Cells are broadly classified as prokaryotic or eukaryotic. The names describe their relationship to a nucleus: pro- means “before,” and kary- refers to the nucleus; eu- means “true.” Bacteria and Archaea are prokaryotes. Animals, plants, fungi, and protists are eukaryotes.
A prokaryote is a mostly unicellular organism whose cells lack a nucleus and other membrane-bound organelles. Its DNA is located in a central region called the nucleoid, rather than enclosed inside a nucleus.
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What is a prokaryote?
A mostly unicellular organism whose cells lack a nucleus and other membrane-bound organelles. Bacteria and Archaea are prokaryotes.
What is the nucleoid?
The region in a prokaryotic cell where its DNA is located. Unlike a nucleus, it is not enclosed by a membrane.
How do a flagellum, pili, and fimbriae differ in function?
Flagella are used for locomotion. Pili can transfer genetic material between bacteria during conjugation, while fimbriae help bacteria attach to host cells.
Why are prokaryotic cells generally small?
Their small size allows ions, organic molecules, and wastes to diffuse quickly over short distances within and around the cell.
What happens to the surface-area-to-volume ratio as a cell grows, and why does it matter?
It decreases because volume grows faster than surface area. A lower ratio can make exchange across the plasma membrane less efficient for the cell’s volume.
Quiz questions
Which two groups of organisms are classified as prokaryotes?Answer: Bacteria and Archaea.
Which four components are found in all cells?Answer: Plasma membrane, cytoplasm, DNA, and ribosomes.
What function can a bacterial capsule support?Answer: It can help the cell attach to surfaces in its environment.
Which approximate diameter ranges describe prokaryotic and eukaryotic cells, respectively?Answer: Prokaryotes: 0.1–5.0 μm; eukaryotes: 10–100 μm.
What is bioremediation?Answer: Using selected or engineered microbes to help remove pollutants from contaminated environments.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.