Catrina Dimayacyac

Chapter 9: Flowers and reproduction

IMPORTANT TERMS:
Alternation of Generations a life cycle with two generations, sporophyte
(diploid) and gametophyte (haploid).
Anther part of the stamen where pollen is actually produced.
Carpels constitute the gynoecium, located at the highest level on the receptacle.
Three main parts are the stigma, style, and ovary.
Coevolution A type of evolution in which two species become increasingly
adapted to each other, resulting in a highly specific interaction.
Compatibility barriers chemical reactions between pollen and carpels that
prevent pollen growth
Complete flowers flowers that have all four types of floral appendages, the
sepals, petals, stamen, and carpel.
Cotyledons In embryos of seed plants, the rather leaf-like structures involved in
either nutrient storage (most dicots and gymnosperms) or nutrient transfer from the
endosperm (most monocots)
Cross-pollination is the pollination of a carpel by pollen from a different
individual.
Double fertilization the process unique to angiosperms in which one sperm
fertilizes the egg (forming a zygote) and the other sperm fertilizes the polar nuclei
(forming the primary endosperm nucleus).
Embryo sac A common synonym for the megagametophyte of flowering
plants
Endosperm - the tissue which is formed during double fertilization only in
angiosperms and which nourishes the developing embryo and seedling.

Epicotyl embryonic shoot located above the cotyledons in the embryo of a

seed.
Fruit the structure that forms from carpels and associated tissues after
fertilization.
Gametes a haploid sex cell, such as an egg (megagamete) or sperm
(microgamete).
Gametophyte a haploid plant that produces gametes.
Heteromorphic Generations a complex life cycle, with at least three distinct
plants (one sporophyte and two gametophytes).
Hypocotyl the portion of an embryo axis located between the cotyledons and the
radicle.
Imperfect flowers A flower lacking either stamens or carpels or both
Incomplete flowers a flower that is missing one or more of the four basic
appendages (petals, sepals, stamens, carpels)
Inflorescence a discrete group of flowers.
Karyogamy fusion of the nuclei of two gametes after protoplasmic fusion.
Ovary the base of the carpel; the region that contains ovules and will develop into
a fruit.
Ovules the structure in a carpel that contains the megasporangium and will
develop into a seed.
Pedicel the stalk of an individual flower.
Perfect flower a flower that has both stamens and carpels
Petals the appendages, usually colored, on a flower, most often involved in
attracting pollinators.
Plasmogamy the fusion of the cytoplasm of two gametes during sexual
reproduction.

Pollen in seed plants, the microspores and microgametophytes (gametophyte

that produces sperm)
Pollen

tube

after

landing

on

compatible

stigma

or

gymnosperm

megasporophyll, a pollen grain germinates with a tube like (pollen tube) process
that carries the sperm cells to the vicinity of the egg cell.
Radicle the main root of a seed; it is the direct continuation of the embryonic
stem.
Receptacle the stem (axis) of a flower, to which all other parts are attached.
Seed coat the protective layer on a seed, develops from one or both
integuments.
Seeds part of a flowering plant that contains the embryo and will develop into a
new plant if sown; a fertilized and mature ovule.
Sepals in flowers, the outermost of the fundamental appendages, most often
providing protection of the flower during its development. (calyx)
Spores single cells that is a means of sexual reproduction; it can grow into a new
organism but cannot fuse like a gamete.
Sporophytes a diploid plant that produces spores.
Stamens - the organs of a flower involved in producing microspores (pollen).
Stigma in the carpel of a flower, the receptive tissue to which pollen adheres.
Style in the carpel, the tissue that elevates the stigma above the ovary
Syngamy the fusion of a sperm and an egg.
Zygote the diploid cell formed as the result of the fusion of two gametes.

REVIEW QUESTIONS:
1.Reproduction can serve two different functions. What are they?

The two different function of reproduction are producing offspring that

have identical copies of the parental genes and generating new individuals that are
genetically different from the parents.

2. Under what conditions is it selectively advantageous for a plant to produce

offspring identical to itself?
If the environment is stable during several lifetimes, it is selectively
advantageous for an organism to reproduce asexually.

3. Imagine a plant that has been well-adapted to a particular habitat, and it

has been reproducing only asexually, so all of its offspring are identical to it.
If the climate or other conditions change such that the plant can no longer
survive in the new conditions, what will happen to all of its offspring? Why?
All of its offspring will die too because they have equally the same
characteristics and adaptation with its parent.

4. With asexual reproduction, are progeny ever more fit, more adapted than
the parent?
No because in asexual reproduction, progeny are never more fit and never
more adapted than the parent.

5. Look at the apples in Fig. 9.1a, all growing on a single tree. Do all of the
seeds in all the apples in the photograph have the same maternal parent? Do
they all have the same paternal parent?
Yes, all of the seeds in all of the apples in the tree have same maternal
parent. No, they dont have the same paternal parents because all the seeds of all
the apples in the tree have different paternal parent.

6. Sexual reproduction produces offspring that are not identical to each other
or to either parent. Usually, some are more well-adapted that the parents,

some are more poorly adapted, most are about as adapted. What is one of
the beneficial aspects of this diversity?
The beneficial aspect of this diversity is in both stable environments and
changing ones, sexual reproduction provides enough diversity of progeny that at
least some are well adapted.

7.

In stable populations, ones that are neither increasing nor decreasing

in abundance (for example, there are a million trees now, there will be a
million trees a thousand years from now), about how many of a plants seeds
survive and grow to adulthood, being able to replace it when it dies? If during
the plants lifetime it produces 100, 000 seeds, how many do not survive, do
not grow and cannot replace it when it dies? (Hint: dont think of humans, we
are an increasing population, not a stable one. Almost all our children
survive, but that is not true of any other species. )
The number of plants seeds which would survive or not depends on the
means of dispersal, the sire where it is dispersed, climate, soil conditions, and
exposure to predators and pathogens. Therefore, we cannot establish a specific
number of seeds which would survive since the result varies.

8.

Describe the life cycle of us humans. Are the tissues and organs in our

bodies made up of diploid cells or haploid ones? Our reproductive organs

make sperm cells in males and egg cells in females. Is this done by mitosis or
meiosis? When our bodies make gametes, does every cell in our body
become a sperm cell or an egg cell, or do just some of the cells in our
reproductive organ do this? Can our haploid sperm and egg cells undergo
mitosis and grow into new animals that look like us but are haploid instead?
(Haploid eggs do grow in bees. They develop into males.) Once a fertilized
egg (zygote) is formed, is it diploid or haploid? Can it immediately undergo
meiosis to make four new sperm cells or egg cells or can it only grow by
mitosis into another person?

The life cycle of mammals such as humans involves the production of haploid

sex cells called gametes of the sex organs by meiosis.

The production of gametes is done by meiosis.

No, only some of the cells in our reproductive organ do this.

No, this haploid cells cannot undergo mitosis and grow into new animals.

A fertilized egg (zygote) becomes diploid.

It can only grow by mitosis into another person.

9.

The plants we are familiar with are called sporophytes or the

sporophyte generation. Do these plants have bodies made up of diploid cells

or haploid ones? In which organs does meiosis occur (two are correct)the
leaves, stems, stamens, roots, carpels or petals? When plants undergo
meiosis, do all cells become haploid, or does meiosis occur in just few cells in
some flower parts?
The sporophytes are made up of diploid cells. Meiosis occurs in the stamens
and carpels. When plants (i.e. sporophytes) undergo meiosis, all cells first become
haploid and not divide into a diploid plant itself resulting into a haploid plant. The
gametes of this haploid plant then undergo syngamy, which results into a new
diploid sporophyte.

10

In animals, meiosis produces gametes (sperm cells and egg cells), but

that does not happen in plants. When some of the cells of a sporophyte
undergo meiosis, what types of cells are produced? What do they grow into?
When some of the cells of a sporophyte undergo meiosis, it grows into an
entire new haploid plant called gametophyte with egg cells and sperm cells
produced. They grow into a diploid sporophyte after it undergoes syngamy forming
a zygote, which then turns into a new diploid sporophyte.

11.

What is a gametophyte? How many different types of gametophytes

are there in a plant life cycle? What do they look like (hint: Fig. 9.5b)? Do the
sporophytes and gametophytes of seed plants ever look like each other?
A gametophyte is a haploid plant that produces gametes. (-phyte meaning
plant, gameto- meaning produces gametes). There are two types of gametophytes:
the

microgametophytes

(male

gametes

or

sperm

produced)

and

the

megagametophye (female gametes or egg). Microgametophytes looks like a pollen

grain with two sperm cells, pollen tube and a vegetative nucleus while the
megagametophyte appears to be oval with one egg and only one polar nuclei in the
middle. A haploid gametophyte does not even remotely resemble a diploid
sporophyte since gametophytes are only tiny mass of cells with no roots, stems,
leaves, or vascular tissues but it is an entire plant. On the other hand, sporophytes
appear to have sex organs located in the flowers in angiosperms.

12.

Draw and label a microgametophyte of a flowering plant. What type of

gamete does it produce? Draw and label a megagametophyte of a flowering

plant. What type of gamete does it produce?

A MICROGAMETOPHYTE.
A microgametophyte produces the sperm cell (gamete)

A MEGAGAMETOPHYTE.

13.

A megagametophyte produces the egg cell (gamete)

Flowers typically have many parts, although some flowers can be

missing some of the standard parts. What is the name of each of the
following parts:
a.

The stalk of the flower pedicel

b.

The end of the stalk, where the other parts are attached receptacle

c.

The parts that are usually green and protect the flower bud as it develops

sepals
d.

The parts that attract pollinators petals

e.

The parts that produce pollen stamens

f.

The parts that receive pollen and which contain ovules carpels

14.

If a flower has all of the parts c, d, e, and f in Question 13 they are said

to be complete flowers. Parts e and f are especially important because they

produce the reproductive cells, the spores. If a flower has both e and f in

Question 13, they are perfect flowers. If they are missing either e or f or
both, they are imperfect flowers.
15.

In flowers that are pollinated by wind or water, Sepals and petals of wind-

pollinated and water-pollinated flowers are often absent and the flowers are
normally inconspicuous although well exposed. Which of the parts in Question 13

is often missing?
Sepals and petals are often missing when they are pollinated by wind
and water.
16.

What is the difference between a perfect and an imperfect flower?

What is the difference between a complete and an incomplete flower?

A perfect flower has both stamens and carpels while an imperfect flower
lacks either the stamens or carpels or both. A complete flower has all the four basic
parts a flower should have namely the petals, sepals, stamens and carpels while an
incomplete flower lacks wither one or more of the four basic parts.

17.

A stamen usually has two parts. The stalk is called a filament and an

upper portion, the anther, which produces the pollen. Only some of the cells
in the upper part undergo meiosis and become pollen grains (microspores).
Those cells are called microspore mother cells or microsporocytes .
Neighboring anther cells, in a layer called the tapetum, act as nurse cells.
18.

Carpels usually have three parts: a stigma that catches pollen grains, a

style that elevates the first part, and an ovary where megaspores are
produced. In this last part, there are placentae that bear small structures
called ovules each with a short stalk called a funiculus and a central mass of
parenchyma called nucellus. One cell in the nucellus will be the megaspore
mother cell or megasporocytes.

19. The megaspore in most flowering plants grows into a megagametophyte

that has seven cells and eight nuclei. Name and describe the seven cells.
The seven cells are one large central cell with two polar nuclei, three
antipodal cells and an egg apparatus.
(1)The large central cell of the embryo sac contains (2) two polar nuclei
and (3) antipodal cells fuse with one of the sperm nuclei to form a highly nutritive
tissue, the endosperm. The three antipodal cells also form on the opposite
(chalazal) end of ovule and later degenerate, serving no obvious function. (1) egg
apparatus is surrounded by a pair of synergids that aid in pollen reaching the egg.

20. After pollen lands on a stigma, it is far away from the ovule with the
megagametophye, which holds the egg (megagamete). How are the two
sperm cells transported from the stigma to the egg?
They are carried by the pollen tube. The pollen tube is the male gametophyte
of seed plants that acts as a conduit to transport the male gamete cells from the
pollen grain, either from the stigma (in flowering plants or angiosperms) to the
ovules at the base of the pistil, or directly through ovule tissue in some
gymnosperms (conifers and gnetophytes).

21. In angiosperms, as a sperm cell enters the egg, it loses both

Mitochondria and . Plastids

such that only the sperm cell nucleus

contributes any DNA to the new zygote. In gymnosperms,

however, the

sperm cell loses only its Mitochondria such that the zygote inherits both
plastids and a nucleus from the sperm cell.
22. After the sperm cell enters a synergid, one fertilizes the egg in a two-step
process. First, there is a fusion of the sper cells protoplasm with that of the
egg, a step called Plasmogamy. Then the sperm cell nucleus fuses with the
egg cell nucleus, the second step called Karyogamy.

23. What happens to the second sperm nucleus, the one that does not
fertilize the egg cell? What is the tissue that develops from this second
fertilization? How is coconut related to this?
a. The second sperm nucleus released from the pollen tube migrates
from the synergid into the central cell. It undergoes karyogamy with
both polar nuclei establishing a triploid containing three full sets of
genes.
b. Endosperm
c.In double fertilization, the endosperm nucleus initiates a dynamic
cytoplasm and the central cell enlarges enormously into a huge cell
with hundreds of nuclei. When the division stops, the dense cytoplasm
fathers around the nuclei. Walls are constructed, thus forming cells.
As for its relation to coconut, the hollow center of a coconut is one
single cell, and the milk is the protoplasm. The coconut meat is the
region where nuclei form cells.

24. In most eudicot seeds, the parts of the embryo are very easy to see.
Describe each of these parts: a. Cotyledons
Epicotyl

b. Radicle

c. Hypocotyl

d.

e. How is the radicle involved in these different root systems

(fibrous and taproot)

a. Cotyledons (seed leaves) are the primordia that initiate from the
end of the embryo farther from the suspensor, they are formed in
embryogenesis. Monocots have only one cotyledon while Dicots have
two.
b. A radicle is the elongation cylinder of an embryo. It is an embryonic
root that becomes the primary root. It contains several primordia for
lateral roots in its pericycle.
c. The hypocotyl is the root junction. It is the stem of the germinating
seed that is found below the cotyledons and above the radicle.

d. The epicotyl is the embryonic shoot above the cotyledons. In most

plants the epicotyl will eventually develop into the leaves of the plant.
e. In a taproot system, the taproot arises from the radicle while in a
fibrous root system, roots arise after the radicle has died.

25. What are albuminous and exalbuminous seeds? Consider corn, peas, and
beansWhich of these seeds are which?
Albuminous seed is mature seed in which endosperm is rather abundant.
Exalbuminous seed is seed in which endosperm is sparse or absent at maturity.
Corn is an example of an Albuminous seed. Peas and beans are example of an
Exalbuminous seed

26.

A After pollination and fertilization, as the ovule develops into a seed,

the ovary matures into a fruit. Many of these have three parts, the exocarp
is the skin or peel, the mesocarp is the flesh and the innermost layer, the
endocarp, may be tough like the pit of a cherry.
27.

What is the difference between self-pollination and cross pollination? If

pollen is transferred from the stamens of a flower to the stigma of the very
same flower, is that cross pollination or self-pollination? If it is transferred
from the stamen of one flower to the stigma of another flower on a different
plant, but a plant that is clone of the first one? Animals dont have pollen, of
course but why is it that most animals never have to worry about the
equivalent problem of self-fertilization? Why cant most animals fertilize
themselves?
Self-pollination is pollination of a carpel by pollen of the same flower or
another flower on the same plant. Self-pollination has the same result as asexual
reproduction because all genes come from the same parent , also self-pollination
allows to set seed and propagate its genes rather lose them when the plants die.

If pollen is transferred from the stamens of a flower to the stigma of the very
same flower that is self-pollination. If it is transferred from the stamen of one flower
to the stigma of another flower on a different plant, but a plant that is clone of the
first one that is still a self-pollination.
Cross pollination is the pollination of a carpel by pollen from a different
individual. With cross pollination, sperm cells and egg cells from different plant
unite, resulting in the new combination of genes.
Animals never have to worry about the equivalent problem of self-fertilization
because they cannot self-fertilize themselves. No individual animal can fertilize
itself. Animals must undergo fertilization by sex cells which are not identical to
increase the genetic diversity of the offspiring.

28.

Describe a species that is dioecious. Name several examples. In order

for sexual reproduction to occur in a dioecious species, how many separate

plants must be involved? Name them all.
A species that is dioecious have individuals that produce only stamminate flowers
and others that produce only carpellate flowers. Marijuana, Dates, Papaya and
Willows are some exmples of Dioecious. There are 4 separate plants involved in
Dioecious they are:
a.

Microgametophytes

b.

Megagametophytes

c.

Staminate sporophytes

d.

Carpellate sporophytes

29. Describe a monoecious species. Name several examples.

A species that is monoecious have stamminate and carpellate flowers on the
same plant. Corn and Cattails are some example of Monoecious

30.

In several and animal species, plants have become modified such that

only its animal partner can pollinate it, and the animals have become
modified such that only its animal partner can pollinate just their plant
partner. What is the name of this type of evolution that results in two
organisms becoming particularly adapted to and dependent on each other?
Coevolution is the type of evolution that results in two organisms becoming
particularly adapted to and dependent on each other

31. Explain the following terms: inferior ovary, superior ovary, actinomorphic
flower, zygomorphic flower. How is each of these modifications selectively
advantageous?
Inferior Ovary-An inferior ovary lies below the attachment of other floral
parts. A pome is a type of fleshy fruit that is often cited as an example, but close
inspection of some pomes (such as Pyracantha) will show that it is really a halfinferior ovary. Flowers with inferior ovaries are termed epigynous. Some examples
of flowers with an inferior ovary are orchids (inferior capsule), Fuchsia (inferior
berry), Asteraceae (inferior achene-like fruit, called a cypsela).
Superior Ovary-A superior ovary is an ovary attached to the receptacle
above the attachment of other floral parts. A superior ovary is found in types of
fleshy fruits such as true berries, drupes, etc. A flower with this arrangement is
described as hypogynous. An example is Hypericum calycinum.
Actinomorphic Flower-Most flowers are actinomorphic ("star shaped",
"radial"), meaning they can be divided into 3 or more identical sectors which are
related to each other by rotation about the centre of the flower. Typically, each
sector might contain one tepal or one petal and one sepal and so on. It may or may
not be possible to divide the flower into symmetrical halves by the same number of
longitudinal planes passing through the axis: Oleander is an example of a flower
without such mirror planes. Actinomorphic flowers are also called radially
symmetrical or regular flowers. Other examples of actinomorphic flowers are the lily
(Lilium, Liliaceae) and the buttercup (Ranunculus, Ranunculaceae).

Zygomorphic Flower- Zygomorphic ("yoke shaped", "bilateral" shape)

flowers can be divided by only a single plane into two mirror-image halves, much
like a yoke or a person's face. Examples are orchids and the flowers of most
members of the Lamiales (e.g., Scrophulariaceae and Gesneriaceae). Zygomorphic
flowers generally have petals of two more different shapes, sizes, and colors. Least
commonly, flowers may have no axis of symmetry at all, typically because their
parts are spirally arranged.

32. What is an inflorescence? The inflorescences of a sausage tree (Figure 929) hang far down out of the tree. How is this of benefit to bats? Why can the
inflorescence of Combretum (Figure 9-30b)attract more pollinators than can
the individual flowers?
Inflorescence is a discrete group of flowers . Flowers of sausage trees (Kigelia)
are pollinated by bats, which do not like to fly among the clutter of leaves because
their sonar does not work well there. Long stalks allow flowers to hang open air
where bats have free access to them.

33. After pollination and then fertilization, what usually happens to each of
the following: stigma, style, carpel, ovule, interguments, and zygote?
Stigma-the base of the stigma turns into the fruit.
Zygote- develops into embryo
Ovule-becomes the seed.
The rest-withers.

34. Fruits are often classified as dry or fleshy. What is the difference? Which
of these two are dehisent, which are indehisent?
Fleshy fruits types are the berry, in which the entire pericarp is soft and pulpy
(e.g., the grape, tomato, banana, pepo, hesperidium, and blueberry) and the drupe,
in which the outer layers may be pulpy, fibrous, or leathery and the endocarp
hardens into a pit or stone enclosing one or more seeds (e.g., the peach, cherry,
olive, coconut, and walnut). The name fruit is often applied loosely to all edible plant

products and specifically to the fleshy fruits, some of which (e.g., eggplant,
tomatoes, and squash) are commonly called vegetables. While Fleshy fruits types
are the berry, in which the entire pericarp is soft and pulpy (e.g., the grape, tomato,
banana, pepo, hesperidium, and blueberry) and the drupe, in which the outer layers
may be pulpy, fibrous, or leathery and the endocarp hardens into a pit or stone
enclosing one or more seeds (e.g., the peach, cherry, olive, coconut, and walnut).
The name fruit is often applied loosely to all edible plant products and specifically to
the fleshy fruits, some of which (e.g., eggplant, tomatoes, and squash) are
commonly called vegetables.

35. in ordinary english, we use the word fruit to mean something sweet and
juicy; however, the following things are fruits; peanut shells, pea pods, bell
peppers, and chilli peppers. What is the characteristic that lets us know
these really are fruits even though they are not sweet? In contrast, bananas
are fruits that do not have this characteristic (they are sterile and new plants
must be grown from buds but sprout near the base of the plant).
Fruits that consist of ripened ovaries and other parts such as the receptacle
or bracts, as in the apple, are called accessory fruits or false fruits. To most of us, a
fruit is a plant part that is eaten as a dessert or snack because it is sweet, but to a
botanist a fruit is a mature ovary of a plant, and as such it may or may not taste
sweet."

36. Some things that we call fruits are not true fruits but instead are
accessory (false) fruits. What is the red part of a strawberry, and what are
the true strawberry fruits? (Hint: see Figure 9-32a) In an apple, what is the
fleshy part that we eat, and what is the core that we throw away?
a. The red part of the strawberry is its receptacle. The true strawberry fruits
are its seeds that came from its ovary.
b. Similarly, in an apple, the fleshy part that we eat is its receptacle and the
core that we throw away is actually its fruit.