| A | B |
|---|
| bacterium | A single-celled organism that is a prokaryote; belongs to one of two kingdoms—Archaebacteria or Eubacteria |
| flagellum | A long, whiplike structure that helps a unicellular organism move |
| binary fission | A form of asexual reproduction in which one cell divides to form two identical cells |
| asexual reproduction | The reproductive process that involves only one parent and produces offspring that are identical to the parent. |
| sexual reproduction | The reproductive process that involves two parents who combine their genetic material to produce a new organism, which differs from both parents |
| conjugation | The process in which a unicellular organism transfers some of its genetic material to another unicellular organism |
| endospore | A small, rounded, thick-walled, resting cell that forms inside a bacterial cell |
| decomposer | An organism that breaks down large chemicals from dead organisms into small chemicals and returns important materials to the soil and water. |
| infectious disease | A disease that can pass from one organism to another |
| toxin | A poison that can harm an organism |
| antibiotic | A chemical that kills bacteria or slows their growth without harming the body cells of humans. |
| virus | A small, nonliving particle that invades and then reproduces inside a living cell |
| host | An organism that provides a source of energy or a suitable environment for a virus or for another organism to live |
| parasite | An organism that lives on or in a host and causes harm to the host. |
| bacteriophage | A virus that infects bacteria |
| vaccine | A substance used in a vaccination that consists of pathogens that have been weakened or killed but can still trigger the immune system into action. |
