Reproduction in Plants - Biology Encyclopedia

Plant reproduction is the process by which plants generate new individuals, or offspring. Reproduction is either sexual or asexual.

Reproductive Technology - Biology Encyclopedia

Reproductive technologies are medical procedures designed to help infertile people have children. These procedures include artificial insemination, in vitro fertilization, embryo adoption, and surrogate mothers.

Reptile - Biology Encyclopedia

The class Reptilia is composed of about 5,100 species, organized in three very closely interrelated groups: the lizards (order Lacertilia), composed of about 3,165 species; the amphisbaenians (order Amphisbaenia), which consist of about 135 species; and the snakes (order Serpentes), which contain about 1,800 species. According to most experts, lizards appeared in the fossil record in the middle Jurassic, about 165 million years ago (although some authorities place the earliest known fossil lizards in the late Permian, about 250 million years ago).

Respiration - Biology Encyclopedia

Respiration refers to the mechanisms for obtaining oxygen from the air and delivering it to the tissues, while eliminating carbon dioxide from the body. It is related to cellular respiration, the biochemical processes that consume this oxygen and generate the carbon dioxide in the course of making adenosine triphosphate (ATP).

Retrovirus - Biology Encyclopedia

Retroviruses are a unique class of single-stranded ribonucleic acid (RNA) containing viruses, which replicate their genome through a double-stranded viral deoxyribonucleic acid (DNA) intermediate in the nucleus of the host cell. This is in contrast to all other RNA-containing viruses that replicate their genomes through double-stranded RNA intermediates almost always in the cytoplasm of host cells.

Reverse Transcriptase - Biology Encyclopedia

Reverse transcriptase catalyzes the formation of double-stranded deoxyribonucleic acid (DNA) from a single-stranded ribonucleic acid (RNA) genome. It is called "reverse" transcriptase because it reverses the usual direction of information flow, from DNA to RNA.

Rhythms of Plant Life - Biology Encyclopedia

Plants exhibit regular, cyclic physiological changes of many sorts. For example, leaflets of wood sorrel, Oxalis, fold downward to a vertical position at night and return to their normal horizontal orientation during the day.

Ribosome - Biology Encyclopedia

The ribosome is the molecular machine inside the cell that makes proteins from amino acids in the process called translation. It binds to a messenger ribonucleic acid (mRNA) and reads the information contained in the nucleotide sequence of the mRNA.

Rivers and Streams - Biology Encyclopedia

On the continents, aquatic ecosystems are of two kinds: lotic ecosystems, in which the water is free-flowing (streams and rivers), and lentic ecosystems, in which the water is relatively stationary. The scientists who specialize in aquatic ecosystems are limnologists.

RNA - Biology Encyclopedia

Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer made up of nucleotides. A nucleotide is composed of a pentose (5-carbon) RNA chains are composed of simpler units called nucleotides.

RNA Processing - Biology Encyclopedia

In the appropriate cell type and at the correct developmental stage, ribonucleic acid (RNA) polymerase transcribes an RNA copy of a gene, the primary transcript. However, the primary transcript may contain many more nucleotides than are needed to create the intended protein.

Roots - Biology Encyclopedia

Plants are autotrophic and make their own food via photosynthesis. However, they must acquire the molecular building blocks for the production of food from the environment.

Scaling - Biology Encyclopedia

Scaling can be defined as the structural and functional consequences of a change in size and scale among similarly organized animals. To examine what "consequences of a change in size" means, consider what would happen if one scaled up a cockroach simply by expanding it by a factor of 100 in each of its three dimensions.

Science Writer - Biology Encyclopedia

In 1999, gene therapy researchers accidentally killed a healthy nineteen-year-old boy and then covered up the evidence. Only the work of two newspaper reporters—one a science writer—brought the story to light.

Secondary Metabolites in Plants - Biology Encyclopedia

Secondary metabolites are chemicals produced by plants for which no role has yet been found in growth, photosynthesis, reproduction, or other "primary" functions. These chemicals are extremely diverse; many thousands have been identified in several major classes.

Seed Germination and Dormancy - Biology Encyclopedia

The embryo, contained within the seed, is the next generation of plant. Thus successful seed germination is vital for a species to perpetuate itself.

Seedless Vascular Plants - Biology Encyclopedia

When one walks through a contemporary forest, all of the surrounding trees are vascular plants. Wood, which is made up primarily of xylem, and bark, which contains phloem, are the major structural elements of the trunks and stems.

Seeds - Biology Encyclopedia

In seed-bearing plants, a seed is the end product of sexual reproduction. It is a mature ovule, comprising an embryo or miniature plant along with food reserves, all within a protective seed coat.

Senescence - Biology Encyclopedia

Senescence refers to all of the changes that take place in a plant that will finally lead to the death of cells, tissues, and, eventually, the whole plant body. These changes can be seen to occur in some cells even in very young, vigorously growing plants.

Separation and Purification of Biomolecules - Biology Encyclopedia

Cell biologists research the intricate relationship between structure and function at the molecular, subcellular, and cellular levels. However, a complex biological system such as a biochemical pathway can only be understood after each one of its components has been analyzed separately.

Sex Chromosomes - Biology Encyclopedia

Sex chromosomes are particular chromosomes that are involved in determining the sex of an organism. In the cells of humans and many other organisms the sex chromosomes consist of a pair of chromosomes called the X and Y chromosomes.

Sex Determination - Biology Encyclopedia

Sex determination refers to the hormonal, environmental, and especially genetic mechanisms that make an organism male or female.