Select the correct statement/s from the following: (A) Spermatogonia always undergo meiotic cell division. (B) Primary spermatocytes divide by meiotic cell division. (C) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division. (D) Spermatozoa are transformed into spermatids. Choose the correct answer from the options given below:
(d) B and C only
Let's analyze each statement regarding spermatogenesis, the process of sperm formation in males, to determine which ones are correct.
Understanding Spermatogenesis: Stages and Cell Divisions
Spermatogenesis is a complex process that involves several stages of cell division and differentiation, starting from spermatogonia in the seminiferous tubules of the testes.
Analysis of Statements on Spermatogenesis Cell Divisions
We will examine each statement provided:
- (A) Spermatogonia always undergo meiotic cell division.
Spermatogonia are diploid (2n) germ cells. They first increase their number by undergoing mitotic cell division. Some spermatogonia then differentiate into primary spermatocytes. Meiosis occurs after the primary spermatocyte stage. Therefore, spermatogonia do not always undergo meiotic division; they first undergo mitosis. This statement is incorrect. - (B) Primary spermatocytes divide by meiotic cell division.
Primary spermatocytes are diploid (2n) cells that enter meiosis. They undergo Meiosis I, a reductional division, to produce two haploid (n) secondary spermatocytes. This division is indeed a meiotic cell division. This statement is correct. - (C) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division.
Secondary spermatocytes are haploid (n) cells formed after Meiosis I. In humans, a haploid set of chromosomes consists of 23 chromosomes. Secondary spermatocytes then undergo Meiosis II, an equational division, to produce four haploid spermatids. Thus, secondary spermatocytes have 23 chromosomes and undergo the second meiotic division (Meiosis II). This statement is correct. - (D) Spermatozoa are transformed into spermatids.
Spermatids are the haploid cells formed from secondary spermatocytes after Meiosis II. Spermatozoa, or mature sperm, are formed from spermatids through a process called spermiogenesis, which involves morphological changes but not cell division. Spermatids are transformed into spermatozoa, not the other way around. This statement is incorrect.
Summary of Statement Correctness
| Statement | Description | Correctness |
|---|---|---|
| A | Spermatogonia always undergo meiotic cell division. | Incorrect |
| B | Primary spermatocytes divide by meiotic cell division. | Correct |
| C | Secondary spermatocytes have 23 chromosomes and undergo second meiotic division. | Correct |
| D | Spermatozoa are transformed into spermatids. | Incorrect |
Based on the analysis, statements (B) and (C) are correct.
Choosing the Correct Option
We need to select the option that corresponds to the correct statements.
- Option (a) A and C only: Incorrect, as A is incorrect.
- Option (b) C only: Incorrect, as B is also correct.
- Option (c) D only: Incorrect, as D is incorrect.
- Option (d) B and C only: Correct, as both B and C are correct statements.
Therefore, the correct option is (d) B and C only.
Revision Table: Key Stages of Spermatogenesis
| Stage | Ploidy | Chromosome Number (Human) | Division Type | Produces |
|---|---|---|---|---|
| Spermatogonia | Diploid (2n) | 46 | Mitosis | More Spermatogonia or Primary Spermatocytes |
| Primary Spermatocyte | Diploid (2n) | 46 | Meiosis I | Secondary Spermatocytes |
| Secondary Spermatocyte | Haploid (n) | 23 | Meiosis II | Spermatids |
| Spermatid | Haploid (n) | 23 | Differentiation (Spermiogenesis) | Spermatozoa (Sperm) |
Additional Information on Sperm Formation
Spermatogenesis is a continuous process occurring in the seminiferous tubules from puberty onwards. It ensures the production of haploid male gametes (spermatozoa) capable of fertilization.
- Spermiogenesis: This is the final phase where non-motile, round spermatids differentiate into motile spermatozoa with a head, neck, middle piece, and tail.
- Chromosome Number: The reduction in chromosome number from diploid (46) in spermatogonia and primary spermatocytes to haploid (23) in secondary spermatocytes, spermatids, and spermatozoa is crucial for maintaining the correct chromosome number in the offspring after fertilization. The ploidy level changes during Meiosis I, where homologous chromosomes separate, reducing the ploidy from 2n to n. Meiosis II separates sister chromatids, maintaining the haploid ploidy level but dividing the cell.
- Hormonal Regulation: Spermatogenesis is regulated by hormones like Gonadotropin-releasing hormone (GnRH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), and testosterone.
Important Questions from Human Reproduction
Arrange the following events chronologically as they occur during embryonic development:
- (A) Appearance of heart sounds
- (B) Development of limbs and digits
- (C) Formation of three primary germ layers
- (D) Separation of eyelids
Choose the correct answer from the options given below:
Which of the following hormone is generally not produced by the placenta?
In plants, continued self-pollination results in
Arrange the stages of oogenesis in order of their occurrence:
A. Formation of ovum & second polar body
B. Meiosis II begins but is held at Metaphase II
C. Meiosis I started but is held at Prophase I
D. Formation of primary oocyte from oogonia
E. Completion of Meiosis-I and formation of secondary oocyte and first polar body
Choose the correct answer from the options given below:
Signals of parturition originate from which of the following?
Human Placental Lactogen
Parturition hormone
Fully developed foetus
Placenta
