Notes:
Seeds
What is a seed?
A seed is a small embryonic plant enclosed in a covering
called the seed coat, usually with some stored food.
The formation of the seed completes the process of
reproduction in seed plants.
Why are seeds advantageous for
plants?
maintain dormancy until better
environmental conditions arise
afford protection to young plant at
vulnerable developmental stage
contain adequate food supply until
photosynthesis is possible
dispersal of plants
Skill: draw internal structure
of seeds
SEED STRUCTURE
External
Seed coat (testa)
Hilum
Embryo
Cotyledon
Epicotyl / Hypocotyl
Pumule
Radical
Seed Coat
AKA testa
The seed coat protects the embryo
Can be of varying thicknesses, depending on the
seed type.
Hilum
Scar from the seed being attached to the parent
plant
Embryo
The embryo is what forms the new plant once the
opportune conditions are present.
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).
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.
Plumule
The shoot tip with a pair of miniature leaves.
The Radicle
The part of the seed where the root develops.
SEED STRUCTURE
Seed coat (testa)
Embryo
Cotyledon
Epicotyl / Hypocotyl
Pumule
Radical
SEED DISSECTION
MATERIALS
Soaked pinto seed
Dissecting microscope
Tweezers
Ruler
SEED DISSECTION
EXTERNAL
INTERNAL
Draw the external
pinto bean
Carefully remove the
seed coat.
Label structures from
notes
Gently pull apart the
two halves of the
seed.
Examine each half
with the dissecting
microscope
Draw what you see
inside the bean
Label structures from
notes
REVIEW THE RULES FOR LAB DRAWING IN YOUR STUDENT GUIDE
BE SURE YOU MEASURE AND RECORD THE LENGTH OF YOUR SEED
Plumule
Embryo
Cotyledon
Radicle
Germination
After seed is formed, dehydration occurs until water is
only about 10-15% of its weight
Seed becomes dormant
When conditions become right, the seed will begin to
develop into a functional plant
Initial process in seed germination
The absorption of water
Release of a plant growth homorne – gibberellin (gibberellic
acid)
Gibberellin causes production of amylase, which hydrolyses
starch into maltose
Maltose is further hydrolysed into glucose, which can be
used in cellelar respiration
The early glucose may also be converted into cellulose to
make new cell walls
Germination
The development of the seed into a
functional plant.
Steps to the emerging plant
1st organ to emerge = radical (seed root)
The shoot tip must break through the soil surface
In many dicots, a hook forms in the hypocotyl &
growth pushes the hook above ground
Stimulated by light, the hypocotyl straightens, raising
the cotyledons & epicotyl
The epicotyl now spreads its 1st foliage leaves
They will begin doing photosynthesis
Water
Uptake water = imbibition
The seed expands and ruptures the testa (seed coat)
Gibberellins signals enzymes to begin digesting stored
material in the endosperm
GA triggers the formation of a-amylase that hydrolyzes
starch in the seed
Oxyen
A-amylase breaks down storage sugars
Converts them to other forms the seed can use
If soil is waterlogged, it might cut off necessary oxygen
supply and prevent the seed from germinating.