Cell Theory and Cell Types Questions and Answers

Q: Which cell type in the human body is normally the longest?

Correct answer: a motor neuronA motor neuron supplying a muscle in the foot has its cell body in the spinal cord and an axon running the whole way down the leg - up to about a metre in an adult, and the longest single cell in the body. The others are all small: a hepatocyte and a red blood cell are measured in micrometres, and a sperm cell is around 50 micrometres including its tail.

Q: A eukaryotic cell is 20 micrometres across and a bacterium 2 micrometres. How many times greater is the volume of the eukaryotic cell, taking both as spheres?

Correct answer: 1,000Volume scales with the cube of the linear dimension, so a tenfold difference in diameter is a thousandfold difference in volume: \[ \left(\frac{20}{2}\right)^3 = 10^3 = 1{,}000. \] The 100 offered is the ratio of surface areas, which scales with the square. That mismatch is the whole reason large cells need internal membranes: volume outgrows the surface available to supply it.

Q: Consider the following statements about microscopy.1. Resolution is limited by the wavelength of the illumination.2. Electron microscopy generally requires the specimen to be dead.3. Magnification and resolution mean the same thing.

Correct answer: 1 and 2 onlyStatements 1 and 2 are correct: resolution is set by the wavelength, and electron microscopy requires a high vacuum along with fixing, dehydration and often metal coating, so the specimen cannot be alive. Statement 3 is the confusion this topic keeps returning to - magnification is how much larger the image is, resolution is how close two points can be and still be seen as two, and enlarging an image beyond its resolution adds nothing.

Q: Multicellularity is advantageous chiefly because it permits

Correct answer: division of labour among specialised cellsOnce cells need not each do everything, they can specialise, and a nerve cell, a muscle cell and a secretory cell can each be built for one job and be far better at it than any general-purpose cell could be. Multicellularity also allows an organism to exceed the size a single cell can reach, but the specialisation is what makes the size worth having.

Q: A cell that has lost the ability to divide but continues to function is best described as

Correct answer: terminally differentiatedA terminally differentiated cell has left the cell cycle permanently and devotes itself to its specialised function - a neuron, a cardiac muscle cell, a mature red blood cell. It is neither damaged nor dying, which distinguishes it from a genome failure and from apoptosis, and it is the opposite end of the scale from the totipotent cell that has differentiated into nothing at all.

61.

Which cell type in the human body is normally the longest?

A.a liver hepatocyte
B.a motor neuron
C.a red blood cell
D.a mature sperm cell

Answer: B

Correct answer: a motor neuron

A motor neuron supplying a muscle in the foot has its cell body in the spinal cord and an axon running the whole way down the leg - up to about a metre in an adult, and the longest single cell in the body. The others are all small: a hepatocyte and a red blood cell are measured in micrometres, and a sperm cell is around 50 micrometres including its tail.

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62.

A eukaryotic cell is 20 micrometres across and a bacterium 2 micrometres. How many times greater is the volume of the eukaryotic cell, taking both as spheres?

A.100
B.20
C.1,000
D.10

Answer: C

Correct answer: 1,000

Volume scales with the cube of the linear dimension, so a tenfold difference in diameter is a thousandfold difference in volume: \[ \left(\frac{20}{2}\right)^3 = 10^3 = 1{,}000. \] The 100 offered is the ratio of surface areas, which scales with the square. That mismatch is the whole reason large cells need internal membranes: volume outgrows the surface available to supply it.

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63.

State whether the following is true or false.
A cell wall and a plasma membrane serve the same function.

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

Answer: D

The membrane controls what enters and leaves and is selectively permeable; the wall is a rigid outer support that is freely permeable to most small molecules. A walled cell possesses both structures, each doing a quite different job from the other.

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64.

Which of the following is not part of modern cell theory?

A.Cells arise spontaneously from organic matter
B.All living things are made up of one or more cells
C.The cell is the basic unit of structure and function
D.New cells arise only from pre-existing cells

Answer: A

Spontaneous generation is precisely what Virchow's addition ruled out, and Pasteur's experiments settled it experimentally. The other three statements together constitute the theory as it now stands, and each of them is accepted without qualification.

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65.

Consider the following statements about microscopy.
1. Resolution is limited by the wavelength of the illumination.
2. Electron microscopy generally requires the specimen to be dead.
3. Magnification and resolution mean the same thing.

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

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: resolution is set by the wavelength, and electron microscopy requires a high vacuum along with fixing, dehydration and often metal coating, so the specimen cannot be alive. Statement 3 is the confusion this topic keeps returning to - magnification is how much larger the image is, resolution is how close two points can be and still be seen as two, and enlarging an image beyond its resolution adds nothing.

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66.

Multicellularity is advantageous chiefly because it permits

A.reproduction without any cell division
B.organisms to dispense with a genome
C.division of labour among specialised cells
D.cells to grow far beyond their normal size

Answer: C

Correct answer: division of labour among specialised cells

Once cells need not each do everything, they can specialise, and a nerve cell, a muscle cell and a secretory cell can each be built for one job and be far better at it than any general-purpose cell could be. Multicellularity also allows an organism to exceed the size a single cell can reach, but the specialisation is what makes the size worth having.

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67.

Assertion (A): A large organism is built from many small cells rather than from a few large ones.
Reason (R): Cells cannot exceed a certain size without starving their own interiors.

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

Answer: D

Both are true and the reason gives the constraint that forces the arrangement: since exchange is limited by surface area, growth is achieved by adding cells rather than by enlarging them, which brings specialisation as a further benefit.

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68.

State whether the following is true or false.
The cell theory was formulated before the microscope was invented.

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

Answer: A

The theory rests entirely on observations that only a microscope could supply, and it followed Hooke's and Leeuwenhoek's work by more than a century and a half. Instrument and idea are inseparable here, since nobody can theorise about what nobody has seen.

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69.

A cell that has lost the ability to divide but continues to function is best described as

A.arrested by a failure of its genome
B.terminally differentiated
C.totipotent and undifferentiated
D.undergoing programmed cell death

Answer: B

Correct answer: terminally differentiated

A terminally differentiated cell has left the cell cycle permanently and devotes itself to its specialised function - a neuron, a cardiac muscle cell, a mature red blood cell. It is neither damaged nor dying, which distinguishes it from a genome failure and from apoptosis, and it is the opposite end of the scale from the totipotent cell that has differentiated into nothing at all.

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70.

The idea that all cells share a common ancestry is supported most strongly by

A.the presence of walls in most cells
B.the fact that all cells contain water
C.the universality of the genetic code
D.the similar sizes of all known cells

Answer: C

Almost every organism reads the same codons as the same amino acids, which would be an extraordinary coincidence had life arisen more than once independently. Size, walls and water content are far weaker evidence, since each varies widely among cells.

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