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Reproduction In Plants & Humans

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Lesson notes

Asexual Reproduction

  • Asexual reproduction involves one parent, no gametes, no fertilisation.
  • Offspring are genetically identical to the parent (clones).
  • Examples: bacteria by binary fission; plants by bulbs, tubers, runners.
  • Advantages: rapid population growth, exploits suitable environments, energy-efficient.
  • Disadvantages: no genetic variation, vulnerable to disease/environmental change.

Binary fission in bacteria

Binary fission in bacteria

Sexual Reproduction & Gametes

  • Sexual reproduction involves fusion of male and female gamete nuclei to form a zygote.
  • Gametes have a haploid nucleus (half the chromosome number; in humans, 23).
  • The zygote has a diploid nucleus (full chromosome number; in humans, 46).
  • Fertilisation = fusion of gamete nuclei, producing genetically varied offspring.
  • Advantages: genetic variation helps adaptation; disadvantages: may produce less successful offspring.

Haploid and diploid cells

Haploid and diploid cells

Sexual Reproduction in Plants

  • Flowers are reproductive organs; male gametes in pollen grains, female in ovules.
  • Pollination = transfer of pollen from anther to stigma (not fertilisation).
  • Insect-pollinated flowers: large, bright petals, scent, nectar, sticky stigma, anthers inside.
  • Wind-pollinated flowers: small, dull petals, no scent/nectar, long filaments, feathery stigma.
  • After pollination, a pollen tube grows down the style; pollen nuclei fuse with ovum (fertilisation).
  • Seed germination requires water, oxygen, and warmth; carbon dioxide not needed.

Structure of an insect-pollinated flower

Structure of an insect-pollinated flower

Male Reproductive System (Human)

  • Testes produce sperm and testosterone; held in scrotum (temperature regulation).
  • Sperm duct carries sperm to urethra; prostate gland adds fluid to form semen.
  • Urethra runs through penis; carries urine or semen (muscle prevents mixing).
  • Penis deposits semen into vagina during intercourse.

The male reproductive system

The male reproductive system

Female Reproductive System (Human)

  • Ovaries produce ova (eggs) and oestrogen.
  • Oviduct (fallopian tube) is site of fertilisation; lined with cilia to move egg.
  • Uterus has thick lining for implantation; cervix is ring of muscle at lower end.
  • Vagina receives penis and sperm during intercourse.

The female reproductive system

The female reproductive system

Gametes & Fertilisation

  • Sperm adapted: flagellum (swim), mitochondria (energy), acrosome enzymes (penetrate egg).
  • Egg adapted: large cytoplasm (food store), jelly coat (prevents multiple sperm after fertilisation).
  • Fertilisation occurs in the oviduct; zygote divides to form embryo.
  • Embryo implants in uterus lining; becomes fetus after 12 weeks.

Fertilisation of the egg by a sperm

Fertilisation of the egg by a sperm

Pregnancy & Placenta

  • Placenta exchanges nutrients (glucose, amino acids, oxygen) and wastes (CO₂, urea) by diffusion.
  • Umbilical cord connects fetus to placenta; blood flows opposite directions, never mixing.
  • Placenta acts as barrier to some toxins/pathogens (but not all, e.g., nicotine).
  • Amniotic fluid cushions the fetus.

The fetus in the uterus

The fetus in the uterus

Sexual Hormones & Menstrual Cycle

  • Testosterone (testes) and oestrogen (ovaries) control secondary sexual characteristics.
  • Menstrual cycle (~28 days): FSH (pituitary) stimulates follicle growth and oestrogen release.
  • Oestrogen thickens uterus lining and triggers LH surge (pituitary) causing ovulation (day ~14).
  • After ovulation, progesterone from corpus luteum maintains lining; if no fertilisation, progesterone falls → menstruation.

Hormone levels during the menstrual cycle

Hormone levels during the menstrual cycle

Sexually Transmitted Infections (STIs)

  • STIs spread via exchange of body fluids during unprotected sex.
  • HIV (virus) infects lymphocytes, reducing immune function, leading to AIDS.
  • Spread controlled by: limiting partners, using condoms, testing, education.
  • Other STIs: chlamydia (bacterial, treatable with antibiotics).

How HIV affects lymphocytes

How HIV affects lymphocytes

Slides

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Practice questions

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  1. 1.Which of the following is a characteristic of asexual reproduction?

    Easy
    • AIt involves the fusion of male and female gametes.
    • BIt produces genetically identical offspring from one parent.
    • CIt increases genetic variation in offspring.
    • DIt requires two parents.
  2. 2.Which structure in a flower produces pollen grains?

    Easy
    • AStigma
    • BStyle
    • CAnther
    • DOvary
  3. 3.Which hormone is primarily responsible for the development of secondary sexual characteristics in males?

    Easy
    • AOestrogen
    • BProgesterone
    • CTestosterone
    • DFSH
  4. 4.Which of the following is an advantage of sexual reproduction over asexual reproduction?

    Easy
    • AOffspring are genetically identical to the parent.
    • BIt is faster and requires less energy.
    • CIt produces genetic variation in offspring.
    • DIt does not require a mate.
  5. 5.Which of the following correctly describes the function of the placenta?

    Easy
    • AIt produces oestrogen and progesterone.
    • BIt allows the exchange of nutrients and waste between mother and fetus.
    • CIt is the site of fertilisation.
    • DIt protects the fetus from all pathogens.
  6. 6.What is the role of luteinising hormone (LH) in the menstrual cycle?

    Medium
    • AIt stimulates the development of the follicle.
    • BIt causes ovulation and stimulates progesterone production.
    • CIt maintains the uterine lining.
    • DIt inhibits FSH release.
  7. 7.A student sets up an experiment to investigate conditions for germination. Four test tubes contain cress seeds on cotton wool. Tube A: dry cotton wool, 20°C; Tube B: moist cotton wool, 20°C; Tube C: moist cotton wool, 4°C; Tube D: moist cotton wool with a layer of oil on top, 20°C. Which tube would not germinate due to lack of oxygen?

    Medium
    • ATube A
    • BTube B
    • CTube C
    • DTube D
  8. 8.Which of the following statements about HIV is correct?

    Easy
    • AHIV is a bacterium that destroys red blood cells.
    • BHIV infects lymphocytes, reducing the body's ability to fight infections.
    • CHIV can be cured with antibiotics.
    • DHIV is only transmitted through sexual contact.

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