antibodies [special proteins, produced in the blood, that kill harmful bacteria]
The body's defense system creates different antibodies for each disease it fights.
atom [a very small part of all things; the smallest part of an element that can join with parts of other elements]
bacteria [living things that are one cell and can be seen only through a microscope; some cause disease]
cell [a small mass of living material that is part of all plants and animals]
chromosome [a line of genes; most human cells contain 46 chromosomes]
compound [a substance containing two or more elements]
dense [close together; thick]
electron [a small part of an atom that has an electrical force]
element [one of more than 100 substances known to science that cannot be separated into other substances]
enzyme [a special kind of protein; it produces changes in other substances without being changed itself]
An enzyme can change other substances without being changed itself.
fetus [unborn young]
fission [a splitting; in atomic fission, the nucleus of an atom is split to produce nuclear energy]
fusion [a joining together; in atomic fusion, atomic particles are joined together to produce nuclear energy]
genes [parts of cells that control the growth and development of living things; genes from the mother and father are passed to the child; genes contain nucleic acid]
Genes in the cell control the growth and development of living things.
genetic engineering [the science of changing the genes of a living thing]
gravity [the force that pulls things toward the center]
image [a reproduction of the appearance of a person or thing]
laser [an instrument that makes a thin, powerful light]
magnet [a piece of iron or other material that has a pulling force; this pulling force is called magnetism]
molecule [the smallest amount of a chemical substance that can exist]
nerve [a thin piece of tissue that sends information through the body to and from the brain]
Nerves carry information between the brain and the other parts of the body.
nucleus [the center part of an atom or cell]
nucleic acid [a molecule that holds the genetic information necessary for life; there are two kinds of nucleic acid: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)]
A molecule of nucleic acid holds the genetic information necessary for life.
nutrient [a food or substance that makes plants, humans or animals grow]
organ [a part of the body that has a special purpose, such as the heart or brain]
organism [a living thing, often so small it can be seen only through a microscope]
particle [a very small piece of matter]
proteins [substances responsible for the growth of tissue and for fixing damaged tissue]
robot [a machine that moves and performs tasks]
tissue [living material; a group of cells that are similar in appearance and do the same thing]
virus [a kind of organism that causes disease]
A virus is a tiny organism that invades cells and causes disease.
x-rays [a kind of radiation that can pass through most solid materials, often used in medicine]
X-ray radiation is used to make images of bones and tissue for medical purposes.
