Reproduction

Male Reproductive System

Structures and functions:

• Testes (in scrotum): produce sperm (by meiosis) and testosterone
• Epididymis: stores and matures sperm
• Vas deferens: tube carrying sperm from epididymis to urethra
• Seminal vesicle: produces fructose-rich fluid to nourish sperm
• Prostate gland: produces alkaline fluid to neutralise vaginal acidity
• Urethra: shared tube for urine and semen
• Penis: delivers sperm during intercourse. Glans: head of penis. Foreskin: covering of glans

Female Reproductive System

• Ovaries: produce eggs (by meiosis) and hormones (oestrogen, progesterone)
• Fallopian tubes (oviducts): where fertilisation occurs; transport egg to uterus via cilia and peristalsis
• Uterus: muscular organ where the embryo implants and develops. Lined by the endometrium
• Cervix: narrow opening between uterus and vagina
• Vagina: birth canal and receives sperm
• Vulva: external genitalia. Labia: protective folds. Clitoris: sensory organ

The Menstrual Cycle (28 days)

1. Menstruation (days 1–5): uterus lining (endometrium) breaks down and is shed
2. Follicular phase (days 1–13): FSH from pituitary stimulates follicle development in ovary. The growing follicle produces oestrogen, which rebuilds the endometrium
3. Ovulation (day 14): surge of LH triggers release of a mature egg from the Graafian follicle
4. Luteal phase (days 15–28): the empty follicle becomes the corpus luteum, which produces progesterone to maintain the endometrium. If no fertilisation → corpus luteum degenerates → progesterone drops → menstruation begins

Pregnancy

Fertilisation → zygote → morula (ball of cells) → blastocyst (hollow ball, implants in endometrium ~day 7) → germ layers form → embryo (weeks 3–8) → foetus (week 9 to birth)

The placenta forms to allow exchange of O₂, nutrients, and waste between mother and foetus. It also produces hormones (progesterone, oestrogen) to maintain pregnancy.

Labour and birth: Oxytocin from pituitary stimulates uterine contractions. Positive feedback loop intensifies contractions until delivery.

Hormonal Control of Reproduction

Hormone	Source	Role
FSH	Pituitary	Stimulates follicle development (female) and sperm production (male)
LH	Pituitary	Triggers ovulation; stimulates corpus luteum
Oestrogen	Ovaries	Rebuilds endometrium; female secondary characteristics
Progesterone	Corpus luteum/placenta	Maintains endometrium; supports pregnancy
Testosterone	Testes	Sperm production; male secondary characteristics
Oxytocin	Pituitary	Stimulates uterine contractions during labour
Prolactin	Pituitary	Stimulates milk production (lactation)

Contraception & Fertility

Contraception methods:

• Natural: rhythm method, withdrawal (less reliable)
• Mechanical: condoms, diaphragm, IUD
• Chemical: contraceptive pill (oestrogen + progesterone prevents ovulation), morning-after pill
• Surgical: vasectomy (males), tubal ligation (females)

Infertility treatments: stimulating ovulation (fertility drugs), artificial insemination (AI), in vitro fertilisation (IVF), intracytoplasmic sperm injection (ICSI), egg freezing.

Screening: antenatal screening (ultrasound, blood tests), genetic screening (e.g. for Down syndrome), postnatal screening (e.g. heel prick test for PKU).

Flower Structure

Flowers contain the reproductive organs of flowering plants:

Part	Function
Sepals	Protect the flower bud before it opens
Petals	Attract pollinators (insects) - often brightly coloured
Stamen (male)	Anther produces pollen; filament supports the anther
Carpel (female)	Stigma receives pollen; style connects to ovary containing ovules
Receptacle	Base of flower that supports all parts

Pollination

Transfer of pollen from anther to stigma.

Feature	Insect-Pollinated	Wind-Pollinated
Petals	Large, colourful, scented	Small, dull, no scent
Nectar	Present (attracts insects)	Absent
Pollen	Sticky, spiky (adheres to insects)	Lightweight, smooth, abundant
Stigma	Sticky, inside flower	Feathery, hangs outside (catches wind-blown pollen)
Anthers	Inside flower	Dangling outside (pollen disperses in wind)

Seed Structure

• Testa: tough outer seed coat - protects embryo
• Embryo: the young plant, consisting of:
  • Radicle: embryonic root (first to emerge during germination)
  • Plumule: embryonic shoot (grows upward toward light)
• Endosperm: food store for the developing embryo

Seeds produce growth regulators that stimulate growth of fruit tissues around them.

Fruit & Seed Dispersal

Seeds/fruits must be dispersed away from the parent plant to reduce competition:

• Wind: light seeds with wings/parachutes (e.g. dandelion, sycamore)
• Water: waterproof shells, air pockets for buoyancy (e.g. coconut)
• Animal (external): hooks or burrs that attach to fur (e.g. burdock)
• Animal (internal): fleshy fruits eaten, seeds pass through digestive system (e.g. blackberry)

Before birth

Ultrasound uses high-frequency sound waves to produce an image of the fetus, confirming the due date, checking growth and the position of the placenta, and detecting some abnormalities. It is non-invasive and carries no known risk.

Blood screening checks the mother's blood group and rhesus factor, immunity to rubella, and levels of markers that indicate raised risk of certain conditions. Anti-D injections prevent rhesus disease in later pregnancies.

Amniocentesis samples amniotic fluid containing fetal cells so chromosomes can be examined, for example to detect Down syndrome; chorionic villus sampling does the same earlier using placental tissue. Both are invasive and carry a small risk of miscarriage, so they are offered where the risk is judged high.

Non-invasive prenatal testing analyses fragments of fetal DNA in a sample of the mother's blood, giving genetic information with no risk to the pregnancy. Fetal monitoring during labour tracks the baby's heart rate, and fetal surgery can now correct some conditions before birth.

After birth

The heel prick test in the first days of life screens for conditions such as phenylketonuria, cystic fibrosis and congenital hypothyroidism, where early treatment prevents serious harm. Newborn hearing screening allows early intervention for language development.

Neonatal intensive care uses incubators for warmth, ventilators and surfactant for immature lungs, and monitored feeding, so babies born as early as 24 weeks can now survive. Vaccination programmes, developmental checks and public health nurse visits continue the care at home.

Issues to consider

These technologies improve outcomes but raise questions about the small risk of invasive tests, informed consent, and the decisions parents face after a diagnosis. Access and cost also differ between countries.

Infertility is the inability to conceive after a year of trying. It affects roughly one couple in six, and the cause lies with either partner about equally often.

Causes

In males: low sperm number, poor sperm motility or abnormal sperm shape, or blocked tubes. In females: failure to ovulate (often hormonal, as in polycystic ovary syndrome), blocked fallopian tubes, endometriosis, or a hostile uterine environment. Age matters for both, and egg number and quality fall sharply after the mid-thirties.

Treatments

• Hormone treatment to stimulate ovulation: drugs increase FSH activity so follicles develop and an egg is released. Risk: multiple births.
• Artificial insemination (AI): sperm from the partner or a donor is placed directly into the uterus. Used for low sperm count or where the cervix blocks sperm.
• In vitro fertilisation (IVF): ovulation is stimulated, eggs are collected, mixed with sperm in a dish, and one or two healthy embryos are transferred to the uterus. Used mainly for blocked fallopian tubes.
• ICSI (intracytoplasmic sperm injection): a single sperm is injected directly into an egg. Used for severe male-factor infertility where sperm cannot penetrate the egg.
• Egg and sperm freezing: gametes are stored in liquid nitrogen, allowing people to preserve fertility before cancer treatment or to postpone childbearing.
• Surrogacy and donor gametes where the uterus or gametes cannot be used.

Biological and ethical implications

Treatments are expensive and emotionally demanding, success rates fall with age, hormone stimulation carries health risks, multiple pregnancies are riskier for mother and babies, and decisions about spare embryos, donor anonymity and surrogacy raise real ethical questions. Screening embryos for genetic disease before implantation helps prevent serious conditions but raises concerns about selection.

Controlling fertility

Methods are grouped as natural (avoiding intercourse near ovulation, tracked by temperature and cycle length), mechanical (condom, diaphragm, IUD; the condom is the only method that also reduces the transmission of sexually transmitted infections), chemical (the contraceptive pill, implant or injection, which supply hormones that prevent ovulation and/or thicken cervical mucus, depending on the formulation), and surgical (vasectomy or tubal ligation, effectively permanent). Each differs in reliability, reversibility, side effects and acceptability, and people choose based on health, circumstances and personal or religious beliefs.

The reproductive hormones form a feedback loop: the hypothalamus releases GnRH, which makes the pituitary release FSH and LH, which act on the ovaries or testes, whose own hormones then feed back to switch the pituitary up or down.

In females: the menstrual cycle as a feedback system

1. FSH stimulates a follicle to grow; the follicle secretes oestrogen.
2. Rising oestrogen rebuilds the endometrium and, at high level, triggers a surge of LH (positive feedback).
3. The LH surge causes ovulation and converts the empty follicle into the corpus luteum.
4. The corpus luteum secretes progesterone, which maintains the endometrium and inhibits FSH and LH (negative feedback), so no new follicle develops.
5. If there is no pregnancy the corpus luteum breaks down, progesterone falls, the lining is shed, and the inhibition is removed so FSH rises again.

In males: a steadier version of the same loop

FSH stimulates sperm production in the seminiferous tubules and LH stimulates the interstitial cells to secrete testosterone. Testosterone maintains sperm production and male secondary sexual characteristics, and exerts negative feedback on the pituitary. Because there is no cyclical ovulation, hormone levels stay fairly constant and sperm are produced continuously from puberty onwards.

Pregnancy, birth and lactation

If fertilisation occurs, the embryo implants in the endometrium and the placenta takes over hormone production, keeping progesterone high so the lining is maintained. At birth, oxytocin from the pituitary drives uterine contractions in a positive feedback loop: contractions push the baby against the cervix, which stimulates more oxytocin, until delivery. After birth prolactin stimulates milk production, while oxytocin causes milk release when the baby suckles.

The reproductive lifespan

Puberty begins when the hypothalamus starts releasing GnRH, switching on FSH and LH. In females the cycle ends at the menopause (typically around age 45-55), when the ovaries stop responding to FSH and LH: oestrogen and progesterone fall, ovulation and menstruation stop, and the falling oestrogen causes symptoms such as hot flushes and bone thinning. Males have no sharp cut-off, though testosterone and sperm quality decline gradually with age.