Porifera - Biology Encyclopedia

Porifera, or sponges, are the simplest and oldest of the multicelled animals, with fossils dating back to Precambrian times. They are aquatic and sessile, living permanently attached to submerged objects.

Porter, Keith - Biology Encyclopedia

In 1945 Keith Porter, with Albert Claude and Ernest F. Fullam, published the first electron micrograph of a complete cell in the Journal of Experimental Medicine.

Predation and Defense - Biology Encyclopedia

Predatory behavior is that which results in the killing of another animal for food. Some predators, such as lions and tigers, are large and ferocious, while others can be small and benign in appearance, such as lady bugs.

Primate - Biology Encyclopedia

The order Primates includes prosimians, monkeys, and apes. Primates are well studied, to a large extent because people are primates.

Prion - Biology Encyclopedia

Unlike all other infectious agents, prions contain no deoxyribonucleic acid (DNA) or ribonucleic acid (RNA). This radical difference has slowed the understanding and acceptance of the infectious properties of prions since their discovery.

Propagation - Biology Encyclopedia

Plant propagation is the art and science of increasing numbers of plants utilizing both sexual and asexual methods. It is not an exaggeration to say that the continued existence of modern civilization depends upon plant propagation.

Protein Structure - Biology Encyclopedia

Proteins are chains of amino acids that fold into a three-dimensional shape. Proteins come in a wide variety of amino acid sequences, sizes, and three-dimensional structures, which reflect their diverse roles in nearly all cellular functions.

Protein Synthesis - Biology Encyclopedia

Proteins are the workhorses of the cell, controlling virtually every reaction within as well as providing structure and serving as signals to other cells. Proteins are long chains of amino acids, and the exact sequence of the amino acids determines the final structure and function of the protein.

Protein Targeting - Biology Encyclopedia

Protein targeting refers to the methods cells use to get proteins to the proper location after synthesis. Proteins play a major role in most cellular processes but must be located properly to serve their functions.

Protista - Biology Encyclopedia

The Protista, or Protoctista, are a kingdom of simple eukaryotic organisms, usually composed of a single cell or a colony of similar cells. Protists live in water, in moist terrestrial habitats, and as parasites and other symbionts in the bodies of multicellular eukaroytes.

Protozoa - Biology Encyclopedia

Protozoa (meaning "first animals") are heterotrophic, single-celled or colonial eukaryotes. Individuals are microscopic and range in size from a few to hundreds of micrometers, depending on the species.

Protozoan Diseases - Biology Encyclopedia

Protozoans are a group of eukaryotic single-celled organisms. Several species of protozoans infect humans and inhabit the body as commensals or parasites.

Psychiatric Disorders, Biology of - Biology Encyclopedia

Mental illnesses affect millions of people each year, and billions of dollars are spent on their treatment and legal fees in the United States alone. Even Colored positron emission tomography (PET) brain scans of a healthy person (top of image) and a person with schizophrenia (bottom).

Psychiatrist - Biology Encyclopedia

A psychiatrist is a physician who treats mental illness. The types of illnesses treated by psychiatrists include clinical depression, bipolar disorder (manic depression), obsessive-compulsive disorder (OCD), attention deficit disorder (ADD), drug and alcohol abuse, and many more.

Psychoactive Drugs - Biology Encyclopedia

Psychoactive drugs are a class of chemical substances that act on the central nervous system and can alter behavior and cognition. All psychoactive drugs are highly fat-soluble and thus cross the blood-brain barrier readily.

Pteridophytes - Biology Encyclopedia

Pteridophtyes are a phylum of plants. They are the vascular plants (those having xylem and phloem tissues) that reproduce by releasing spores rather than seeds, and they include the highly diverse true ferns and other graceful, primarily forest-dwelling plants.

Public Health Careers - Biology Encyclopedia

Public health takes a population–based approach to address the physical, mental, and environmental health concerns of communities. With such information the appropriate health promotion and disease prevention is applied to improve and enhance quality of life.

Radiation Hybrid Mapping - Biology Encyclopedia

Radiation hybrid mapping is a genetic technique that was originally developed for constructing long-range maps of mammalian chromosomes. It is based on a statistical method to determine not only the distances between deoxyribonucleic acid (DNA) markers but also their order on the chromosomes.

Radionuclides - Biology Encyclopedia

Radionuclides or radioisotopes are radioactive isotopes of elements that are extremely important tools in biochemistry and cell biology. Radionuclides allow scientists to tag specific molecules without altering the structure or function of the studied compounds.

Recombinant DNA - Biology Encyclopedia

Recombinant deoxyribonucleic acid (DNA) technology allows the creation and manipulation of DNA sequences that come from different sources, even different species. The development of recombinant DNA technology in the 1970s was hailed as the most exciting invention since the development of transistors some twenty to thirty years earlier.

Remote Sensing - Biology Encyclopedia

At its simplest definition, remote sensing is obtaining information about an object by a device that is not in contact with the object. In ecology remote sensing usually involves sensors on satellite platforms or airplanes.

Replication - Biology Encyclopedia

There is no more critical issue in the origin of life than a method for the faithful and timely replication of genetic information. Genes are encoded in deoxyribonucleic acid (DNA), which is made of four types of nucleotides, distinguished by the bases adenine (A), guanine (G), cytosine (C), and thymine (T).