Unit 13 Human reproductive system and sexual maturation
Key unit competence: Analyse the structure, functions and processes of the human reproductive system in relation to the understanding of sex and gender.
Key ideas
- Sex is biological (male or female body, set by chromosomes and reproductive organs). Gender is the roles and behaviour a society expects of men and women; gender roles are learned, not decided by biology, and they can change.
- Male organs: two testes in the scrotum (kept cooler than body temperature) make sperm and the hormone testosterone; sperm mature and are stored in the epididymis; the sperm duct carries them to the urethra; the seminal vesicles, prostate gland and Cowper's glands add fluids with nutrients that help sperm swim; sperm plus fluids form semen; the penis transfers semen; the urethra also carries urine.
- Female organs: two ovaries make ova (eggs) and the hormones oestrogen and progesterone; each oviduct (Fallopian tube) carries the ovum, moved by cilia, and is the site of fertilisation; the uterus has muscular walls and a lining (endometrium) where the baby develops; the cervix is a ring of muscle at the neck of the uterus; the vagina receives the penis and is the birth canal; the external parts form the vulva.
- Gametogenesis: spermatogenesis in the seminiferous tubules of the testes produces millions of small, motile sperm continuously from puberty; oogenesis in the ovaries produces one large, non-motile ovum at a time, with stored food. Sperm have a head (nucleus, acrosome), middle piece (mitochondria) and tail.
- Sex determination: body cells have 23 pairs of chromosomes, including one pair of sex chromosomes: females XX, males XY. Every ovum carries an X; half of the sperm carry X and half carry Y. X sperm + ovum → girl (XX); Y sperm + ovum → boy (XY). So the father's sperm decides the sex, with a 50% chance of each.
- Puberty (about 9 to 16 years) is when the body becomes sexually mature. The pituitary gland releases FSH and LH, which make the testes produce testosterone and the ovaries produce oestrogen and progesterone. Changes in both: growth spurt, pubic and underarm hair, acne, strong emotions. Boys: voice deepens, beard, muscles grow, sperm production begins. Girls: breasts develop, hips widen, menstruation begins (menarche). Puberty starts at different ages for different people, and this is normal.
- The menstrual cycle lasts about 28 days (often 21 to 35). Menstrual phase (days 1 to 5): the endometrium is shed with blood. Follicular phase: an egg matures in a follicle and the lining rebuilds. Ovulation (about day 14): an egg is released into the oviduct. Luteal phase: the lining thickens further; if the egg is not fertilised, progesterone falls and menstruation starts again. Menopause (about 45 to 55 years) is when the cycles stop.
- Good menstrual hygiene: change pads regularly, wash daily, keep a calendar of periods; menstruation is a normal process, not a disease, and should never be a reason for shame or teasing. Culture, tradition and religion shape how people talk about sex and reproduction; schools and families can give accurate information respectfully.
Common misconceptions
- "Menstruation is a sickness." No: it is a normal part of the menstrual cycle when the uterus lining is shed.
- "The mother decides whether a baby is a boy or a girl." No: all ova carry X; the sperm (X or Y) decides.
- "All children start puberty at the same age." No: it can begin anywhere from about 9 to 16 years.
- "Fertilisation happens in the uterus." No: it normally takes place in the oviduct; the embryo then implants in the uterus.
Worked examples
Example 1. Explain why the testes are in the scrotum outside the body.
Solution
Sperm production needs a temperature slightly lower than body temperature (about 2 to 3 °C cooler). The scrotum keeps the testes outside the body cavity, where they stay cooler.
Example 2. A girl starts her period on 2 July and her cycle is 29 days long. When should her next period start, and about when will she ovulate?
Solution
Next period: 2 July + 29 days = 31 July. Ovulation happens about 14 days before the next period: about 17 July.
Practice questions
Name the parts of the male reproductive system and give one function of each.
Show answer
Testes: make sperm and testosterone. Scrotum: keeps testes cool. Epididymis: stores and matures sperm. Sperm duct: carries sperm. Seminal vesicles/prostate: add fluid with nutrients. Urethra: carries semen and urine. Penis: transfers semen.
Common mistake: Saying the bladder makes sperm.
Name the parts of the female reproductive system and give one function of each.
Show answer
Ovaries: make ova and oestrogen/progesterone. Oviducts: carry ova; site of fertilisation. Uterus: baby develops. Cervix: ring of muscle at the uterus neck. Vagina: receives the penis; birth canal.
Common mistake: Saying fertilisation happens in the ovary.
Explain how the sex of a baby is determined.
Show answer
Females are XX and make ova with X; males are XY and make sperm with X or Y. An X sperm with an ovum gives XX (girl); a Y sperm gives XY (boy). The father's sperm decides; each time the chance is 50%.
Common mistake: Saying the mother determines the sex.
List three changes in boys and three in girls during puberty.
Show answer
Boys: voice deepens, beard and body hair, muscles develop, sperm production begins. Girls: breasts develop, hips widen, menstruation begins, pubic hair.
Common mistake: Listing the same changes for both without the differences.
Describe the four phases of the menstrual cycle.
Show answer
Menstrual phase: lining shed with blood (days 1 to 5). Follicular phase: an egg matures, lining rebuilds. Ovulation: egg released (about day 14). Luteal phase: lining thickens; if no fertilisation, it breaks down and menstruation begins again.
Common mistake: Saying ovulation happens during menstruation.
Compare spermatogenesis and oogenesis in three ways.
Show answer
Sperm in testes, ova in ovaries; many small motile sperm vs one large non-motile ovum at a time; sperm production continues from puberty, ova are released about once a month until menopause.
Common mistake: Saying ova can swim.
Distinguish between sex and gender.
Show answer
Sex is the biological difference between male and female (chromosomes, organs). Gender is the roles and behaviour society expects; these are learned and can change.
Common mistake: Using the words as if they meant the same.
Give three ways a girl can keep good hygiene during menstruation.
Show answer
Change pads regularly; wash the body daily with clean water; dispose of used pads properly and wash hands; keep a calendar to be prepared.
Common mistake: Saying girls should stay away from school.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The hormone from the pituitary that triggers ovulation is: a. menopause 2. The male sex hormone is: b. LH 3. The main function of the scrotum is to: c. keep the testes cooler than the body 4. The stopping of menstrual cycles in older women is: d. testosterone Show answer
1 → b (LH) · 2 → d (testosterone) · 3 → c (keep the testes cooler than the body) · 4 → a (menopause)
- Luteinising hormone causes the follicle to release the egg.
- It causes male secondary sexual characteristics.
- Cooler testes produce sperm efficiently.
- It usually occurs between 45 and 55 years.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
sperm duct · sperm and gland fluids · oviduct · changes in hormone levels- Semen is made of .
- Moodiness during puberty is mainly due to .
- The tube that carries sperm from the testis to the urethra is the .
Show answer
1: sperm and gland fluids · 2: changes in hormone levels · 3: sperm duct
- Seminal vesicles and prostate add fluid.
- It is a normal part of development.
- Also called the vas deferens.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The hormone that causes female secondary sexual characteristics is: a. oestrogen 2. The first menstrual period in a girl's life is called: b. small and able to swim 3. Compared with an ovum, a sperm is: c. menarche 4. The male gonads that produce sperm are the: d. testes Show answer
1 → a (oestrogen) · 2 → c (menarche) · 3 → b (small and able to swim) · 4 → d (testes)
- It is made by the ovaries.
- It usually happens between 9 and 15 years.
- The ovum is large and non-motile.
- Testes also produce testosterone.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
a boy (XY) · XX · either, depending on the mother · ovulation- The sex chromosomes of a human female are .
- A sperm carrying a Y chromosome fertilises an ovum. The baby will be .
- Release of an egg from the ovary is called .
Show answer
1: XX · 2: a boy (XY) · 3: ovulation
- Males are XY.
- The ovum always gives an X.
- It happens about day 14 of a 28-day cycle.