At what stage does a developing sperm cell begin to grow a tail?
spermatid
primary spermatocyte
spermatogonium
secondary spermatocyte
The Correct Answer is A
A. spermatid: This is the stage where spermiogenesis occurs, which is the physical transformation of a non-motile round cell into a specialized spermatozoon. During this phase, the cell develops a flagellum, or tail, condenses its nucleus, and forms an acrosomal cap. It is a morphogenetic process rather than a cellular division.
B. primary spermatocyte: This diploid cell is prepared to undergo meiosis 1 to reduce the chromosome count. At this stage, the cell is large and spherical, lacking any specialized locomotory structures like a flagellum. Its primary physiological focus is DNA replication and genetic recombination through synapsis and crossing over.
C. spermatogonium: These are the stem cells of the germline located on the basement membrane of the seminiferous tubules. They undergo mitosis to maintain the cell population but do not possess any characteristics of a mature sperm cell. They are simple cuboidal epithelial cells with no flagellar precursors or tail structures.
D. secondary spermatocyte: These haploid cells are the products of the first meiotic division and are destined to undergo meiosis 2. They remain spherical in shape and do not yet initiate the morphological changes required for swimming. The development of the tail is reserved for the post-meiotic differentiation phase.
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Related Questions
Correct Answer is D
Explanation
A. atrial natriuretic peptide: This hormone is released by the heart in response to atrial stretch and actually promotes sodium excretion rather than retention. It inhibits the release of renin and aldosterone to lower blood pressure. It acts as a physiological antagonist to the sodium-retaining mechanisms of the kidney.
B. parathyroid hormone: The primary target of this hormone in the renal system is the distal convoluted tubule where it stimulates calcium reabsorption. It also inhibits phosphate reabsorption in the proximal tubule to manage mineral homeostasis. It does not play a significant role in systemic sodium ion retention.
C. antidiuretic hormone: Also known as vasopressin, this hormone primarily regulates water permeability in the collecting duct by inserting aquaporin-2 channels. While it affects osmolarity, it does not directly transport sodium ions. Its main function is the regulation of free water clearance to control plasma concentration.
D. aldosterone: This mineralocorticoid acts on the principal cells of the collecting duct to upregulate apical sodium channels and basolateral sodium-potassium pumps. This results in significant sodium reabsorption back into the blood, followed osmotically by water. It is the definitive hormone for long-term sodium balance regulation.
E. renin: Renin is a proteolytic enzyme, not a hormone that acts directly on the collecting duct to transport ions. It initiates the biochemical cascade that eventually produces angiotensin 2 and aldosterone. Its role is regulatory and enzymatic rather than being a direct transport-stimulating effector.
Correct Answer is B
Explanation
A. they are about the same size: The human oocyte is one of the largest cells in the body, visible to the naked eye. In contrast, the spermatozoon is significantly smaller, consisting primarily of a nucleus and a flagellum. This vast difference in cytoplasmic volume reflects their differing roles in providing nutrients for the zygote.
B. they have the same number of chromosomes: Both human egg and sperm are haploid gametes resulting from the process of meiosis. They each contain 23 chromosomes, which is exactly half of the 46 chromosomes found in a diploid somatic cell. Upon fertilization, the fusion of these nuclei restores the diploid state of the zygote.
C. about the same number of each is produced per month: Males produce millions of sperm cells daily through continuous spermatogenesis. Females generally release only a single secondary oocyte during each monthly ovarian cycle. This discrepancy in production rates ensures that at least one sperm reaches the egg despite a hostile environment.
D. they have the same degree of motility: Spermatozoa are highly motile cells that use a flagellum to swim through the female reproductive tract toward the egg. The oocyte is non-motile and relies on the beating of cilia within the uterine tubes for transport. They possess entirely different structural adaptations for movement within the reproductive system.
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