The Female Reproductive System

Hormone: Oestrogen. Source organ: Ovaries (developing follicles). Event: Oestrogen stimulates the proliferation of the endometrial lining of the uterus, preparing it for possible implantation of a fertilised egg.

Step 1: Understanding the assertion.
The embryo with 8 to 16 blastomeres is indeed called a morula. This stage follows after the fertilized egg divides multiple times and forms a solid ball of cells.

Step 2: Verifying the reason.
The reason given is also correct. After the morula forms, it continues to divide and transforms into the trophoblast, which is essential for the implantation of the embryo in the uterine wall.

Step 3: Conclusion.
Both the assertion and reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is (A).
Final Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

Step 1: Understanding the phases of the menstrual cycle.
The menstrual cycle in human females is divided into three phases: Phase I, Phase II, and Phase III. The phases are associated with different hormonal changes and physiological events in the body. The diagram shown represents the timeline of these phases.
Step 2: Analysis of options.

• (A) Primary follicle of ovary matures into Graafian follicle in phase II: Correct. In Phase II, the primary follicle matures into the Graafian follicle due to the action of hormones like FSH (follicle-stimulating hormone).
• (B) The hormone secreted in large amounts in phase III is also responsible for maintaining pregnancy in human females: Correct. In Phase III, progesterone is secreted by the corpus luteum, and this hormone is crucial for maintaining pregnancy.
• (C) Corpus luteum secretes progesterone in phase I, however it degenerates completely in phase III: Incorrect. The corpus luteum starts secreting progesterone in Phase II, not Phase I, and it degenerates if pregnancy does not occur, typically after Phase III.

Step 3: Conclusion.
Thus, the correct answer is (D) Both (A) and (B), as both statements are accurate in the context of the menstrual cycle.
Final Answer: Both (A) and (B).