All living things are made of cells, but not all cells are organized the same way. Prokaryotic cells, such as bacteria, are smaller and simpler, while eukaryotic cells, such as animal and plant cells, are larger and more complex. The biggest difference is that eukaryotic cells have a nucleus that stores DNA, while prokaryotic cells do not.
This comparison matters because cell structure affects how organisms grow, reproduce, get energy, and respond to their environment.
Prokaryotic DNA is usually found in a region called the nucleoid, and many prokaryotes also have plasmids that carry extra genes. Eukaryotic cells divide their work among membrane-bound organelles, such as mitochondria, chloroplasts, the endoplasmic reticulum, and the Golgi apparatus. This internal organization lets eukaryotic cells perform many specialized tasks at the same time.
Understanding these cell types helps explain topics such as disease, antibiotics, evolution, genetics, and the differences between single-celled and multicellular life.
Key Facts
- Prokaryotic cells do not have a nucleus, while eukaryotic cells have DNA enclosed in a nucleus.
- Typical prokaryotic cell size is about 0.1 to 5 micrometers, while typical eukaryotic cell size is about 10 to 100 micrometers.
- Both prokaryotic and eukaryotic cells have a plasma membrane, cytoplasm, DNA, and ribosomes.
- Eukaryotic cells contain membrane-bound organelles, while prokaryotic cells generally do not.
- Magnification = image size / actual size.
- Examples of prokaryotes include bacteria and archaea; examples of eukaryotes include animals, plants, fungi, and protists.
Vocabulary
- Prokaryotic cell
- A cell that lacks a nucleus and membrane-bound organelles.
- Eukaryotic cell
- A cell that has a nucleus and membrane-bound organelles.
- Nucleus
- A membrane-bound structure in eukaryotic cells that contains most of the cell's DNA.
- Organelle
- A specialized structure inside a cell that performs a specific function.
- Nucleoid
- The region in a prokaryotic cell where its DNA is located.
Common Mistakes to Avoid
- Saying prokaryotes have no DNA is wrong because prokaryotic cells do have DNA, but it is not enclosed in a nucleus.
- Calling all single-celled organisms prokaryotes is wrong because many single-celled organisms, such as yeast and many protists, are eukaryotic.
- Thinking only eukaryotic cells have ribosomes is wrong because both prokaryotic and eukaryotic cells use ribosomes to make proteins.
- Assuming bigger cells are always better is wrong because smaller prokaryotic cells can exchange materials quickly and reproduce very rapidly.
Practice Questions
- 1 A bacterium is 2 micrometers long and an animal cell is 20 micrometers long. How many times longer is the animal cell than the bacterium?
- 2 A drawing of a eukaryotic cell is 50 mm wide. The actual cell is 25 micrometers wide. Convert 50 mm to micrometers and calculate the magnification using Magnification = image size / actual size.
- 3 A cell has DNA, ribosomes, cytoplasm, and a plasma membrane, but no nucleus or membrane-bound organelles. Explain whether it is more likely prokaryotic or eukaryotic and give one reason.