Cell Theory and Cell Types Questions and Answers

Q: An electron microscope achieves higher resolution than a light microscope because electrons

Correct answer: have a much shorter wavelength than lightAn electron accelerated through 100 kV has a wavelength of a few picometres, some hundred thousand times shorter than visible light, and since the diffraction limit scales with wavelength the attainable resolution improves accordingly. In practice lens aberrations keep electron microscopes well short of that theoretical figure, but they still resolve to atomic dimensions.

51.

An electron microscope achieves higher resolution than a light microscope because electrons

A.travel considerably faster than photons
B.carry an electrical charge that light lacks
C.pass through specimens without absorption
D.have a much shorter wavelength than light

Answer: D

Correct answer: have a much shorter wavelength than light

An electron accelerated through 100 kV has a wavelength of a few picometres, some hundred thousand times shorter than visible light, and since the diffraction limit scales with wavelength the attainable resolution improves accordingly. In practice lens aberrations keep electron microscopes well short of that theoretical figure, but they still resolve to atomic dimensions.

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52.

A transmission electron microscope differs from a scanning electron microscope in that the transmission instrument

A.passes electrons through a thin section
B.produces a three-dimensional surface view
C.can examine living specimens directly
D.uses visible light for its final image

Answer: A

Passing the beam through reveals internal structure in a very thin slice, while the scanning instrument reflects electrons off a coated surface to give its characteristic three-dimensional appearance. Neither instrument can examine living material.

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53.

Consider the following statements about cell size.
1. A typical bacterium is smaller than a typical animal cell.
2. The surface area to volume ratio falls as a cell grows.
3. Cell size is limited chiefly by the strength of the plasma membrane.

A.All of them
B.1 and 2 only
C.3 only
D.1 only

Answer: B

The first two are correct. The third names the wrong constraint: the limit is set by the need to exchange materials fast enough across a surface that grows more slowly than the volume it must serve, so a cell reaches a ceiling long before its membrane fails mechanically.

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54.

Which of these is the largest?

A.a ribosome subunit
B.a virus particle
C.a typical eukaryotic cell
D.a typical soil bacterium

Answer: C

A eukaryotic cell of ten to a hundred micrometres dwarfs a bacterium of one or two, which in turn dwarfs a virus of a few tens of nanometres and a ribosome smaller still. The scale spans about four orders of magnitude.

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55.

State whether the following is true or false.
Cyanobacteria are eukaryotic because they carry out photosynthesis.

A.True only at large scales
B.False only at small scales
C.True
D.False

Answer: D

They are bacteria, with no nucleus and no chloroplasts, and they photosynthesise on internal thylakoid membranes instead. The endosymbiotic theory in fact holds that chloroplasts descend from ancestors of this very group of organisms, taken up long ago by an ancestral eukaryote.

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56.

Archaea differ from bacteria most fundamentally in

A.the chemistry of their membranes and walls
B.possessing a true membrane-bound nucleus
C.being unable to survive extreme conditions
D.having no genetic material of their own

Answer: A

Ether-linked membrane lipids and walls lacking peptidoglycan set them apart, and molecular phylogeny places them as a separate domain of life. They remain prokaryotic, having no nucleus, so the difference is chemical and genetic rather than structural.

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57.

Assertion (A): Archaea are classed in a domain of their own rather than among the bacteria.
Reason (R): Their membrane lipids and gene sequences differ profoundly from bacterial ones.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the grounds: the differences run deeper than those separating many bacterial groups from one another, and in several respects the archaeal machinery is closer to the eukaryotic than the bacterial.

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58.

A differentiated cell in a multicellular organism owes its character to

A.the number of chromosomes it carries
B.the size of its plasma membrane
C.which of its genes are expressed
D.which genes it has physically retained

Answer: C

The genome is common to nearly all the cells, so identity comes from patterns of expression that are established during development and then maintained. This is why a differentiated nucleus can sometimes be reprogrammed.

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59.

State whether the following is true or false.
Cell theory applies to unicellular organisms as fully as to multicellular ones.

A.False
B.True only at large scales
C.False only at small scales
D.True

Answer: D

A single-celled organism is one cell that performs every function of life, which is exactly what the theory claims cells to be capable of. Multicellularity divides those functions among specialised cells rather than changing the principle.

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60.

A tissue is best defined as

A.a group of similar cells with a shared function
B.any collection of cells found within one organ
C.the outer covering of an organ or blood vessel
D.a single cell that has become highly specialised

Answer: A

Similarity of cell type and unity of function are both required, which is what distinguishes a tissue from the several tissues that make up an organ. Muscle, nerve, epithelial and connective are the four principal animal types.

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