Post on 24-Feb-2016
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Great Oaks from Little Acorns Grow
It all starts with a seedI Can… Describe the basic anatomy and physiology of a seed and explain the process of germination.
I Will… • Label a diagram of a basic seed• Describe the function of seed parts• Describe conditions for maintaining
dormancy and promoting germination• List the steps of seed germination
What is a seed?
Answer: A plant embryo & food source
Anatomy of a Seed:
Plumule
Epicotyl Hypocotyl
Hilum
Seed CoatTesta
Cotyledon/Endosperm
Radicle
1. Seed Coat / Testa – Outer protective covering.
2. Cotyledon / Endosperm – Food laden “seed leaves”. Provides growing embryo with energy.
3. Epicotyl – Growing tip of embryo and future plant.
4. Hypocotyl – Develops into plant stem5. Radicle – Root tip of plant6. Plumule – Develops into first true leaves
for photosynthesis7. Hilum – Seed scar; marks previous
attachment point to parental fruit/plant
Physiology of Seed Parts
Seed Dormancy• Stasis prior to germination• Metabolism falls• Number of organelles per cell falls• Dehydration – water content falls• Vacuoles in cells deflate• Food reserves become dense and
crystalline
Maintaining Dormancy• Physical barriers• Seed coat / Testa is waxy• Waterproof• Impermeable to oxygen
• Physical state – dehydrated
• Chemical inhibitors present• Salts, mustard oils,
organic acids, alkaloids• Growth promoters absent
Seed Viability• Viability: When a seed is capable of
germinating after all necessary environmental conditions are met.
• Average life span of a seed is 10 – 15 years• Some very short-lived • e.g. willow (< 1 week)
• Some very long-lived• e.g. mimosa 221years
• Conditions important for longevity:• Cold, Dry, Anaerobic
• Conditions maintained in seed banks
Seed Germination – The breaking of dormancy; growth of embryo and its penetration of the seed coat.
Breakdown BarriersAbrasion of seed coat (soil particles)
Decomposition of seed coat (soil microbes, gut enzymes)
Cracking of seed coat (fire)Change in Physical State
RehydrationDestruction and Dilution of Inhibitors
Light, temperature, waterProduction of Growth Promoters
Germination Steps:
1.Seed coat breaks down
2.Radicle becomes root
3.Hypocotyl and epicotyl become stem and growth tip
4.Plumule become first photosynthesis leaves
Great Oaks from Little Acorns Grow
It all starts with a seedLearning Check: Why does seed viability vary
from just a week to hundreds of years in different plant species? Consider environmental factors in your answer.
Anatomy of a Seed:
Germination