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This article discusses how the human skeletal system offers clues to the history of life on earth. Paleontologists find fossils of ancient creatures and determine the age of the fossils by measuring the depth of the strata or by determining the amounts of certain radioactive isotopes. From the skeletal fragments a paleontologist finds, he or she can learn much about the shape of the bones, muscles, skin and other tissues that must have fit over them.

The article offers a list of vocabulary terms useful for persons interested in the human skeletal system. Some of the terms listed are 'acromegaly,' 'bunion,' 'clavical' and 'humerus'.

This article discusses the human spine. An adult has 26 vertebrae that fit together to form the spine. Ligaments hold the spine together, and it is supported by many muscles, which allow it to move. Below each of the vertebrae is a cushion of cartilage. A hole passes through each vertebrae to form the spinal canal. The spinal cord runs down from the brain through the spinal canal. The cervical vertebrae support the skull. The 12 thoracic vertebrae attach to the ribs. The back muscles are supported by the next five vertebrae called the lumbar vertebrae. The five vertebrae in the hip area are called the sacrum. The final four vertebrae are called the coccyx, or tailbone. The curve of the backbone allows a person to balance better than if their back was straight. The spine can absorb a lot of pressure and it is very flexible.

Presents definitions of terms related to the nervous system, such as migraine.

This article provides information on the various diseases that affect the mind. People with a mental illness may see or hear things that are not really there which is called hallucination; Paranoia occurs when people think that others are trying to hurt them all the time, and they may turn against those who love them and are really tying to help them; Mild forms of mental illness are sometimes called neuroses.

This article focuses on the various diseases and disorders of the human brain. Some children are born with hereditary conditions such as Down syndrome, which prevent them from learning as quickly as other children; Cerebral palsy is a condition due to a development defect or damage to the brain during birth; Huntington's disease is a hereditary disorder that usually does not show ant effects until middle age.

This article focuses on the autonomic nervous system of the human body which are nerves involved in the control and coordination of body activities from a part of the peripheral nervous system. The term autonomic literally means self-controlled and independent of outside influences; Emergencies that arise in one's life are handled by the sympathetic nervous system; Like the nerves of the sympathetic nervous system, those of the parasympathetic nervous system are also motor nerves.

This article focuses on how nerve messages travel, in connection with the function of the nervous system. Messages are sent along the nerves to and from the brain and spinal cord; Scientists believe that nerves carry messages by a kind of electrochemical reaction; Chemical reactions in one part of the nerve fiber produce electric charges that in turn start off a chemical reaction in the next part of the fiber.

This chapter provides information on algae. Algae comes in different forms. Some are simple creatures that are found in oceans and others have become adapted to living in extreme temperatures. Certain algae have special partnerships with fungi. They live together and form a single mosslike organism called a lichen. All algae contain chlorophyll. Some algae produce a bad tasting oil and contaminate water supplies while some are helpful.

This chapter provides information on protozoans. Protozoans are single-celled organisms that have many animal-like characteristics. Their name comes from Greek words meaning first animals. They were classified in the animal kingdom in the phylum protozoa because of their characteristics. They come in different shapes, too. Scientists classify protozoans according to the way they move which are flagellates, sarcodines, ciliates and sporozoans.

This chapter focuses on the kingdom Protista. The only identifying feature common to all protists is that each is surrounded by a membrane. Protist is defined as a eukaryote that is not a fungus, plant or animal. Most protists are tiny single-celled organisms, but among the multicellular protists are giant kelps. Most protists live in water but some, such as slime molds, live on land in damp soil or moist decaying trees.

This chapter discusses the difficulty experienced by scientists in classifying bacteria because of their different structures and lifestyles. Scientists think that all living things can be divided into one of three domains: Eucarya, Archae and Bacteria. To simplify matters, bacteria was divided into two groups, the archaebacteria and true bacteria. Bacteria can be divided into four groups according to their shapes. They are bacilli, cocci, spirilla and vibrios.

This chapter provides information on viruses. The discovery of viruses was taken in 1892 when a Russian botanist named Dmitri Ivanovsky tried to figure out the cause of a disease that produced spots on tobacco leaves. It was until 1939 that a virus was actually seen using an electron microscope. Viruses are not cells nor are they made of cells. They infect cells of all kinds of living things. Scientists use observations to classify viruses such as their shape and what host they infect.

This chapters focuses on bacteria. Bacteria are among the simplest and smallest of all living things. Today, most scientists classify bacteria and cyanobacteria in the Monera kingdom. They usually reproduce by splitting into two identical bacteria. They also play an important role in the balance of nature and in science and industry. Bacteria cause many different diseases in humans such as cholera and leprosy.

This chapter describes the discovery of microbes. In 1676 Antonie van Leeuwenhoek used a magnifying lens to look at a drop of pond water where tiny creatures are wriggling which he knew were alive because of the way they moved. Many believed that these tiny living things came from nonliving things which is called spontaneous generation. In 1860 French scientist Louis Pasteur showed the concept of biogenesis showing that life can only arise from living things.

This chapter deals with taxonomy. Taxonomy is the science of classifying or arranging living things into groups based on characteristics they share. Each living thing is given a two-part name based on some important characteristics. In the microworld there are many more kinds of living organisms that do not seem to fit very well into either the plant or the animal kingdom. Biologists usually classify living things into five kingdoms: monerans, protists, fungi, plants and animals.

Defines several terms and phrases related to the excretory system.

This section describes the process of excretion through the lungs. Waste carbon dioxide in the cells diffuses out, passes in through the capillaries, then travels to the heart through blood vessels. From the heart carbon dioxide is carried by the blood to the lungs. From the lungs the waste carbon dioxide is breathed out into the air.

This section presents information on the kidneys. It is are purplish brown and about the size of an adult's fist. The inward curve of a kidney is called the hilus. It surrounded by a thin, tough, transparent membrane called the renal capsule.

This section presents information on the excretory system of land animals and plants. Plants pass out waste gases through tiny holes in the plant leaves, called stomata. An insect's excretory system consists of organs called Malpighian tubules. Amphibians, reptiles, birds and mammals have kidneys that help in the excretion of waste products.

This article discusses gene therapy which was developed to correct genetic defects and cure diseases. Researchers can fertilize a single human egg with a single sperm in a test tube or laboratory culture dish and can screen embryos for a variety of defects. Biologists warn that the earth's biological diversity is decreasing. Many species are becoming extinct in rain forests and other vanishing wild areas.

This article focuses on the earliest mammals which include prosimians, anthropoids and hominoids. The first humanlike primates or hominids were the Autralopithecines that lived in Africa. Scientists believe that the connecting link between Australopithecines and the first true humans was the emergence of Homo habilis. The Cro-Magnons had a brain capacity that was the same as humans.

This article discusses the theories of chemical evolution. There are five main eras in evolution, archeozoic, proterozoic, paleozoic, mesozoic and cenozoic. Each era marks the beginning or ending of a significant geological or biological event, such as the mass extinction of a species. The earth's early atmosphere was probably filled with the gases methane, ammonia, nitrogen, hydrogen and water vapor with small amounts of carbon dioxide and sulfur compounds.

This article discusses the theory of evolution known as neo-Darwinism or the synthetic theory of evolution which was expanded by biologist Gregor Mendel. Chemical units called genes determine traits that are passed from one generation to another. In each pair of genes, one may be dominant and the other may be recessive. Mutations may occur while the genes are being copied, during the formation of the sex cells.

This article focuses on fossil records, the most significant evidence for evolution. The term fossil refers to any evidence of ancient life. It is possible to distinguish the older fossils from the more recent ones through stratigraphy. The chemical elements that make up rocks and fossils are a mixture of forms called isotopes.

This article discusses the concept of creationism and the theories of naturalist Charles Darwin. Darwin studied the theories of other scientists and incorporated many of their ideas into his own thoughts about evolution. In 1831, he was chosen for a five-year scientific expedition on the ship called the H.M.S. Beagle. His theory of evolution states that organisms that are best suited to the changing environment survive and produce offspring, the process is called natural selection.

This article focuses on the beliefs of many scientists that the world has been continually changing through a process called evolution. The discovery of DNA, the chemicals that carry genetic information that is passed on from one generation to the next, has allowed modern scientists to define species precisely. Fossils of plants and animals provided information for scientists. Paleontologists believe that more species that ever existed are extinct.

The article provides a list of vocabulary terms useful for persons interested in learning about the human digestive system. Some of the words include 'bile,' 'bulimia,' 'nutrient' and 'scurvy'.

The article provides information on food poisoning. The most common cause of food poisoning is bacteria. Food manufacturers use various methods to keep foods free of harmful germs or to prevent them from multiplying. Bacteria may get into foods during packing, shipping or preparation. Some bacteria make poisons as the grow in food. Vomiting and diarrhea are the results of the body's efforts to protect itself. The vomiting center can also be stimulated by pain, motion sickness or strong emotions. Diarrhea can cause severe dehydration.

The article provides information on the mouth's involvement in the process of digestion. Humans can eat a wide variety of foods because they have four kinds of teeth. Strong jaw muscles allow people to grind up food with great force. The covering on a tooth is called enamel. Cavities occur when bacteria turn sugar and other carbohydrates into an acid that eats away at the enamel. Seeing a dentist regularly is important. Fluoride in toothpaste protects teeth by helping to strengthen the enamel. Doctors believe that some digestive problems are caused by eating too quickly. INSET: DID YOU KNOW....

The article provides information on how living organisms get food. Green plants turn water, carbon dioxide and minerals into organic materials by using energy from sunlight to power their chemical reactions. Animals that eat only plants are called herbivores. Animals that eat only other animals are called carnivores. Humans are omnivores, which means they eat both plants and animals. Living creatures are linked together in food chains. Single-celled organisms such as the ameba take in food materials from the water in which they live. Other single-celled organisms such as the paramecium has some structures for getting and digesting food. INSET: GUTLESS PARASITES.

Discusses several aspects of time and biological rhythms. Background on the sleep disturbances suffered by U.S. astronauts; Information on the rate of breast cancer in Kyoto, Japan; Role of melatonin in the body.

Presents information on the biological clock of human beings. Effect of several inventions on rhythms; Discussion on the relationship between shiftwork and the rhythms of a person's body; Details on the Daylight Saving Time.

Provides information on seasonal rhythms. Discussion on several hibernating animals; Effects of daylight on biological rhythms; Background on the mating season of animals; Details on seasonal affective disorder.

Discusses several monthly cycles. Effects of the different phases of the moon; Information on symptoms of premenstrual syndrome; Background on the breeding ritual of Samoan palolo worms; Details on the overlapping of biological rhythms.

Presents information on circadian rhythms. Details on the sleep movements of plants; Role of the chemical melatonin in the human body; Background on the suprachiasmatic nucleus; Discussion on the occurrence of ultradian rhythms.

Focuses on the measurement of time. Discussion on the movement of heavenly bodies; Background on the earliest devices used for measuring time; Information on several ancient calendars; Details on the different units of time.

Discusses the biological rhythms influencing processes on earth. Background on the rotation of the earth; Information on the different seasons; Effects of the phases of the moon.

Presents information on the significance of time to human beings. Discussion on biological rhythms; Background on chronobiologists; Details on biological calendars.

This article discusses how to keep the human skeletal system healthy. An important part of preventative care for the skeleton is good posture. Sitting and standing straight, sleeping in a bed that supports the back, and bending the knees while lifting heavy objects can help to avoid back problems. Stretching exercises help keep muscles and joints from getting stiff. Exercise and eating well are important for keeping the skeletal system healthy.

This article discusses artificial limbs. Modern artificial limbs look realistic and move very much like a real limb. An artificial leg weighs much less than a real leg. Muscles in the upper part of the body swing an artificial leg forward. In bionic limbs, movements are powered by tiny electrical impulses from the nerves in the stump.

This article discusses treatments for human skeletal problems. For a fracture to heal perfectly the broken parts of the bone must be held perfectly still in a cast or by placing the person in traction. If a bone is badly broken or smashed, an orthopedic surgeon may have to screw or pin pieces of bone together. Corrective casts and braces may be used to straighten abnormal curvatures of the spine. Surgery can also help to correct cleft palate or talipes. Doctors have sophisticated tools to diagnose skeletal problems. One tool is an arthroscope. Physical therapists are an important part of the medical team treating people with skeletal system problems. People suffering from backaches that will not go away may go to a chiropractor. Doctors called osteopaths use manipulation and massage to help with bone-related aches and pains.

This article discusses human skeletal deformities. Many types of skeletal deformities are caused by errors that occur while a fetus is developing inside its mother. Such conditions as cleft palate and spina bifida are the result of failure of bones to fuse on schedule. Talipes is a malformation in which the foot is twisted out of shape. Injury, disease or poor posture may distort the normal spine curvature. This condition, called kyphosis, can cause lung and heart problems. Other spinal deformities are lordosis and scoliosis. In acromegaly the bones of the face, hands and feet are enlarged. A bunion is a bulging of the joint at the base of the big toe usually caused by genetics.

This article discusses painful bones and joints. Lack of exercise and lack of calcium-rich foods in the diet, plus a decrease in vitamin D from lack of exposure to the sun, can result in brittle bones that may break easily. This is known as osteoporosis. After menopause, a decrease in the estrogen hormones also contributes to osteoporosis. When a person has rheumatoid arthritis their joints become swollen and painful. Too much wear and tear on joints can cause osteoarthritis. Bursitis is an inflammation of the fluid-filled sacs in the joints as a result of repeated pressure. When a person performs the same action over and over they can develop repetitive motion injuries such as carpal tunnel syndrome. In a disease called gout, the body does not properly dispose of a waste product called uric acid. Some people suffer from temporomandibular joint disease.

This article discusses broken bones, strains and sprains. A broken bone is often called a fracture. A broken bone is called a compound fracture if the bone pierces the skin. Injuries to joints in the legs are the most common sports injuries. A dislocation occurs when a bone slips out of its joint. Ligaments and tendons can be torn or overstretched. When ligaments that hold a joint together are overstretched the injury is called a sprain. Backaches are among the most common skeletal system complaints. Back muscle or ligament strain can cause a pain in the lower back called lumbago.

This article discusses the relationship between growth rates and gender differences. During adolescence, sex hormones work with growth hormones to help the body grow. These sex hormones are responsible for the differences between the skeleton of a man and that of a woman. The male sex hormones, called androgens, help the bones to grow strong and thick. Female sex hormones, called estrogen, tend to make the hip bones broader. Before puberty, the legs grow faster than the trunk, but after the sexual development is complete, the growth of the long bones soon stops. Because women experience puberty earlier than men, boys' legs have a year or two more to grow.

This article discusses the connection between exercise and bone growth. The amount a person's bones will grow depends to some degree on how much exercise they get. The more stress that is placed on a bone, the more it will grow. Athletes develop much stronger and heavier bones than people who do not get much exercise. Bone thinning can be a problem for hospital patients and astronauts.

The article discusses human growth. One factor of how tall a person will grow is genetics. Also, the human growth hormone is produced in the pituitary gland and helps determine how tall a person will be. Eating enough protein, vitamins and minerals can also determine how tall a person will grow. Vitamin D helps the body to absorb calcium and phosphorus. Children who do not get enough of this vitamin develop rickets.

This article discusses the human skeletal system and its ability to grow and change. Parts of the bones are constantly being built up and broken down. Normally these two processes balance each other out. In older people the bone-repair systems do not work as well. They may become shorter and their bones will be lighter and weaker. This thinning of the bones with age is called osteoporosis. Bones will get stronger and thicker if a person does a lot of heavy work or exercise.

This article discusses how bones grow. Bone are able to grow because of cartilage. The end portion of a long bone is called the epiphysis and the shaft is called the diaphysis. The cartilage plate that separates these two plates is an important growth center. The cartilage cells on the side of the plate next to the epiphysis continually form new rows and columns of cartilage cells. On the other side of the plate the cartilage is replaced with bone. The bone-building cells that make new bone tissue are called osteoblasts. The replacement of soft cartilage with bone is called ossification. Marrow cavities also grow as long as the bones themselves do.