1. Life (Level 1)
   1. Death
      1. Suicide (Level 3)
         1. Suicide crisis
         2. Suicide intervention
         3. Suicide methods
         4. Suicide prevention
   2. Abiogenesis (Level 3)
   3. Organism (Level 3)
      1. Earliest known life forms
      2. Model organism
      3. Microorganism
         1. Bacteriophage
   4. Carbon-based life
   5. Non-cellular life
   6. Artificial life
2. Biology (Level 2)
   1. Human biology
   2. Microbiology
      1. Microbiological culture
   3. Mycology
   4. Synthetic biology
3. Evolution (Level 2)
   1. History of life (Level 4)
      1. Timeline of the evolutionary history of life
   2. Introduction to evolution
4. Neuroscience
   1. Brain–computer interface
   2. Clinical neuroscience
   3. Neural network (biology)
   4. Neuroplasticity
   5. Sense
5. Organic matter
   1. Amber
   2. Ivory
   3. Pearl
6. Paleontology (Level 3)
   1. Fossil
      1. Living fossil
      2. Transitional fossil
      3. Trace fossil
      4. Petrified wood
   2. Micropaleontology
   3. Paleobotany
   4. Paleoecology
7. Phylogenetics
   1. Binomial nomenclature
   2. Taxonomy (biology) (Level 3)
      1. Cladistics
         1. Clade
            1. Crown group
      2. Incertae sedis
      3. Synonym (taxonomy)
      4. Taxon
      5. Taxonomic rank
         1. Domain (biology)
         2. Kingdom (biology)
         3. Phylum
         4. Class (biology)
         5. Order (biology)
         6. Family (biology)
            1. Type genus
            2. Tribe (biology)
         7. Genus
            1. Type species
         8. Species (Level 3)
            1. Infraspecific name
            2. Subspecies
8. Bioinformatics
   1. Computational biology
   2. Proteomics
9. Biomechanics
10. Systems biology
11. Ethnobiology

1. Anatomy (Level 3)
2. Anatomical variation
3. Dissection
4. Morphology (biology)
5. Organ (biology)
   1. Organ system
6. Tissue (biology)
   1. Histology
7. Sexual dimorphism
8. Bacterial cell structure
   1. Bacterial capsule
   2. Endospore
   3. Pilus
9. Biofilm
10. Bird anatomy
11. Fish anatomy
12. Insect morphology

1. Head
   1. Cheek
2. Neck
3. Thorax
4. Digit (anatomy)
5. Abdomen
   1. Navel
   2. Peritoneum
6. Buttocks
7. Body fluid
   1. Extracellular fluid
8. Beak
9. Claw
10. Fin
11. Gland
12. Tail

This section contains 29 articles.

1. Circulatory system
2. Blood
   1. Blood plasma
   2. Blood cell
      1. Platelet
      2. Red blood cell
      3. White blood cell
         1. Neutrophil
         2. Eosinophil
         3. Basophil
         4. Mast cell
3. Blood vessel
   1. Artery
   2. Arteriole
   3. Capillary
   4. Vein
   5. Venule
4. Endothelium
5. Heart (Level 3)
   1. Aorta
   2. Atrium (heart)
   3. Heart valve
   4. Ventricle (heart)
6. Lymphatic system
   1. Lymph
   2. Lymph node
   3. Lymphatic vessel
7. Spleen
8. Blood–brain barrier

This section contains 7 articles.

1. Endocrine system
   1. Adrenal gland (Level 4)
   2. Hypothalamus
   3. Parathyroid gland
   4. Pineal gland
   5. Pituitary gland
   6. Thyroid (Level 4)

This section contains 26 articles.

1. Anus
2. Appendix (anatomy)
3. Esophagus (Level 4)
4. Feces
5. Gallbladder
6. Large intestine
   1. Cecum
   2. Rectum
7. Liver
   1. Bile
8. Mouth
   1. Palate
   2. Lip
   3. Saliva
      1. Salivary gland
   4. Tooth
      1. Dentition
      2. Gums
9. Pancreas (Level 4)
10. Pharynx
11. Small intestine
    1. Duodenum
    2. Jejunum
    3. Ileum
12. Stomach
13. Throat

This section contains 9 articles.

1. Immune system (Level 3)
2. Antibody (Level 4)
3. Antigen
4. B cell
5. Dendritic cell
6. Macrophage
7. Natural killer cell
8. T cell
9. Thymus

This section contains 13 articles.

1. Integumentary system
2. Breast
   1. Nipple
3. Feather
4. Fingerprint
5. Fur
6. Hair
   1. Hair follicle
7. Nail (anatomy)
8. Scale (zoology)
9. Skin
   1. Epidermis
   2. Dermis

This section contains 6 articles.

1. Muscular system
2. Cardiac muscle
3. Muscle cell
4. Sarcomere
5. Skeletal muscle
6. Smooth muscle

This section contains 77 articles.

1. Nervous system
   1. Central nervous system
   2. Peripheral nervous system
2. Antenna (biology)
3. Brain (Level 3)
   1. Brainstem
      1. Medulla oblongata
      2. Midbrain
      3. Pons
   2. Cerebellum (Level 4)
   3. Cerebral cortex
   4. Cerebrum
      1. Frontal lobe
      2. Occipital lobe
      3. Parietal lobe
      4. Temporal lobe
         1. Amygdala
         2. Hippocampus
4. Cerebrospinal fluid
5. Glia
6. Nerve
   1. Cranial nerves
   2. Spinal nerve
7. Neuron
   1. Axon
   2. Dendrite
   3. Myelin
   4. Synapse
8. Spinal cord
9. Autonomic nervous system
   1. Parasympathetic nervous system
   2. Sympathetic nervous system
10. Sensory nervous system
    1. Synesthesia
11. Auditory system
    1. Ear (Level 3)
       1. Eardrum
       2. Ossicles
       3. Cochlea
       4. Hair cell
    2. Hearing
       1. Auditory cortex
12. Taste
    1. Bitter taste evolution
    2. Pungency
    3. Sweetness
    4. Tongue
    5. Umami
13. Olfactory system
    1. Nose
    2. Sense of smell
14. Somatosensory system
    1. Pain
    2. Proprioception
15. Visual system
    1. Eye
       1. Cornea
       2. Eyelid
       3. Iris (anatomy)
       4. Lens (vertebrate anatomy)
       5. Optic nerve
       6. Photoreceptor cell
          1. Cone cell
          2. Rod cell
       7. Pupil
       8. Retina
       9. Tears
       10. Vitreous body
    2. Visual perception
       1. Accommodation (vertebrate eye)
       2. Color vision
          1. Monochromacy
          2. Dichromacy
          3. Trichromacy
          4. Tetrachromacy
          5. Purkinje effect
       3. Visual cortex

This section contains 18 articles.

1. Reproductive system
   1. Sex organ
   2. Female reproductive system
      1. Clitoris (Level 4)
      2. Fallopian tube
      3. Ovary
      4. Placenta
      5. Uterus
         1. Cervix
      6. Vagina (Level 4)
         1. Hymen
   3. Male reproductive system
      1. Penis
         1. Foreskin
         2. Glans penis
      2. Prostate
      3. Testicle
         1. Scrotum

This section contains 8 articles.

1. Respiratory system
2. Gill
3. Lung (Level 3)
   1. Bronchus
   2. Pulmonary alveolus
4. Larynx
5. Thoracic diaphragm
6. Trachea

This section contains 36 articles.

1. Skeleton
2. Bone
   1. Bone marrow
3. Antler
4. Carpal bones
5. Clavicle
6. Femur
7. Fibula
8. Horn (anatomy)
9. Humerus
10. Hyoid bone
11. Jaw
12. Joint
    1. Ankle
    2. Elbow
    3. Knee
    4. Wrist
13. Maxilla
14. Metacarpal bones
15. Metatarsal bones
16. Patella
17. Pelvis
18. Phalanx bone
19. Radius (bone)
20. Rib cage
    1. Rib
    2. Sternum
21. Sacrum
22. Scapula
23. Skull
24. Tarsus (skeleton)
25. Tibia
26. Ulna
27. Vertebral column
28. Exoskeleton
29. Mollusc shell

This section contains 11 articles.

1. Connective tissue
   1. Adipocyte
   2. Adipose tissue
   3. Cartilage
   4. Fibroblast
   5. Ligament
   6. Tendon
2. Epithelium
   1. Basement membrane
3. Muscle
4. Nervous tissue

This section contains 7 articles.

1. Bladder
2. Kidney
   1. Nephron
3. Urethra
4. Ureter
5. Urinary system
   1. Urine

This section contains 32 articles.

1. Plant anatomy
2. Plant morphology
3. Plant nutrition
4. Bulb
5. Flower
   1. Gynoecium
   2. Petal
   3. Sepal
   4. Stamen
6. Fruit
   1. Berry (botany)
   2. Nut (fruit)
7. Herbaceous plant
8. Leaf
9. Rhizome
10. Root
    1. Aerial root
    2. Taproot
11. Seed
12. Seedling
    1. Cotyledon
    2. Hypocotyl
    3. Radicle
13. Shrub
14. Stolon
15. Stoma
16. Strobilus
17. Tree (Level 3)
18. Tuber
19. Vine
    1. Liana
    2. Tendril

This section contains 8 articles.

1. Plant stem
2. Bark (botany)
3. Branch
4. Cortex (botany)
5. Pith
6. Stele (biology)
7. Trunk (botany)
8. Twig

This section contains 8 articles.

1. Epidermis (botany)
2. Endodermis
3. Ground tissue
4. Meristem
5. Vascular tissue
   1. Phloem
   2. Xylem
6. Vascular cambium

1. Ascus
2. Basidium
3. Conidium
4. Hypha
5. Mycelium
6. Sporangium
7. Thallus

This section contains 53 articles.

1. Physiology
   1. Plant physiology
2. Blinking
3. Breathing
4. Cardiac cycle
5. Chemosynthesis
6. Circadian rhythm
7. Digestion
8. Excretion
   1. Burping
   2. Defecation
   3. Flatulence
   4. Urination
9. Healing
   1. Coagulation
   2. Hemostasis
   3. Wound healing
10. Homeostasis
    1. Acid–base homeostasis
    2. Blood sugar level
    3. Osmoregulation
11. Metabolism (Level 3)
    1. Biosynthesis
    2. Bradymetabolism
    3. Catabolism
    4. Gluconeogenesis
    5. Metabolomics
    6. Secondary metabolite
12. Muscle contraction
13. Photosynthesis
    1. Light-dependent reactions
    2. Calvin cycle
    3. Biological carbon fixation
       1. C3 carbon fixation
       2. C4 carbon fixation
       3. Crassulacean acid metabolism
14. Respiration (physiology)
15. Thermoregulation
    1. Warm-blooded
    2. Thermogenesis
    3. Ectotherm
    4. Endotherm
    5. Eurytherm
    6. Poikilotherm
    7. Mesotherm
    8. Homeothermy
    9. Heterothermy
    10. Stenotherm
    11. Kleptothermy
    12. Gigantothermy
    13. Thermostability
    14. Thermolabile
16. Transpiration

This section contains 2 articles.

1. Developmental biology
2. Development of the human body

This section contains 15 articles.

1. Cuticle
2. Embryo
3. Embryology
4. Fetus
5. Imago
6. Larva
7. Longevity
8. Metamorphosis
9. Moulting
10. Nymph (biology)
11. Ontogeny
12. Puberty
13. The Pupa
14. Tadpole
15. Umbilical cord

This section contains 11 articles.

1. Reproduction
2. Asexual reproduction
   1. Parthenogenesis
3. Sex
   1. Sexual reproduction
   2. Female
   3. Male
4. Gamete
5. Germline
6. Microbial cyst
7. Spore

This section contains 19 articles.

1. Egg
   1. Oogenesis
   2. Egg white
   3. Yolk
2. Birth
3. Lactation
4. Pregnancy (mammals)
5. Pregnancy in fish
6. Semen
   1. Ejaculation
   2. Insemination
7. Sperm
   1. Spermatogenesis
8. Animal embryonic development
   1. Zygote
   2. Cleavage (embryo)
   3. Blastulation
   4. Gastrulation
   5. Germ layer

This section contains 17 articles.

1. Human reproduction
   1. Pregnancy
      1. Human embryonic development
      2. Human fertilization
      3. Miscarriage
   2. Childbirth
      1. Breech birth
      2. Multiple birth
      3. Preterm birth
      4. Postterm pregnancy
      5. Stillbirth
2. Menstrual cycle (Level 4)
   1. Menstruation
   2. Ovulation
   3. Premenstrual syndrome
3. Menopause
   1. Hot flash

This section contains 13 articles.

1. Plant reproduction
2. Alternation of generations (Level 4)
3. Gametophyte
   1. Antheridium
   2. Archegonium
4. Germination
5. Oogonium
6. Plant embryonic development
7. Plant reproductive morphology
8. Pollen
9. Pollination
10. Sporophyte
11. Vernalization

1. Biochemistry
2. Chemical biology
3. Biomolecule
4. Structural biology

This section contains 5 articles.

1. Alkaloid
2. Caffeine (Level 4)
3. Cocaine (Level 4)
4. Morphine
5. Nicotine

This section contains 7 articles.

1. Biological pigment
2. Carotenoid
   1. Β-Carotene
   2. Lutein
3. Chlorophyll
4. Melanin
5. Rhodopsin

This section contains 19 articles.

1. Carbohydrate
2. Monosaccharide
   1. Deoxyribose
   2. Fructose
   3. Galactose
   4. Glucose
   5. Glyceraldehyde
   6. Ribose
3. Disaccharide
   1. Lactose
   2. Maltose
   3. Sucrose
4. Polysaccharide
   1. Agar
   2. Cellulose
   3. Chitin
   4. Glycogen
   5. Pectin
   6. Starch

This section contains 30 articles.

1. Hormone
2. Adrenaline
3. Androgen
   1. Testosterone
4. Aldosterone
5. Cortisol
6. Dopamine (Level 4)
7. Endorphins
8. Estrogen
9. Glucocorticoid
10. Growth hormone
11. Insulin (Level 4)
12. Leptin
13. Melatonin
14. Oxytocin
15. Progestogen
    1. Progesterone
16. Secretin
17. Thyroid hormones
18. Vasopressin
19. Plant hormone
    1. Abscisic acid
    2. Auxin
    3. Brassinosteroid
    4. Cytokinin
    5. Florigen
    6. Gibberellin
    7. Jasmonate
    8. Salicylic acid
    9. Strigolactone

This section contains 8 articles.

1. Lipid (Level 3)
2. Fat
3. Fatty acid
   1. Omega-3 fatty acid
   2. Omega-6 fatty acid
4. Lipopolysaccharide
5. Lipoprotein
6. Phospholipid

This section contains 15 articles.

1. Nucleic acid
2. DNA (Level 3)
3. RNA (Level 3)
   1. Messenger RNA
   2. Transfer RNA
   3. Ribosomal RNA
4. Adenosine triphosphate
5. Nucleic acid structure
   1. Base pair
   2. Nucleotide
   3. Adenine
   4. Cytosine
   5. Guanine
   6. Thymine
   7. Uracil

This section contains 5 articles.

1. Neurotransmitter
2. Acetylcholine
3. Catecholamine
4. γ-Aminobutyric acid
5. Glutathione

This section contains 38 articles.

1. Protein (Level 3)
2. Amino acid (Level 4)
   1. Proteinogenic amino acid
   2. Essential amino acid
   3. Alanine
   4. Arginine
   5. Asparagine
   6. Aspartic acid
   7. Cysteine
   8. Glutamic acid
   9. Glutamine
   10. Glycine
   11. Histidine
   12. Isoleucine
   13. Leucine
   14. Lysine
   15. Methionine
   16. Phenylalanine
   17. Proline
   18. Serine
   19. Threonine
   20. Tryptophan
   21. Tyrosine
   22. Valine
3. Collagen
4. Enzyme (Level 4)
5. Gelatin
6. Glycoprotein
7. Hemoglobin
8. Histone
9. Keratin
10. Peptide
11. Peptidoglycan
12. Protein (nutrient)
13. Protein biosynthesis
14. Protein structure
15. Proteome
16. Gluten

This section contains 3 articles.

1. Steroid
2. Cholesterol
3. Steroid hormone

1. Molecular biology
2. Gene expression
3. Central dogma of molecular biology
4. Genetic code (Level 4)
5. DNA replication
   1. DNA polymerase
   2. DNA ligase
   3. Helicase
6. DNA repair
7. Transposable element
8. Non-coding DNA
9. Transcription (biology)
   1. Enhancer (genetics)
   2. Operon
   3. Promoter (genetics)
   4. RNA polymerase
   5. Terminator (genetics)
   6. Transcription factor
   7. Transcriptome
10. Post-transcriptional modification
    1. RNA splicing
       1. Exon
       2. Intron
    2. MicroRNA
    3. RNA interference
11. Translation (biology)
12. Post-translational modification
    1. Protein folding
    2. Ubiquitin
13. Regulation of gene expression
14. Non-coding RNA
15. Reverse transcriptase
    1. Complementary DNA
16. Restriction enzyme
17. Cloning vector
18. Expression vector

This section contains 12 articles.

1. Zoology
   1. Entomology
   2. Herpetology
   3. Ichthyology
   4. Malacology
   5. Mammalogy
   6. Ornithology
2. Animal (Level 2)
   1. Animal consciousness
3. Animal coloration (Level 4)
   1. Camouflage (Level 4)
   2. Mimicry

This section contains 45 articles.

1. Ethology
2. Intelligence (Level 3)
3. Sleep
   1. Sleep in animals
   2. Rapid eye movement sleep
   3. Siesta
   4. Wakefulness
   5. Yawn
4. Dormancy
   1. Hibernation
   2. Aestivation
   3. Diapause
5. Carnivore
   1. Hematophagy
   2. Hypercarnivore
   3. Insectivore
   4. Predation (Level 4)
   5. Scavenger
6. Herbivore
   1. Grazing
   2. Browsing (herbivory)
7. Omnivore
   1. Hypocarnivore
   2. Mesocarnivore
8. Imprinting (psychology)
9. Animal locomotion
   1. Arboreal locomotion
   2. Bipedalism
      1. Facultative bipedalism
   3. Quadrupedalism
   4. Tripedalism
   5. Unipedalism
   6. Flying and gliding animals
10. Animal migration (Level 4)
    1. Bird migration
11. Animal sexual behaviour
    1. Copulation (zoology)
    2. Mating
12. Fight-or-flight response
13. Instinct
14. Sociality
    1. Eusociality
15. Swarm behaviour
    1. Flock (birds)
    2. Herd

1. Botany (Level 3)
2. Plant (Level 2)
   1. Carnivorous plant
   2. Flowering plant (Level 4)
      1. Dicotyledon
         1. Eudicots
         2. Magnoliids
      2. Monocotyledon
   3. Weed
3. Plant pathology

This section contains 6 articles.

1. Cell biology
2. Antibiotic sensitivity testing
3. Staining
   1. Gram stain
   2. Endospore staining
   3. Ziehl–Neelsen stain

This section contains 33 articles.

1. Cell death
   1. Necrosis
   2. Programmed cell death
      1. Apoptosis
      2. Autophagy
2. Cell signaling
   1. Cytokine
   2. Ligand (biochemistry)
   3. Receptor (biochemistry)
      1. G protein-coupled receptor
   4. Signal transduction
   5. Biochemical cascade
   6. Second messenger system
3. Cellular differentiation
   1. Somatic cell
   2. Stem cell (Level 4)
      1. Embryonic stem cell
      2. Hematopoietic stem cell
4. Cellular respiration
   1. Anaerobic respiration
   2. Citric acid cycle
   3. Electron transport chain
   4. Glycolysis
   5. Oxidative phosphorylation
5. Fermentation
6. Membrane transport
   1. Passive transport
      1. Facilitated diffusion
   2. Active transport
      1. ATPase
      2. Endocytosis
      3. Exocytosis
7. Protein targeting

This section contains 5 articles.

1. Cell cycle
2. Fission (biology)
3. Meiosis
4. Mitosis (Level 4)
5. Plasmid

This section contains 16 articles.

1. Cell (biology) (Level 2)
2. Cell junction
3. Cell membrane
   1. Lipid bilayer
   2. Membrane potential
   3. Membrane protein
4. Cilium
5. Cytoplasm
   1. Cytosol
6. Cytoskeleton
   1. Microfilament
      1. Actin
      2. Myosin
   2. Microtubule
7. Flagellum
8. Symbiogenesis (Level 4)

This section contains 18 articles.

1. Organelle
2. Endomembrane system
3. Cell nucleus (Level 4)
   1. Chromatin
   2. Chromosome
   3. Nuclear envelope
   4. Nucleolus
4. Centriole
5. Endoplasmic reticulum
6. Golgi apparatus
7. Lysosome
8. Mitochondrion (Level 4)
   1. Mitochondrial DNA
9. Peroxisome
10. Proteasome
11. Ribosome (Level 4)
12. Vacuole
13. Vesicle (biology and chemistry)

This section contains 7 articles.

1. Plant cell
2. Cell wall
3. Chloroplast
   1. Chloroplast DNA
   2. Thylakoid
4. Plastid
5. Plasmodesma

1. Ecology (Level 2)
2. Autotroph
3. Biome
4. Biodiversity
   1. Biodiversity loss
5. Biogeography
6. Biogeographic realm
7. Bioindicator
8. Biological dispersal
   1. Seed dispersal
9. Biological interaction
   1. Competition (biology)
   2. Symbiosis
      1. Commensalism
      2. Mutualism (biology)
      3. Parasitism (Level 4)
10. Biological life cycle
11. Biomagnification
12. Biosphere
13. Carrying capacity
14. Community (ecology)
15. Conservation biology
16. Detritivore
17. Decomposer
18. Disturbance (ecology)
19. Ecological niche
    1. Niche construction
20. Ecological resilience
21. Ecological succession
22. Ecosystem
23. Ecosystem collapse
24. Ecosystem model
25. Ecosystem service
26. Endangered species
27. Endemism
28. Energy flow (ecology)
29. Extinction
30. Extremophile
31. Food chain
32. Food web
33. Habitat (Level 4)
34. Habitat destruction
35. Habitat fragmentation
36. Heterotroph
37. Insular biogeography
38. Invasive species (Level 4)
39. Keystone species
40. Landscape ecology
41. Land change science
42. Lotka–Volterra equations
43. Microbial ecology
44. Microbiome
45. Population
    1. Population growth
46. Primary production
47. r/K selection theory
48. Ecological restoration
49. Sustainability (Level 4)
50. Trophic cascade
51. Urban ecology
52. Wildlife conservation
    1. Wildlife

1. Genetics (Level 3)
   1. Introduction to genetics
2. Gene (Level 3)
3. Heredity
4. Mendelian inheritance
   1. Allele
   2. Dominance (genetics)
   3. Genotype
   4. Penetrance
   5. Phenotype
   6. Zygosity
5. Ploidy
6. Sex-determination system
7. Sex linkage
8. Genetic linkage
9. Extranuclear inheritance
10. Mutation
    1. Chromosome abnormality
    2. Chromosomal translocation
    3. Point mutation
    4. Mutagen
11. Genetic recombination
    1. Homologous recombination
12. Horizontal gene transfer
13. Quantitative genetics
    1. Heritability
14. Reverse genetics
15. Molecular genetics
16. Genome
    1. Genomics
    2. Human genome (Level 4)
       1. Human Genome Project
    3. DNA sequencing
    4. Metagenomics
17. Molecular evolution
18. Epigenetics
    1. Epigenomics
       1. Epigenome
19. Hybrid (biology) (Level 4)
    1. Heterosis
    2. Inbreeding
20. Eugenics
21. Dysgenics

1. Evolutionary biology
2. Evolutionary developmental biology
3. Divergent evolution
4. Convergent evolution
5. Parallel evolution
6. Phylogenetic tree
7. Population genetics
   1. Hardy–Weinberg principle
   2. Natural selection (Level 3)
   3. Gene flow
   4. Genetic diversity
   5. Genetic drift (Level 4)
   6. Genetic admixture
   7. Haplogroup
   8. Founder effect
   9. Population bottleneck
8. Sociobiology
9. Systematics
10. Adaptation (Level 4)
11. Coevolution
12. Fitness (biology)
13. Homology (biology)
14. Last universal common ancestor
15. Macroevolution
16. Microevolution
17. Reproductive isolation
18. Speciation
19. Evolution of bacteria
20. Evolution of birds
21. Evolution of brachiopods
22. Evolution of fish
23. Evolution of fungi
24. Evolution of insects
25. Evolution of mammals
26. Evolution of molluscs
27. Evolution of reptiles
28. Evolution of spiders
29. Evolution of tetrapods
30. Evolutionary history of plants
31. Viral evolution