Plant Reproduction

• Reproduction


  One of the vital functions by which organisms produce offspring
• Two major reproductive methods

  • Asexual Reproduction
  • Sexual Reproduction
• Asexual Reproduction

  • Only one parent
  • No gender
  • Rapid process
  • No gametes formed
  • Favourable conditions
  • All offspring are identical to the parent cell. CLONES of each other.
  • No variety between daughter cells.
  • Usually carried out by microscopic organisms.
• Which organisms reproduce asexually?

  • Kingdom Monera -> Bacteria
  • Protesta -> Unicellular organism
  • Fungi
• Mitosis

  • Asexual Reproduction involves cell division known as MITOSIS
  • Mitosis -> Cell division where one cell divides into two
• Types of Asexual Reproduction

  • Binary Fission
  • Spore Formation
  • Molding
  • Budding
• Binary Fission

  Carried out by unicellular organisms where:

  • the nucleus first DIVIDES into two
  • the cytoplasm shrinks and forms two daughter cells
  • the parent cell keeps the original vacuole and the daughter cells produce their own.
• Budding

  Formation of a 'bulge' (outgrowth) on the body.

  • It enlarges, developing by rapid cell division
  • Then it detaches, forming new species.
  • Examples: Yeast, Hydra
• Spore Formation

  • Fungi, mosses and ferns produce SPORES
  • When ripe, they release and germinate successfully if they settle in the favourable conditions.
  • Hyphae develop swellings (sporangium).
  • Hundreds of spores are formed, and the sporangium bursts open.

  
• Molding

  • The spore attaches to a host.
  • Once attached, it produces enzymes.
  • The enzymes digest the food, turning it into a squishy form.
• Sexual Reproduction

  • Two parents (male and female)
  • Female saves energy to develop the embryo
  • Male produces gametes that fertilize the female gamete
  • Gametes form by MEIOSIS
  • The gametes fuse to form a ZYGOTE
  • Slow process
  • Takes place in unfavourable conditions which provides a mean of survival.
• Meiosis - EXTRA INFORMATION


  A type of cell division that results in 4 daughter cells each with half the number of chromosomes of the parent cell.

  (Occurs only in sexually reproductive organisms)

  Meiosis occurs in the:

  • male flowering parts to produce pollen
  • female floral parts to produce egg cells
• Hermaphrodite


  An organism which forms both male and female gametes.
• Petal

  • Brightly coloured and scented to attract insects for pollination.
  • Arranged in a cylindrical / circle form and number of petals vary.
  • A nectary is found at the base of each petal which produces nectar.
• Sepals

  • Also known as the 'calyx'
  • Protects the flower bud and carries out photosynthesis
• Stamen

  • Male reproductive system
  • Each stamen consists of an anther and filament
  • Anther -> Consists of 4 pollen sacs inside where pollen grains are produced.
  • Filament -> Supports the anther.
• Carpel

  • The female reproductive organs
  • Each carpel consists of an ovary bearing a style and stigma
  • Inside the ovary there are ovules
  • Stigma -> Sticky surface to receive pollen grains
  • Style -> Supports the stigma
• Receptacle


  The swollen end of the flower stalk which holds the flower up.

  In some cases after fertilization, it becomes fleshy and edible (pears, strawberries, apples).
• Structure of a flower

  Angiosperms -> Flowering Plants

  
• Pollination


  The transfer of pollen grains from an anther to a stigma
• Two types of pollination

  • Self-Pollination (prevented)
  • Cross-Pollination
• Self-Pollination

  • When the pollen reaches the stigma of the same plant.

  It is prevented because:

  • Flower parts mature at different times
  • Unisexual flower
  • Pollen tubes cannot germinate in the same plant
  • Different level of stigma and anther

  
• Cross-Pollination

  • When the pollen is carried from the anthers of one flower to the stigma of another. (SAME SPECIES)

  
• Example of the pollination methods

  • Sunflower pollen cannot fertilize rose ovaries because their genetic make-up is different.
  • Rose pollen can fertilize baby rose ovaries because they are of the same species and have the same genetic make-up
• Process of Pollination/Fertilization

  • The pollen lands on the stigma and an immediate chemical reaction takes place.
  • The pollen grain absorbs liquid from the stigma and a microscopic pollen tube grows out of the grain.
  • The tube grows down from the style into the ovary where it enters a small hole called the micropyle in an ovule.
  • The male nucleus enters through the micropyle into the ovary and the gametes fuse together to form a zygote.

  
• Wind-Pollination

  • Inflorescences carry groups of flowers on the same stalk.
  • Each floret has very large reproductive organs and both the anthers and stigma can be seen hanging out.
  • The anthers produce light pollen grains that are easily blown by the wind to be caught by the feathery stigmas held by protruding styles.

  
• Structure of Wind-Pollinated flowers

  • Flowers are small and inconspicuous; Often have green petals
  • No scent or nectar (Because the pollen grains are carried off by the wind, there is no need to attract insects)
  • Anthers are large and loosely attached to produce large quantities of smooth, light pollen grains.
  • Stigmas project outside the flower.
  • Sometimes appear during colder & drier seasons.
• Pollen grain formation

  Pollen grains are made by MEIOSIS (meaning each pollen grain is a male gamete)
• Pollen sac opening

  When the pollen sacs are ripe, they split open to expose the pollen grains
• Pollen transfer to insect

  An insect i.e. a bee, comes to visit the flower for nectar, it lands on the petals and its abdomen brushes against the split anthers, causing the pollen grains to stick against it
• Pollen transfer to stigma


  The bee then flies to another flower and when its weight pushes down the petals, only the stigma sticks out and touches the insect's body, the pollen grains stick to the stigma's sticky surface
• Pollination

  An immediate chemical reaction takes place when the pollen grains stick to the stigma
• Insect-Pollination


  Look at the picture below

  
• After Fertilization

  • The fertilized egg cell starts to divide several times and produces a miniature plant called an embryo
• The Embryo

  • Consists of a tiny root called the radicle
  • A shoot called the plumule with special leaves called cotyledons (the food storage)

  
• The Seed

  • The embryo grows in the seed.

  There are two types of seeds:

  • Monocotyledons (monocots)
  • Dicotyledons (dicots)

  
• Monocotyledons

  • In monocotyledons, the food store is found in a special tissue called the ENDOSPERM which is found outside the cotyledon.
  • Examples: Wheat, Corn

  
• Dicotyledons

  • In dicotyledons, food made in the leaves of the parent plant is carried via the phloem to the cotyledons.
  • These grow into 2 very large cotyledons with stored starch around the embryo.
  • Examples: Common bean, Castor bean

  
• Monocots and Dicots

  • In both monocots and dicots, the outer wall of the ovule becomes thicker and harder, forming the seed coat; TESTA.
  • As the seeds grow, the ovary also becomes much larger and the petals and stamens shrivel and fall off. The ovary is now called a FRUIT.

  
• What happens to the flower as it becomes a fruit?

  Sepals -> Wither & fall off

  Stamens -> Wither & fall off

  Petals -> Wither & fall off

  Ovary -> Becomes fruit

  Ovary wall -> Becomes fruit wall

  Ovule -> Seed

  Integument -> Seed coat (testa)

  Fertilized egg cell -> Becomes embryo surrounded by endosperm which supplies food to it.