Catastrophism and Earth’s History

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Endosymbiotic theory Noun

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[en-doh-sim-by-ot-ik thee-uh-ree]

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Endosymbiotic theory

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The theory that eukaryotic organelles, like mitochondria, originated from free-living prokaryotes being engulfed by another host cell.

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Example: This diagram shows how an ancestral host cell engulfed smaller bacteria, which over time became the mitochondria and chloroplasts inside modern complex cells.

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Amino acids Noun

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[uh-mee-noh as-ids]

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Amino acids

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The organic compounds containing both carboxyl and amino groups that serve as the fundamental building blocks of proteins.

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Example: This diagram shows the basic chemical structure of an amino acid, highlighting its main parts: an amino group, a carboxyl group, and a side chain.

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Protocells Noun

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[proh-toh-sels]

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Protocells

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Self-organized, spherical collections of lipids proposed as a stepping-stone toward the origin of the first living cells.

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Example: This diagram shows a liposome, a simple sphere with a lipid bilayer membrane. Scientists believe protocells, the earliest precursors to life, were similar structures.

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Coacervates Noun

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[koh-as-er-veyts]

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Coacervates

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Bead-like droplets of organic molecules, such as amino acids, that can form spontaneously in water as a protocell model.

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Example: This microscope image shows coacervates, tiny droplets with a boundary separating them from the surrounding water, considered a step toward the first cells.

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'RNA world' hypothesis Noun

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[ar-en-ay wurld hy-poth-uh-sis]

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'RNA world' hypothesis

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A scientific hypothesis proposing that RNA was the primary form of genetic and catalytic material before DNA evolved.

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Example: This diagram shows the 'RNA world' hypothesis, where early life used RNA for both storing genetic information (self-replication) and creating proteins, unlike modern life.

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Prokaryote Noun

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[proh-kar-ee-oht]

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Prokaryote

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A microscopic single-celled organism that lacks a distinct nucleus and other specialized membrane-bound organelles.

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Example: This diagram shows a prokaryote, a simple single-celled organism without a nucleus. Its genetic material (nucleoid DNA) floats in the cytoplasm.

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Anaerobic Adjective

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[an-uh-roh-bik]

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Anaerobic

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Describing a biological process or organism that can function and live in the complete absence of molecular oxygen.

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Example: This diagram shows alcoholic fermentation, an anaerobic process. It illustrates how organisms can break down sugar (glucose) to get energy (ATP) without using oxygen.

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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 through cellular respiration.

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Example: A plant uses sunlight, water, and carbon dioxide to create its own food (sugars) and releases oxygen as a byproduct.

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Eukaryote Noun

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[yoo-kar-ee-oht]

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Eukaryote

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An organism consisting of a cell or cells in which the genetic material is DNA within a distinct nucleus.

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Example: This diagram shows a Eukaryote cell, which has its DNA inside a membrane-enclosed nucleus, a key feature that distinguishes it from simpler cells.

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Mitochondria Noun

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[mahy-tuh-kon-dree-uh]

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Mitochondria

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Organelles in eukaryotic cells that generate most of the cell's supply of energy in the form of ATP.

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