Prokaryotic & Eukaryotic cells

Correct answer: B. Well-defined nuclear membrane

Correct answer: B, a well-defined nuclear membrane. Prokaryotic cells do not have a membrane-bound nucleus. Their genetic material is present in a nucleoid region, which lies in the cytoplasm and is not surrounded by a nuclear envelope. First, distinguish the two cell types: eukaryotic cells have a true nucleus, while prokaryotic cells do not. A is wrong because the cell membrane is essential and present. B is correct because the nuclear membrane is absent. C is wrong because ribosomes are present and make proteins. D is wrong because many prokaryotes, including bacteria, possess a cell wall. Memory cue: “pro” means an earlier, simpler cell plan; “no true nucleus” is the key distinction.

Correct answer: B. Protista

Correct answer: B, Protista. Paramecium is a unicellular eukaryote, so it has a well-defined nucleus and membrane-bound organelles. It lives mainly in freshwater and moves with cilia, but its most useful classification clue here is its single-celled eukaryotic organisation. A is wrong because Monera contains prokaryotes without a true nucleus. B is correct because traditional five-kingdom classification places many unicellular eukaryotes, including Paramecium, in Protista. C is wrong because Paramecium is not a fungus and does not have the typical fungal body organisation. D is wrong because Animalia generally includes multicellular animals, whereas Paramecium is a single cell. Memory cue: unicellular eukaryote usually points to Protista in the five-kingdom system.

Correct answer: B. 70S

Direct answer: B, 70S. Prokaryotic cells contain 70S ribosomes, which are made of a 50S large subunit and a 30S small subunit. The S symbol means Svedberg unit, a measure of sedimentation behaviour; it is not a simple arithmetic mass unit, so 50S plus 30S is described as 70S rather than 80S. A is wrong because 80S ribosomes are typical of the cytoplasm of eukaryotic cells. C and D are individual subunit values associated with ribosomes, not the complete prokaryotic ribosome: 50S is the large subunit and 30S is the small one. Memory cue: prokaryote = 70S; eukaryotic cytoplasm = 80S.