Great Oaks from Little Acorns Grow It all starts with a seed

1. Great Oaks from Little Acorns Grow It all starts with a seed I 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

2. What is a seed? Answer: A plant embryo & food source

3. Anatomy of a Seed: Epicotyl Hypocotyl Plumule Hilum Radicle Seed Coat Testa Cotyledon/Endosperm

4. Physiology of Seed Parts Seed Coat / Testa – Outer protective covering. Cotyledon / Endosperm – Food laden “seed leaves”. Provides growing embryo with energy. Epicotyl – Growing tip of embryo and future plant. Hypocotyl – Develops into plant stem Radicle – Root tip of plant Plumule – Develops into first true leaves for photosynthesis Hilum – Seed scar; marks previous attachment point to parental fruit/plant

5. 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

6. 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

7. 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

8. Seed Germination – The breaking of dormancy; growth of embryo and its penetration of the seed coat. Breakdown Barriers Abrasion of seed coat (soil particles) Decomposition of seed coat (soil microbes, gut enzymes) Cracking of seed coat (fire) Change in Physical State Rehydration Destruction and Dilution of Inhibitors Light, temperature, water Production of Growth Promoters

9. Germination Steps: Seed coat breaks down Radicle becomes root Hypocotyl and epicotyl become stem and growth tip Plumule become first photosynthesis leaves

10. Great Oaks from Little Acorns Grow It all starts with a seed Learning Check: Why does seed viability vary from just a week to hundreds of years in different plant species? Consider environmental factors in your answer.

11. Anatomy of a Seed:

12. Germination