Q1. [4] medium exam-ready
Read the following passage and answer the questions that follow:
During the development of an embryo inside the mother's uterus, the embryo requires a constant supply of glucose and oxygen, and must also get rid of metabolic waste products. A specialised disc-like structure embedded in the uterine wall accomplishes this. On the embryo's side, this structure has finger-like projections that increase the surface area for exchange, while on the mother's side, there are spaces filled with blood that surround these projections. The entire development of the child inside the mother's body takes approximately nine months.
(i) Name the specialised disc-like structure described above and name the finger-like projections on the embryo's side. (1 mark)
(ii) How does the embryo receive glucose and oxygen through this structure, and how are waste products removed? (1 mark)
(iii) What is the term for the stage of development when the embryo attaches to the uterine wall? Describe one change the uterine lining undergoes to prepare for this. (1 mark)
(iv) If the egg is not fertilised, what event occurs approximately every month in the uterus? What does this event involve, and approximately how long does the complete cycle take? (1 mark)
Generated by claude-sonnet-4-6 · 2026-06-26 01:02 · grounding rag
Model Answer
(i) The specialised disc-like structure is the placenta. The finger-like projections on the embryo's side are called villi.
(ii) Glucose and oxygen pass from the mother's blood (in the blood spaces surrounding the villi) into the embryo's blood through the placenta's large surface area. Waste substances generated by the embryo are transferred back into the mother's blood through the placenta for removal.
(iii) The stage when the embryo attaches to the uterine wall is called implantation. The uterine lining becomes thick and spongy, and is richly supplied with blood to nourish the growing embryo.
(iv) Menstruation occurs. The thickened uterine lining breaks down and comes out through the vagina as blood and mucus. This cycle takes roughly one month (the bleeding itself lasts about two to eight days).
Source: Chapter 7, Sections 7.3.3(b) and 7.3.3(c)
---
Explanation
- Villi is the key term examiners expect for the finger-like projections; do not write "finger-like projections" as the answer.
- For (ii), make it clear that exchange happens across the placenta — direction matters (mother → embryo for nutrients; embryo → mother for waste).
- "Implantation" is the expected term for (iii); the lining change detail earns the mark.
- For (iv), name the event (menstruation), briefly describe what it involves (breakdown of lining as blood + mucus), and state the cycle duration — all three elements are needed for the mark.