HL 1 Biology

9.3b Plant Reproduction

<<Flowering, Pollination and Fertilization>>

  • Vegetative structures: young plants (which grows roots.stems and leaves) that are formed  when seed germinates
  • change from vegetative to reproductive phase  = when meristems in shoot start to produce partts of fowers instead of leaves
  • nectar-secreating glands: attract insects
  • anthers: produce pollen (containing male gametes)
  • filaments: hold anthers in position
  • pollinated flower: if another flower’s pollen brushes into the flowers stigma
  • fertilization: pollen tube carries male gametes to fertilize the ovary
  • ovary: located inside small rounded structure, ovule; develops into a seed; ovary develops into fruit

<<Control of Flowering>>

  • length of darkness
    • long-day plants flower in summer when nights have become short
    • short-day plants flower in autumn, when nights become long
  • phytochrome: pigment in leaves that is used to measure the length of dark periods
    • PR converts into PFR when absorbs red light of wavelength 660nm
    • PFR converts to PR when absorbs far-red light of 730 nm wavelength
    • PR more stable in PFR
  • PFR is active form of phytochrome + receptor proteins are present in cytoplasm to which PFR binds but not PR
    • long day plants: large amount of PFR build in the end of short nights to bind to receptor, which promotes transcription of genes for flowering
    • short-day plants: receptor inhibits transcription of genes needed for flowering when PFR binds to it (at end of long nights, PFR barely remaining so inhibition fails and plant flowers)


Sowing Times for Soybeans (p.132)

1) The growth of the soybean plants sown on the different dates initially had a very low rate of increase in the number of nodes per plant. But we see that the plants that were sown the earliest in date, produced the greatest number of nodes. Between May and Jun, the number of nodes start to increase as the slope of the line because steeper. Yet all soybean conditions show the same rate at which they produce nodes and once they all reach to the end of July, it is apparent the plants all stop producing the nodes.

2) (a) Around the start of 14- Aug.

(b) The factors that trigger flowering in soybeans are  the day length. It is visible the length of the day is short (apparent at the end of August),  and the plant slowly stops producing the number of nodes. In the day length, it is the length of darkness that matters and triggers the whole plants. These phytochromes function as they absorb red light and trigger the flowering of the plant.

3)  The advantage of sowing the crop as early as possible is that there will be more nodes produced as the plant can start to germinate at an early stage in the year. Also, as they are germinated more quickly, the flowering time will function at an early stage causing more fruits to be produced per plant.

4) Two possible disadvantages of sowing soybeans earlier than the dates used in the trail is that there are possible risks of droughts which can cause the plants to be damaged or even frost/bad weather conditions. Also, flowers may bloom in a very early season depending on the day sown as well.




One thought on “9.3b Plant Reproduction

  1. Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations.

    Data-based questions: sowing times for
    page 132
    1 Answer should to refer to:
    • For all planting dates there is an initial low rate of increase in the number of nodes.
    • A linear increase in the number of nodes.
    • All groups produce nodes at the same rate/slope of lines are approximately equal.
    • All plants stop producing new nodes at the same time.
    • The earliest plantings produce the greatest number of nodes.
    2 a Approximately 20 August.
    b Day length is a key factor; day (light) length grows shorter in late August; critical day length reached/soybeans are short day plants.
    3 Earlier planting yields more nodes; by flowering time more fruits produced per plant.
    4 Possible frost risk; possible drought risk; early flowering if day length is critical length early in season.

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