Microorganisms On and In the Human Body

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Organism Noun

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[or-guh-niz-uhm]

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Organism

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An individual living entity, such as an animal, plant, or single-celled life form, that can function independently.

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Example: This image shows a single-celled amoeba, a complete living thing and a basic example of an organism.

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Microorganism Noun

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[mahy-kroh-awr-guh-niz-uhm]

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Microorganism

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A microscopic living being, such as a bacterium, that is too small to be seen without a microscope.

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Example: This image shows a single-celled amoeba, a type of microorganism, with its irregular shape and simple internal parts visible inside.

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Microscopic Adjective

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[mahy-kruh-skop-ik]

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Microscopic

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Describing something so small in size that it is only visible with the aid of a microscope.

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Example: This image from a powerful microscope shows bacteria, which are microscopic organisms. The scale bar shows each one is about 1 micrometer long.

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Scale Noun

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[skeyl]

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Scale

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The relative size or extent of something, used to compare objects of vastly different dimensions from macroscopic to microscopic.

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Example: This image shows a balance scale, a tool used to measure mass by comparing an object of unknown mass with objects of known mass.

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Micrometer Noun

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[mahy-kroh-mee-ter]

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Micrometer

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A unit of length equal to one millionth of a meter, commonly used for measuring the size of cells.

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Example: This image shows how to read a micrometer by labeling its different scales, which combine to measure tiny distances with high precision.

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Nanometer Noun

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[nan-o-mee-ter]

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Nanometer

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A unit of length equal to one billionth of a meter, often used for measuring molecules and viruses.

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Example: This image compares the sizes of different viruses and a bacterium, using nanometers (nm) to show how this tiny unit of measurement is used.

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Cell Noun

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[sel]

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Cell

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The smallest structural and functional unit of an organism, which is considered the fundamental building block of all life.

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Example: This diagram shows a simple animal cell and labels its main parts, including the nucleus, cytoplasm, cell membrane, mitochondria, and vacuole.

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Unicellular Adjective

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[yoo-ni-sel-yuh-ler]

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Unicellular

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Describing a living organism that consists of only a single cell which performs all essential life functions.

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Example: This image shows an Amoeba, an organism made of only one cell, which is the definition of a unicellular organism.

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Multicellular Adjective

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[muhl-tee-sel-yuh-ler]

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Multicellular

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Describing a living organism composed of many different, specialized cells that work together to sustain the organism.

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Example: This image shows that a large muscle is built from many tiny, individual muscle cells working together, just like all multicellular organisms.

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Molecule Noun

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[mol-i-kyool]

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Molecule

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A group of two or more atoms held together by chemical bonds, representing the smallest unit of a substance.

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Example: This diagram shows a water molecule (H₂O), where two hydrogen atoms (H) are chemically bonded to one oxygen atom (O).