Reproduction in Plants

• Types of reproduction


  • Sexual reproduction
  • Asexual reproduction
• Sexual reproduction


  • Involves 2 parents
  • Involves gametes from both parents that fuse together
  • Meiosis is needed for production of gametes
  • Produce genetically different offspring
  • Show variation
  • Slower
  • Produce fewer number of offspring
• Asexual reproduction


  • Involves 1 parent
  • No gametes so no meiosis, only mitosis is involved
  • Produce genetically identical offspring
  • Showing no variation
  • Faster
  • Produce larger number of offspring
• Examples of asexual reproduction

  • Bacteria
  • Potato tuber
  • Multicellular fungi
• Asexual reproduction in bacteria

  1. DNA replicates

  2. Cell size increases

  3. Cell starts to divide

  4. Producing two genetically identical daughter cells
• Asexual reproduction in potato tuber

  1. Potato has buds

  2. Buds divide by mitosis

  3. Grow a shoot, part of which is aerial shoot and another part underground

  4. Aerial shoot develops leaves

  5. Leaves carry photosynthesis

  6. Producing glucose

  7. Glucose condenses into sucrose

  8. Sucrose translocated through phloem

  9. To the tips of the underground shoot

  10. To swell and be stored as starch

  11. Forming a new potato tuber

  
• Asexual reproduction in multicellular fungi

  1. Spore grows feeding hyphae

  2. Release extracellular enzymes to break down large food substances

  3. Absorb the food substances (glucose) by feeding hyphae to be used as a source of energy from respiration

  4. Grow aerial hyphae

  5. Carry sporangium in which cells divide by mitosis

  6. Produce more spores

  7. Sporangium will rupture so spores released to be carried away by air

  8. Falling on another food source

  
• Stigma

  Surface that receives the pollen grain, produces nutritive substances to help pollen grain develop into pollen tube
• Style

  Holds the stigma and allows the passage of pollen tube
• Ovary


  Contains ovules that contain female nucleus
• Micropyle


  Small opening in the ovule allowing the male gamete/nucleus to enter the ovule for fertilisation
• Anther


  Produces pollen grains that contain male nucleus/gamete
• Filament


  Holds the anther to deliver/release the pollen grains for pollination
• Nectary gland

  Found at the base below the ovary, secretes the sugary fluid to attract pollinators
• Sepals


  Green, protect the flower when it's a bud
• Petals


  Large coloured leaves that attract pollinators (insects) and protect the reproductive organs
• Advantages of sexual reproduction

  • Variation (due to meiosis, fertilisation and mutation)
  • Allow adaptation to new environmental conditions
  • Allowing selection and evolution
  • Reduce competition, increasing survival chance
  • Increase gene pool and maintain biodiversity
  • Reducing chance of extinction
  • Less chance for genetic diseases to be inherited
• Disadvantages of sexual reproduction

  • Slower
  • Produce fewer number of offspring
  • Needs 2 parents
  • Wastage of gametes (sperm, pollen grains)
  • Parents have favorable characteristic, less chance to be inherited
• Advantages of asexual reproduction

  • Faster
  • Produce more offspring
  • Needs only one parent
  • Less energy wastage
  • Parents have favorable characteristic, more chance for the offspring to be well adapted
• Disadvantages of asexual reproduction

  • No/less variation (mutation is the only source of variation)
  • Allow less adaptation to new environmental conditions
  • Less selection and evolution
  • More competition, decreasing survival chance
  • Decrease gene pool and biodiversity
  • Increase risk of extinction
  • More chance for genetic diseases to be inherited
• Importance of variation

  • To allow adaptation to new environmental conditions such as climate change, predation, introducing new species, change in food source
  • Allows selection and evolution
  • Reduce competition, so increasing survival chance and reduce risk of extinction
  • Increase in gene pool so increase in genetic diversity so increase/maintain in biodiversity
• Types of pollination


  • Self-pollination
  • Cross-pollination
• Self-pollination


  Occurs in bisexual flower, transfer of pollen grain from anther of a flower to the stigma of the same flower or in same plant
• Implications of self-pollination


  • Less variation, offspring become more homozygous
  • Variation due to mutation has lower chance to be expressed
  • Less adaptation to new environmental conditions, less selection and evolution
  • Increase competition, thus decrease survival chance
  • Less gene pool and genetic diversity, so increase risk of extinction
  • If there is a disease, it will be more frequently inherited
• Advantages of self-pollination


  • Doesn't rely on pollinators
  • No wastage of gametes
  • Offspring will be well adapted to conditions near parents
• Cross-pollination


  Occurs in bisexual or unisexual, transfer of the pollen grain from anther of a flower to the stigma of another flower on another plant but of same species
• Implications of cross-pollination


  • More variation, offspring will become more heterozygous
  • Variation due to mutation has higher chance to be expressed
  • More adaptation to new environmental conditions, more selection and evolution, decrease in competition, increase survival chance, increase gene pool and genetic diversity, reduce risk of extinction
  • Diseases are less frequently inherited
• Disadvantages of cross-pollination


  • Rely on pollinators
  • Wastage of gametes
  • Less chance for the offspring to inherit favorable characteristic from parents
• Characteristics of wind pollination

  • Petals are small/with dull colors and no guide lines
  • Nectary gland is absent
  • Stigma is feather with large surface area to trap pollen grains from air
  • Stamen are hanging/dangling outside the petals for the wind to carry pollen grain easily
• Characteristics of insect pollination

  • Larger colored petals with nectary guide lines
  • Scented
  • Have nectary gland
  • Stamen and stigma are enclosed inside the petals
  • Stigma with sticky surface
• Characteristics of pollen grains

  • Larger in size, sticky
  • Smaller in size, lighter and dry pollen grains
• Characteristics of pollen grains (number)

  • Larger in number
  • Smaller in number
• Pollination


  1. Pollen grain lands on the stigma

  2. Pollen tube grows down through the style where the pollen tube/grain release extracellular enzymes which digest its way through style

  3. Male nucleus travel down through pollen tube and enter the ovule through micropyle, where male and female nuclei fuse to form a zygote
• Seed formation

  1. Male and female nuclei fuse together to form a zygote, which will divide by mitosis to form an embryo

  2. Embryo will develop into a plumule (grow into a shoot) and radical (grow into a root)

  3. Cytoplasm with food storage form cotyledon

  4. Wall of ovule will form the seed testa

  
• Factors needed for seed germination

  • Warm temperature for enzymatic activity
  • Oxygen for aerobic respiration to release energy for cell division
  • Water as medium for enzymatic activity/metabolic reaction

  
• Seed germination

  1. Water will enter through the micropyle where in presence of optimum temperature, enzymes become activated and they start to break down food storage

  2. More water will enter the seed, so it swells and seed testa will split, allow oxygen to diffuse into the seed, used for aerobic respiration to release energy for cell division and forming new molecules

  3. Plumule will grow into shoot

  4. Radical will grow into a root

  
• Dormant seed is where conditions needed for seed germination are not provided

  
• Dry mass is decreasing, food storage is being used up/broken by activated enzymes where the plant uses glucose for respiration (respiration only)
• Small leaves develop, yet slow rate of photosynthesis so showing a slight increase in dry mass
• Leaves are bigger so higher rate of photosynthesis, photosynthesis is higher than rate of respiration so increase in dry mass