1. Life (Level 1)
2. Death (Level 2)
   1. Brain death
   2. Decomposition (Level 4)
   3. Suicide (Level 3)
3. Organism (Level 3)
   1. Model organism (Level 4)
   2. Microorganism (Level 4)
4. Carbon-based life
5. Non-cellular life
6. Artificial life
7. Biology (Level 2)
   1. Human biology
   2. Microbiology (Level 4)
      1. Microbiological culture
   3. Mycology (Level 4)
8. History of life (Level 3)
   1. Abiogenesis (Level 3)
   2. Earliest known life forms
9. Neuroscience (Level 4)
   1. Neural network (biology)
   2. Neuroplasticity
10. Organic matter
    1. Amber (Level 4)
    2. Ivory (Level 4)
    3. Pearl (Level 4)
11. Bioinformatics
    1. Computational biology
    2. Proteomics
12. Biomechanics (Level 4)
13. Systems biology
14. Ethnobiology

1. Paleontology (Level 3)
2. Fossil (Level 4)
   1. Trace fossil
   2. Petrified wood
3. Micropaleontology
4. Paleobotany
5. Paleoecology
6. Transitional fossil

1. Phylogenetics (Level 4)
2. Binomial nomenclature (Level 4)
3. Taxonomy (biology) (Level 3)
4. Cladistics
   1. Clade
      1. Crown group
5. Incertae sedis
6. Synonym (taxonomy)
7. Taxon

This section contains 14 articles.

1. Taxonomic rank
2. Domain (biology) (Level 4)
3. Kingdom (biology) (Level 4)
4. Phylum
5. Class (biology)
6. Order (biology)
7. Family (biology)
   1. Type genus
   2. Tribe (biology)
8. Genus
   1. Type species
9. Species (Level 3)
   1. Infraspecific name
   2. Subspecies

1. Anatomy (Level 3)
2. Anatomical variation
3. Dissection (Level 4)
4. Morphology (biology)
5. Organ (biology) (Level 4)
   1. Organ system
6. Tissue (biology) (Level 4)
   1. Histology
7. Sexual dimorphism (Level 4)
8. Biofilm

1. Body (biology)
2. Gland (Level 4)
3. Exocrine gland
   1. Mucus
4. Body fluid
   1. Extracellular fluid
   2. Venom (Level 4)
5. Muscular system (Level 4)
6. Genitourinary system

This section contains 28 articles.

1. Head (Level 4)
   1. Beak
   2. Cheek
   3. Proboscis
   4. Snout
2. Neck
   1. Throat
3. Thorax (Level 4)
4. Thorax (arthropod anatomy)
5. Digit (anatomy)
6. Abdomen (Level 4)
   1. Navel
   2. Peritoneum
7. Body cavity
   1. Abdominal cavity
8. Buttocks
9. Claw
10. Hoof
11. Fin
    1. Bird wing
    2. Fish fin
    3. Insect wing
12. Limb (anatomy)
    1. Flipper (anatomy)
    2. Webbed foot
13. Arthropod leg
14. Tail
15. Torso

This section contains 25 articles.

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

This section contains 8 articles.

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

This section contains 32 articles.

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

This section contains 16 articles.

1. Immune system (Level 3)
   1. Adaptive immune system
   2. Innate immune system
2. Antibody (Level 4)
3. Antigen
4. B cell
5. Dendritic cell
6. Macrophage
7. Natural killer cell
8. T cell
9. White blood cell (Level 4)
   1. Neutrophil
   2. Eosinophil
   3. Basophil
   4. Mast cell
10. Thymus

This section contains 19 articles.

1. Integumentary system (Level 4)
2. Feather (Level 4)
3. Fingerprint (Level 4)
4. Hair (Level 4)
   1. Body hair
   2. Fur (Level 4)
   3. Hair follicle
   4. Pubic hair
   5. Whiskers (Level 4)
5. Nail (anatomy) (Level 4)
6. Scale (zoology) (Level 4)
7. Skin (Level 3)
   1. Epidermis
   2. Dermis
8. Spine (zoology)
9. Stinger (Level 4)
10. Structural coloration
11. Sweat gland
    1. Perspiration

This section contains 91 articles.

1. Nervous system (Level 3)

This section contains 25 articles.

1. Central nervous system (Level 4)
2. Meninges
3. Cerebrospinal fluid
4. Spinal cord (Level 4)
5. Motor neuron

This section contains 20 articles.

1. Brain (Level 3)
2. Brainstem (Level 4)
   1. Medulla oblongata
   2. Midbrain
   3. Pons
3. Thalamus
4. Cerebellum (Level 4)
5. Cerebrum (Level 4)
   1. Cerebral cortex (Level 4)
      1. Frontal lobe
         1. Broca's area
         2. Motor cortex
      2. Occipital lobe
      3. Parietal lobe
      4. Temporal lobe
         1. Wernicke's area
   2. Amygdala
   3. Basal ganglia
   4. Corpus callosum
   5. Hippocampus

This section contains 8 articles.

1. Peripheral nervous system (Level 4)
   1. Ganglion (Level 4)
2. Nerve
   1. Cranial nerves
   2. Spinal nerve
3. Autonomic nervous system
   1. Parasympathetic nervous system
   2. Sympathetic nervous system

This section contains 57 articles.

1. Sense (Level 3)
2. Sensory nervous system (Level 4)
   1. Sensory neuron
   2. Synesthesia
3. Antenna (zoology)
4. Auditory system (Level 4)
   1. Ear (Level 3)
      1. Outer ear
         1. Earwax
      2. Eardrum
      3. Ossicles
      4. Cochlea
      5. Hair cell
   2. Hearing (Level 4)
      1. Auditory cortex
5. Lateral line
6. Taste (Level 4)
   1. Bitter taste evolution
   2. Pungency
   3. Sweetness
   4. Umami
7. Olfactory system (Level 4)
   1. Nose (Level 4)
      1. Nostril
   2. Sense of smell (Level 4)
      1. Odor (Level 4)
8. Somatosensory system (Level 4)
   1. Pain (Level 4)
   2. Proprioception
9. Vestibular system

This section contains 27 articles.

1. Visual system (Level 4)
2. Eye (Level 3)
   1. Compound eye (Level 4)
   2. Cornea
   3. Eye color
   4. Eyelid
   5. Iris (anatomy)
   6. Lens (vertebrate anatomy)
   7. Optic nerve
   8. Photoreceptor cell
      1. Cone cell
      2. Rod cell
   9. Pupil
   10. Retina
   11. Simple eye in invertebrates
   12. Tears
   13. Vitreous body
3. Visual perception (Level 4)
   1. Accommodation (vertebrate eye)
   2. Visual acuity
   3. Color vision (Level 4)
      1. Monochromacy
      2. Dichromacy
      3. Trichromacy
      4. Tetrachromacy
      5. Purkinje effect
   4. Visual cortex

This section contains 23 articles.

1. Reproductive system (Level 4)
2. Sex organ (Level 4)

This section contains 14 articles.

1. Female reproductive system (Level 4)
2. Clitoris (Level 4)
3. Fallopian tube
4. Mammary gland
   1. Breast (Level 4)
   2. Nipple
   3. Udder
5. Ovary (Level 4)
6. Placenta (Level 4)
7. Pouch (marsupial)
8. Uterus (Level 4)
   1. Cervix
9. Vagina (Level 4)
   1. Hymen

This section contains 7 articles.

1. Male reproductive system (Level 4)
2. Penis (Level 4)
   1. Foreskin
   2. Glans penis
3. Prostate
4. Testicle (Level 4)
   1. Scrotum

This section contains 8 articles.

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

This section contains 37 articles.

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

This section contains 23 articles.

1. Connective tissue (Level 4)
   1. Adipocyte
   2. Adipose tissue
   3. Cartilage (Level 4)
      1. Hyaline cartilage
   4. Fibroblast
   5. Ligament (Level 4)
   6. Tendon (Level 4)
2. Epithelium (Level 4)
   1. Basement membrane
3. Muscle (Level 4)
   1. Cardiac muscle
   2. Muscle cell (Level 4)
   3. Sarcomere (Level 4)
   4. Skeletal muscle (Level 3)
   5. Smooth muscle
4. Nervous tissue (Level 4)
   1. Neuron (Level 4)
      1. Axon
      2. Dendrite
   2. Myelin
   3. Synapse
   4. Glia

This section contains 7 articles.

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

This section contains 3 articles.

1. Bird anatomy
2. Fish anatomy
3. Insect morphology

This section contains 24 articles.

1. Plant anatomy (Level 4)
2. Plant morphology (Level 4)
3. Plant nutrition
4. Bud
5. Bulb
6. Herbaceous plant
7. Leaf (Level 4)
8. Rhizome
9. Root (Level 4)
   1. Aerial root
   2. Taproot
10. Seedling
    1. Cotyledon
    2. Hypocotyl
    3. Radicle
11. Shrub (Level 4)
12. Stolon
13. Stoma (Level 4)
14. Tree (Level 3)
15. Tuber
16. Tumbleweed
17. Vine
    1. Liana
    2. Tendril

This section contains 8 articles.

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

This section contains 10 articles.

1. Flower (Level 3)
   1. Gynoecium
   2. Petal
   3. Sepal
   4. Stamen
2. Fruit (Level 3)
   1. Berry (botany) (Level 4)
   2. Nut (fruit) (Level 4)
3. Seed (Level 3)
4. Strobilus

This section contains 9 articles.

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

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

This section contains 26 articles.

1. Physiology (Level 3)
   1. Plant physiology
2. Action potential
3. Bioluminescence
4. Blinking
5. Breathing (Level 3)
6. Cardiac cycle
7. Circadian rhythm (Level 4)
8. Digestion (Level 3)
   1. Regurgitation (digestion)
9. Excretion (Level 4)
   1. Belching
   2. Defecation (Level 4)
   3. Flatulence
   4. Urination
10. Healing
    1. Coagulation
    2. Hemostasis
    3. Wound healing
11. Homeostasis
    1. Acid–base homeostasis
    2. Blood sugar level (Level 4)
    3. Osmoregulation
12. Muscle contraction (Level 4)
13. Respiration (physiology) (Level 4)
14. Transpiration (Level 4)

This section contains 16 articles.

1. Thermoregulation (Level 4)
2. Warm-blooded
3. Thermogenesis
4. Ectotherm
5. Endotherm
6. Eurytherm
7. Poikilotherm
8. Mesotherm
9. Homeothermy
10. Heterothermy
11. Stenotherm
12. Kleptothermy
13. Bradymetabolism
14. Gigantothermy
15. Thermostability
16. Thermolabile

This section contains 17 articles.

1. Developmental biology (Level 4)
2. Development of the human body (Level 4)

This section contains 15 articles.

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

This section contains 63 articles.

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

This section contains 37 articles.

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

This section contains 17 articles.

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

This section contains 14 articles.

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

1. Biomolecule (Level 4)

This section contains 1 article.

1. Alkaloid (Level 4)

This section contains 7 articles.

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

This section contains 20 articles.

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

This section contains 2 articles.

1. Adenosine triphosphate (Level 4)
2. Nicotinamide adenine dinucleotide

This section contains 40 articles.

1. Hormone (Level 3)
2. Pheromone (Level 4)

This section contains 28 articles.

1. Androgen
   1. Testosterone (Level 4)
2. Aldosterone
3. Cortisol
4. Endorphins
5. Estrogen (Level 4)
   1. Estradiol
6. Ghrelin
7. Glucocorticoid
8. Growth hormone
9. Insulin (Level 4)
10. Leptin
11. Melatonin
12. Oxytocin (Level 4)
13. Progestogen
    1. Progesterone
14. Secretin
15. Thyroid hormones
16. Vasopressin

This section contains 9 articles.

1. Neurotransmitter
2. Acetylcholine
3. Catecholamine
   1. Adrenaline (Level 4)
   2. Dopamine (Level 4)
   3. Norepinephrine
4. γ-Aminobutyric acid
5. Glutathione
6. Serotonin

This section contains 10 articles.

1. Plant hormone (Level 4)
2. Abscisic acid
3. Auxin
4. Brassinosteroid
5. Cytokinin
6. Florigen
7. Gibberellin
8. Jasmonate
9. Salicylic acid
10. Strigolactone

This section contains 8 articles.

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

This section contains 14 articles.

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

This section contains 39 articles.

1. Protein (Level 3)
2. Collagen
3. Enzyme (Level 4)
4. Gelatin
5. Glycoprotein
6. Hemoglobin (Level 4)
   1. Glycated hemoglobin
7. Histone
8. Keratin
9. Peptide
10. Peptidoglycan
11. Protein (nutrient) (Level 4)
12. Protein biosynthesis
13. Protein structure
14. Proteome
15. Gluten

This section contains 23 articles.

1. Amino acid (Level 4)
2. Proteinogenic amino acid
3. Essential amino acid
4. Alanine
5. Arginine
6. Asparagine
7. Aspartic acid
8. Cysteine
9. Glutamic acid
10. Glutamine
11. Glycine
12. Histidine
13. Isoleucine
14. Leucine
15. Lysine
16. Methionine
17. Phenylalanine
18. Proline
19. Serine
20. Threonine
21. Tryptophan
22. Tyrosine
23. Valine

This section contains 3 articles.

1. Steroid (Level 4)
2. Cholesterol (Level 4)
3. Steroid hormone

1. Metabolism (Level 3)
2. Biosynthesis
3. Catabolism
4. Gluconeogenesis
5. Metabolomics
6. Secondary metabolite
7. Chemosynthesis
8. Fermentation (Level 4)

This section contains 6 articles.

1. Cellular respiration (Level 4)
2. Anaerobic respiration
3. Citric acid cycle
4. Electron transport chain
5. Glycolysis (Level 4)
6. Oxidative phosphorylation

This section contains 7 articles.

1. Photosynthesis (Level 3)
2. Light-dependent reactions
3. Calvin cycle
4. Biological carbon fixation
   1. C3 carbon fixation
   2. C4 carbon fixation
   3. Crassulacean acid metabolism

This section contains 11 articles.

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

This section contains 49 articles.

1. Ethology (Level 4)
2. Intelligence (Level 3)
3. Animal cognition
4. Animal consciousness
5. Sleep (Level 3)
   1. Sleep in animals
   2. Rapid eye movement sleep
   3. Siesta
   4. Wakefulness
   5. Yawn
6. Dormancy
   1. Hibernation (Level 4)
   2. Aestivation
   3. Diapause
7. Imprinting (psychology)
8. Animal migration (Level 4)
   1. Bird migration
9. Animal sexual behaviour
   1. Copulation (zoology)
   2. Mating
10. Fight-or-flight response
11. Instinct (Level 4)
12. Sociality (Level 4)
    1. Eusociality
13. Swarm behaviour
    1. Flock (birds)
    2. Herd

This section contains 12 articles.

1. Carnivore (Level 4)
   1. Hematophagy
   2. Hypercarnivore
   3. Insectivore
   4. Predation (Level 4)
   5. Scavenger (Level 4)
2. Herbivore (Level 4)
   1. Grazing (Level 4)
   2. Browsing (herbivory)
3. Omnivore
   1. Hypocarnivore
   2. Mesocarnivore

This section contains 10 articles.

1. Animal locomotion (Level 4)
2. Aquatic locomotion
3. Arboreal locomotion
4. Bipedalism (Level 4)
   1. Facultative bipedalism
5. Quadrupedalism
6. Terrestrial locomotion
7. Tripedalism
8. Unipedalism
9. Flying and gliding animals

1. Botany (Level 3)
2. Aquatic plant
3. Carnivorous plant (Level 4)
   1. Pitcher plant
   2. Protocarnivorous plant
4. Weed (Level 4)
5. Plant pathology

This section contains 6 articles.

1. Cell biology (Level 4)
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 (Level 4)
      1. Apoptosis
      2. Autophagy
2. Cell migration
3. Cell polarity
4. Cell signaling (Level 4)
   1. Cytokine
   2. Ligand (biochemistry)
   3. Receptor (biochemistry)
      1. G protein-coupled receptor
   4. Signal transduction
   5. Biochemical cascade
   6. Second messenger system
5. Cellular differentiation
   1. Somatic cell
   2. Stem cell (Level 4)
      1. Embryonic stem cell
      2. Hematopoietic stem cell
6. Membrane transport
   1. Passive transport
      1. Facilitated diffusion
   2. Active transport (Level 4)
      1. ATPase
      2. Endocytosis
      3. Exocytosis
7. Protein targeting

This section contains 5 articles.

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

This section contains 47 articles.

1. Cell (biology) (Level 2)
2. Cell junction
3. Biological membrane
   1. Cell membrane (Level 4)
   2. Lipid bilayer
   3. Membrane potential
   4. Membrane protein
4. Cilium
5. Cytoplasm (Level 4)
   1. Cytosol
6. Cytoskeleton (Level 4)
   1. Actin filament
      1. Actin
      2. Myosin
   2. Microtubule
7. Flagellum (Level 4)
8. Symbiogenesis (Level 4)
9. Organelle (Level 4)
10. Endomembrane system
11. Cell nucleus (Level 4)
    1. Chromatin
    2. Chromosome (Level 4)
    3. Nuclear envelope
    4. Nucleolus
12. Centriole (Level 4)
    1. Centrosome
13. Endoplasmic reticulum (Level 4)
14. Golgi apparatus (Level 4)
15. Lysosome (Level 4)
16. Mitochondrion (Level 4)
    1. Mitochondrial DNA
17. Peroxisome
18. Proteasome
19. Ribosome (Level 4)
20. Vacuole (Level 4)
21. Vesicle (biology and chemistry)

This section contains 7 articles.

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

This section contains 4 articles.

1. Bacterial cell structure
2. Bacterial capsule
3. Endospore
4. Pilus

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

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

1. Genetics (Level 3)
   1. Introduction to genetics
2. Gene (Level 3)
3. Heredity (Level 3)
4. Mendelian inheritance (Level 4)
   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 (Level 4)
    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)
    3. DNA sequencing
       1. Human Genome Project
    4. Metagenomics
17. Molecular evolution
18. Epigenetics (Level 4)
    1. Epigenomics
       1. Epigenome
19. Hybrid (biology) (Level 4)
    1. Heterosis
    2. Inbreeding
20. Eugenics
    1. Dysgenics

1. Evolution (Level 2)
   1. Introduction to evolution
2. Evolutionary biology
3. Evolutionary developmental biology
4. Divergent evolution
5. Convergent evolution
6. Parallel evolution
7. Phylogenetic tree
8. 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
9. Sociobiology
10. Systematics
11. Adaptation (Level 4)
12. Coevolution
13. Fitness (biology)
14. Homology (biology)
15. Last universal common ancestor
16. Macroevolution
17. Microevolution
18. Reproductive isolation
19. Speciation
20. Living fossil
21. Evolution of bacteria
22. Evolution of birds
23. Evolution of brachiopods
24. Evolution of fish
25. Evolution of fungi
26. Evolution of insects
27. Evolution of mammals
28. Evolution of molluscs
29. Evolution of reptiles
30. Evolution of spiders
31. Evolution of tetrapods
32. Evolutionary history of plants
33. Viral evolution

This section contains 3 articles.

1. Human evolution (Level 3)
2. Hominini
3. Missing link (human evolution)

This section contains 23 articles.

1. Australopithecine
2. Graecopithecus
3. Sahelanthropus
4. Orrorin
5. Australopithecus (Level 4)
   1. Australopithecus anamensis
   2. Australopithecus afarensis
      1. Lucy (hominid)
   3. Australopithecus africanus
      1. Taung Child
   4. Australopithecus bahrelghazali
   5. Australopithecus deyiremeda
   6. Australopithecus garhi
   7. Australopithecus sediba
6. Ardipithecus
   1. Ardipithecus kadabba
   2. Ardipithecus ramidus
      1. Ardi
7. Kenyanthropus
8. Paranthropus (Level 4)
   1. Paranthropus aethiopicus
   2. Paranthropus boisei
   3. Paranthropus robustus

This section contains 32 articles.

1. Homo
2. Homo ergaster
3. Homo floresiensis
4. Homo gautengensis
5. Homo habilis (Level 4)
6. Homo luzonensis
7. Homo rudolfensis
8. Penghu 1
9. Homo erectus (Level 4)
   1. Dmanisi hominins
   2. Java Man
   3. Lantian Man
   4. Nanjing Man
   5. Peking Man
   6. Solo Man
   7. Tautavel Man
   8. Yuanmou Man
10. Denisovan (Level 4)
11. Homo antecessor
12. Ceprano Man
13. Homo heidelbergensis
14. Homo naledi
15. Neanderthal (Level 4)
16. Homo rhodesiensis
17. Early modern human
    1. Cro-Magnon (Level 4)
    2. Herto Man
    3. Manot 1
    4. Red Deer Cave people
    5. Mitochondrial Eve
    6. Y-chromosomal Adam
18. Interbreeding between archaic and modern humans