The menstrual cycle, fertilization and the embryo
Answers are for parents and teachers.
1
In one cycle the bleeding lasts 3 days, the egg-maturing stage 11 days and the corpus luteum stage 14 days. How long is the cycle, and on which day does ovulation occur?
3 + 11 + 14 = 28 days. Ovulation comes at the end of the egg-maturing stage: 3 + 11 = day 14.
2
In an invented cycle of 30 days the egg is released on day 16. How long does the corpus luteum stage last, and which two hormones does the corpus luteum make?
30 − 16 = 14 days. The corpus luteum makes oestrogen and progesterone.
3
A zygote divides and the number of cells doubles each time. After how many doublings are there 64 cells, and how many chromosomes does each cell hold?
2 × 2 × 2 × 2 × 2 × 2 = 64, so 6 doublings. Each cell holds the same 46 chromosomes as the zygote.
4
Name the three stages in the book’s plan of development, say how long each lasts, and give one development of the first stage.
The first, second and third stages, each of three months (3 × 3 = 9 months). In the first stage, for example, the nervous system and heart begin to form.
5
A friend says that smoking and alcohol only matter after a baby is born. Using the placenta, explain why this is wrong, and say whom a pregnant woman should ask.
The placenta lets alcohol and nicotine pass from the mother’s blood to the embryo, and they can cause serious harm before birth. A pregnant woman should ask her doctor.