plants 2-1

• Reproduction in plants


  The process by which plants can increase their numbers for the next generation. Plants have to reproduce in order to survive.
• Types of plant reproduction

  • Asexual (through vegetative means)
  • Sexual (involving male and female gametes)
• Asexual reproduction


  • The offspring are all genetically identical as this is clonal reproduction (propagation)
• Sexual reproduction


  • Advantage of increasing genetic diversity
• Vegetative propagation methods


  • From stems eg. strawberries that produce stolons
  • From tubers eg. axillary buds on potato tubers
  • From young shoots on banana plants called suckers
  • From stems as in roses

  
• Bananas have no seeds

  
• Pineapples grow by vegetative propagation

  
• Roses are propagated from stem cuttings
• Sexual reproduction - production of seeds

  1. Requires the fusion of male and female gametes to produce a zygote (embryo) followed by seed production

  2. Male gamete = pollen grains

  3. Female gamete = ovules

  4. Gametes are found in the flowers

  5. Transfer of male gamete to ovules initiates fertilization

  6. Male gametes produced in anthers

  7. Female gametes found in the ovary
• Pollination and fertilization


  1. The process of transfer of the male pollen to the female stigma (receptive part of the female flower) is called pollination

  2. Pollen can be transferred by wind or insects

  3. Insect pollinated flowers are attractive and produce nectar to reward the pollinators
• Alder produces lots of pollen
• Pollinators are endangered
• Fruit


  A plant structure that contains seeds
• Not all fruits have seeds eg. Bananas, strawberries, but they need pollination to form a fruit

  
• Coconut is a fruit with a large seed

  
• There are no seeds in corn kernels
• Each corn kernel comes from one ovule, fertilized by a pollen grain
• Fertilization in plants


  1. The pollen grain has 2 sperm nuclei

  2. The pollen grain germinates on the stigma and produces a germ tube

  3. The germ tube grows down the style

  4. When it reaches the ovary it seeks out the opening in the ovule called a micropyle

  5. One sperm nucleus fuses with the egg nucleus to form the zygote (2n)

  6. The second sperm nucleus fuses with the 2 polar nuclei to form the endosperm (3n) which is the food storage for the developing embryo

  7. This is called "double-fertilization"
• Development of zygote (embryo)

  1. The zygote divides several times to form an embryo

  2. The embryo differentiates to form a root and shoot apex

  3. The ovary expands and the wall becomes the seed coat

  4. Each fertilized ovule forms one seed

  5. Plants can have one seed eg. avocado, or multiple seeds eg. peas

  6. The ovary wall can also be fleshy eg. peach

  7. Each seed has one or two cotyledons depending on if it is a monocot or dicot plant species

  8. Seeds will germinate to form a root and shoot and the plant has now been propagated sexually
• Methods for plants to spread seeds far and wide

  • Make lots of seeds that spread by wind
  • Make seeds float on water
  • Make seeds spiny so they catch on to animals, humans
  • Make seeds aerodynamic
  • Make fruits attractive so seeds inside them are spread
  • Make fruits fleshy and attractive for animals to eat
• Pine trees produce male and female flowers (cones)

  
• Cottonwood trees disperse their seeds by wind in June