The megasporocyte divides by meiosis to produce the

haploid megaspores.

Of the four megaspores, generally only one remains.

Within the embryo sac, cell walls develop around some

of the nuclei, forming the egg and 2 other cells, the

synergids.

Other nuclei are not enclosed in cell walls. Some of these, the polar

nuclei, are located in the central region of the embryo sac.

This shows the mature ovule with the embryo sac

fully developed. Note that the egg and synergids

are located at the micropylar end and that the polar

nuclei are not far from the same end.

The phenomenon of two sperm nuclei combining with

different nuclei from the female gametophyte is termed

double fertilization, a phenomenon nearly unique to

angiosperms.

Chapter 23b-Angiosperms

Double Fertilization

The ovule is the site of meiosis and ultimately the formation of the

seed.

The ovule develops one or more layers of sterile tissue,

the integuments along with a megasporocyte, which is

embedded in the nucellus.

The pollen tube grows through the micropyle and the 2

sperm nuclei are released.

Flowers Vary in their Architecture

Symmetry is also used to characterize flowers

Flower parts may be free or united (fused).

A flower with all four parts is a complete flower.

If it lacks one or more parts, it is an incomplete flower.

If a flower has both androecium and gynoecium (male

and female) it is called a perfect flower.

If only one sex is present, it is an imperfect flower.

Regular symmetry is when all the flower parts

Sedum

Irregular symmetry is when the flower parts are not equal.

Pisum

Sedum In Sedum, the petals, sepals, stamens, and pistils are

completely separate and free.

In Narcissus, the petals are fused over part of their length

to form a tube.

Ovary position also varies.

In some plants, the ovaries are clearly situated above the point of attachment of the other flower parts.

In other plants, the ovaries appear to be placed below the point of attachment of the other flower parts.

Superior ovary in Tulipa. Inferior ovary in Narcissus.

A cluster of flowers is called an inflorescence

Fruits are derived from the ovary of the flower.

Fruits are of three types:

Angiosperms-Fruits

Stamen

Stigma

Ovary

Raspberry flower

Aggregate fruit

Stamen

Carpels

Carpel (fruitlet)

Raspberry fruit

Fruits protect seeds, aid in seed dispersal, and

can be a factor in seed germination.

Fruit structure is highly constant for the same species in

different environments and therefore fruits are used in

classification.

Simple fruits are derived from a single ovary, the ovary

may have one or more carpels.

Aggregate fruits are derived from many separate ovaries

of a single flower, all attached to a common receptacle.

A simple fruit – the almond

A simple fruit – the legume, found in

peas, beans, etc.

Fruits may be dehiscent (splits open) or indehiscent.

Pineapple inflorescence

Multiple fruit

Flower

Each

segment

develops

from the

carpel

of one

flower

Pineapple fruit

Multiple fruits are the enlarged ovaries of multiple flowers

that more or less fuse together.

The almond has only a single carpel with one ovule.

Legumes have a single ovary and carpel, but there

are multiple ovules.

The follicle develops from a single carpel and opens

along only 1 side.

Additional simple, dehiscent fruits:

Follicle (Ex: Magnolia)

Capsule (Poppy)

Capsules are simple fruits derived from compound ovaries

Simple fruits can also be indehiscent, either dry or fleshy.

Other dry, indehiscent simple fruits include: achene

Other dry, indehiscent simple fruits include: caryopsis

Other dry, indehiscent simple fruits include: samara

One of the most common fleshy simple fruits is the drupe.

The almond is also a drupe, but we don’t see the

fleshy part. The initial fleshy pericarp eventually dries

and becomes the hard covering of the seed.

Nuts are one type of dry, indehiscent fruit.

The sunflower “seed” is actually an achene; the shell is

the pericarp.

The “seeds” of corn and other grasses. The caryopsis

differs from the achene in that the pericarp is firmly

attached to the seed.

The wings are outgrowths from the ovary wall.

The winged fruits of maples and elms.

Plants that produce drupes include

Other fleshy, simple fruits include:

Berry

Other fleshy, simple fruits include:

Pepo

Other fleshy, simple fruits include:

Hesperidium

A heperidium is another specialized berry and includes

the citrus fruits.

Other fleshy, simple fruits include:

Pome

The pome is derived from an inferior ovary.

Berries are derived from a compound ovary, and many

seeds are embedded in the fleshy pericarp.

The tomato is a berry.

The cucurbits (watermelon, cucumber, squash) are

pepos.

Pepos are specialized berries except with a rind that is a

layer of tissue from the receptacle.

The thick peel that has numerous oil cavities is the

exocarp and mesocarp.

Seeds are the structures containing the embryonic plant.

Technically, they are mature ovules.

In cotton, initially after fertilization, the zygote

nucleus divides frequently while the primary

endosperm nucleus divides rapidly to form the

endosperm.

Endosperm

Embryo The endosperm is one type of nutrient-rich tissue

that will feed the developing plant when it germinates.

cotyledons

Cotyledon

Shoot tip

Radicle

The embryo continues to develop,

The embryo ultimately develops a shoot tip at one end

and an embryonic root (called a radicle) at the other.

The primary endosperm nucleus

The integuments of the ovule

The are many variations on the development of the embryo.

Both onion (left) and grasses (foxtail, right) have abundant

endosperm in the mature seed.

Germination – growth of the embryo into a plant.

The most basic of these is the single cotyledon of

the monocots vs. the 2 cotyledons of the dicots. 2 cotyledons in the dicot,

castor bean

A single cotyledon in the

monocot, onion

The endosperm is a major food storage for the

germinating seed in many monocots.

Foxtail dry seed cell

Germination in garden bean.

The seed is mostly made up of the two cotyledons. Initial stages of

germination, however, involve other parts of the embryo, the

hypocotyl and epicotyl.

The plant stays below ground at first, but the

elongating hypcotyl raises the cotyledons, still

enclosed in the seed coat.

The epicotyl enlongates further and the first true foliage leaves develop.

The cells of the embryo and nutritive parts of

the seed are tightly packed with storage

structures containing starch, proteins, and

lipids.

As the bean seed starts to germinate, the hypocotyl

elongates as the radicle starts to develop into a

root.

Germination

The first step of germination is imbibition,

Cells rapidly develop a high metabolic rate and the storage bodies diminish.

The hypocotyl is a structure just at the base of the

cotyledons.

The epicotyl

The epicotyl then starts to elongate as the cotyledons

emerge from the seed coat.

The cotyledons, which are primarily storage, eventually wither as the plant continues to grow.

In grasses like corn, the shoot and root are enveloped by

2 tubular sheaths

Study outline for Chapter 23b-Angiosperms

Label the angiosperm life cycle with the terms below:

sporophyte

gametophyte

anther

filament

pollen sac

pollen

integuments

micropyle

ovule

polar nuclei

synergids

egg

sperm

endosperm

embryo

seed

seedling

stigma

style

ovary

pollen tube

embryo sac

Use the figure above to describe the angiosperm life cycle. Please include an explanation of double fertilization

in your answer.

Study outline for Chapter 23b-Angiosperms

Define the following term of floral characteristics:

complete flower

incomplete flower

perfect flower

imperfect flower

Define the following term of floral characteristics and be able to recognize each characteristic.

regular flower

irregular flower

free floral parts

fused floral parts

superior ovary

inferior ovary

inflorescence

panicle

umbel

compound umbel

spike solitary

disc flowers

ray flowers

What are the 3 types of fruits?

Define simple fruit.

Define aggregate fruit.

Define multiple fruit.

Define dehiscent.

Define indehiscent.

Define the following fruit types and know two examples for each type of fruit.

Dry, simple fruits

legume

follicle

capsule

nut

achene

samara

caryopsis

Which of the fruits listed above are dehiscent?

Which of the fruits listed above are indehiscent?

Fleshy, simple fruits

drupe

berry

hesperidium

pepo

pome

Aggregate fruit

Multiple fruit

Study outline for Chapter 23b-Angiosperms

Define germination.

Define inhibition.

Define the following terms below and label the images provided:

radicle

cotyledon

epicotyl

hypocotyl

seed coat

foliage leaves

coleoptile

coleorhiza

Which image is a monocot?

Which image is a eudicot?