Reproduction

Asexual reproduction

• Single parent cell divides into two daughter cells
  • Advantage: No energy/time consumption to find a mate
• Offspring are genetically identical to parent
  • This can be both an advantage or disadvantage
    • If the environment suits the organism, then it will thrive.
    • If not, or if the environment changes to become less suitable, then disadvantage

Sexual reproduction

• Involves the fusion of male and female gametes to form a zygote which then divides repeatedly and becomes an embryo
• Disadvantages: time/energy used up to find a mate (animals), or for pollination (in plants)
• Advantages:
  • Genetic variation: offspring may be better adapted to changes in the environment

Reproduction in flowering plants

• Flowers are main reproductive organ
• Depending on species, flowering plants may have male and female reproductive organs in
  • same flower
  • different flowers on same plant
  • flowers of different plants
• Overall process of sexual reproduction in flowering plants:
  • Male pollen transferred to female part of flower
  • Male and female gametes fuse to form zygote
  • Zygote develops to form embryo within seed
  • Seeds are dispersed, and germinate in the soil

Structure of flowers

Text

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Male parts of flower

• Stamen = Filament supporting an anther
• Meiosis happens in cell lining of pollen sacs to form gametes
  • As they develop, they form into a pollen grain
  • When mature the anther split (length-wise) to release the pollen grains

Female parts of flower

• Pistil = stigma (where pollen lands) + style
  • Pollination = transfer of pollen grain from anther to stigma
• Ovary at the base of the carpel contains ovule(s)
  • Ovule contains egg cell (female gamete) surrounded by egg sac
    • (see textbook diagram)

Pollination: wind-pollinated vs insect-pollinated flowers

Textbook table 3.1 (page 93)

• In summary:
  • insect-pollinated plants have large colourful petals, good scent, nectaries - i.e. features suitable for attracting insects. Pollen grain tends to be sticky/spiky.
  • wind-pollinated plants tend to have large, exposed anthers and stigma, to maximize chances of pollen transfer. Lots of pollen produced.

Fertilisation in flowering plants

Read description on figure 3.11 on page 196

In summary, the pollen grain grows a pollen tube through the style, into a small hole (called micropyle) in the layers protecting the egg sac. Male gamete from pollen grain fuses with the egg cell; zygote is formed. The ovule wall toughens as zygote develops, to form the seed coat. In many plants the tissue surrounding the ovule develops into a fruit.

Germination

• Seeds get dispersed
  • By the wind or water (aquatic plants)
  • Fruits eaten by animals, excreted onto the soil
• blah blah
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