9.3a Plant Reproduction

13/04/2013 § Leave a comment

Up next on HL Biology, season 10 – Seed Structure & Germination, episode 4! In all seriousness, this is the second to last blog, also part one of the Plant Reproduction portion of the unit. Okay.

(Also, I hope everyone’s alright after that earthquake.)

This is a seed.

A seed is made up of an embryo root, embryo shoot, and cotyledon – either one or two depending on whether it’s a monocot or a dicot. The seed coat is called the testa and in it is a small hole called the micropyle. Seeds, though immobile, can travel long distances from their parent plant – called seed dispersal – and this is what helps spread the species around the environment.

In order for a seed to germinate (grow), they need need need water. Among the other things they need include oxygen in order to do respiration. Of course, plants know how to do anaerobic respiration, too, but remember that the addition of oxygen produces a much larger output than without oxygen. And another thing they need – warmth, which is what energizes the enzyme-catalyzed metabolic reactions. Temperatures that are too low fail to initiate germination but high temperatures – as we know – denatures enzymes therefore enzyme activity would be quite slow.

So, what happens during germination? WELL, LET ME TELL YOU.

  1. water is first absorbed and activates the cells metabolically
  2. gibberellin, a plant growth hormone, is produced in the cotyledons
  3. gibberellin stimulates amylase, the enzyme that turns starch into maltose
  4. the maltose is then moved from the food stores into the growth regions, which are the embryo root and shoot
  5. maltose is converted to glucose, used then for aerobic respiration or to make cellulose/other materials necessary for growth

And when the leaves have opened up, the plant can start photosynthesis to supply itself with food for further growth! Independent plants. Cool? Yeah, I’d say so.

Essay Questions

  1. The main part of growing plants are roots, stems and leaves. Draw a plant diagram to show the arrangement of tissues in the stem of a dicotyledonous plant.
  2. Draw a labelled diagram showing the tissues present in a dicotyledonous leaf.
  3. Explain the functions of the different tissues of a leaf.
  4. Explain the role of auxin in phototropism.
  5. Outline the adaptations of plant roots for absorption of mineral ions from the soil.
  6. Describe the process of mineral ion uptake into roots.
  7. Describe how water is carried by the transpiration stream.
  8. Explain how abiotic factors affect the rate of transpiration in a terrestrial plant.
  9. List three abiotic factors which affect the rate of transpiration in a typical mesophytic plant.
  10. Explain how wind affects the rate of transpiration from a leaf.
  11. Outline adaptations of xerophytes.
  12. Outline the role of the phloem in the active translocation of biochemicals.
  13. Draw the structure of a dicotyledonous animal-pollinated flower
  14. Describe the metabolic events of germination in a starchy seed.
  15. Explain the conditions needed for seed germination.
  16. Explain how flowering is controlled in long-day and short-day plants.



Page 129, fire and seed dormancy in a plant of chaparral

1. The scale bars in the electron micrographs represent 1 µm. Calculate the thickness of waxy cuticle between the testa and the embryo and food stores inside the control seed. —> 0.75 cm ÷ 1.35 cm = 0.55 cm * 1 µm = 0.55 µm OR 55 nm

2. The lanthanum solution appears as dark staining in the electron micrographs and shows how far water was able to penetrate. Deduce how far water could penetrate into the control seeds. —> The dark stains line the outer coat of the waxy cuticle therefore water can only penetrate the seed up to the waxy cuticle.


  • a) Compare the staining of the waxy cuticle in the smoke-treated seeds with the staining of the cuticle in the control seeds. —> The control seed is clear of almost any stains whereas the cuticle of the smoke-treated seeds have a line of a dark strain.
  • b) Suggest a hypothesis for the germination of plants of Emmenanthe penduliflora after fires, based on the differences in staining that you have described. —> After the fires, the waxy cuticle could have broken down (or melted, as wax does) in the heat, allowing the water to penetrate the waxy cuticle to go to the embryo.

4. Suggest two advantages to Emmenanthe penduliflora of dormancy ending after fires in the chaparral. —> After the fires have ended, the waxy cuticle would have broken down (melted?) enough to let water in, which then allows for germination. If dormant, the seed could start to germinate! Also, if dormancy ends right after the fires, this means that seeds that could have been germinating (not dormant) won’t be damaged or interrupted by the fires. It would be perfect timing for them – dormancy during the fire keeps the seed safe and dormancy ending allows germination.

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