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 StateRehydration

Destruction and Dilution of InhibitorsLight, 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