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A vaccine is a biological product that stimulates the immune system to recognize and combat a pathogenic microorganism (virus, bacterium) without causing the disease. It contains inactivated or attenuated infectious agents or specific p…

A vacuole is a compartment surrounded by a membrane and filled mainly with water and dissolved substances.In plant cells, the large central vacuole stores water, ions, pigments, nutrients, or waste products.It also helps maintain the ri…

A vein is a blood vessel that returns blood from the organs to the heart.Its wall is generally thinner and less muscular than that of an artery because the blood pressure is lower.Many veins have valves that prevent blood from flowing i…

A virus is an extremely small acellular microorganism that cannot live or reproduce independently. It consists of a core of nucleic acid, either DNA or RNA, surrounded by a protein coat called a capsid, and sometimes a lipid envelope.Th…