真核與原核細胞超微結構：练习题

Which structure is a characteristic feature of prokaryotic cells but is absent in eukaryotic animal cells?

A student observes a cell under a light microscope using an eyepiece graticule and a stage micrometer. The stage micrometer has divisions of \(0.1\text{ mm}\). At \(40\times\) objective magnification, \(10\) divisions of the stage micrometer align with \(40\) divisions of the eyepiece graticule. A cell is measured to be \(12\) eyepiece units long. What is the actual length of the cell in \(\mu\text{m}\)?

In a flowering plant, a pollen grain lands on a stigma and begins the process of double fertilisation. If the generative nucleus divides to form two male gametes, and one fuses with the egg cell, what is the correct outcome for the second male gamete?

What is the primary function of the acrosome in a mammalian sperm cell during fertilisation?

During the process of fertilisation in mammals, the cortical reaction is a critical step. Which of the following best describes the purpose of this reaction?

A student observes a cell with circular DNA, 70S ribosomes, and a capsule. Explain why these features indicate the cell is prokaryotic rather than eukaryotic.

Independent assortment occurs during metaphase I of meiosis. For a cell with a diploid number of \( 2n = 6 \), calculate the number of possible chromosome combinations in the gametes, assuming no crossing over occurs.

During the transport of extracellular enzymes, proteins are modified in a specific organelle after leaving the rough endoplasmic reticulum. Identify this organelle and describe its primary role in this process.

Protein transport within eukaryotic cells involves several membrane-bound organelles.

(a) Explain the roles of the rough endoplasmic reticulum (rER) and the Golgi apparatus in the production and secretion of an extracellular enzyme. (4)
(b) Suggest how the ultrastructure of a mucus-secreting goblet cell would differ from that of a muscle cell, relating the differences to the cell's function. (2)

Stem cells have the potential to treat a wide variety of human diseases, but their use is a subject of significant ethical debate.

(a) Distinguish between totipotent and pluripotent stem cells, and identify where each type can be found in a human embryo. (3)
(b) Explain how differential gene expression leads to the specialisation of a stem cell into a specific cell type, such as a cardiomyocyte. (3)
(c) Discuss the ethical implications of using embryonic stem cells in medical therapies compared to the use of induced pluripotent stem (iPS) cells. (2)