Reproductive System & Reproductive Health

• Reproduction is the process by which living things make new individuals of their own kind.
• No organism lives forever, so reproduction keeps the species from dying out.
• Parents pass on a copy of their genes (instruction book) to offspring.
• The zygote is the single first cell of every new individual.
• The zygote is diploid – it has the full restored set of chromosomes.

Reproduction is the process by which living things make new individuals of their own kind.

No organism lives forever, so reproduction keeps the species from dying out.

Parents pass on a copy of their genes (instruction book) to offspring.

The zygote is the single first cell of every new individual.

The zygote is diploid – it has the full restored set of chromosomes.

• Asexual reproduction needs one parent and gives identical clones.
• Sexual reproduction needs two parents (male and female) and gives variation.
• Variation helps a species survive changing conditions.
• Each parent makes a sex cell called a gamete carrying half the chromosomes.
• Most higher animals, including humans, reproduce sexually.
• Parents — One — Two
• Offspring — Identical clones — Show variation
• Speed — Fast, simple — Slower
• Examples — Budding in Hydra, spores — Humans, most plants

Asexual reproduction needs one parent and gives identical clones.

Sexual reproduction needs two parents (male and female) and gives variation.

Variation helps a species survive changing conditions.

Each parent makes a sex cell called a gamete carrying half the chromosomes.

Most higher animals, including humans, reproduce sexually.

• A chromosome is a thread-like structure that carries the genes.
• A human body cell has 46 chromosomes arranged as 23 pairs.
• A cell with the full double set is diploid (2n).
• A cell with only half the set is haploid (n) – 23 in humans.
• Sperm and egg are haploid so that 23 + 23 = 46 at fertilisation.
• Diploid — 2n — 46
• Haploid — n — 23

A chromosome is a thread-like structure that carries the genes.

A human body cell has 46 chromosomes arranged as 23 pairs.

A cell with the full double set is diploid (2n).

A cell with only half the set is haploid (n) – 23 in humans.

Sperm and egg are haploid so that 23 + 23 = 46 at fertilisation.

• Mitosis makes two identical cells with the same number (46 to 46).
• Mitosis is used for growth, repair and asexual reproduction.
• Meiosis is a reduction division that halves the number (46 to 23).
• Meiosis produces the haploid gametes.
• Making gametes is gametogenesis: spermatogenesis (male), oogenesis (female).
• Mitosis — 46 to 46, identical — Body cells, growth
• Meiosis — 46 to 23, halved — Gametes

Mitosis makes two identical cells with the same number (46 to 46).

Mitosis is used for growth, repair and asexual reproduction.

Meiosis is a reduction division that halves the number (46 to 23).

Meiosis produces the haploid gametes.

Making gametes is gametogenesis: spermatogenesis (male), oogenesis (female).

• Homogametes (isogametes) look alike, e.g. in alga Ulothrix.
• Heterogametes look different: small motile male, large still female.
• Isogamy = fusion of two same-sized gametes (Spirogyra, Ulothrix).
• Anisogamy = fusion of two different-sized gametes (Eudorina).
• Oogamy = large non-moving egg fuses with small moving sperm (Volvox, humans).
• Isogamous — Same size — Spirogyra, Ulothrix
• Anisogamous — Different size — Eudorina
• Oogamous — Big egg + tiny sperm — Volvox, Fucus, human

Homogametes (isogametes) look alike, e.g. in alga Ulothrix.

Heterogametes look different: small motile male, large still female.

Isogamy = fusion of two same-sized gametes (Spirogyra, Ulothrix).

Anisogamy = fusion of two different-sized gametes (Eudorina).

Oogamy = large non-moving egg fuses with small moving sperm (Volvox, humans).

• Its two jobs are to make sperms and to deliver them into the female body.
• The testes are the primary male sex organs that make sperms and testosterone.
• Testes hang in a skin pouch, the scrotum, which keeps them cooler than body temperature.
• Sperms form inside coiled seminiferous tubules, supported by Sertoli (nurse) cells.
• The vas deferens carries sperms toward the urethra in the penis.
• Semen = sperms plus fluid from seminal vesicle, prostate and bulbourethral glands.

The testes are the primary male sex organs that make sperms and testosterone.

Testes hang in a skin pouch, the scrotum, which keeps them cooler than body temperature.

Sperms form inside coiled seminiferous tubules, supported by Sertoli (nurse) cells.

The vas deferens carries sperms toward the urethra in the penis.

Semen = sperms plus fluid from seminal vesicle, prostate and bulbourethral glands.

• Spermatogenesis happens in the seminiferous tubules from puberty onward.
• The diploid starting cell is the spermatogonium (46 chromosomes).
• A primary spermatocyte undergoes meiosis I to give two haploid secondary spermatocytes.
• One primary spermatocyte finally yields four haploid spermatids.
• Spermatids reshape into sperms by spermiogenesis, then are released by spermiation.
• A mature sperm has four parts: head, neck, middle piece and tail.
• Spermatogonium — 46 (2n) — 1
• Primary spermatocyte — 46 (2n) — 1
• Secondary spermatocyte — 23 (n) — 2
• Spermatid / Sperm — 23 (n) — 4

Spermatogenesis happens in the seminiferous tubules from puberty onward.

The diploid starting cell is the spermatogonium (46 chromosomes).

A primary spermatocyte undergoes meiosis I to give two haploid secondary spermatocytes.

One primary spermatocyte finally yields four haploid spermatids.

Spermatids reshape into sperms by spermiogenesis, then are released by spermiation.

• The ovaries are the primary female sex organs that make eggs and hormones.
• The fallopian tube (oviduct) carries the egg and is where fertilisation occurs.
• The uterus (womb) shelters and nourishes the developing baby.
• Oogenesis begins before birth and produces the egg (ovum).
• One primary oocyte gives only one ovum plus tiny polar bodies.
• Females normally release one egg per cycle (ovulation).
• Ovary — Makes eggs and hormones
• Fallopian tube — Site of fertilisation
• Uterus — Shelters the embryo
• Vagina — Receives sperms; birth canal

The ovaries are the primary female sex organs that make eggs and hormones.

The fallopian tube (oviduct) carries the egg and is where fertilisation occurs.

The uterus (womb) shelters and nourishes the developing baby.

Oogenesis begins before birth and produces the egg (ovum).

One primary oocyte gives only one ovum plus tiny polar bodies.

Females normally release one egg per cycle (ovulation).

• The menstrual cycle in human females repeats about every 28 days.
• Ovulation (release of the egg) occurs around day 14, mid-cycle.
• If no fertilisation occurs, the uterus lining sheds as menstruation (bleeding).
• Oestrogen and progesterone are the main female hormones controlling the cycle.
• The cycle starts at puberty (menarche) and ends near 45-50 (menopause).

The menstrual cycle in human females repeats about every 28 days.

Ovulation (release of the egg) occurs around day 14, mid-cycle.

If no fertilisation occurs, the uterus lining sheds as menstruation (bleeding).

Oestrogen and progesterone are the main female hormones controlling the cycle.

The cycle starts at puberty (menarche) and ends near 45-50 (menopause).

• Fertilisation is the fusion of one sperm with one egg, forming a zygote.
• In humans fertilisation occurs in the fallopian tube (oviduct).
• The zygote divides repeatedly to form an embryo that implants in the uterus.
• The placenta supplies the embryo with food and oxygen from the mother.
• Human pregnancy (gestation) lasts about nine months (280 days).
• Birth of the fully formed baby is called parturition.

Fertilisation is the fusion of one sperm with one egg, forming a zygote.

In humans fertilisation occurs in the fallopian tube (oviduct).

The zygote divides repeatedly to form an embryo that implants in the uterus.

The placenta supplies the embryo with food and oxygen from the mother.

Human pregnancy (gestation) lasts about nine months (280 days).

Birth of the fully formed baby is called parturition.

• The flower is the reproductive organ of a flowering plant.
• The stamen (anther + filament) is the male part making pollen grains.
• The pistil/carpel (stigma, style, ovary) is the female part holding ovules.
• Pollination is the transfer of pollen from the anther to the stigma.
• Self-pollination is within the same flower; crosspollination is between two flowers.
• Pollen reaching the ovule causes fertilisation, and the ovule becomes a seed.
• Anther — Stamen (male) — Makes pollen
• Stigma — Pistil (female) — Receives pollen
• Ovary — Pistil (female) — Holds ovules, becomes fruit

The flower is the reproductive organ of a flowering plant.

The stamen (anther + filament) is the male part making pollen grains.

The pistil/carpel (stigma, style, ovary) is the female part holding ovules.

Pollination is the transfer of pollen from the anther to the stigma.

Self-pollination is within the same flower; crosspollination is between two flowers.

Pollen reaching the ovule causes fertilisation, and the ovule becomes a seed.

• Puberty is when the body becomes capable of reproduction (about 10-14 years).
• Secondary sexual characters appear, e.g. facial hair in boys, breasts in girls.
• Testosterone (male) and oestrogen (female) drive these changes.
• Contraception (birth control) is used to prevent unwanted pregnancy.
• STDs like AIDS and syphilis spread through sexual contact.
• A balanced diet, hygiene and awareness support good reproductive health.

Puberty is when the body becomes capable of reproduction (about 10-14 years).

Secondary sexual characters appear, e.g. facial hair in boys, breasts in girls.

Testosterone (male) and oestrogen (female) drive these changes.

Contraception (birth control) is used to prevent unwanted pregnancy.

STDs like AIDS and syphilis spread through sexual contact.

A balanced diet, hygiene and awareness support good reproductive health.