Natural Sciences 1

Homeostasis is a concept that is central to any understanding of physiology. Homeothermy is a superficially similar word, but as the -thermy ending suggests, it refers to body temperature—in this instance, the active maintenance of a steady body temperature.

This is a fundamental tenet of biology, part of the cell theory first propounded in the 1830s and 1840s. The other part of this theory is: all cells come from preexisting cells.

Stomata (singular form is stoma) are openings in the epidermis of the plant through which gases or water vapor may pass. Two guard cells arranged around the stoma act as doors and regulate the size of the opening, controlling the loss of water vapor and exchange of gases by opening or closing the pore.

All cellular elements of the blood—white cells and red cells—are made in the bone marrow from a single type of parent cell, called the stem cell. Platelets are not cellular but are derived from the breakup of a larger cell also produced in the bone marrow.

Other animals such as birds have different sex-chromosome arrangements, but in mammals, XX denotes a female and XY a male.

In animal cells, when the oxygen-requiring pathways are not available for using glucose, fermentation is resorted to in order to make ATP, with the production of lactic acid (also called lactate).

The first letter of the genus name is always capitalized, as in Mus. The species name is written in lowercase (e.g., musculus). Both are printed in italics or underlined in handwritten manuscripts.

Tropical rain forests have nutrients and other resources concentrated in the vegetation and animals, and the small amount of nutrients found in the soil are located shallowly, in the first few inches of soil.

Modern taxonomy, of which binomial nomenclature is an important part, uses Latin or Latinized words, since Latin is a dead and, therefore, fixed language. Each organism has a two-part name, as in Homo sapiens. Higher groupings (such as class or order) lump related organisms together.

Oste- in the class name Osteichthyes means "bone." Chondrichthyes are the cartilaginous fish, Agnatha, the jawless fish.

Photosynthetic autotrophs provide the entry point for solar energy, which can then be shuffled among members of a food chain going from level to level.

The kidney consists of many nephrons. Each nephron has these features: a glomerulus, Bowman's capsule, the loop of Henle, the collecting duct, and several convoluted tubules that lead to and from the loop of Henle. There are more than 1 million nephrons in each human kidney.

Of the five factors listed, all but flooding will kill a greater proportion of individuals if population density is high (e.g., higher population density increases the chances of passing infections among individuals).

Chordata is a phylum in kingdom Animalia.

The Miller-Urey experiment used simulated lightning and a mixture of compounds that were presumed to have existed on Earth before life came about. Organic compounds were produced, supporting the hypothesis that such compounds could arise independent of organisms.

mRNA (messenger RNA) is a transcript of the DNA being expressed. tRNA (transfer RNA) is a cloverleaf-shaped molecule that has an amino acid on one end and an anticodon, specific to that amino acid, on the other end. rRNA (ribosomal RNA) is part of the ribosome.

An estuary forms, for instance, where a river empties into the ocean, and dilutes the ocean water with freshwater.

The first photosynthetic organisms modified this early environment by producing oxygen during photosynthesis. Subsequent life forms were very different from the first organisms, as they evolved in an oxygen-rich atmosphere.

The name suggests major, "macro" means big. Macroevolution is applied to the bigger events of evolution with long time frames, while microevolution is used to refer to the many minor changes that occur over shorter periods of time, such as in the number or form of chromosomes.

Aldosterone and ADH (anti-diuretic hormone) are key hormones in the regulation of the kidneys. Testosterone and estrogen are sex hormones.

Passive immunity results from the transfer of antibodies and is therefore temporary. The protection they confer lasts only as long as the antibodies persist in the recipient's body. Active immunity results from the stimulation of the animal's immune system by an antigen, which results in production of the organisms own antibodies. A toxoid is a toxin (such as that produced by the tetanus bacillus) that has been treated to render it innocuous, while retaining its activity as an antigen.

Only about 10 percent of the energy of one trophic level is passed on to the next. The great loss of energy progressively reduces the biomass that can be supported at each trophic level.

Earth is about 5 billion years old, and the first signs of life are bacteria-like fossils that are 3 billion years old.

The incorrect terms come from other areas of biology as diverse as molecular biology (episome), immunology (epitope), or anatomy (epiphysis). It is imperative to make use of important clues, such as that one answer ends in -phyte, which refers to plants.

Cladogenesis may also be involved in a similar evolutionary process called adaptive radiation. Choice B. describes the other form speciation may take, anagenesis. Choice D. defines allopatric speciation.

In parasitism, the host is harmed; in mutualism, both organisms benefit from the interaction.

Choices B., D., and E. are derived from ectoderm, while choice C. comes from endoderm.

Choices B., C., and D. are features of the eukaryotic cell, while a nucleoid region is associated with Prokaryotes.

Mitosis progresses from prophase to metaphase, to anaphase, and finally to telophase. Cytokinesis refers to the actual splitting of one cell into two distinct daughter cells, following the nuclear division of mitosis. Not all cells that undergo mitosis follow with cytokinesis. For instance, muscle cells are frequently multinucleate.

Cortex and medulla are used as names for the parts of several organs, such as the adrenal medulla and cerebral cortex.

Basically, a population is composed of the individuals of one species occupying a specific area.

Human somatic cells have 46 chromosomes: 22 autosomal pairs, plus one set of sex chromosomes (XX or XY).

Purkinje fibers and the Bundle of His are part of the cardiac conduction system that carries the impulses originating in the SA (sinoatrial) node.

Structures are considered analogous only if they share a similar function. Homology requires that the organs or features share a common evolutionary origin. Homologous structures may be different in form or function. Some structures are homologous and analogous, such as the rear legs of dogs or cows and the legs of people. They have a common origin and a common function.

Of the biologists listed, only von Frisch and, to a lesser degree, Huxley, were involved in studies of animal behavior.

Meiosis I results in one cell and one polar body. The second round of meiosis (Meiosis II) involves a division of this cell, and produces the ovum and two more polar bodies.

While a total of 38 ATP molecules is produced, the net yield is only 36 ATP, since at the start of glycolysis 2 ATP molecules are used to phosphorylate the glucose molecule (often called "priming the pump"). Note that this yield of ATP is theoretical—actual net yields are not this high.

Do not confuse endosperm with fruit, which is a ripened ovary enclosing the seeds.

This is a fundamental difference between the two groups and the basis for the naming them. The deutero- part of the name refers to two, meaning the two openings (mouth and anus) of the adult organism.

The seventeenth-century discovery of the circulation of the blood by English physician William Harvey was a milestone in the history of biology and medicine.

All other answers are also geologic eras, except Silurian, which is a period in the Mesozoic era.

Thylakoid membrane is found within chloroplasts. The complex molecules that carry out the reactions of the light-dependent phase of phtotosynthesis are located there. The matrix and cristae are features of mitochondria.

Glycolysis is an anaerobic process that does not require free oxygen. "Kreb's cycle" and "citric acid cycle" are synonyms.

Some carbon in the oceans exists as compounds that act as a pH buffer; much of it is also found in insoluble deposits. The other reservoirs (or sinks) listed also hold considerable amounts of carbon.

Glucose, galactose, and fructose are monosaccharides, while maltose and lactose are disaccharides. Choice C. is the disaccharide sucrose. Choice E. is the disaccharide lactose.

Meristems are areas of active cell division in plants, and they give rise to permanent tissue. Apical meristem occurs in stem and root tips. Ground meristem is the source of pith and cork. Protoderm is a meristem that produces epidermis. Procambium gives rise to vascular tissue (xylem and phloem). Lateral meristem is found in roots and stems surrounding phloem.

Both urea and uric acid are nitrogenous wastes, but they come from the catabolism (breakdown) of different nitrogen-containing compounds. An important clue here is the word purine, a nitrogenous base that occurs in nucleic acids.

It is impossible to specify one particular outcome, as the genotype of the second plant is unknown—it might be TT or Tt. Note that choice B., which might seem to be another possible correct answer, lists a genotype and genotypic ratio. The question asks for phenotypes or phenotypic ratios.

Blood moves through arteries due to fluid pressure generated by the heart and muscles in the arterial walls. Veins and lymph vessels are at much lower pressure, and much of the movement of fluids through such vessels is due to the working of skeletal muscle, rather than blood pressure. Valves materially assist in this action by preventing backflow.

Only certain bacteria or blue-green algae (monerans known as cyanobacteria) can remove nitrogen gas from the atmosphere. Nitrogen is converted to ammonia (NH₃) or nitrate (NO₃-).