VACCINE: A substance consisting of weakened, dead, or incomplete portions of viruses that produces an immune response in the body to that virus.
VALID: True; correct; trustworthy; reliable.
VALENCE ELECTRON: An electron in an atom's outermost energy shell / orbital. These are the electrons that are involved in bonding.
VACUOLE: An organelle found in cells that are used for the storage of water or food. Plants have a large central vacoule!
VARIABLE: Something that you can change during an experiment.
VECTOR: A disease vector is an organism that carries a disease from one host to another. Many vectors are insects. For example, malaria involves a mosquito vector, and Lyme disease involves a tick vector.
VESTIGIAL STRUCTURE: A structure in a present-day organism that no longer has a job, but was probably useful for the organism's ancestor. Vestigial structures provide evidence of evolution. An example of a vestigial structure is the appendix in humans or small leg bones in some species of snakes.
VIRUS: A disease-causing, nonliving particle composed of an inner core of nucleic acid (DNA or RNA) surrounded by a protein coat. Viruses reproduce inside of living cells, called host cells.
VOLUME: The amount of space an object or substance takes up