reproduction in humans

• Asexual reproduction


  The production of two genetically identical offspring from one parent
• Advantage and disadvantage of asexual reproduction (Higher/Supplement)

  • Advantage - It produces lots of offspring quickly
  • Disadvantage - It does not introduce variation and so all offspring are susceptible to the same environmental pressures as the parents
• Sexual reproduction


  The production of two genetically different offspring from the fusion of the nuclei from two gametes
• Fertilisation


  The fusion of the nuclei from two gametes (sex cells)
• Gametes have haploid nuclei (23 chromosomes) whereas zygotes have diploid nuclei (23 pairs of chromosomes)
• Advantage and disadvantage of sexual reproduction (Higher/Supplement)

  • Advantage - It introduces variation
  • Disadvantage - It is slower and produces a limited amount of offspring
• Function of sepals in an insect pollinated plant


  The sepal is a hard coating that protects the developing flower in a bud
• Function of petals in an insect pollinated plant


  The petals attract the insects so that they can pollinate the plant
• Function of anthers in an insect pollinated plant

  The anthers contain the pollen sacs which contain the male sex cells of the plant
• Function of stigma in an insect pollinated plant

  These are the sticky parts of the plant designed to capture the pollen grains
• Function of ovaries in an insect pollinated plant

  They contain ovules which will grow into seeds when they are fertilised by pollen
• Pollen grain from insect pollinated plant

  It has spikes on it to make it sticky to be picked up by insects
• Pollen grain from wind pollinated plant


  It is smooth so that it can be carried by the wind easily
• Pollination


  Where pollen grains are transferred from the anthers to the stigma
• Self-pollination (Higher/Supplement)


  Where pollen grains are transferred from the anthers to the stigma of the same plant
• Cross-pollination (Higher/Supplement)


  Where pollen grains are transferred from the anthers of one plant to the stigma of another plant of the same species
• Advantage of self-pollination (Higher/Supplement)

  • There is a greater chance of fertilisation as it does not rely on pollinators
• Disadvantage of self-pollination (Higher/Supplement)

  • Genetic variation decreases and the plant is less able to adapt to the environment
• Advantage of cross-pollination (Higher/Supplement)

  • The plants are more able to adapt to environmental changes and there is increased genetic variation
• Disadvantage of cross-pollination (Higher/Supplement)

  • The plants are reliant on insect populations for fertilisation
• What happens when a pollen grain lands on the stigma of a plant (Higher/Supplement)

  1. A pollen tube grows through the style to reach the ovule in the ovary

  2. The nucleus from the pollen grain then travels down the pollen tube to reach the ovule
• Fertilisation


  When the nucleus of a pollen grain fuses with the nucleus of an ovule
• Environmental conditions that affect seed germination

  • Oxygen availability
  • Water availability
  • A suitable temperature
• Fertilisation


  The fusion of the nucleus of a male gamete with the nucleus of a female gamete
• Environmental conditions that affect seed germination

  • Oxygen availability
  • Water availability
  • A suitable temperature
• Functions of the testes

  • They produce hormones
  • They produce sperm
• Functions of the penis

  • Used as the male sex organ
  • Used as an excretory organ
• Functions of the male urethra


  • It allows urine to exit the body from the bladder
  • It is used during ejaculation to release semen
• Function of the scrotum


  It holds and protects the testes
• Function of the sperm duct

  It carries sperm from the testes to the urethra
• Function of the prostate gland

  It produces prostate fluid which combines with sperm cells to make sperm
• Functions of the ovaries


  • They produce eggs
  • They produce hormones
• Functions of the vagina

  • To receive the penis during intercourse
  • It is used as the birth canal during childbirth
• Function of the oviduct

  To create a passage between the ovary and the uterus for the egg to travel down
• Functions of the cervix

  • To allow menstrual blood to flow out of the vagina
  • To channel the sperm into the uterus
• Sperm cells are significantly smaller than egg cells
• Sperm cells are long and thin with a head and tail whereas egg cells are large and in the shape of a sphere or ovoid
• Sperm cells have large energy stores and a long tail to help them to move quickly, egg cells do not have this and so are relatively non-motile
• There are many more sperm cells than egg cells (up to 100 million sperm per millilitre of ejaculate)
• Adaptive features of sperm cells

  • Long flagellum
  • Contain enzymes