gravity [the force that pulls things toward the center] Gravity is the force that pulls things toward the center.
image [a reproduction of the appearance of a person or thing] An image is a picture of someone or something.
laser [an instrument that makes a thin, powerful light] A laser makes a thin, powerful beam of light.
magnet [a piece of iron or other material that has a pulling force; this pulling force is called magnetism] A magnet pulls on objects of iron or steel.
molecule [the smallest amount of a chemical substance that can exist] A molecule is the smallest part of a chemical substance.
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.
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.
nucleus [the center part of an atom or cell] The nucleus is the center part of an atom or cell.
nutrient [a food or substance that makes plants, humans or animals grow] Food is a nutrient that makes humans and animals grow.
organ [a part of the body that has a special purpose, such as the heart or brain] The heart and the brain are organs.
organism [a living thing, often so small it can be seen only through a microscope] An organism is a living plant or animal of any size.
particle [a very small piece of matter] A particle is a very small piece of matter.
proteins [substances responsible for the growth of tissue and for fixing damaged tissue] Proteins fix damaged tissue and help tissue grow.
robot [a machine that moves and performs tasks] A robot is a machine that moves and does work.
tissue [living material; a group of cells that are similar in appearance and do the same thing] Tissue is a group of living cells.
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.
