Explanation:
Spermatogonia lie closest to the basement membrane, while primary and secondary spermatocytes occupy progressively more luminal positions. Spermatids are nearer the lumen, and spermatozoa are released into the lumen after differentiation.
2. A cell in the adluminal compartment of a seminiferous epithelium contains duplicated chromosomes and has not yet completed the first meiotic division. Which cell is it most likely to be?
A.
Type A spermatogonium
B.
Type B spermatogonium
C.
Primary spermatocyte
D.
Secondary spermatocyte
Correct Answer:
Primary spermatocyte
Explanation:
A primary spermatocyte has undergone premeiotic DNA replication and enters meiosis I. It is therefore located in the adluminal compartment and possesses duplicated chromosomes before producing secondary spermatocytes.
3. Which transition changes a cell from diploid to haploid without immediately reducing the amount of DNA per chromosome set from its post-replication state?
A.
Spermatogonium to primary spermatocyte
B.
Primary spermatocyte to secondary spermatocyte
C.
Secondary spermatocyte to spermatid
D.
Spermatid to spermatozoon
Correct Answer:
Primary spermatocyte to secondary spermatocyte
Explanation:
Completion of meiosis I separates homologous chromosomes, producing haploid secondary spermatocytes. Each chromosome still consists of two chromatids, so the DNA content remains greater than that of a mature haploid spermatid.
4. Which pair of consecutive spermatogenic cell stages is separated specifically by meiosis II?
A.
Spermatogonia and primary spermatocytes
B.
Primary spermatocytes and secondary spermatocytes
C.
Secondary spermatocytes and spermatids
D.
Spermatids and spermatozoa
Correct Answer:
Secondary spermatocytes and spermatids
Explanation:
Meiosis II separates sister chromatids in each secondary spermatocyte and produces haploid spermatids. Meiosis I separates homologous chromosomes, whereas spermiogenesis converts spermatids into spermatozoa.
5. A defect prevents the completion of meiosis I but does not affect spermatogonial mitosis. Which abnormal cell-layer pattern would be expected?
A.
Accumulation of spermatogonia with absence of primary spermatocytes
B.
Accumulation of primary spermatocytes with reduced secondary spermatocytes and spermatids
C.
Accumulation of spermatids with normal spermatozoa formation
D.
Normal primary spermatocytes with selective loss of spermatogonia
Correct Answer:
Accumulation of primary spermatocytes with reduced secondary spermatocytes and spermatids
Explanation:
Primary spermatocytes are the cells that undergo meiosis I. Blocking this division causes them to accumulate and prevents the normal formation of secondary spermatocytes, spermatids, and later spermatozoa.
6. Which statement best distinguishes secondary spermatocytes from primary spermatocytes in a seminiferous tubule?
A.
Secondary spermatocytes are diploid and have not replicated their DNA.
B.
Secondary spermatocytes are haploid and contain chromosomes still composed of two sister chromatids.
C.
Secondary spermatocytes are haploid and contain fully condensed spermatozoal nuclei.
D.
Secondary spermatocytes are diploid and arise directly from spermatids.
Correct Answer:
Secondary spermatocytes are haploid and contain chromosomes still composed of two sister chromatids.
Explanation:
Meiosis I makes secondary spermatocytes haploid by separating homologous chromosomes, but sister chromatids remain joined until meiosis II. Their nuclei are therefore distinct from both diploid primary spermatocytes and differentiated spermatozoa.
7. Which cell layer is expected to show the greatest number of cells capable of mitotic self-renewal within the spermatogenic series?
A.
Spermatogonial layer
B.
Primary spermatocyte layer
C.
Secondary spermatocyte layer
D.
Spermatid layer
Correct Answer:
Spermatogonial layer
Explanation:
Spermatogonia form the basal proliferative layer and include cells that maintain the germ-cell population through mitotic divisions. Primary and secondary spermatocytes undergo meiosis, while spermatids undergo differentiation rather than mitotic self-renewal.
8. A histological section shows cells with small, round, haploid nuclei adjacent to the luminal side of the seminiferous epithelium, but their tails and flagella are not yet developed. These cells are most likely:
A.
Type B spermatogonia
B.
Primary spermatocytes
C.
Secondary spermatocytes
D.
Spermatids
Correct Answer:
Spermatids
Explanation:
Spermatids are haploid products of meiosis II and are located close to the lumen. They have not yet undergone spermiogenesis, so they lack the fully developed morphology of spermatozoa.
9. Which sequence correctly describes the chromosome and chromatid status of the major spermatogenic layers after premeiotic DNA replication has occurred?
A.
Primary spermatocyte: 2n, duplicated; secondary spermatocyte: n, duplicated; spermatid: n, unduplicated
B.
Primary spermatocyte: n, unduplicated; secondary spermatocyte: 2n, duplicated; spermatid: n, duplicated
C.
Primary spermatocyte: 2n, unduplicated; secondary spermatocyte: n, unduplicated; spermatid: 2n, duplicated
D.
Primary spermatocyte: n, duplicated; secondary spermatocyte: n, unduplicated; spermatid: 2n, unduplicated
Correct Answer:
Primary spermatocyte: 2n, duplicated; secondary spermatocyte: n, duplicated; spermatid: n, unduplicated
Explanation:
After DNA replication, a primary spermatocyte remains diploid but has duplicated chromosomes. Meiosis I produces haploid secondary spermatocytes with duplicated chromosomes, and meiosis II produces haploid spermatids with unduplicated chromosomes.
10. If the layer immediately adjacent to the lumen contains elongated cells with highly condensed nuclei and developing flagella, which process has most recently transformed the preceding cell layer?
A.
Mitotic proliferation of spermatogonia
B.
Meiosis I of primary spermatocytes
C.
Meiosis II of secondary spermatocytes
D.
Spermiogenesis of spermatids
Correct Answer:
Spermiogenesis of spermatids
Explanation:
Elongated cells with condensed nuclei and developing flagella are spermatozoa. They arise when spermatids undergo spermiogenesis, a differentiation process involving nuclear condensation and formation of the sperm tail.
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Spermatogenic Cell Layers
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