Reproduction in plants and animals

• Asexual Reproduction


  Does not involve sex cells or fertilisation, only one parent is required, offspring are genetically identical to the parent and each other (clones)
• Advantages of asexual reproduction in crop plants


  • Good characteristics (high yield, disease-resistant, hardy) can be reproduced asexually so entire crop will show same characteristics
• Sexual Reproduction


  Fusion of nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell), offspring are genetically different from each other
• Gametes Definition


  Sex cells (sperm and ovum in animals, pollen nucleus and ovum in plants) with haploid nuclei (half the normal number of chromosomes)
• Zygote


  Fertilised egg cell with diploid nucleus (full number of chromosomes)
• Advantages of sexual reproduction in crop plants

  • Increases variation, may produce genetic variants better able to cope with changes
• Disadvantages of sexual reproduction in crop plants

  • Variation may lead to offspring less successful than parent plant
• Flowers are the reproductive organ of the plant
• Insect-pollinated flowers


  • Contain both male and female reproductive parts, produce pollen with male gamete nucleus, pollen transferred by insects
• Parts of a flower


  • Petals
  • Sepals
  • Stamens
  • Carpel
• Wind-pollinated flowers


  • Produce large amounts of small, lightweight pollen grains, no need for insect attraction
• Pollen from insect-pollinated flowers is larger, heavier and often has spikes/hooks

  pollen from wind-pollinated flowers is smaller and smoother
• Pollination


  Transfer of pollen from anther to stigma
• Fertilisation


  Fusion of pollen nucleus and ovum nucleus in ovule, forming zygote
• Pollen tube grows down style towards ovary, containing pollen nucleus that fuses with ovum nucleus
• Factors required for seed germination: water, oxygen, warmth
• Conditions tested for seed germination

  • Tube A: water, oxygen, warmth
  • Tube B: no water
  • Tube C: no oxygen
  • Tube D: low temperature
• Self-pollination


  • Pollen from a flower lands on its own stigma or another flower on the same plant, reduces genetic variation in offspring
• Cross-pollination


  • Pollen from one plant transferred to stigma of another plant of same species, increases genetic variation
• Female reproductive structures


  • Ovaries
  • Fallopian tubes
  • Uterus
  • Cervix
  • Vagina
• Fertilisation


  The fusion of the nuclei from a male gamete (sperm cell) and a female gamete (egg cell)
• Fertilisation occurs in the oviducts
• Gametes


  • Have adaptations to increase the chances of fertilisation and successful development of an embryo
• Pregnancy: Growth & Development of the Fetus

  1. Zygote travels towards the uterus

  2. Zygote divides to form an embryo

  3. Embryo embeds in uterus lining (implantation)

  4. Embryo grows and develops into a fetus

  5. Gestation period is 9 months
• The fetus in the uterus

  • Surrounded by an amniotic sac containing amniotic fluid
  • Umbilical cord joins fetus's blood supply to the placenta
• The Placenta & Umbilical Cord

  1. Fetus develops and grows by gaining nutrients from mother's blood

  2. Fetus's blood connects to and from the placenta by the umbilical cord

  3. Waste products removed from fetus's blood in the placenta

  4. Molecules move by diffusion across placenta

  5. Placenta acts as a barrier to toxins and pathogens

  6. Umbilical cord cut and tied off after birth

  7. Placenta detaches and is pushed out after birth
• It is worth learning at least two specific substances that move in either direction across the placenta
• Primary sexual characteristics

  Present during development in the uterus, differences in reproductive organs between males and females
• Secondary sexual characteristics


  Changes that occur during puberty as children become adolescents, controlled by release of hormones
• Some changes occur to both boys and girls, including growth of sexual organs and body hair. Emotional changes also occur due to increased hormone levels.
• The Menstrual Cycle

  1. Starts in early adolescence, controlled by hormones

  2. Ovulation occurs around day 14

  3. Failure to fertilise egg causes menstruation

  4. Menstruation lasts 5-7 days and signals start of next cycle

  5. Uterus lining thickens after menstruation in preparation for implantation
• FSH


  Follicle-stimulating hormone released by pituitary gland, causes egg to start maturing in ovary and stimulates ovaries to release oestrogen
• LH


  Luteinising hormone released by pituitary gland, causes ovulation and stimulates ovary to produce progesterone
• Oestrogen

  Causes growth and repair of uterus lining, inhibits production of FSH
• Progesterone


  Maintains thickness of uterus lining, prevents uterus lining from breaking down if pregnancy occurs
• Interaction between menstrual cycle hormones

  FSH stimulates follicle development, follicle produces oestrogen, high oestrogen triggers LH release causing ovulation, corpus luteum produces progesterone
• Where hormones involved in the menstrual cycle are made and act
• Sexually Transmitted Infections (STIs)

  Infections passed on through unprotected sexual intercourse and exchange of body fluids
• HIV


  Human Immunodeficiency Virus, can lead to development of AIDS
• How HIV affects the Immune System

  Infects lymphocytes, reduces number of lymphocytes and antibodies, decreases ability to fight infections, leads to AIDS