Sexual Reproduction in Flowering Plants and Variation

Sexual Reproduction in Flowering Plants

Flowering plants reproduce sexually by creating seeds, a process involving flower anatomy (anther and stigma), pollen transfer (pollination), fertilization (fusion of gametes), and seed dispersal. Key components include the stamen (male) and carpel (female), with types like cross or self-pollination. Germination requires water, oxygen, and warmth.

Parts of a Flowering Plant

• Male Part (Stamen):
  • Anther: Produces and releases pollen (male gametes).
  • Filament: Supports the anther.
• Female Part (Carpel/Pistil):
  • Stigma: Sticky top part that traps pollen.
  • Style: Tube connecting the stigma to the ovary.
  • Ovary: Contains ovules (female gametes).
• Other Parts: Petals (attract insects), Sepals (protect the bud), and the Receptacle.

  

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Types of Pollination

Pollination is the transfer of pollen from the anther to the stigma.

• Self-Pollination: Pollen travels from the anther to the stigma of the same flower or another flower on the same plant.
• Cross-Pollination: Pollen moves from the anther of one plant to the stigma of a different plant of the same species. This increases genetic diversity.
• Agents of Pollination: Insect (bright petals, nectar) or Wind (feathery stigmas, light pollen).

  

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Seed Germination

Germination is the process where a seed starts to grow into a new plant.

• Requirements (O.W.W.):
  • Oxygen: For respiration.
  • Water: To activate enzymes and break the seed coat.
  • Warmth: For enzyme activity.
• Process: The radicle (root) emerges first, followed by the plumule (shoot).

  

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Continuous vs. Discontinuous Variation

• Continuous Variation: Traits that have a range of intermediate values (e.g., plant height, leaf length).
  • Graph: Normal distribution curve (bell curve).
  • Causes: Controlled by many genes and affected by the environment.
• Discontinuous Variation: Traits that fall into distinct, clear-cut categories with no intermediates (e.g., petal color, seed shape).
  • Graph: Bar graph (distinct bars).
  • Causes: Controlled by one or a few genes, rarely affected by the environment.

    

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Summary Table: Variation