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

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

Anatomy of a Seed: Plumule Epicotyl Hypocotyl Hilum Seed Coat Testa Seed Coat Testa Cotyledon/E ndosperm 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 stem 5.Radicle – Root tip of plant 6.Plumule – Develops into first true leaves for photosynthesis 7.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 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

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 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.

Anatomy of a Seed:

Germination