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- vaccine: A preparation of killed or weakened pathogens that is used to stimulate the vertebrate immune system as a protection against future attack by that pathogen.
- vacuole: A large water-filled vesicle found in plant cells. Vacuoles help maintain the shape of plant cells and can also be used to store food molecules.
- vagina: The reproductive structure in female animals into which the penis of a male deposits sperm.
- vascular cambium: A type of lateral meristem tissue that contributes to secondary growth by dividing to form new vascular tissues. Compare cork cambium.
- vascular system: The tissue system in plants that is devoted to internal transport.
- vector: In DNA technology, a piece of DNA that is used to transfer a gene or other DNA fragment from one organism to another.
- vein: A blood vessel that carries blood to the heart. Compare artery.
- ventricle: A chamber in a heart that receives blood from the atrium and contracts to propel blood away from the heart. Compare atrium.
- vertebrates: A group of animals with backbones. Vertebrates include fish, amphibians, mammals, birds, and reptiles.
- vesicle: A small, membrane-enclosed sac found in the cytosol of eukaryotic cells.
- vestibular apparatus: A collection of mechano receptors and associated structures in the ear that plays a central role in maintaining the sense of balance in vertebrates.
- vestibule: The portion of the vestibular apparatus that contains the otoliths and mechanoreceptors that make it possible to detect gravitational pull.
- vestigial organ: A structure or body part that served a purpose in an ancestral species, but is currently of little or no use to the organism that has it.
- villus (pl. villi): One of numerous tiny projections that increase the absorptive surface of the small intestine.
- virus: An infectious particle consisting of nucleic acids and proteins. A virus cannot reproduce on its own, and must instead use the cellular machinery of its host to reproduce.
- vitamin: An organic compound required by consumers in small amounts.