Substitution mutation
- Substrate
- Substrate-level phosphorylation
- Substratum
- Succession
- Sucrose
- Sugar
- Sugar-phosphate backbone
- Supercoiling
- Survival of the fittest
- Sustainability
- Symbiont
- Symbiosis
- Symmetry
- Sympathetic nervous system
- Sympatric speciation
- Symport
- Synapomorphy
- Synapse
- Synapsis
- Synaptonemal complex
- Synchondrosis
- Syncytium
- Synecology
- Synergy
- Syngamy
- Synthesis
- Synthesis phase
- Systematics
T
- T tubule
- Tactile sense
- Taxa
- Taxis
- Taxon
- Taxonomy
- Telophase
- Telophase I
- Telophase II
- Temperate phage
- Temperate virus
- Terminal electron acceptor
- Terminal web
- Termination
- Terminator
- Terrestrial
- Terrestrial animal
- Terrestrial plant
- Territoriality
- Tertiary consumer
- Test cross
- Tetanus
- Theory
- Thermophile
- Thermotropism
- Thigmotropism
- Thin filament
- Thoracic duct
- Threatened species
- Thylakoid
- Thymine
- Tight junction
- Tissue
- Tissue perfusion
- Tonicity
- Tonoplast
- Topology
- Totipotent
- Totipotent cell
- Toxin
- Tracheary elements
- Tracheid
- Tracheophyte
- Traits
- Transcellular fluid
- Transducer
- Transduction
- Transfection
- Transferase
- Transformation
- Transgene
- Transgenic organisms
- Translation
- Translocation
- Transmembrane proteins
- Transmission
- Transmutation
- Transmutation of species
- Transpiration
- Transport
- Transposition
- Transposon
- Trigger
- Triglyceride
- Triploblastic
- TRNA
- Trophic
- Trophic level
- Tropic
- Tropism
- Tropomyosin
- True breeding
- Tuber
- Tubule
- Tumor
- Turgid
- Turgidity
- Turgor
- Turgor pressure
V
- Vaccination
- Vacuolization
- Variance
- Variation
- Variety
- Vascular bundle
- Vascular plants
- Vascular tissue
- Vasculature
- Vector
- Vegetable
- Vegetative Cell
- Vegetative propagation
- Vegetative reproduction
- Vein
- Ventilation
- Vertex
- Vertical gene transfer
- Vesicle
- Vestigial
- Vestigial organ
- Vicariance
- Vicariant speciation
- Virulent virus
- Virus
- Vitamin
- Vitreous humor
- Viviparous
- Voluntary muscle
- Vulnerable species
