This document discusses plant biology and seed structure. It explains that seeds contain an embryo and stored food to nourish the young plant. Seeds have an external coat and internal structures like the embryo, cotyledon, hypocotyl and radical. Different seeds are shown. Seed dispersal methods include wind, water, animals and explosion. Seed dormancy and the factors influencing germination like water, oxygen, temperature and light are also outlined.

1. P L A N T B I O L O G Y : Z O L J A R G A L C H I N B A T
THE SEED

2. 2
SEEDS
• Seeds contain a young, developing plant
embryo
• Seeds are covered with a protective seed
coat.
• Inside is stored food or endosperm that the
young plant uses as it begins to sprout or
germinate.
• Seeds form from ripened ovules after
fertilization

3. SEED STRUCTURE
• External
• Seed coat (testa)
• Hilum
• Embryo
• Cotyledon
• Epicotyl / Hypocotyl
• Plumule
• Radical

4. SEED COAT
• testa
• The seed coat protects the embryo
• Can be of varying thicknesses, depending on the seed
type.

5. HILUM
• Scar from the seed being attached to the parent plant

6. EMBRYO
• The embryo is what forms the new plant once the
opportune conditions are present.

7. COTYLEDON
• The cotyledon is the first
leaf that germinates.
• It is filled with stored
food that the plant uses
before it begins
photosynthesis.
• Some plants have 1
cotyledon (monocot)
and some have 2
cotyledons (dicot).

8. EPICOTYL /HYPOCOTYL
• The basis for the plant’s
stem.
• It is known as the epicotyl
above the cotyledon and a
hypocotyl below the
cotyledon.
• These grow upward in
response to light.

9. PLUMULE
The shoot tip with a pair of miniature leaves.

10. THE RADICLE
• The part of the seed where the root develops.

11. THE STRUCTURES OF THREE DIFFERENT
SEEDS ARE SHOWN HERE 

12. 12
Parts of a Seed

13. Seed

14. • Flowering plants have different adaptations to enable
their seeds to be dispersed as far away as possible.
• The different methods of seed dispersal are…
• by wind
• by animals
• by water
• by explosion
REPRODUCTION IN PLANTS — GETTING THE SEEDS
DISPERSED
Seed Dispersal

15. by Explosion
by
wind
seed dispersal
by
water
Adaptations for reproduction
plants
by
animals

16. DISPERSAL BY WIND
• Some seeds are carried to a new
place by the wind. These seeds are
very light.
• The seeds of the orchid are almost
as fine as dust.
• Many have hairy growths which act
like little parachutes and carry the
seeds far away from the parent
plant.
• The seeds of the dandelion are
carried by the wind.
dandelion
Orchid

17. DISPERSAL BY WATER
• Water lily and the coconut palm are
carried by water.
• Coconuts can travel for thousands of
kilometres across seas and oceans.
• The original coconut palms on South
Sea islands grew from fruits which
were carried there from the mainland
by ocean currents.

18. DISPERSAL BY ANIMALS
• The animal eats the fruit but only the juicy
part is digested.
• The stones and pips pass through the
animal's digestive system and are excreted
to form new plants. This can be far away
from the parent plant.
• Blackberry, cherry and apple seeds are
dispersed in this way.
• Birds also like to eat fruit and they help to
disperse seeds to other areas through their
droppings.
• Squirrels collect nuts like acorns and bury
them for winter food, but they often forget
where they have buried them and these
grow into new trees.
• Some fruits like that of the burdock plant
have seeds with hooks.
• These catch on the fur of animals and are
carried away.

19. DISPERSAL BY EXPLOSION
• Some plants have pods that
explode when ripe and
shoot out the seeds.
• Lupins, gorse and broom
scatter their seeds in this
way.
• Pea and bean plants also
keep their seeds in a pod.
When the seeds are ripe
and the pod has dried, the
pod bursts open and the
peas and beans are
scattered.

20. SEED DORMANCY
What is seed dormancy?
Seed dormancy means to delay germination until
favorable environmental conditions are present for
seed germination and sprout growth.
• Types of dormancy
1. Primary dormancy delays initial seed germination
2. Secondary dormancy

21. PRIMARY DORMANCY
• Seed coat physical dormancy- is when the seed coat
prevents the seed from absorbing water.
• Seed coat mechanical dormancy- is when the seed
coat prevents the embryo from breaking through.
• Chemical dormancy- is when chemicals within the
seed coat prevent the seed from germination.
• Morphological dormancy- is when the seed has not
completed at the time the seed leaves the plant
• Physiological or intermediate dormancy- occurs
because a physiological condition is not being met.
• Deep dormancy- is when plants stay dormant until
favorable conditions are met, usually involving a period
of cooling.
• Double dormancy- is the combination of any of the
previously mentioned factors.

22. SECONDARY DORMANCY
• Secondary dormancy prevents the seed from
germinating after it absorbs water.
Is caused by temperature extremes, prolonged
darkness, prolonged light water stress, or oxygen
extremes.

23. SEED GERMINATION
• What is it?
Process that causes a seed to begin to grow
into a new plant.
• Factors influencing germination
1.Water
2.Oxygen
3.Temperature
4.Light

25. WATER AND OXYGEN
Water
• Mature seeds have relatively little moisture to
prevent decay.
• Seeds usually mature in fall.
• To germinate, seeds must take in water.
Oxygen
• Oxygen in the presence of enough moisture causes
respiration to start.
• This creates energy for the germination process.

26. TEMPERATURE AND LIGHT
Temperature
• Most seeds go through a cold period before
germination.
• Helps prevent seeds from sprouting as soon as they
mature.
• Proper temp. for most seeds= 68-85 F.
Light
• Amount of light needed varies.
• Depth of seed planting influences this.
• Too deep=not enough light oxygen.
• Too shallow may=too much light.