Archaea differ from bacteria most fundamentally in
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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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.
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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A differentiated cell in a multicellular organism owes its character to
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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State whether the following is true or false.
Cell theory applies to unicellular organisms as fully as to multicellular ones.
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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A tissue is best defined as
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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Which cell type in the human body is normally the longest?
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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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?
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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State whether the following is true or false.
A cell wall and a plasma membrane serve the same function.
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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Which of the following is not part of modern cell theory?
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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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.
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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