Endosymbiotic Theory

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Endosymbiosis Noun

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[en-doh-sim-by-oh-sis]

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Endosymbiosis

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A symbiotic relationship where one organism lives inside another, with both organisms benefiting from the arrangement.

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Example: This diagram shows an ancestral cell engulfing smaller bacteria, which over time evolve into mitochondria and chloroplasts inside a modern cell, illustrating endosymbiosis.

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Eukaryotic Cell Noun

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[yoo-kar-ee-ot-ik sel]

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Eukaryotic Cell

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A type of cell that has a membrane-bound nucleus and other membrane-bound organelles, such as mitochondria.

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Example: This diagram shows a eukaryotic cell, which contains complex, membrane-bound organelles like the nucleus and mitochondria, the latter explained by endosymbiotic theory.

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Prokaryotic Cell Noun

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[pro-kar-ee-ot-ik sel]

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Prokaryotic Cell

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A type of cell lacking a membrane-enclosed nucleus and other membrane-enclosed organelles, found in the domains Bacteria and Archaea.

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Example: This diagram shows the key parts of a prokaryotic cell, like its free-floating DNA in the nucleoid region and lack of a nucleus.

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Symbiosis Noun

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[sim-by-oh-sis]

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Symbiosis

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A close and long-term interaction between two different biological species.

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Example: This image shows how a clownfish and sea anemone help each other survive, an example of symbiosis called mutualism.

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Organelle Noun

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[or-guh-nel]

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Organelle

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A specialized subunit within a cell that has a specific function and is often enclosed within its own membrane.

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Example: This diagram shows how a simple cell swallowed a bacterium long ago, which then became a permanent part inside, an organelle called a chloroplast.

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Mitochondria Noun

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[my-toh-kon-dree-uh]

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Mitochondria

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An organelle in eukaryotic cells that generates most of the cell's supply of chemical energy in the form of ATP.

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Example: This diagram shows a mitochondrion's key parts, including its own DNA and ribosomes, which supports the endosymbiotic theory that it was once a separate organism.

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Chloroplast Noun

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[klor-uh-plast]

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Chloroplast

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An organelle found in plant cells and eukaryotic algae that conducts photosynthesis.

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Example: This diagram shows a chloroplast's key structures, including its double membrane, which is evidence for the endosymbiotic theory that it was once a bacterium.

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Photosynthesis Noun

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[foh-toh-sin-thuh-sis]

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Photosynthesis

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The process used by plants and other organisms to convert light energy into chemical energy, creating glucose and oxygen.

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Example: This diagram shows how a plant uses light, water, and carbon dioxide to create its food (carbohydrates) and release oxygen, the process of photosynthesis.

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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 single-celled prokaryotic microorganisms that have cell walls but lack organelles and an organized nucleus.

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Example: This diagram shows the labeled parts of a bacterium, a simple prokaryotic cell. The endosymbiotic theory proposes that organelles like mitochondria were once free-living bacteria.

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DNA Noun

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[dee-en-ey]

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DNA

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Deoxyribonucleic acid, a self-replicating molecule that carries the genetic information in nearly all living organisms.

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Example: This diagram shows the DNA double helix, made of a sugar-phosphate backbone and base pairs, which holds the genetic code for living things.