REVIEW

PollinationPollination is the transfer of pollen to the surface of the stigma

PollinationSelf pollination may occur if the pollen arrives at the stigma of the same flower or another flower on the same plant

Pollination• Cross pollination

occurs when the pollen arrives at the stigma of a flower of another plant of the same species

Pollination• Insects, wind, birds or other agents

are often required for the transfer

Fertilization

After pollination, a pollen tube forms, producing a path that the sperm will follow to the egg (in the ovary)

When the pollen tube penetrates the

ovary, two sperm are released to accomplish “double fertilization”

LOOK! TWO SPERM!

One sperm fuses

with the

egg nucleus

to form a zygote

The other spermfuses with

endosperm nuclei, which will develop

into the parts of the seed that nourish the young seedling

(then, a seed develops)

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

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.

PlumuleThe shoot tip with a pair of miniature leaves.

The Radicle• The part of the seed where the root

develops.

SEED DISSECTION

MATERIALS– Soaked bean seed– Dissecting microscope– Tweezers– Ruler

SEED DISSECTION

EXTERNAL– Draw the external bean– Label structures from

notes

INTERNAL– Carefully remove the seed

coat. – 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

BE SURE YOU MEASURE AND RECORD THE LENGTH OF YOUR SEED

Plumule

Cotyledon

EmbryoHypocotyl

Epicotyl

Radicle

Seed Dispersal

Seed dispersal is the movement or transport of seeds away from the parent plant.

Seeds are dispersed so as to avoid competition and increase chances of germination. Seeds that fall and sprout beneath the parent

plant have little chance of competing successfully for nutrients.

Seed dispersal is the movement or transport of seeds away from the parent plant.

Seeds are dispersed so as to avoid competition and increase chances of germination. Seeds that fall and sprout beneath the parent

plant have little chance of competing successfully for nutrients.

Germination

Germination is the process by which a seed or spore sprouts and begins to

grow.

How Germination Happens

The first organ to emerge from the

germinating see is the radicle, the

embryonic root.

How Germination Happens

The shoot breaks through the soil

surface. In many eudicots, a hook

forms in the hypocotyl, and

growth pushes the hook above

ground.

How Germination Happens

Stimulated by light, the hypocotyl straightens, raising the cotyledons and epicotyl. The epicotyl now spreads its first foliage leaves, which become green and begin making food by photosynthesis.

What’s Required for Germination?

Water:Imbibition means the uptake of water. Causes

the seed to expand and rupture the seed coat. Water uptake triggers the release of hormones called gibberellins (GA for short) which signal enzymes to begin digesting the storage materials of the endosperm or cotyledons, and the nutrients are transferred to the growing regions of the embryo. For example, GA triggers the release of α-amylase, an enzyme that breaks down starch.

What’s Required for Germination?

OxygenGerminating seeds are very metabolically

active. For example: α – amylase is breaking down storage sugars (such as starch) and converting them to other forms more useful to the seed. Oxygen is necessary for this process. If the soil is waterlogged, it might cut off the necessary oxygen supply and prevent the seed from germinating.

Growth

Remember

Differentiated plant cells generally cannot divide or produce cells of a different type. Growth can only occur at the meristem. A meristem is the tissue in all plants consisting of undifferentiated cells (meristematic cells) found in zones of the plant where rapid mitosis provides new cells. As these cells differentiate, they provide new plant tissue.

Apical Meristems

Found in the stem of buds and

growing root tips that enable the plant to grow

longer.

Lateral Meristems (AKA Cambium)

Surround the established stem of a

plant and causes them to grow laterally (larger in diameter). There are two kinds:

vascular cambium cork cambium

Phototropism

Plants can control their direction of growth towards or away from environmental stimuli.