Kids Research Express

Toxin, poisonous substance produced by the metabolic activities of certain living organisms, including bacteria, insects, plants, and reptiles. Some bacteria secrete toxins in tissues that they colonize; these are true toxins. Other bacteria retain most of the poisonous material within themselves, and the toxins are liberated only when the bacteria become disintegrated by chemical, physical, or mechanical means. In addition to bacterial toxins, the characteristic poisons and venoms produced by various plants are called phytotoxins, and those produced by animals are called zootoxins. The more important true toxins causing infection in humans are those of botulism, dysentery, tetanus, and diphtheria. Because of their extreme susceptibility to various chemical and physical influences, such as light, heat, and age, toxins are difficult to isolate, and knowledge of toxins has been gained through the lesions and symptoms that they produce when injected into animals. Although all toxins are p...

Serotonin, neurotransmitter, or chemical that transmits messages across the synapses, or gaps, between adjacent cells. Among its many functions, serotonin is released from blood cells called platelets to activate blood vessel constriction and blood clotting. In the gastrointestinal tract, serotonin inhibits gastric acid production and stimulates muscle contraction in the intestinal wall. Its functions in the central nervous system and effects on human behavior—including mood, memory, and appetite control—have been the subject of a great deal of research. This intensive study of serotonin has revealed important knowledge about the serotonin-related cause and treatment of many illnesses. Serotonin is produced in the brain from the amino acid tryptophan, which is derived from foods high in protein, such as meat and dairy products. Tryptophan is transported to the brain, where it is broken down by enzymes to produce serotonin. In the process of neurotransmission, serotonin is transferred f...

Casein, group of proteins precipitated when milk is mildly acidified. Casein constitutes about 80% of the total proteins in cow's milk and about 3% of its weight. It is the chief ingredient in cheese. When dried, it is a white, amorphous powder without taste or odor. Casein dissolves slightly in water , extensively in alkalies or strong acids. Casein is used as a food supplement and as an adhesive, a constituent of water paints, and a finishing material for paper and textiles. A variety of casein, known by the modified name paracasein, is preferred for making a plastic, through the reaction of the casein with formaldehyde , that goes into the manufacture of buttons and other small objects. It is produced by adding the enzyme rennin to milk, forming a precipitate different from the material precipitated by acids.

Calorie, metric unit of heat measurement. The small, or gram, calorie (cal) is usually specified in science and engineering as the amount of heat required to raise the temperature of 1 g of water from 14.5° to 15.5° C. The temperature interval is sometimes specified in other ways. The definition now generally accepted and standard in thermochemistry, is that 1 cal equals 4.1840 joules (J). A slightly different calorie is used in engineering, the international calorie, which equals 1/860 international watt-hour (W h). A large calorie, or kilocalorie (Cal), usually referred to as a calorie and sometimes as a kilogram calorie, equals 1000 cal and is the unit used to express the energy -producing value of food in the calculation of diets.

Antioxidants are also used in industry as product additives and in food processing and preservation. Industrial antioxidants slow or prevent oxidative damage that causes food to spoil, rubber to harden, fats and oil to change color or go rancid, and gasoline to oxidize. Foods that are commonly preserved with antioxidant additives include cheese, bread, and oil. Antioxidants used as food preservatives include vitamin C and the synthetic antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). These antioxidants are added to foods in concentrations of much less than 1 percent.

Vitamin C , also known as ascorbic acid, is a well known antioxidant that may prevent cataracts and cancers of the stomach, throat, mouth, and pancreas. It may also prevent the oxidation of LDL cholesterol, lowering the risk of heart disease. Foods that are high in vitamin C include strawberries, oranges, broccoli, and brussels sprouts. Beta-carotene absorbs free radicals that target molecules in the cell membrane. Studies suggest that in addition to reducing the risk of cataract, cancer, and heart attack, beta-carotene may also reduce the risk of stroke. Beta-carotene occurs naturally in orange-colored fruits and vegetables and dark green, leafy vegetables. Some of the best sources of beta-carotene are sweet potatoes, spinach, and carrots. As an antioxidant, vitamin E may also protect from heart disease and cataract and may strengthen the immune system. Good sources of vitamin E include wheat germ oil and sunflower seeds.

Carcinogen, any chemical, biological, or physical agent that can potentially be a cause of cancer. The term is most commonly applied to chemicals introduced into the environment by human activity. Researchers label a substance a carcinogen if it causes a statistically significant increase in some form of neoplasm, or anomalous cell growth, when applied to a population of previously unexposed organisms. The modes of cancer initiation are still little understood, however, and efforts to establish the carcinogenic hazards of substances have aroused great controversy. The question of the usefulness of laboratory tests on animals in assessing human risks is particularly complex. The more recent development of short-term tests using cell cultures of microorganisms, however, is considered a major advance in carcinogen research. Substances indicted as carcinogenic over the past few decades include the pesticides DDT, Kepone, and EDB; the synthetic hormone DES; the artificial sweetener cyclamat...

About 5 percent of the oxygen humans breathe is converted into free radicals. The presence of free radicals in the body is not always detrimental. Free radicals produced in normal cellular metabolism are vital to certain body functions, such as fighting disease or injury. When tissue is diseased or damaged, the body’s immune system sends disease fighting cells to the site, where they produce free radicals in an effort to destroy foreign invaders. But as the body ages or is subjected to environmental pollutants, such as cigarette smoke, overexposure to sunlight, or smog, the body becomes overwhelmed by free radicals. An excessive number of free radicals causes damage by taking electrons from key cellular components of the body, such as protein , lipids , and deoxyribonucleic acid (DNA), the molecule that carries genetic information in every living cell. These reactions make cells more vulnerable to cancer-causing chemicals, called carcinogens . Free radicals may lead to heart disease ...