Prokaryotic and Eukaryotic Cells

Objective: Identify membranes, cytoplasm, genetic material, and ribosomes.

All cellular organisms have a plasma membrane separating cellular contents from the surroundings, cytoplasm where many processes occur, genetic material, and ribosomes that build proteins. The details of these structures vary. Not every cell has a wall, nucleus, chloroplast, or mitochondrion. A membrane is selectively permeable rather than an impenetrable shell. The presence of shared basic features supports comparisons across life without implying identical internal organization.

Objective: Describe bacterial and archaeal cell organization accurately.

Bacteria and archaea are prokaryotes: their cells do not enclose DNA in a membrane-bound nucleus. They contain ribosomes and a plasma membrane, and many have a cell wall, though wall composition differs. Their DNA is generally concentrated in a nucleoid region, and some also have plasmids. Prokaryotes can have specialized internal structures; “no membrane-bound nucleus” does not mean “no organization.” Many are unicellular, and metabolic diversity among them is extensive.

Objective: Connect internal membranes to specialized cellular roles.

Eukaryotic cells have a membrane-bound nucleus and an endomembrane system that helps compartmentalize processes. Many eukaryotes also have mitochondria; plants and algae with photosynthetic cells have chloroplasts. Protists, fungi, plants, and animals are eukaryotic groups, but their cells differ in walls, plastids, and organization. Compartmentalization allows some processes to occur in distinct chemical environments and supports coordination through transport among compartments. The presence of a nucleus alone does not establish that an organism is multicellular.