HL 1 Biology

9.3a Plant Reproduction

<<Seed Structure and Dispersal>>

  • Seed: package containing an embryo plant and food reserves (all inside a protective seed coat)
  • Consists of = embryo root, embryo shoot, and 1 or 2 cotyledons (depends if mono- dicotyledonous)
  • Cotyledons: embryo leaves and many contian food reserves of seed
  • endosperm: a special food storage tissue in some seeds, instead of cotyledons
  • testa: seed coat
  • micropyle: small hole through testa, located next to a scar where seed was attached to parent plant
  • Seed dispersal: traveling long distances from the parent plant; reduces competition between offspring/parents; helps to spread species
  • Dormancy: allows time for seeds to disperse and avoid germination at an unfavorable time even if given required conditions;


  • need water to germinate
    • seeds are dry
    • helps rehydrate cells
    • for some seeds, needed to wash out hormone that inhibits germination
  • involves growth of embryo root. shoot (this needs water)
  • need oxygen
    • metabolic rate of dry/dormant seed: close to zero
    • after water absorbed, metabolic processes + aerobic cell respiration starts
  • need warmth
    • since involves enzyme-catalysed metabolic reactions
  • gibberellin: plant hormone
    • synthesis of gibberellin occurs at start of germination
    • this stimulates mitosis + cell division in the embryo
    • stimulates production of amylase in starchy seeds
    • needed to break down starch in food reserves into maltose
    • this maltose is converted into sucrose/glucose by other enzymes (which is essential to all parts of embryo for aerobic cell respiration)


Fire and Seed Dormancy in a Plant of the Chaparral (p.129)

1) 0.5µm

2) It is apparent that the lanthanum solution was able to reach the outside of the waxy cuticle yet was unable to travel any further. Thus the water was able to penetrate into the control seeds all the way through the testa but could not go through the embryo.

3) (a) In the smoke treated seed the staining is apparent all the way through to the waxy cuticle where as in the control seed, the stain is only visible in the testa. Thus it is visible the staining in the waxy cuticle of the smoke treated seeds suggests the water was able to penetrate further than the control seed which had no staining in the waxy cuticle.

(b) I hypothesize that the fire on the Emmenanthe peduliflora  will enable the seed to germinate and the penetration of water will travel further. The fire seems to have broken down the cuticle, and allowed the water to penetrate further into the seed. Without fire, the seed would unable to germinate due to the presence of a healthy cuticle.

4) Two advantages to Emmenanthe penduliflora of dormancy ending after fires in the chaparral include the increase in nutrients and the supply of more light for germination. As this particular species does not have to compete, the more nutrients and light will enable the plant to expand in population.

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