The characteristic that best defines a eukaryotic cell is
Answer: A
Dividing the interior into compartments allows incompatible reactions to run at once in different chemical conditions at once. The other three features are shared with prokaryotes and so distinguish nothing at all between the two groups.
Please log in or register to report this question.
Consider the following statements about prokaryotes and eukaryotes.
1. Prokaryotic cells are generally smaller than eukaryotic cells.
2. Both possess ribosomes, though of different sizes.
3. Only eukaryotes possess a cell wall.
Answer: B
The first two are correct. The third is wrong in both directions: most bacteria have a wall of peptidoglycan, while animal cells, which are eukaryotic, have no wall at all. Walls are therefore no guide to which group a cell belongs to.
Please log in or register to report this question.
The endosymbiotic theory accounts for the origin of
Answer: C
Both organelles have their own circular DNA, 70S ribosomes and double membranes, and both divide independently of the cell. The evidence points to free-living bacteria taken up by an ancestral host cell, which retained rather than digested them.
Please log in or register to report this question.
Consider the following evidence cited for the endosymbiotic theory.
1. Mitochondria possess their own circular DNA.
2. Chloroplast ribosomes resemble those of bacteria.
3. Both organelles are bounded by a single membrane.
Answer: D
The first two are among the strongest lines of evidence. The third is wrong, and indeed the double membrane is itself part of the argument, the inner one deriving from the engulfed bacterium and the outer from the host vesicle.
Please log in or register to report this question.
State whether the following is true or false.
Mitochondria can be synthesised from scratch by a cell that has lost them all.
Answer: A
Correct answer: False
Mitochondria arise only by the growth and division of existing mitochondria, in the same way cells do - a legacy of their bacterial ancestry. A cell that lost all of them could not build one, because most mitochondrial proteins are nuclear-encoded but the organelle’s own genome, membranes and import machinery cannot be assembled from nothing. It is why mitochondria are inherited maternally through the egg cytoplasm.
Please log in or register to report this question.
Cells specialised for absorption, such as those lining the small intestine, increase their exchange capacity by
Answer: B
A brush border of microvilli multiplies the membrane area many times without enlarging the cell. It is the standard solution to the surface-to-volume limit wherever exchange has to be maximised, and the same trick appears in the kidney tubule.
Please log in or register to report this question.
A red blood cell in a mature human lacks
Answer: C
Extruding the nucleus makes room for more haemoglobin and lets the cell deform through narrow capillaries. The cost is an inability to repair itself or to divide, which limits its working life to about four months in circulation.
Please log in or register to report this question.
Assertion (A): A mature mammalian red blood cell cannot divide.
Reason (R): It has no nucleus and therefore no chromosomal DNA to replicate.
Answer: D
Both are true and the reason gives the cause directly: division requires a genome to be copied and segregated into the daughters, and this cell discarded its own genome during maturation in the bone marrow, keeping only its haemoglobin.
Please log in or register to report this question.
Stem cells are distinguished by their capacity to
Answer: A
Correct answer: divide and give rise to specialised cells
A stem cell has two properties together: it can divide to renew itself, and its daughters can differentiate into specialised types. Either alone is insufficient - many cells divide without differentiating, and a differentiated cell that cannot renew is not a stem cell. The range of types available defines the grade, from totipotent through pluripotent to the multipotent cells of adult tissues.
Please log in or register to report this question.
A totipotent cell differs from a pluripotent cell in that a totipotent cell can form
Answer: B
The zygote and its first few descendants are totipotent, able to make both embryo and the extraembryonic tissues around it. Pluripotent cells can form every tissue of the body proper but not the extraembryonic membranes, which is a narrower capacity.
Please log in or register to report this question.
