Biology, PLA-REF
How do plants feed themselves? How did dogs evolve from wolves? What good is the appendix in humans, anyway? Such questions fall within the domain of biology, which seeks to understand living organisms and their vital processes (although the jury’s still out on what our appendixes are for). Biology’s diverse fields include botany, ecology, evolution, genetics, medicine, physiology, and zoology.
Biology Encyclopedia Articles By Title
plasmodesma, microscopic cytoplasmic canal that passes through plant-cell walls and allows direct communication......
Plasmodiophoromycota, phylum of endoparasitic slime molds in the kingdom Chromista. Some scientists assign Plasmodiophoromycota......
plasmodium, in fungi (kingdom Fungi), a mobile multinucleate mass of cytoplasm without a firm cell wall. A plasmodium......
platelet, colourless, nonnucleated blood component that is important in the formation of blood clots (coagulation).......
pleomorphism, the existence of irregular and variant forms in the same species or strain of microorganisms, a condition......
pleura, membrane lining the thoracic cavity (parietal pleura) and covering the lungs (visceral pleura). The parietal......
Pleurococcus, genus of green algae (family Chaetophoraceae). Pleurococcus species sometimes form a thin green covering......
pleuropneumonia, lung disease of cattle and sheep, characterized by inflammation of the lungs and caused by the......
ploidy, in genetics, the number of chromosomes occurring in the nucleus of a cell. In normal somatic (body) cells,......
plumage, collective feathered covering of a bird. It provides protection, insulation, and adornment and also helps......
pneumoconiosis, any of many lung diseases caused by the inhalation of a variety of organic or inorganic dusts or......
pneumonia, inflammation and consolidation of the lung tissue as a result of infection, inhalation of foreign particles,......
poison, in biochemistry, a substance, natural or synthetic, that causes damage to living tissues and has an injurious......
- Introduction
- Cell Membrane, Biochemistry, Transport
- Topical Skin, Biochemistry, Effects
- Dose, Exposure, Biochemistry
- Biotransformation, Toxicity, Antidotes
- Allergies, Toxins, Symptoms
- Carcinogenesis, Toxins, Chemicals
- Toxins, Venoms, Chemicals
- Herbicides, Toxicity, Chemicals
- Air Pollution, Chemicals, Health
- Drugs, Abuse, Biochemistry
- Plant Toxins, Phytotoxins, Alkaloids
- Animal, Zootoxins, Biochemistry
- Radiation, Toxicity, Effects
- UV Rays, Toxins, Health Effects
polio, acute viral infectious disease of the nervous system that usually begins with general symptoms such as fever,......
polychaete hypothesis, theory that conodonts (minute toothlike structures found as fossils in marine rocks) are......
polyembryony, a condition in which two or more embryos develop from a single fertilized egg, forming what in humans......
polyglandular autoimmune syndrome, either of two familial syndromes in which affected patients have multiple endocrine......
polymerase chain reaction ( PCR), a technique used to make numerous copies of a specific segment of DNA quickly......
polymorphism, in biology, a discontinuous genetic variation resulting in the occurrence of several different forms......
polymyalgia rheumatica, joint disease that is fairly common in people over the age of 50, with an average age of......
polyomavirus, (family Polyomaviridae), any of a subgroup of minute oncogenic DNA viruses of the family Polyomaviridae.......
polyp, in medicine, any growth projecting from the wall of a cavity lined with a mucous membrane. A polyp may have......
polyploidy, the condition in which a normally diploid cell or organism acquires one or more additional sets of......
Polyporales, large order of pore fungi within the phylum Basidiomycota (kingdom Fungi). The 2,300 known species......
pons, portion of the brainstem lying above the medulla oblongata and below the cerebellum and the cavity of the......
population ecology, study of the processes that affect the distribution and abundance of animal and plant populations.......
portobello mushroom, (Agaricus bisporus), widely cultivated edible mushroom. One of the most commonly consumed......
post-traumatic stress disorder (PTSD), emotional condition that sometimes follows a traumatic event, particularly......
postmature birth, in humans, any birth that occurs more than 42 weeks after conception, at which time placental......
postsynaptic potential (PSP), a temporary change in the electric polarization of the membrane of a nerve cell (neuron).......
potassium deficiency, condition in which potassium is insufficient or is not utilized properly. Potassium is a......
Pott disease, disease caused by infection of the spinal column, or vertebral column, by the tuberculosis bacillus,......
powdery mildew, plant disease of worldwide occurrence that causes a powdery growth on the surface of leaves, buds,......
poxvirus, (family Poxviridae), any of a group of viruses constituting the family Poxviridae responsible for a wide......
precocious puberty, abnormally early onset of human sexual development. In girls, precocious puberty is defined......
pregnancy, process and series of changes that take place in a woman’s organs and tissues as a result of a developing......
- Introduction
- Duration, Development, Trimesters
- Uterus, Placenta, Development
- Fertilization, Embryo, Implantation
- Anatomy, Physiology, Organs
- Gastrointestinal, Nutrition, Development
- Urinary Tract, Nutrition, Development
- Blood Changes, Nutrition, Care
- Metabolism, Hormones, Nutrition
- Prenatal Care, Testing, Nutrition
- Abnormal Changes, Complications, Risks
- Abortion, Fetal Development, Complications
- Systemic Diseases, Complications, Risks
- Adrenal Glands, Hormones, Development
- Gastrointestinal, Diseases, Symptoms
- Gestational Diabetes, Nutrition, Exercise
- Placental Inflammation
- Trophoblastic Disease, Placenta, Embryo
premature birth, in humans, any birth that occurs less than 37 weeks after conception. A full-term pregnancy lasts......
prenatal development, in humans, the process encompassing the period from the formation of an embryo, through the......
- Introduction
- Implantation, Placentation
- Amniotic Sac, Embryo, Fetus
- Growth, Differentiation, Fetal
- Embryonic Form, Growth, Development
- Fetal Growth, Nutrition, Environment
- Fetal Growth, Organs, & Systems
- Brain Development, Neural Migration, Neurons
- Sense Organs
- Muscles, Growth, Development
- Urinary System, Fetal Growth, Hormones
- Embryo, Placenta, Amniotic Sac
- Abnormalities, Complications, Risks
presbycusis, gradual impairment of hearing in old age. Ordinarily it is not experienced until after the age of......
presbyopia, loss of ability to focus the eye sharply on near objects as a result of the decreasing elasticity of......
presentation, in childbirth, the position of the fetus at the time of delivery. The presenting part is the part......
prevalence, in epidemiology, the proportion of a population with a disease or a particular condition at a specific......
primatology, the study of the primate order of mammals—other than recent humans (Homo sapiens). The species are......
proctitis, acute inflammatory infection of the anus and rectum. The most common cause of proctitis is the direct......
progeria, any of several rare human disorders associated with premature aging. The two major types of progeria......
prokaryote, any organism that lacks a distinct nucleus and other organelles due to the absence of internal membranes.......
prolapse, a downward protrusion of an internal organ out of its normal cavity. The term is usually applied to protrusion......
pronephros, most primitive of the three vertebrate kidneys, active in the adults of some primitive fish (lampreys......
prophase, the initial stage of mitosis and of the mitotic division of meiosis, characterized by the formation of......
proprioception, the perception by an animal of stimuli relating to its own position, posture, equilibrium, or internal......
prostate gland, chestnut-shaped reproductive organ, located directly beneath the urinary bladder in the male, which......
protist, any member of a group of diverse eukaryotic, predominantly unicellular microscopic organisms. They may......
protoplasm, colorless ground substance of living material within cells, constituting the cytoplasm and organelles......
protozoal disease, disease caused by protozoans. These organisms may remain in the human host for their entire......
protozoan, organism, usually single-celled and heterotrophic (using organic carbon as a source of energy), belonging......
- Introduction
- Unicellular, Microscopic, Diversity
- Amoeba, Pseudopodia, Movement
- Microbes, Ecology, Industrial
- Parasites, Pathogens, Disease
- Cell Structure, Nutrition, Reproduction
- Locomotion, Movement, Cilia
- Ingestion, Digestion, Nutrition
- Mixotrophy, Nutrition, Autotrophy
- Asexual Reproduction, Cysts, Budding
- Adaptations, Nutrition, Movement
- Evolution and paleontology
protozoology, the study of protozoans. The science had its beginnings in the latter half of the 17th century when......
pseudocopulation, the action of a male insect, such as a bee, wasp, or fly, that tries to mate with a flower whose......
pseudohermaphroditism, a condition in which the individual has a single chromosomal and gonadal sex but combines......
pseudopodium, temporary or semipermanent extension of the cytoplasm, used in locomotion and feeding by all sarcodine......
pseudorabies, viral disease mainly of cattle and swine but also affecting sheep, goats, dogs, cats, raccoons, opossums,......
pseudotuberculosis, any of several diseases that are marked by the formation of tubercle-like nodules, similar......
pseudoxanthoma elasticum, inherited disease in which the premature breakdown of exposed skin occurs. It is characterized......
psilocybin mushroom, any of several species of hallucinogenic fungi found across a number of genera, especially......
psittacine beak and feather disease, debilitating disease of birds cause by a circovirus that infects wild and......
psittacosis, infectious disease of worldwide distribution caused by the bacterial parasite Chlamydia psittaci and......
psoriasis, a chronic, recurrent inflammatory skin disorder. The most common type, called plaque psoriasis (psoriasis......
psorosis, disease of Citrus plant species caused by several related viruses (family Ophioviridae). Given that the......
psychological development, the development of human beings’ cognitive, emotional, intellectual, and social capabilities......
psychosis, any of several major mental illnesses that can cause delusions, hallucinations, serious defects in judgment......
psychosomatic disorder, condition in which symptoms of physical (somatic) illness or disease are worsened by mental......
pterygium, abnormal wing-shaped fold of the conjunctiva (the mucous membrane lining the eyelids and covering most......
ptosis, drooping of the upper eyelid. The condition may be congenital or acquired and can cause significant obscuration......
puberty, in human physiology, the stage or period of life when a child transforms into an adult normally capable......
puerperal fever, infection of some part of the female reproductive organs following childbirth or abortion. Cases......
puerperium, the period of adjustment after childbirth during which the mother’s reproductive system returns to......
puffball, any of various fungi in the phylum Basidiomycota, found in soil or on decaying wood in grassy areas and......
pulmonary circulation, system of blood vessels that forms a closed circuit between the heart and the lungs, as......
pulmonary stenosis, narrowing of either the pulmonary valve—the valve through which blood flows from the right......
pupa, life stage in the development of insects exhibiting complete metamorphosis that occurs between the larval......
pupil, in the anatomy of the eye, the black centre opening within the iris through which light passes before reaching......
pure culture, in microbiology, a laboratory culture containing a single species of organism. A pure culture is......
purpura, presence of small hemorrhages in the skin, often associated with bleeding from body cavities and in tissues.......
pustule, a small circumscribed elevation of the skin that is filled with pus, a fluid mixture containing necrotic......
pycnidium, variable and complex flask-shaped asexual reproductive structure, or fruiting body, in fungi (kingdom......
pylorus, cone-shaped constriction in the gastrointestinal tract that demarcates the end of the stomach and the......
Q fever, acute self-limited systemic disease caused by the rickettsia Coxiella burnetii. Q fever spreads rapidly......
quadriceps femoris muscle, large fleshy muscle group covering the front and sides of the thigh. It has four parts:......
r-selected species, species whose populations are governed by their biotic potential (maximum reproductive capacity,......
rabies, acute, ordinarily fatal, viral disease of the central nervous system that is usually spread among domestic......
rat-bite fever, relapsing type of infection in which the causative bacteria are transmitted to humans by the bite......
reactive arthritis, disorder characterized primarily by joint pain that also sometimes affects the eyes, urogenital......
reactive attachment disorder, rare condition in which infants and young children fail to form emotional bonds with......
reagin, type of antibody found in the serum and skin of allergically hypersensitive persons and in smaller amounts......
receptor, molecule, generally a protein, that receives signals for a cell. Small molecules, such as hormones outside......
rectocele, disorder in which the rectum bulges into the back wall of the vagina. It is caused when the muscles......
rectum, terminal segment of the digestive system in which feces accumulate just prior to discharge. The rectum......
red algae, (division Rhodophyta), any of about 6,000 species of predominantly marine algae, often found attached......
red blood cell, cellular component of blood, millions of which in the circulation of vertebrates give the blood......
reflex, in biology, an action consisting of comparatively simple segments of behaviour that usually occur as direct......
reflex arc, neurological and sensory mechanism that controls a reflex, an immediate response to a particular stimulus.......
