Which of the following best describes a unicellular organism that lacks a nucleus and membrane-bound organelles?

• A. Fungus
• B. Bacterium
• C. Alga
• D. Protozoan

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the key terms in the question. A unicellular organism means it is made up of a single cell. The question also specifies that the organism lacks a nucleus and membrane-bound organelles.
2. Step 2: Recall the classification of organisms based on cell structure. Organisms without a nucleus and membrane-bound organelles are called prokaryotes, while those with these features are eukaryotes.
3. Step 3: Identify which groups from the options are prokaryotic. Bacteria are prokaryotes, meaning they do not have a nucleus or membrane-bound organelles.
4. Step 4: Recognize that fungi, algae, and protozoa are eukaryotes. They have a nucleus and membrane-bound organelles, even if they are unicellular (like some protozoa and algae).
5. Step 5: Conclude that the best description for a unicellular organism lacking a nucleus and membrane-bound organelles is a bacterium, as it fits the prokaryotic cell structure.