Section 3: Reproduction and inheritance

• SEXUAL REPRODUCTION

  Fertilisation of two sex cells (one gamete from each parent) produced by Meiosis to form a zygote which will develop into non-identical offspring

  ADVANTAGES

  Increases variation

  Offspring can adapt to new environment

  Susceptible to diseases due to variation (less harmful to population)

  DISADVANTAGES

  Time-consuming to find mating partnerNot possible for isolated members
• ASEXUAL REPRODUCTION

  Reproduction by a single parent to produce genetically identical offspring (clones) via Mitosis

  ADVANTAGES

  Rapid increase in populationThrive in suitable environment

  DISADVANTAGES

  Decreases variation

  Vulnerable to change in environment due to inadaptability Less susceptible to diseases due to decreased variation (more harmful to population)
• FERTILISATION

  Fusion of haploid gamete to produce diploid zygote that undergoes Mitosis to develop into an Embryo

  EXPLANATION:

  • An Egg Cell and Sperm Cell are haploid gametes, containing 23 chromosomes (half of the 46 chromosomes in a Zygote)
  • Due to this, reproducing requires the fusion of two haploid gametes via fertilisation to form a diploid Zygote containing 46 chromosomes (half from each parent)
  • As diploid Zygote carries a mixture of genetic information from both parents, Zygote will undergo Mitosis to develop into an embryo exhibiting genetic variation

  
• SEPALS: Leaf-shaped structure on the outermost part of flower that protects unopened flower
• PETALS: Brightly coloured leaves surrounding the reproductive part of flower to attract pollinators (e.g, insects)
• STAMENS: Male part of the Flower composed of the Filament and Anther
• FILAMENT: Slender stalk supporting the Anther to make it accessible to pollinators (e.g, insects)
• ANTERS: Lobes on top of the Filament that produces the male gamete of flowering plant - Pollen
• PISTILS: Female part of the Flower composed of the Stigma, Style, Ovule
• STIGMA: Sticky, receptive tip of the Pistil that is responsible for catching Pollen
• STYLE: Tube-shaped connection between Stigma and Ovule that elevates Stigma to catch Pollen
• OVULE: Structure that contains female reproductive cells which develops into Seed after fertilisation
• Insect Pollinated Flower is a Flower that distributes Pollen via Insects.
• Petals of an Insect Pollinated Flower are large and brightly-coloured to attract Insect pollinators.
• Nectar of an Insect Pollinated Flower is scented to attract Insect pollinators.
• An Insect Pollinated Flower has a moderate amount of Pollen grains due to insects being efficient pollinators.
• Pollen grains of an Insect Pollinated Flower are Sticky and spiky to attach to Insects.
• Anthers of an Insect Pollinated Flower that produce Pollen are stiff and firmly attached to Filaments inside of Flower to brush against Insects.
• Stigma of an Insect Pollinated Flower is sticky and inside the Flower to catch Pollen when brushed against Insects.
• A Wind Pollinated Flower is a Flower that distributes Pollen via Wind.
• Petals of a Wind Pollinated Flower are small and dull, usually green or brown, as they do not need to attract insects.
• Nectar of a Wind Pollinated Flower is not scented, as it does not need to attract insects.
• A Wind Pollinated Flower has large amounts of Pollen to increase the chances of pollination.
• Pollen grains of a Wind Pollinated Flower are smooth and light, making them easy to be carried by wind.
• Anthers of a Wind Pollinated Flower that produce Pollen are loosely attached to long Filaments outside of the Flower to easily release Pollen via wind.
• Stigma of a Wind Pollinated Flower is feathery and outside the Flower to catch drifting Pollen grains.
• GERMINATION


  Process by which Seed emerges from period of dormancy and begins to sprout
• CONDITIONS NEEDED FOR SEED GERMINATION

  WATER

  Water is needed to metabolically activate enzymes to break down food reserves of Starch into Glucose (source of energy for growth)

  OXYGEN

  Oxygen is needed for aerobic respiration to produce energy in the form of ATP for growth

  WARMTH

  Optimum temperature is needed for optimal enzyme activity to facilitate survival and growth of Seed
• Cotton wool is placed at the bottom of four boiling tubes, each containing five Cress Seeds.
• Each test tube is individually set up: Test Tube A: moist cotton wool and placed in warm environment (hot water bath set at appropriate temperature), Test Tube B: dry cotton wool and placed in warm environment (hot water bath set at appropriate temperature), Test Tube C: moist cotton wool and is placed in cold environment (bucket of ice), Test Tube D: cotton wool soaked in boiled Water that is cooled off, and layered with Oil on top.
• After all test tubes are set up, Cress Seeds in each respective test tube is allowed to adjust to new environment for a fixed number of days.
• After a fixed number of days has passed, results are compared via: Number of Cress Seeds germinated and Height of Germinated Seed.
• Test tube A - Control (All factors present) - yes, Test tube B - Water - No, Test tube C - Temperature - No, Test tube D - Oxygen - No.
• SEED AND FRUIT FORMATION

  EXPLANATION:

  • Pollination involves the transfer of Pollen grain from an Anther (male plant structure) to a Stigma (female plant structure)
  • Hence, when Pollen grain lands on Stigma, this causes a Pollen tube to grow down the Style until it reaches an Ovule within the Ovary
  • This allows the Nucleus of Pollen grain to pass along the Pollen tube to fuse with Nucleus of Ovule via fertilisation
  • As a result, Ovule will form a Seed, while Ovule wall forms the Seed coat, and the rest of Carpel will develop into a Fruit to carry the Seed

  
• RUNNER (NATURAL)


  • In Runners, cells split off from parent plant to grow side branches that forms Plantlets, specialising into root hair cells
  • As a result, Plantlets will grow roots and plant will evolve, forming plant that is genetically identical to parent plant via asexual reproduction (clone)

  
• CUTTINGS (ARTIFICIAL)

  • In Cuttings, specific plant tissue (typically undifferentiated shoot) is selected from stock plant and sterilised
  • Tissue sample is then explanted and grown in petri dish containing sterile nutrient agar gel
  • Explant is treated with growth hormones (auxins) to stimulate Shoot and Root development
  • As a result, growing Shoot can be continuously divided and separated to form new samples
  • Once Root and Shoot are developed, the cloned plant is then transferred to Soil

  
• Germination is the process by which a seed emerges from a period of dormancy and begins to sprout
• Testa is the tough outer seed coat that protects the embryonic plant
• Micropyle is a small pore in the outer covering of the seed that allows the passage of water via osmosis
• Cotyledon contains food stores of starch for the seed and forms the embryonic leaves