Bacteria

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Prokaryote Noun

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[pro-kar-ee-oht]

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Prokaryote

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A single-celled organism that lacks a nucleus and membrane-bound organelles, belonging to the domains Archaea or Bacteria.

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Example: This diagram shows the structure of a bacterium, a key example of a prokaryote. It highlights the nucleoid area, where DNA is located without a surrounding nucleus.

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Archaea Noun

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[ahr-kee-uh]

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Archaea

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A domain of single-celled prokaryotes with a distinct evolutionary history and unique biochemistry compared to bacteria.

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Example: This diagram shows the labeled parts of an archaean cell, including its DNA in the nucleoid, ribosomes, cell wall, and a flagellum for movement.

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Bacteria Noun

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[bak-teer-ee-uh]

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Bacteria

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A domain of diverse, single-celled prokaryotes that are the most abundant organisms on Earth, found in various habitats.

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Example: This image shows the three main shapes of bacteria: spherical (cocci), rod-shaped (bacilli), and spiral (spirilla), which is a key way to classify them.

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Spirilli Noun

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[spy-ril-ee]

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Spirilli

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A term describing prokaryotic cells that exhibit a distinct helical or spiral shape, contributing to their motility.

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Example: This diagram shows that Spirilli are spiral-shaped bacteria that are rigid and have a wavy or corkscrew appearance, often with flagella for movement.

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Cocci Noun

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[kok-sahy]

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Cocci

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A term for prokaryotic cells that are spherical or ovoid in shape, often found in clusters or chains.

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Example: This image shows the spherical (ball-like) shape of cocci bacteria, which is their main identifying feature.

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Bacilli Noun

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[buh-sil-ahy]

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Bacilli

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A term for prokaryotic cells that are rod-shaped, one of the three most common bacterial morphologies.

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Example: This diagram shows a bacillus, a type of bacterium with a rod-like shape, and labels its key parts like the cell wall and flagellum.

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Gram staining Noun

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[gram steyn-ing]

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Gram staining

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A laboratory technique used to differentiate bacterial species into two large groups based on their cell wall properties.

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Example: Gram staining is a lab technique that uses dyes to show a key difference between types of bacteria, staining Gram-positive bacteria purple and Gram-negative pink.

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Gram-positive Adjective

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[gram-poz-i-tiv]

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Gram-positive

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Describes bacteria with a thick cell wall that retains the crystal violet dye during Gram staining, appearing purple.

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Example: Gram-positive bacteria have a thick outer layer of peptidoglycan above their cytoplasmic membrane, which helps them retain a specific stain.

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Gram-negative Adjective

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[gram-neg-uh-tiv]

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Gram-negative

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Describes bacteria with a thin cell wall and an outer membrane that do not retain the primary stain, appearing red.

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Example: This diagram shows the layers of a Gram-negative bacterium's cell wall, which has a thin peptidoglycan layer between an inner and outer membrane.

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Cell Wall Noun

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[sel wawl]

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Cell Wall

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A rigid protective layer surrounding the plasma membrane of most prokaryotic cells, providing structural support and shape.

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Example: This diagram shows the cell wall as the rigid outer layer that provides structure and a fixed, boxy shape to these onion (plant) cells.