Flower Structure and Function
Read the section in the text concerning sexual reproduction in flowering
plants and seed
development. Flowers are modified leaves which contain specialized
organs, ovaries and anthers, in which meiosis occurs forming gametes,
eggs and sperm nuclei. The flower is where sexual reproduction in
angiosperms occurs. This
process consists of pollination and double fertilization. After
fertilization the zygote will develop
into an embryo which is surrounded by a seed coat which in turn
is encased by the fruit.
There are four main parts of a flower - sepals, petals, pistils
and stamens. Your could say that the
flower is the result of four whorls of modified leaves borne on
a receptacle. The receptacle is
actually a modified stem apex. The apex becomes flattened and leaf
primordia are simulated by
plant hormones to develop into the four modified flower parts.
In your notes draw a figure showing the following parts of the flower:
receptacle, sepal, petal,
stamen (anther and filament), pistil or carpel (stigma, style and
ovary with ovule). See text for
examples.
| \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ | Location of Receptacle | Function and Parts |
| Sepals | ||
| Petals | ||
| Stamens- filiment, anther | ||
| Carpel or Pistil - Stigma, Style, Ovary |
The receptacle is actually a modified stem apex formed on a pedicel. The apex becomes flattened (receptacle) and leaf primordia are simulated by plant hormones to develop into the four modified flower parts.
Location of Receptacle
Function and Parts
Sepals)
Outermost Whorl
(calyx)
Petals
2nd Whorl
(corolla)
Stamens
3rd Whorl
filament, anther
(androecium)
Carpels
4th Whorl center
Stigma, Style, Ovary - Ovule
(gynoecium)
Formation of Male Gametes
Refer to figures in text.
The male gametes, sperm, are formed in the pollen grains. Pollen
grains develop in the stamen
(anther) portion of the flower. Explain the steps involved in the
formation of the pollen grain
beginning with the microsporangia and ending with a mature pollen
grain. Include the following:
microspore mother cell, microspores, tube nucleus, generative
nucleus, protein pollen coat. Give
the ploidy - haploid, diploid, or triploid for each
of these structures. Indicate the type of cell
division (mitosis or meiosis) which forms these structures.
Draw a figure showing the events
described above.
Microspore mother cell undergoes which type of cell division and
forms how many microspores?
How many pollen grains are formed from 200 microspore mother cells?
(800)
Pollen grains develop in the stamen (anther) portion
of the flower.
(collectively called androecium)
microsporangia (tissue which makes up the anther.
microspore mother cell (microsporocytes) (2n)
microspores (1n)
tube nucleus (1n)
generative nucleus (1n)
protein pollen coat
tapetum (2n) Nutritive layer of surrounding cells which
will become microspores.
Formation of Female Gametes
The female gametes, egg, are formed in the ovules.
Ovules develop in the carpel (ovary) portion of the flower.
(placentae, funiculus, nucellus, integuments,
micropyle)
megasporangia (2n)
megaspore mother cell (2n)
megaspores (1n)
surviving megaspore (1n)
egg sac nuclei containing an egg, two polar nuclei, 2 synergid nuclei and 3 antipodal nuclei (all 1n)
Give the ploidy for these structures ? haploid, diploid, triploid. Indicate the type of cell division (mitosis or meiosis) which form these structures.
Megaspore mother cell undergoes which type of cell division and forms how many megaspores?
Do all four of the megaspores survive?
How many mitotic divisions does each megaspore undergo
to form the 8 nucleated egg sac?
Refer to figures in text.
Pollination:
Bisexual-
Inbreeding
Outbreeding
Unisexual-
Wind - small flowers, lacking sepals, small fruit and seeds
Insects/ Animals – nectar, petals, odiferous, large flowers,
Double Fertilization
Refer to figures in text.
Explain the germination of the pollen grain on top of the stigma.
Include the part played by the
tube nucleus, generative nucleus, and pollen tube.
What is the function of the tube nucleus?
What is the function of the generative nucleus?
What type of cell division occurs when the generative nucleus divides to form sperm?
How many sperm nuclei are formed?
Explain double fertilization. Include the terms zygote, endosperm
nucleus, sperm, pollen tube,
micropyle. Draw a figure showing the parts of an ovule and the events
leading to double
fertilization (include embryo sac, the eight nuclei, integuments).
Two sperms are required for
double fertilization. One sperm(1n) combines with the egg(1n)
to form a zygote(2n). This zygote
divides by mitosis to form an embryo. The embryo is made up of three
parts - cotyledon (one or
two depending if its a monocot or dicot), epicotyl (develops above
the cotyledon and forms the
stem), and the hypocotyl (develops below the cotyledon and forms
the root). The second
sperm(1n) combines with two polar nuclei (each being 1n) to form
an endosperm (3n) nucleus.
This endosperm divides by mitosis to form the endosperm of the seed.
Endosperm is a tissue
which will provide nourishment for a germinating and growing embryo
from a seed until it
becomes autotrophic. The integuments (outside the ovule)
will form a seed coat surrounding
the embryo and endosperm if present). In some plants the endosperm
is absorbed after it has
formed by the cotyledon.
Seeds consist of the following parts: embryo (cotyledon, epicotyl,
hypocotyl), endosperm (if
present) and seed coat.
In other words a mature ovule in a seed.
A peach flower contains how many ovules?
A pumpkin flower contains how many ovules?
Identify in your notes identify the structures which develop
from the zygote and the endosperm
nucleus. Include the ploidy (haploid, diploid, triploid) for these
structures.
From which flower parts do the following structures develop?
fruit, seed coat, embryo,
endosperm.
If the egg is fertilized and the ovule develops into a seed, plant
hormones will be released by the
ovule inducing the ovary to form a fruit. The function
of the fruit is one of seed dispersal.
Animal may pick up ht fruit with seeds and distribute it to other
locations.
Examples of fruits: apples, beans, corn, nuts, tomatoes, melons, etc.
In most cases if the egg is not fertilized the flower will fall off
and no fruit will be produced.
However, in some cases if the egg is not fertilized the ovary can
be forced to develop into a fruit
by plant hormones. The result of this are seedless fruits. Examples
are: grapes, oranges, bananas,
watermelons, pineapple, etc.
Parthenocarpic fruits are seedless fruits.
Check Test. Fill in the ploidy (1n, 2n, 3n) of the following structures.
| CELL NUCLEUS | PLOIDY |
| microspore | |
| megaspore mother cell | |
| polar nuclei | |
| tube nucleus | |
| endosperm | |
| cell from cotyledon | |
| zygote | |
| cell from seed coat | |
| egg |
Seed Germination and Growth of the Embryo
Refer to figures in text.
From your reading compare the germination process of a corn seed
and a bean seed. Include the
following - cotyledon, epicotyl, hypocotyl, endosperm and seed coat,
In your notes draw a figure
and label these structure of the germinating seed.
Examine the life cycle of the flowering plant. Note that during the
life cycle there are two
multicellular structures. The main plant body which is diploid is
called the sporophyte generation
and the smaller structure in the stamen and ovary which are haploid
are called the gametophyte
generation. Explain alternation of generation.
Gametophyte generation begins with meiosis of the megaspore mother
cell in the female or
meiosis of the microspore mother cell in the male and ends with
fertilization. Sporophyte
generation begins with fertilization and ends with meiosis in the
anther or ovary.
Would the sporophyte generation always be diploid?
Would the gametophyte generation always be haploid?
FOR LABORATORY WORK
Life Cycle for All Plants
sporophyte generation (2n) > mother cell (mega,micro
or plain) > meiosis > spores (mega, micro, plain) >
mitosis >form gametophyte generation (1n) > form gametes by mitosis
> fertilization > sporophyte generation (2n)
To check if you have mastered this concept work through the following
genetic problem involving
sexual reproduction in a flowering plant. The pollen from
a plant with
the genotype of "aa" is placed on the stigma of a pistil from a
plant with the genotype of "Aa".
List the genotypes for the following structures formed by the cross
described above:
| STRUCTURES | GENOTYPE |
| microspores (1n) | a only |
| megaspores (1n) | A or a |
| microspore mother cell (2n) | aa only |
| embryo(2n) - cotyledon, epi-, or hypo- | Aa or aa |
| endosperm (3n) | aAA or aaa |
| egg (1n) | A or a |
| sperm nuclei | a only |
| seed coat (2n) | Aa - develops from female flower |
| fruit (2n) | Aa - develops from female flower |
| zygote (2n) | Aa or aa |
| polar nucleus (1n) | A or a |
(five questions will be taken from the part above)
Accessory Fruit additional floral parts are included
with ovule.
(apple and pears the core is the ovary and
the fleshy tissue from floral parts)
Fruit Classification:
Simple Fruit - derived single carpel or several fused carpels
Aggregate – derived from single flower many pistils (raspberries, black berries, strawberries)
Multiple – derive from many flowers (pineapples, mulberries,
Osage orange
Simples Fruits:
Berries – flesh is soft throughout (tomato, peppers, grapes)
Drupes – inner part is hard or stony pit (peachs, cherries, plums)
Pomes - fleshy part comes from floral
parts and inner core is textured (apple,
pear)
Dry Fruits – Laboratory
From which flower parts do the following structures develop? fruit, seed coat, embryo, endosperm.
In most cases if the egg is not fertilized the flower will fall off and no fruit will be produced.
However, in some cases if the egg is not fertilized the ovary can be forced to develop into a fruit by plant hormones. The result of this are seedless fruits. Examples are: grapes, oranges, bananas, watermelons, pineapple, etc.
Parthenocarpic fruits are seedless fruits.
Apomixis - Seeds with no fertilization
Flower Types
Complete Flower - contains all four flower parts -
sepals, carpels, stamens, carpels
Incomplete Flower - lacking any of the four flower
parts
Perfect Flower - contains at least the stamen and carpel
(pistil)
Imperfect Flower - contains either a stamen or carpel
(pistil)
Male Staminate Flowers
Female Carpellate or Pistillate Flowers
Plant types:
Monoecious - Plant which contains imperfect flowers, both male and female flowers, on the same plant. Example - corn
Dioecious - Plant which contains imperfect flowers,
male or female flowers, on separate plants. Example - holly
tree
Classification of Angiosperms
Division Magnoliophyta 120 million years ago
Flowers developed with double
fertilization
Wood
Vessels in place of Tracheids
Herbaceous and Woody Plants
emerged
Magnoliopsida (dicots)
Refer to examples in text.
Liliopsida (monocots) Branched off from early dicots.
Refer to examples in text.
Subclass Arecidae - Palms, Philodendron (spadix)
Subclass Commelinidae - grasses, sedges, zebrine, spiderwort
Subclass Zingiberidae – bromeliads, banana
Subclass Liliidae – lilies, orchids
GYMNOSPERMS
Pines: Study the life cycle of a typical pine tree in the text. Note the following:
The conspicuous plant form is diploid
or the sporophyte generation.
Gametophyte generation is inconspicuous
inside of developing pine cones.
Two types of spores are formed male spores
from microspore mother cells and female spores from
megaspore mother cells.
Spores (megaspores and microspores) are
formed after meiosis which are not air borne to disperse the
genetic material of the plant. The megaspore
mother cell forms four megaspores by meiosis but only one
survives, the surviving megaspore
divides by mitosis forming a multicellular gametophyte containing
an
egg inside an ovule of the female cone.
The microspore mother cell forms four microspores by meiosis
and all four survive. Each microspore
divides by mitosis forming a multicellular gametophyte called a
pollen grain. A sperm (nonflagellated)
will form inside the pollen grain. These pollen grains are borne
inside of a male cone and mature pollen
grains are male gametophytes.
Sperm are formed by mitosis inside the pollen
grain.
Eggs are formed by mitosis inside the female
gametophyte.
Sperm are nonmotile; however the pollen
grains are wind borne..
Pine have well developed vascular tissue
(xylem and phloem).
After fertilization the ovule surrounding
the female gametophyte forms a seed. Seeds contains the young
embryo. Seed protects and nourishes the
young growing embryo.
Seeds present. No fruit, double
fertilization, or endosperm
Life cycle: zygote grows into an embryo which is encased
in a seed, the seed germinates and grows into the large conspicuous sporophyte
(2N) with true vascular tissue, the mature saprophyte produces male and
female cones, the female cone forms sporangium tissue with an egg
sac, the sporangium tissue release individual diploid cells called megaspore
mother cells into the egg sac, these megaspore mother cells divide by meiosis
forming four haploid megaspores, three of these megaspores die and only
one survives (end of sporophyte beginning of female gametophyte), the surviving
megaspore divides by mitosis into the multicellular female gametophyte
which contains a single egg in an egg sac, the male cone forms sporangium
tissue with a pollen sac, the sporangium tissue release individual diploid
cells called microspore mother cells into the pollen sac, these microspore
mother cells divide by meiosis forming four haploid microspores, (end of
sporophyte beginning of male gametophyte), each of these microscopes divide
by mitosis and forms a pollen grain with a single sperm, pollen is
released into the air (pollination) where it moves to a female cone, pollen
tube grows and the sperm moves through the tube to fertilize an egg inside
of an ovule (end of gametophyte and beginning of sporophyte), back
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