Prokaryotic and Eukaryotic Cells
Compare a bacterial cell with plant and animal cells: a free loop of DNA and plasmids on one side, a nucleus and membrane-bound organelles on the other. Sets the size scale the rest of cell biology works in.
What a learner can do afterwards
- Names the parts a bacterial cell has and the parts it does not, and says which structures a plant cell adds to the animal set.
- Places a bacterium, an animal cell and a plant cell in size order using micrometres.
- Says why plasmids matter to a bacterium even though they sit outside the main chromosome.
1 · Read
Cells fall into two broad groups. Prokaryotes are mostly single-celled organisms of the Bacteria and Archaea domains. They have no nucleus and no membrane-bound organelles. Their DNA sits as a free loop in a central nucleoid, plus small rings called plasmids.
Animals, plants, fungi, and protists are all eukaryotes. Their DNA is locked inside a true nucleus, and the cell carries specialised organelles: mitochondria release energy, ribosomes build proteins, membranes control traffic. A plant cell then adds three things animals lack: a wall, chloroplasts, and a big vacuole.
Size tells the same story. All cells share a membrane, cytoplasm, DNA, and ribosomes, but bacteria are about ten times smaller than animal cells, measured in micrometres. Microscopes reveal the gap: stain, magnify, and compare the micrographs.
Remember plasmids even though they sit outside the main chromosome. They are small DNA rings swapped between bacteria, often carrying antibiotic resistance. That swap is why they matter far beyond their size.
Bacteria carry a free DNA loop without a nucleus, while plant and animal cells lock DNA in one.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.