Plant Reproduction

Plant Reproduction

  • Process by which plants can increase their numbers for the next generation
  • Must reproduce in order to survive
  • It an be asexual (vegetative means) or sexual (male and female gametes)
  • In asexual reproduction the offspring are all genetically identical as this is clonal reproduction (propagation, through leaves and stems)
  • In sexual reproduction there is the advantage of increasing genetic diversity

Vegetatively Propagated plants (asexual)

  • From stems
    • Strawberries that produce stolon
      • Stolon is a side shoot that gives rise to a new plant
      • Seeds on top are ovules. Useless. Not really seeds
  • From tubers
    • Axillary buds on potato tubers
      • Cut the axillary bud from the potatoes to give rise to new plant
  • From young shoots on banana plants called suckers
    • Shoots from the side of a banana plant near the root gives rise to new plants
  • From stems in roses
    • From stem cutting
  • Pineapples are grown from propagation
    • Take the top of the pineapple and plant it to grow a new fruit

Sexual Reproduction - Production of Seeds

  • Requires the fusion of male and female gametes to produce a zygotes (embryo) followed by seed production
  • Male gametes
    • Pollen grains
  • Female gamete
    • Ovules
  • Games are found in the flowers. It requires the transfer of the male gamete to the ovules to initiate fertilization
  • Male gametes are produced in anthers
  • Female gametes are produced in the ovary

Pollination and fertilization are needed for seed production

  • Process of transfer of male pollen to the female stigma (receptive part of the female flower) is called pollination
  • Pollen can be transferred by wind
    • In grasses or tress
    • Requires production of very large amounts of pollen each spring
  • Pollen can be transferred by insects
    • Bees and wasps and moths, animals like bats and hummingbirds
  • Insect pollinated flowers are attractive and produce nectar to reward the pollinators
  • Alder produces lots of pollen

Cross Pollination

  • Pollen from the anther of one plant (where male gametes are produced) is transferred to the stigma (receptive part) of a different plant
  • Pollen from the stamens stick to a bee as it collects food from the flower
  • Bees travel to another plant of the same type
  • Pollen on the bee sticks to a pistil of a flower on the other plant

After pollination a fruit is formed

  • A plant structure that contains seeds is a fruit
  • Not all fruits have seeds (banana, strawberries) but they need pollination to form a fruit

A flower gives rise to a fruit

Each corn kernel comes from 1 ovule fertilized by a pollen grain

  • One stigma can be traced back to 1 seed
  • When it is rip stigma turns black

Pine tress produce male and female cones

  • Female cones, ovulate cones have ovules that contain gametophytes which makes eggs
  • In male cones, male sports develop into male gametophytes called pollen grains

Steps in Fertilization

  • Pollen grain has 2 sperm nuclei
  • The grain germinates on the stigma of the same plant species and produces a germ tube
  • Germ tube grows down the style
  • The germ tube reaches the ovary it looks for the opening in the ovule called a micropyle
  • One sperm nucleus fuses with the egg nucleus inside the ovule to form the zygote (2n)
  • The second sperm nucleus fuses with the 2 polar nuclei to form the endosperm 3n which is the food storage for the developing embryo
  • Called double fertilization

1 sperm fuses with egg nucleus to form the zygote, other sperm fertilizes with 2 polar nuclei to form the endosperm 3n which is food storage for the embryo

Development of Zygote (embryo)

  • Zygote divides several times to form an embryo
  • Embryo differentiates to form a root and shoot apex
  • Ovary expands and the walls becomes the seed coat
  • Each fertilized ovule forms one seed. Plants can have 1 seed like an avocado or multiple seeds like peas
  • Ovary walls can be fleshy like a peach
  • Each seed has one or two cotyledons depending on if it is a monocot or dicot plant species
  • Seeds will germinate to form a root and shoot and the plant has now be propagated sexually

How to Spread Seeds Far and Wide

  • For survival plants must produce lots of seeds and spread them as far as possible
  • Allows opportunity for survival in a different environment
  • Plants have many different methods to spread seeds
    • Make lots of seeds that spread by wind
      • Grass seeds
    • Make seeds that float on water
      • Coconut husk floats on water
    • Make seed spiny so it catch on to humans and animals
      • Fruit of puncture vine has spines to catch on organisms
    • Make seeds aerodynamic
      • Dandelion seeds and maple seeds
    • Make fruits attractive so seeds inside them are spread
      • Animals eat fruit and seeds are in feces
    • Make fruits fleshy and attractive for animals to eat (droppings contain seeds)