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									AP Biology                                                               Name _____________________
Ch. 38 Tutorial


Where do male and female gametophytes develop?

What does fertilization produce? What does it develop into?

What does a seed contain?

What does the ovary develop into?

38.1 Angiosperm Life Cycle

Angiosperms are plants that reproduce by means of flowers. Flowers are showy, colorful structures made of
modified leaves. A flower usually contains both male and female reproductive structures.

 (you will need to answer each question in the pull down menu to get to the next step. You will benefit on the quiz by reviewing the
                                                   order of this life cycle – hint!)

In this activity, you can review the sequential stages of the angiosperm life cycle. First, what process occurs in
the ovary that initiates the development of female gametophytes? ____________________

Inside an ovule, the megasporocyte (2n) undergoes meiosis to form four cells, but only one of these survives as
the megaspore (n). The megaspore develops into the female gametophyte, but how does this happen?

The nucleus of the megaspore divides by mitosis three times, resulting in one large cell with eight haploid nuclei.
Membranes then grow between these nuclei to form a multicellular structure called the embryo sac, which is the
female gametophyte. The large egg cell is located at one end of the embryo sac.

Meanwhile, what happens in the anther to initiate the development of male gametophytes?

A diploid cell within the anther divides by meiosis to form four microspores (n). What happens next?

Each microspore (n) divides once by mitosis to form two cells. A tough wall is formed around the outside, creating
a male gametophyte, or pollen grain. Now what happens? ________________________________

Pollen grains are transferred by wind, water, or an animal to a sticky stigma in a flower of the same plant or
another individual of the same species. What happens when the pollen grains get there?

After a pollen grain lands on the stigma, it forms a pollen tube that elongates downward through the style into
the ovary. Two sperm nuclei (n) form inside the pollen tube. What is the next step in the life cycle?
The pollen tube enters the ovary and releases the two sperm nuclei into the embryo sac. One sperm nucleus
fertilizes the egg, forming a diploid zygote. The other sperm nucleus fuses with two nuclei in the center of the
ovule to form a triploid (3n) cell that will develop into a nutritive tissue called endosperm. What happens after
this double fertilization? __________________________________

The triploid cell divides rapidly by mitosis to form endosperm, a tissue rich in starch, lipids, and proteins. The
zygote divides by mitosis to form a sporophyte embryo with a rudimentary root and one or two cotyledons (seed
leaves). The integument of the ovule becomes a tough seed coat, with the embryo and endosperm inside. As the
ovules develop into seeds, the ovary surrounding the ovules develops into the fruit, which will protect and help
disperse the seeds. What now happens to complete the life cycle? ________________________________

The fruit falls to the ground and seeds germinate. A seedling uses the food stored in the endosperm and
cotyledons to grow until it can begin photosynthesis. The young plant grows into a mature sporophyte, which
flowers and the cycle continues.

38.2 Seed and Fruit Development

The function of flowering is to produce seeds and disperse them to locations where the young plants are likely to
survive. At each step, there is an emphasis on protecting the offspring. This activity reviews some of the most
important steps.

Events in seed formation begin with with _________________, in which wind or animals bring pollen to the

The growth of pollen tubes caused the flower to discard (abscise) its colorful parts (petals and stamens). After
pollen arrives, the bright petals are a hazard; they attract animals that might eat the delicate young fruit.

An ovary contains one or more ovules that will become seeds if they are fertilized. One ovule is shown here, with
the front removed to reveal the parts. The ovule is attached to the ovary wall by a stalk that provides nutrients.

Starting from a pollen grain at the stigma (not shown), a pollen tube grows down the style to the ovule. It carries
two sperm nuclei that enter the ovule. One sperm nucleus fuses with the egg cell to make a zygote, which is the
first cell of the embryo. The other sperm nucleus fuses with two nuclei in the central cell, making a triploid
nucleus. This triploid cell will grow and divide to make a food-storing tissue, the endosperm.

This ovule has been fertilized and will become a seed. Each of its cells contains one or more sets of chromosomes,
but the number of sets (the ploidy) differs among parts of the ovule.

Taking food through its stalk, the developing seed expands its endosperm and embryo. When the embryo is
mature and dormant, the integuments develop into a protective seed coat and detach from the ovary wall.

Cotyledons absorb food from the endosperm and transfer it to the embryo. However, plants vary in the time
when the endosperm delivers its stored food.

(first seed- on left) In some seeds, the ____________ persists until the seed germinates. Then the endosperm
breaks down; the cotyledons absorb the released food and pass it immediately to the rest of the embryo.

This happens in most monocotyledons, such as corn, wheat, and other cereals. It also happens in some
dicotyledons, such as the castor bean (source of castor oil).
(second seed) In some seeds, the _____________________breaks down while the seed is still developing. The
cotyledons absorb and store the released food, becoming very large and thick. When the seed germinates, the
cotyledons deliver the stored food to the rest of the embryo.

This pattern happens in most dicotyledons and accounts for the very large cotyledons in peanuts, peas and beans.

When seeds are _________________, the ovaries change their function and develop into seed-dispersing
structures called fruits.

There are many patterns of fruit development, but they can all be divided into two categories: dry fruits and
fleshy fruits.

(first fruit – on left) In dry fruits, the ovary ____________________________. It may develop hooks that
catch animal fur as in this example. Or the ovary and other flower parts may form a wing or a parasol or hairs to
catch the wind. Sometimes the dry ovary builds tensions that, when released, will shoot the seeds into the air.

(second fruit) In fleshy fruits, such as tomatoes and peaches, the outer tissues of the ovary thicken and become
________________________________. Fleshy fruits invite animal dispersal; the seeds are ingested and, if
they escape digestion, they are excreted with fertilizer -- hopefully in a choice location.

Seeds contain dormant embryos with a food supply and a protective coat. They can usually sense the
___________________________, causing the young plant to resume its growth when conditions favor survival.

Seeds often germinate underground, and the delicate shoot tip and young leaves need protection as they force
their way through the soil. There are three common forms of protection which are …

Label the seed and flower below:

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