Chapter summary
Reproduction in humans, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Sexual reproduction combines genetic information
What event forms a zygote, and why are offspring genetically varied?
Key idea and reminders
Sexual reproduction involves fusion of male and female gamete nuclei to form a zygote and produces genetically dissimilar offspring.
- Male gamete nucleus + female gamete nucleus -> zygote.
- Sexual reproduction produces genetically dissimilar offspring.
- Ovulation, fertilisation and later cell division are distinct events.
Keep in mind: A zygote forms after male and female gamete nuclei fuse. An unfertilised egg is still a gamete.
02
Trace the male reproductive system
Where are sperm made, and how do they leave the body?
Key idea and reminders
Testes produce sperm; sperm ducts carry them towards the urethra, where gland fluids contribute to semen.
- Testes produce sperm and testosterone.
- The scrotum holds the testes outside the main body cavity at a suitable lower temperature.
- Sperm ducts transport sperm; the prostate contributes fluid; the urethra passes through the penis.
Keep in mind: Sperm are produced in the testes. The prostate contributes fluid to semen.
03
Trace the female reproductive system
Where are eggs released, fertilised and supported after implantation?
Key idea and reminders
Ovaries release eggs; oviducts are the usual site of fertilisation; the uterus supports development after implantation.
- Ovaries produce eggs and the hormones oestrogen and progesterone.
- An oviduct carries the released egg towards the uterus.
- The cervix is the narrow neck of the uterus; the vagina opens to the outside.
Keep in mind: They have different roles: egg production and release, transport and usual fertilisation, then implantation and development.
04
The menstrual cycle
How do oestrogen and progesterone connect ovulation with preparation for implantation?
Key idea and reminders
Oestrogen rebuilds the lining; progesterone helps maintain it after ovulation. Falling levels allow menstruation if pregnancy is not established.
- Menstruation sheds uterine lining; ovulation releases an egg from an ovary.
- Oestrogen promotes repair and thickening of the lining; progesterone maintains it.
- Cycle length and ovulation timing vary. A calendar cannot guarantee an infertile day.
Keep in mind: Day 14 belongs to a simplified example. Timing varies, sperm can survive for several days, and the fertile phase extends around ovulation.
05
From fertilisation to implantation
Why are fertilisation and implantation different events in different places?
Key idea and reminders
Fertilisation normally occurs in an oviduct. The zygote divides into a ball of cells that travels to the uterus and implants in its lining.
- Fertilisation: gamete nuclei fuse, usually in an oviduct.
- Zygote -> repeated divisions -> ball of cells.
- Implantation: ball of cells embeds in the uterine lining.
Keep in mind: Fertilisation involves fusion of gamete nuclei. Implantation happens later when the developing ball of cells embeds in the uterine lining.
06
Explain HIV transmission accurately
Which route could transmit HIV, and which barrier interrupts it?
Key idea and reminders
HIV transmission requires particular body fluids and an entry route; ordinary social contact does not transmit it.
- Routes include sexual exposure, contaminated blood/injecting equipment, and transmission during pregnancy, birth or breastfeeding.
- Condoms, sterile equipment, screened blood and effective HIV treatment reduce transmission.
- HIV is not transmitted by hugging, sharing food or ordinary classroom contact.
Keep in mind: HIV needs specific exposure routes. It is not spread by ordinary social contact, and sustained undetectable viral load on treatment prevents sexual transmission.