Cell Theory and Cell Types Questions and Answers

Answer: A

Correct answer: Robert Hooke

Hooke coined the word in 1665, describing thin slices of cork in his Micrographia. What he saw were the empty walls of dead plant cells, and they reminded him of the small rooms - cells - of a monastery. He was therefore naming a structure rather than discovering life in it; that came with Leeuwenhoek a few years later.

Answer: B

Correct answer: Anton van Leeuwenhoek

Leeuwenhoek ground his own single-lens microscopes to a quality nobody matched for over a century, and with them observed bacteria, protozoa and spermatozoa in the 1670s, calling them animalcules. The distinction from Hooke is worth holding: Hooke named the empty compartments of dead cork, Leeuwenhoek watched living single-celled organisms swimming.

Answer: C

Schleiden argued it for plants and Schwann extended it to animals, uniting the two kingdoms under one generalisation about all living things. Their formulation lacked the third element, concerning where new cells come from, which Virchow supplied.

Answer: D

It completed cell theory by denying that cells form spontaneously from unorganised material. Pasteur's experiments on spontaneous generation supported the principle experimentally, but the phrase and its place in cell theory belong to Virchow.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 are the first two tenets of cell theory. Statement 3 is the doctrine of spontaneous generation, which cell theory explicitly replaced - the third tenet, in Virchow’s phrase, is that every cell arises from a pre-existing cell. Pasteur’s swan-neck flask experiments settled the question for good.

Answer: B

Correct answer: False

A virus has a genome and a protein coat but no cytoplasm, no ribosomes and no metabolism of its own, and it cannot arise from a pre-existing virus by division. It replicates only by commandeering a cell’s machinery, so it fails every tenet of cell theory. That is why viruses are described as infectious agents rather than as organisms.

Answer: C

Correct answer: a nucleus bounded by a membrane

The membrane-bound nucleus is the defining difference and the one the names record - karyon is Greek for kernel. Both cell types have a plasma membrane and ribosomes, and cell walls occur in both groups, so none of those separates them. The nuclear envelope brings a wider consequence with it: transcription and translation are separated in space, which is what allows the RNA processing eukaryotes depend on.

Answer: D

The Svedberg values describe sedimentation rather than mass, which is why the subunits do not sum arithmetically to the whole. The difference from the eukaryotic 80S ribosome is what several classes of antibiotic exploit for their selectivity.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is precisely why the drugs work. Bacterial ribosomes are 70S, built from 30S and 50S subunits; eukaryotic cytoplasmic ribosomes are 80S, from 40S and 60S. Tetracyclines, aminoglycosides and macrolides bind the bacterial subunits and not the human ones, which is what gives them their selective toxicity. Mitochondrial ribosomes are 70S, which is where some of these drugs’ side effects come from.

Answer: B

Many have extensive internal membranes, the thylakoids of cyanobacteria and the folded mesosomes of some bacteria among them. What they lack is a nucleus and the other membrane-bound organelles, which is a narrower claim.