Biology • Year 12 • Module 5 • Lesson 4
Mammalian Reproduction — Fertilisation, Implantation, Pregnancy and Birth
Lock in the anatomy, sequence and hormone vocabulary that describes how a mammalian zygote becomes a newborn.
1. Label the journey from oviduct to uterus
The diagram below shows the female reproductive tract during the first week after fertilisation in a placental mammal. Write the missing labels into boxes A–H. Each label is taken from the lesson's Key Terms or Cards 1–2. 8 marks
- A — tube where ovum travels _______________________
- B — site where sperm + egg fuse _______________________
- C — hollow ball of cells (stage name) _______________________
- D — process of repeated mitosis _______________________
- E — thickened uterine lining _______________________
- F — name of event at the wall _______________________
- G — hormone produced after implantation _______________________
- H — zygote chromosome number _______________________
| Box | Your label |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: zygote, blastocyst, implantation, placenta, embryo, fetus, oxytocin, prolactin, hCG, progesterone. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | A hollow ball of cells formed after repeated mitotic division, which is ready to embed in the uterine lining. | |
| 2.2 | An organ formed from both maternal and embryonic tissues that allows exchange of gases, nutrients and wastes without mixing blood directly. | |
| 2.3 | The hormone produced after implantation that helps maintain progesterone support in early pregnancy. | |
| 2.4 | The embedding of the blastocyst into the uterine wall. | |
| 2.5 | The diploid cell formed when a sperm nucleus fuses with an egg nucleus in the oviduct. | |
| 2.6 | The hormone that maintains the uterine lining (endometrium) so that pregnancy can continue after implantation. | |
| 2.7 | The hormone that stimulates uterine contractions during labour and also contributes to milk ejection after birth. | |
| 2.8 | The earlier developmental stage of the offspring in which major organs and the body plan begin forming. | |
| 2.9 | The later developmental stage of the offspring in which growth and maturation of formed organs dominate. | |
| 2.10 | The hormone that stimulates milk production by the mammary glands after birth. |
3. Function recall
Answer each question in 1–2 sentences. Use precise biological language from the lesson. 10 marks (2 each)
3.1 What is the function of the acrosome of a mammalian sperm cell?
3.2 What is the function of the many mitochondria in the midpiece of a sperm cell?
3.3 What is the function of the nutrient-rich cytoplasm of the egg cell?
3.4 What is the function of the placenta during pregnancy?
3.5 What is the function of oxytocin at birth and immediately after birth?
4. Cloze paragraph — the mammalian reproductive timeline
Fill each blank with one term from the word bank below. Each term is used once. 10 marks
Word bank: oviduct · diploid · blastocyst · uterine lining · placenta · progesterone · hCG · oxytocin · prolactin · fetus
In mammals, fertilisation usually occurs in the (4.1) when a haploid sperm fuses with a haploid egg. The resulting zygote is (4.2) , having restored the species' normal chromosome number. Repeated mitotic divisions during cleavage produce a hollow ball of cells called a (4.3) , which travels into the uterus and embeds in the (4.4) during implantation.
After implantation, the embryonic tissues release (4.5) , which helps maintain hormonal support for the uterine lining. As development continues, the (4.6) forms from both maternal and embryonic tissues and becomes the site of exchange of gases, nutrients and wastes. (4.7) is the dominant hormone that keeps the endometrium suitable for the developing embryo throughout pregnancy. Once major organ systems are established, the developing offspring is called a (4.8) .
At the end of pregnancy, (4.9) stimulates rhythmic uterine contractions that drive labour. After birth, (4.10) stimulates milk production by the mammary glands, while oxytocin also contributes to milk ejection during feeding.
Q1 — Labelled diagram
A: oviduct (also accept fallopian tube / uterine tube). B: site of fertilisation — the upper part of the oviduct where sperm meets egg. C: blastocyst. D: cleavage (repeated mitotic division of the zygote). E: uterine lining / endometrium. F: implantation. G: hCG (human chorionic gonadotrophin) — released after implantation. H: diploid (2n).
Q2 — Term–definition matches
2.1 blastocyst • 2.2 placenta • 2.3 hCG • 2.4 implantation • 2.5 zygote • 2.6 progesterone • 2.7 oxytocin • 2.8 embryo • 2.9 fetus • 2.10 prolactin.
Q3.1 — Function of the acrosome
The acrosome is a cap-like structure at the head of the sperm containing digestive enzymes. These enzymes break down the protective layers around the egg, allowing the sperm head to penetrate the egg membrane so the nuclei can fuse.
Q3.2 — Function of midpiece mitochondria
The mitochondria in the midpiece carry out aerobic respiration to supply ATP. This ATP powers the beating of the flagellum, providing the energy the sperm needs to swim from the cervix up through the uterus to the oviduct.
Q3.3 — Function of egg cytoplasm
The nutrient-rich cytoplasm provides energy stores, organelles and structural material that the zygote and early embryo use during cleavage. Mammalian embryos rely on these maternal stores until implantation establishes nutrient supply from the placenta.
Q3.4 — Function of the placenta
The placenta is the exchange organ between maternal and fetal blood systems. Oxygen and nutrients diffuse from mother to fetus and carbon dioxide and other wastes pass in the opposite direction without direct mixing of blood, and the placenta also secretes hormones that help maintain pregnancy.
Q3.5 — Function of oxytocin
During labour, oxytocin stimulates strong rhythmic contractions of the smooth muscle of the uterus that push the fetus through the cervix. After birth, oxytocin also triggers milk ejection (the let-down reflex) from the mammary glands in response to suckling.
Q4 — Cloze paragraph answers
4.1 oviduct • 4.2 diploid • 4.3 blastocyst • 4.4 uterine lining • 4.5 hCG • 4.6 placenta • 4.7 progesterone • 4.8 fetus • 4.9 oxytocin • 4.10 prolactin.