Integrated Science SME

Key Unit competence: Describe modes of reproduction in plants
                                              and apply various methods of asexual and
                                              Sexual reproduction as means of increasing
                                              crop yield.

Introductory Activity 14
A.
The kingdom Plantae comprises about 260,000 known species including
flowering and non-flowering plants. All plants have a general organization
which includes vegetative and reproductive organs. Plants reproduce
through different ways. Use the books and other source of information to
do the following:

1. Write on how lower organisms such unicellular plant and another like
cassava, sugar cane and apple reproduce.

2. Describe the techniques used by people to grow Irish potatoes,
cassava and bananas.

3. Describe each of the following methods of asexual reproduction:
fragmentation, budding and spore formation.

B.
1. Observe the following pictures and suggest what is going on.

2. How are the pictures below related to reproduction in flowering plants.

14.1. Comparison between sexual and asexual reproduction

Application activity 14.1

Observe the figures below taken from environment and answer the
following questions.

a). Name the figure A and B.
b). Where the smallest (young ones) of banana come from?
c). How the young bananas have been reproduced?
d). How the young one of goat has been reproduced?
e). Compare the modes of reproduction of banana plant and a goat.

Asexual Reproduction

Prokaryote like bacteria and unicellular organisms reproduce asexually by
cell division or binary fission of the parent cell. This is a type of reproduction
done by a single organism without production of gametes. It usually results
in the production of identical offspring, the only genetic variation arising as a
result of random mutation among the individuals.

Sexual Reproduction
Sexual reproduction is a type of reproduction in which two parents are
involved, each capable of producing gametes. It is essentially cellular in
nature which involves the fertilization of one haploid gamete with another,
producing a new diploid cell called the zygote. The union of structurally
similar physiologically different gametes is called isogamy. This is found
only in lower forms such as Protozoa. The following is summary table of
difference between asexual and sexual reproduction.

Application activity 14.1
1. Distinguish sexual and asexual reproduction.

14.2. Asexual reproduction in plants

14.2.1. Asexual reproduction and its methods

Activity 14.2.1.a
Brainstorm on asexual reproduction in lower organisms and write reports
as an out-of-class activity.
There are five common modes of asexual reproduction: fission, budding,
vegetative reproduction, spore formation and fragmentation.

1. Fission
An important form of fission is binary fission. In binary fission, the parent
organism is replaced by two daughter organisms, because it literally divides
in two. Organisms, prokaryotes, and eukaryotes (such as unicellular fungi),
reproduce asexually through binary fission; most of these are also capable
of sexual reproduction. Another type of fission is multiple fission that is
advantageous to the plant life cycle. Multiple fission at the cellular level
occurs in many algae. The nucleus of the parent cell divides several times by
mitosis, producing several nuclei. The cytoplasm then separates, creating
multiple daughter cells.

2. Budding
Some cells split via budding resulting in a ‘mother’ and ‘daughter’ cell. The
offspring organism is smaller than the parent. Budding is also known on a
multicellular level.

3. Vegetative reproduction
Vegetative reproduction is a type of asexual reproduction found in plants
where new individuals are formed without the production of seeds or spores
by meiosis or syngamy. Examples of vegetative reproduction include the
formation of miniaturized plants called plantlets on specialized leaves (for
example in kalanchoe) and some produce new plants out of rhizomes or
stolon (for example in strawberry). Other plants reproduce by forming bulbs
or tubers (for example tulip bulbs and dahlia tubers). Some plants produce
adventitious shoots and suckers that form along their lateral roots.
Plants that reproduce vegetative may form a clonal colony, where all the
individuals are clones, and the clones may cover a large area.

4. Spore formation
Many multicellular organisms form spores during their biological life cycle in
a process called sporogenesis. Plants and many algae on the other hand
undergo sporic meiosis where meiosis leads to the formation of haploid
spores rather than gametes. These spores grow into multicellular individuals
(called gametophytes in the case of plants) without a fertilization event. Then
in the plant life cycle. Fungi and some algae can also utilize true asexual
spore formation, which involves mitosis giving rise to reproductive cells
called mitospores that develop into a new organism after dispersal.

Activity 14.2.1.b
Demonstration of asexual reproduction by fragmentation in algae

Requirements
Glass beakers of 500ml, Scalpel, Forceps, Pins, Spatula, Weighing
balance, Labels, Artificial, fertilizers, Clear river water and Spirogyra
(algae).

Procedure
1. Label five beakers of the same size as A, B, C, D and E. Pour water
in each beaker. Weigh several measures of artificial fertilizers of 1 g
each.
2. Transfer 1g of fertilizer to beaker A, then 2g to beaker B, 3g to beaker
C, 4g to beaker D Then lastly put 5g of fertilizers to beaker E. Note
the concentration of fertilizers is increasing from A- E.
3. Using forceps pick spirogyra and put it on a tile. Add several drops
of water to avoid drying. Tease off a piece of spirogyra using a pin.
Cut that piece into 5 fragments of the same length and transfer each
piece into the beaker.
4. Stand the beakers in a place where they can receive adequate sunlight
for the seven days. On the next day start to examine the fragments in
each beaker every day and record any observable changes such the
increase in size of the spirogyra.
Draw a table as this shown here and record your observation

5. Fragmentation
Fragmentation is a form of asexual reproduction where a new organism
grows from a fragment of the parent. Each fragment develops into a mature,
fully grown individual. Fragmentation is seen in many organisms such as
fungi, and plants. Some plants have specialized structures for reproduction
via fragmentation, such as gemma in liverworts. Most lichens, which are a

symbiotic union of a fungus and photosynthetic algae, reproduce through
fragmentation to ensure that new individuals contain both symbionts. These
fragments can take the form of soredia, dust-like particles consisting of
fungal hyphen wrapped around photobiont cells.

Application activity 14.2.1
1. Write on the types of asexual reproduction.
2. Explain the term fragmentation and give one example of plant which
reproduces by using this type of asexual reproduction.

14.2.2. Advantages and disadvantages of asexual reproduction

Activity 14.2.2

Make discussion on asexual reproduction in lower organisms and higher
plants, outlining advantages and disadvantages.

a. Advantages of asexual reproduction
• As it occurs by mitosis,the offspring are genetically identical not only
to their parents but also amongst themselves. This is advantageous,
for example in agriculture where successive generations of plant retain
the desired qualities or high yield of flowers, fruits and cereals.
• It is faster as it does not involve stages such development of gonads,
gamete formation, fertilization, fruit and seed formation and their
dispersal. So plant can be rapidly propagated vegetatively using
cuttings, bulbs, offsets and other parts.

b. Disadvantages of asexual reproduction
• It is suited to the environments that are generally stable in terms of
humidity, soil, temperature and light. If there is a drastic change in the
environment, the individuals may not be able to cope with the change
and so gradually die off.

• It can lead to overcrowding of the individuals plants around the parent
plant and this can lead to excessive competition for soil nutrients, light
and moisture. The new individuals will therefore become weak and
only a few may survive.

Application activity 14.2.2
Explain the advantages and disadvantages of asexual reproduction.

14.2.3. Vegetative and artificial propagation in flowering plants

Activity 14.2.3

Demonstration of asexual reproduction in plants by cuttings

Requirements
Growth medium or moist soil, sweet potatoes vines, elephant grass,
sugarcane or cassava stems, secateurs/sharp knife and rooting hormone.

Procedure
1. Collect clean and healthy stems from cassava, sugarcane or potato
plants.
2. Using a secateurs/sharp knife, cut the stem of either cassava,
sugarcane or sweet potato stems into suitable sizes.
3. Place them in either suitable medium of growth or apply rooting
hormone if available or plant them in moist soil in the school garden.
4. Leave the set up for about 13 days, and then observe the development
of roots and leaves at nodes.
Draw and record what you will observe after 13 days on the development
of roots and leaves at nodes.

Artificial vegetative propagation is the deliberate production of new plants
from parts of old plants by humans. This can be done by following three
methods: Cutting, layering, and grafting.

a. Cutting
This is simple procedure in which part of the plant is removed by cutting and
placed in a suitable medium for grow. The part of the plant which is removed
by cutting it from the parent plant is called a ‘cutting’. In this method one-
year-old stem of root is cut from a distance of 20 to 30 cm. and is buried in
the moist soil in natural position. After sometime, roots develop from this
cutting and it grows into a new plant. This method is commonly used in rose
and sugar cane. Care is taken that nodes which were lower in parent plant
(morphologically) are put in the soil, while the morphologically higher nodes
are kept up. Adventitious roots are given off at the lower nodes.

b. Layering
This method of vegetative propagation is used in those plants whose soft
branches occur near the ground such as jasmine plant. In this method, a
branch of the plant which is near to the ground is pulled towards the ground
and a part of this branch is covered with moist soil leaving the tip of this
branch above the ground. After sometime, roots develop from that part of
the branch which was buried in the soil. This branch is then cut of along with
the roots from the parent plant and develops into a new plant. This method
of asexual reproduction is also used in the production of plants such as
Bougainvillea, jasmine, guava, strawberries, lemon, China rose etc.

c. Grafting
In this method of vegetative propagation the stems of two different plants are
joined together so as to produce a new plant containing the characters of
both plants. Out of the two plants one plant has a strong root system while
the other has a better flower or fruit yield. The plant of which the root system
is taken is called ‘stock’, while the other plant of which the shoot is selected
is known as ‘scion’ or ‘graft’. These two stems i.e. the stock and the scion
are fitted together by making slanting cuts in them and bound tightly with a
piece of cloth and is covered with a polythene sheet.

While joining the scion with the stock care should be taken that the diameter
of the stock and scion chosen for grafting should be equal. Scion gets the
mineral and water from the soil through the stock and develops branches
and produce fruits. This method of propagation is used in mango, apple,
banana, pear, grape, pineapple and peach.

Vegetative and artificial reproduction in flowering plants
The reproductive part of the plant is a flower. The union of male and female
gametes to form a zygote is called fertilization. The transfer of pollen grains
from the anther to the stigma of the same flower or the different flower is
called pollination. In nature, plants reproduce asexually in a variety of ways.
The vegetative reproductive parts in flowering plant are stem, branches, and
leaves and they have the following characteristics:

Characteristics of the stem
• Stem develops from the plumule of embryo.
• Stem is generally the ascending part of the plant axis.
• It bears a terminal bud for growth in length.
• The stem is differentiated into nodes and internodes. The stem nodes
possess dissimilar appendages called leaves.

• The young stem is green and capable of performing photosynthesis.
• In the mature state it bears flowers and fruits. Leaves and stem
branches develop exogenously.
• Stem exposes leaves, flowers and fruits to their most suitable position
in the aerial environment for optimum function, Hair, if present, is
commonly multicellula.
• Stems are usually positively phototropic, negatively geotropic and
negatively hydrotropic.

Characteristics of the leaf
• It is dissimilar lateral flattened outgrowth of the stem.
• The leaf is exogenous in origin.
• It is borne on the stem in the region of a node.
• An axillary bud is often present in the axil of the leaf.
• Leaf has limited growth. An apical bud or a regular growing point is
absent.
• The leaf base may possess two lateral outgrowths called stipules.
• A leaf is differentiated into three parts: leaf base, petiole and lamina.
• The lamina possesses prominent vascular strands called veins.
• It is green and specialized to perform photosynthesis.
• Leaf bears abundant stomata for exchange of gases and it is the major
seat of transpiration.

Characteristics of the branches
A branch or tree branch is a woody structural member connected to but not
part of the central trunk of a tree. Large branches are known as boughs
and small branches are known as twigs. Due to a broad range of species of
trees, branches and twigs can be found in many different shapes and sizes.

Application activity 14.2.3
1. Discuss on the methods of artificial vegetative propagation.
2. Cassava produces flowers, fruits and seeds. Why people prefer to
grow cassava by cutting rather than using seed?

14.2.4. Application of artificial propagation in growing improved
varieties of plants

Activity 14.2.4

Using addition resources to your textbook available in your school such
as the books from the school library and search further information from
the internet. Discuss on application of artificial propagation in growing
improved varieties of plants.

Artificial vegetative propagation is usually used in agriculture for the
propagation (or reproduction) of those plants which produce either very few
seeds or do not produce viable seeds. Some examples of such plants which
are reproduced by artificial vegetative propagation methods are: Banana,
Pineapple, Orange, Grape, Rose, etc.

Vegetative propagation of particular cultivars that have desirable
characteristics is very common practice. Reasons for preferring vegetative
rather than sexual means of reproduction vary, but commonly include greater
ease and speed of propagation of certain plants, such as many perennial root
crops and vines. Another major attraction is that the resulting plant amounts
to a clone of the parent plant and accordingly is of a more predictable quality
than most seedlings. However, as can be seen in many variegated plants,
this does not always apply, because many plants actually are chimeras and
cuttings might reflect the attributes of only one or some of the parent cell
lines.

Man-made methods of vegetative reproduction are usually enhancements
of natural processes, but they range from rooting cuttings to grafting and
artificial propagation by laboratory tissue culture. In horticulture, a “cutting”
is a piece that has been cut off from a mother plant and then caused to
grow into a whole plant. A popular use of grafting is to produce fruit trees,
sometimes with more than one variety of the same fruit species growing from
the same stem. Rootstocks for fruit trees are either seedlings or propagated
by layering.

Application activity 14.2.4
1. Describe the methods of artificial vegetative propagation.
2. Elaborate on the characteristics of vegetative reproductive parts
in a flowering plant
3. Explain the application of artificial propagation in growing
improved varieties of plants.

14.3. Sexual reproduction in plants

14.3.1. Alternation of generation in bryophytes and
pteridophytes

Activity 14.3.1
Visit library and computer lab and search the comparison of the lifecycles
of mosses and ferns and present them on Manilla paper.

The life cycle of an organism is the progressive sequence of changes
which an organism goes through from the moment of fertilization to death.
During its life cycle, the organism produces new generations of individuals
which repeat continuously the process. New generations are produced by
reproduction, which may be sexual or asexual. The life cycle involves the
mitosis and meiosis. In this lesson, we will make concern on how meiosis
can affect the life cycle of living organisms.

The life cycle is seen in seaweeds, mosses ferns and their relatives. Their
life cycles start with the sexually mature adult plants. Since they produce
gametes, they are called the gametophytes (gamete plants). These are
haploid, as they produce eggs and sperms. The egg and sperm fuse to
produce a diploid zygote, but this does not develop directly into a new
gametophyte. Instead it grows (by mitotic divisions) into another plant which
is quite distinct from the gametophyte called sporophyte (spore plant).The
function of sporophyte is to produce spores.In bryophytes, the sporophyte
depends on gametophyte for nourishment. As spores are formed by meiosis,
they are haploid. When the later are dispersed by wind on suitable soil,
they germinate and grow by mitosis into gametophytes, which then repeat
the sequence of life cycle. Ferns and mosses consist of two distinct plants:
haploid gametophyte and diploid sporophyte, which alternate each other
within the life cycle. This phenomenon is known as alternation of generation.

So, Alternation of generation is a phenomenon in the plant life cycle in which
a diploid stage a sporophyte alternates with a haploid stage of gametophyte.

The importance of alternation of generation to organisms
• Spores produced can survive hash conditions and only germinate
when conditions are favorable.
• It ensures rapid multiplication of the plant species as spores are usually
produced in vast numbers.
• Interdependence between the gametophyte and sporophyte
generations ensure that both generations exist at any given time. This
prevents extinction of the plant species.

The life cycle in mosses involves alternation of generations between the
diploid (2n)sporophyte and haploid gametophyte. In bryophytes, the
gametophyte is adominant stage of the life cycle, while the sporophyte is
dependent on gametophyte for supplying water and nutrients. Gametes are
formed in special reproductive organs at the tips of gametophytes.Sperms
are produced in antheridia (singular: antheridium), and eggs in archegonia
(singular: archegonium). Some species produce both sperms and eggs on
the same plant, whereas others produce sperms and eggs on separate
plants.

During fertilization which requires water, the sperms released from antheridia
fuse with the eggs and form a diploid (2n) zygote. The zygote grows into
the sporophyte. Sporophyte is a long stalk ending in a capsule in which
haploid spores are formed by meiosis. When spores become mature

enough, the capsule bursts and spores are scattered by wind. Under suitable
conditions, spores then germinate by forming underground filaments called
protonemata (singular: protonema). Small buds produced by protonemata
give rise to new gametophyte plants which can start the cycle again.

Bryophytes grow in habitats where water is available constantly because for
fertilization to occur, the sperm of bryophyte must swim to an egg. Without
water, this movement is impossible. Because of this dependence on water
for reproduction, bryophytes must live in habitats where water is available at
least part of the year.

b. Alternation of generations in pteridophytes (ferns)

Pteridophytes also exhibit alternation of generations. Ferns are formed
of true roots, stem and leaves (fronds) with vascular tissues. They have
lignified tissues. The horizontal underground stem is called rhizome which
bears adventitious roots. The leafy plant is a sporophyte. Mature leaves
commonly called fronds bearing yellow or orange masses of sporangia
which are grouped into the structures called sori (singular: sorus) on their
lower side.

Ferns have a life cycle in which the diploid (2n) sporophyte is the dominant
generation, large (some fern trees can have 7 m of height), and differentiated
into leaf, stem and roots with vascular tissues, while the haploid gametophyte
(prothallus) is very simple with few millimeters. In ferns, the sporophyte
produces haploid spores by meiosis. This is done on the underside of the
leaf called frond, in sporangia (singular: sporangium). Sporangia are grouped
into sori (singular: sorus).

When spores are mature enough, the sporangia burst and spores are
released on ground. If conditions are favorable, spores germinate and grow
into the haploid heart-shaped gametophytes , which grows independently
of sporophyte. Antheridia and archegonia found underside of gametophyte
produce sperms and eggs respectively. During fertilization, sperms swim
towards eggs and fuse together to form diploid zygotes, which grow and
develop into new sporophytes. As sporophyte grows, the gametophyte dries
and dies.

Application activity 14.3
1. Explain the meaning of the term alternation of generation.
2. How is water essential in the life cycle of a bryophyte?
3. What is the archegonium and antheridium?
4. How are these structures important in the life cycle of a moss plant?
5. What is the dominant stage of the fern life cycle?
6. Explain the relationship of the fern gametophyte and sporophyte.
7. Compare the gametophyte and sporophyte stages of the plant cycle.
Which is haploid? Which is diploid?
8. How do bryophytes reproduce asexually?

14.3.2. Types, structure and functions of flowers

Activity 14.3.2

Collect different forms of flowers from the school compound or around the
school, such as hibiscus, morning glory, sweet potato, or maize flower (or
any type of flower in your community not necessarily the ones mentioned
here)
1. Observe and describe the structures of collected flowers.
2. How do collected flowers differ externally?
3. Cut one of the flowers into two halves, draw and label one half of
flower.

A typical hermaphrodite or bisexual flower contains the following parts:
• Pedicel: It is the stalk which attaches the flower on the main floral axis.

• Receptacle: It is the swollen part at the end of the stalk where other
parts of the flower are attached.

• The calyx: It is the set of sepals, generally having green colour. They
protect the internal parts of the flower. In some plants, the sepals are
coloured and are called petaloids.

• The corolla: It is the set of petals, with different colours and nectar
glands that produce sugary substances which participate in attraction of
pollinating agents. In some plants, the petals are green and are called
sepaloids. Both calyx and corolla are collectively called perianth. They
are called floral envelope or accessory organs as they do not participate
directly in reproduction, or in formation of fruits and seeds, they all insure
the protection of internal parts of the flower.

• Androecium: It is the male reproductive organs of the flower. It consists
of many stamens. A stamen consists of: the filament which supports
anther, and anther which contains the pollen grains or male gametes.

• Gynoecium/pistil: It is the female reproductive organ. It consists of
many carpels, and each carpel is made of: stigma (plural: stigmata),
style and ovary with ovules.

a). The stigma: Receive pollen grains from anther during pollination.
b). Style: Supports the stigma in a good position to receive pollen grains.
c). Ovary: A sac where ovules are produced. Ovules become seeds
after fertilisation.

b. Types of flowers
1. According to absence of some reproductive parts of the flower, we can
distinguish:

i. Unisexual flower: A flower that consists of one type of reproductive
organ. This can be staminate: unisexual male (with androecium
only), or carpellate: unisexual female (with gynoecium only). E.g.
flower of papaya.

ii. Bisexual or hermaphrodite flower: A fl ower with the two
reproductive organs. It contains both male and female reproductive
organs (androecium and gynoecium). E.g. flowers of beans.
Dioecious plants are plants that have male flowers and female flowers
on separate plants (e.g. papaya/pawpaw) while monoecious plants
are plants that have both male and female flowers on the same plant
(e.g. maize).

2. According to the position of ovary in the point of insertion of calyx, corolla
and stamen, we can distinguish:
i. A flower with inferior ovary: It is when the ovary is located below
the point of insertion of calyx, corolla and stamens.

ii. A flower with superior ovary: It is when the ovary is located over
the point of insertion of calyx, corolla and stamens.

iii. The semi-infer or semi-super flower: When ovary is neither infer
nor super but in the middle of receptacle which is hollowed.
• When sepals are joined together, the flowers are called gamosepal,
and where are not joined together, the flower is called dialysepal.
• When petals are joined together, the flowers are called gamopetal,
and when are not joined together, the flower is called dialypetal.
When they are absent, the flower is called apetal.

3. According to the shape and symmetry of the flower, we can distinguish:

i. Zygomorphic or irregular flower: A flower with a bilateral symmetry.
The flower cannot be divided into two similar halves. E.g. flowers of
beans, cassia.

ii. Actinomorphic or regular flower: A flower with a radial symmetry.
The flower can be divided into two or more planes to produce similar
halves. E.g. flowers of coffee, orange.

4. Dichogany: It is when male and female organs of the flower mature at
different times. We can distinguish:

• Protandry: When stamens mature before pistil.

• Protogyny: When pistil matures before stamen.

5. Inflorescence is when two or more flowers borne on a common stalk.

c. Representation of the number and characteristics of a flower
There are two ways by which we can present the number and characteristics
of different parts of the flower. These ways include: floral diagram and floral
formula.

Floral formula
The fl oral formula indicates the number and characteristics of different
floral organs. It varies from one flower to another. By convention, there are
standard symbols that are used to represent different parts of the flower and
their characteristics:

K: for calyx, K5: calyx with five free sepals, K(5): calyx with five fused sepals.

C: for corolla, C5: corolla with five free petals, C(5): corolla with five fused
petals.

P: for perianth, P4: four free tepals, P(4): four fused tepals, P2+2: four tepals
in two whorls of three each.

A: for Androecium or stamen, A5: androecium with five free stamens, A(5):
five fused stamens, A5+5: ten stamens in two whorls of five each, A0:
stamens absent, A∞: stamens indefinite in number, A(9)+1: androecium of
10 stamens nine fused together and one free.

G: for pistil or gynoecium, G₂: two free carpels, G₂: two fused carpels, G0:
carpels absent, G₂: Bicarpellary, syncarpous semi-inferior ovary.

Representation of the symmetry of flower:
Փ: zygomorphic or irregular
: Actinomorphic or regular flower.
Representation of sex of the flower: ♂: staminate flower, ♀: pistillate
flower,

Bisexual flower
The floral formula is specific to each species of plant.

Examples
Write a floral formula of coffee having
• The bilateral symmetry
• Hermaphrodite flower
• 1 calyx with 5 fused sepals
• 1 corolla with 5 petals
• 5 fused stamens
• 1 pistil with 2 carpels each one with infer ovary of 2 chambers

Answer: (5S)+ (5P) +(5A)+ 2C-2 or K(5) + C(5) + A(5) + G-2(2)
Write a floral formula of Irish potato having
• 5 free sepals
• 5 free petals
• 5 free stamens
• 2 fused carpels with 2 chambers having many ovules
• 1 infer ovary
• Bisexual flower
• Radial symmetry

Application activity 14.3.2
1. What are the male and female structures of a flower?
2. How might be an advantage for a plant to have many flowers together
in a single structure?
3. Where does the female gametophyte develop?
4. Describe the flower and how it is involved in reproduction.

14.3.3. Pollination and double fertilisation in flowering plants

Activity 14.3.3

Visit a computer lab, download and describe the videos of the process
of double fertilization in flowering plants, and search more information to
identify different pollinating agents

1. Pollination
Pollination is transfer of pollen grains from anther to the stigma.

a). Types of pollination: There are two types of pollination such as: self-
pollination and cross-pollination.

i. Self-pollination: It is the transfer of pollen grains from anther to the
stigma of the same flower, or of different flowers but of the same
plants. It involves one plant. E.g. flowers of maize and beans.

ii. Cross-pollination: It is the transfer of pollen grains from anther to
the stigma of the flower of another plants. It involves two plants. E.g.
flowers of pawpaw.

b). Main Pollinating agents
Flower structure is closely related with the way they are pollinated. This
means that flowers are adapted to specific agents or mode of pollination.
The common agents of pollination are: insects (entomophily), wind
(anemophily), water (hydrophily), humans (anthropophily), and birds
(ornithophily).

Characteristics of insect-pollinated flowers (entomophilous flowers)
• Flowers produce the nectar to attract pollinators.
• Flowers have large brightly coloured corolla to attract pollinators.
• Production of scents to attract pollinators.
• The surface of the stigma should be sticky to hold pollen grains.
• Pollen grains are sticky and rough enough to remain on the surface of
stigma.

Characteristics of wind-pollinated flowers (enemophilous flowers)
• The flowers have large stigma to hold pollen grains.
• The surface of the stigma should be sticky to hold pollen grains.
• Pollen grains are rough enough to remain on the surface of stigma.
• The flowers are or are not brightly-colored.
• They have or do not have scent.
• They do or do not secrete nectar.
• They produce large quantities of pollen grains, as much of them never
reach the stigmas.

2. Double fertilization and events after fertilization in flowering plants
Double fertilization is a complex fertilization mechanism of flowering plants
(angiosperms). This process involves the joining of a female gametophyte
(megagametophyte, also called the embryo sac) with two male gametes
(sperm).

a. Development of pollen grains and plant ovules
i. Development of pollen grains

The pollen grains are produced in the anthers while the ovules are produced
in the ovary.

Pollen grains
Each anther has four pollen sacs which contain many diploid microspore
mother cells that undergo meiosis to form four microspores each. At first,
the four microspores remain together as tetrads. The nucleus of each
microspore then divides by mitosis, forming a generative nucleus and a
tube or vegetative nucleus. At this point, the content of the pollen grain
may be considered as the male gametophyte. A two-layered wall forms

around each pollen grain. The outer wall, the exine is thick and sculptured.
The inner wall, the intine is thin and smooth. There are many pores or
apertures in the wall through which a pollen tube may emerge.

ii. Development of Plant ovule
Each ovule is attached to the ovary wall by a short stalk called funicle. The
main tissue in the ovule is the nucellus which is enclosed and protected by
the integuments.

At one end of the ovule, there is a small pore called micropyle. A single
diploid megaspore mother cell in the nucellus undergoes meiosis,
producing four megaspores. Three of the four megaspores degenerate,
while the remaining cell, called the embryo sac, grows to many times its
original size. The nucleus of the embryo sac divides mitotically three times,
resulting in eight haploid nuclei which are arranged in groups of four nuclei
at the two poles. At this point, the contents of the embryo sac may be
regarded at the female gametophyte.

One nucleus from each pole migrates to the centre of the embryo sac.
These two nuclei are called polar nuclei, and they fuse to form a single
diploid nucleus. Meanwhile, cell walls form around the remaining six nuclei
and they form the synergids, antipodals and the egg (ovum). Only the egg
functions as the female gamete.

In summary, the pollen grain contains two haploid nuclei: one called
generative nucleus, and the other the tube nucleus.

On the other hand, the ovule or embryonic sac contains eight nuclei:
• Three antipodal nuclei/cells at one end
• Two polar nuclei/cells in the middle of ovule
• Two synergids (non-functional nuclei)
• One big egg cell.

The process of double fertilization
Double fertilization begins when a pollen grain adheres to the stigma of the
carpel, the female reproductive structure of a flower.

The pollen grain then takes in moisture and begins to germinate, forming a
pollen tube that extends down toward the ovary through the style.

The growth of the pollen tube is controlled by the pollen tube nucleus. In
the pollen tube, the generative nucleus divides mitotically into two haploid
nuclei which are the male gamete nuclei. These follow behind the tube
nucleus as the pollen tube grows down the style towards the ovule. The
tip of the pollen tube then enters the ovary and penetrates through the
micropyle opening, releasing the two sperms in the megagametophyte or
ovule.

The tube nucleus degenerates, leaving a clear passage for the entry of
male nuclei. One nucleus fertilizes the egg cell to form a diploid zygote
(2N), which will grow into a new plant embryo; the other fuses with polar
nuclei to form a triploid nucleus (3N), which will grow into a food-rich tissue
known as endosperm, which nourishes the seedling as it grows.

This process is described as double fertilisation and is typical of
angiosperms. If there is more than one ovule in the ovary, each must be
fertilised by separate pollen grain and hence the fruit will have many seeds
genetically different from each other.

3. Events in a flower after fertilization
After fertilisation, the calyx, corolla, stamens and style may wither gradually
and fall off, but in some flowers the calyx may persist. The ovule forms the
seed, the two integuments of the ovule will form the seed coat, and the ovary
will develop into fruit, with the ovary wall forming the pericarp (fruit wall).
The diploid zygote undergoes cell division to form the embryo, the triploid
primary endosperm nucleus develops into endosperm, a store used by the
developing embryo. This persists in endospermic seeds of monocotyledons.

The micropyle persists as a small hole in the seed coat through which water
is absorbed during germination.

Application activity 14.3.3
1. Are angiosperms typically wind or animal pollinated? How does this
process occur?
2. What is meant by the term endosperm?
3. How are brightly coloured petals advantageous to the plant?
4. What do you understand by the term double fertilization?
5. What happens to the antipodal cells and synergids cells after
fertilization?

14.3.4. Structures and types of fruits and seeds

Activity 14.3.4

Observe slides containing micrographs of different fruits and seeds.
According to their characteristics:
1. Differentiate fruits.
2. Draw and show a structure of seed as seen on microscope

Below are some examples of fruits:

A fruit is a structure formed from the ovary of a flower, usually after the
ovules have been fertilized. In nature, a fruit is normally produced only after
fertilization of ovules has taken place, but in many plants, largely cultivated
varieties such as seedless citrus fruits, grapes, bananas, and cucumbers,
fruit matures without fertilization, a process known as parthenocarpy. Ovules
within fertilized ovaries develop to produce seeds. In unfertilized varieties,
seeds fail to develop, and the ovules remain with their original size.

A fruit consists of two main parts; pericarp (fruit wall) and the seed. The
pericarp has three layers: epicarp or exocarp (outermost), mesocarpe
(middle) and endocarp (inner).

The fruit can have a dry pericarp or fleshy pericarp. The fruits with fleshy
pericarp include: berry and drupe. Drupe is a fleshy fruit with only one seed,
E. g. avocado.

Berry is a fleshy fruit having many seeds inside of it. E.g. tomatoes, orange,
and pawpaw.

The fruits with dry pericarp include indehiscent fruit or dehiscent fruit.
Indehiscentfruits do not open. Seeds remain inside of the fruits. E.g. fruits of
coconuts. Dehiscent fruits open and release seeds. These include: dehiscent
fruits with one carpel, and those with many carpels. Dehiscent fruits with one
carpel include; those which open along one side, e.g. follicle; and those
which open along both sides, e.g. legume (beans).

Fruits of eucalyptus are exam of dehiscent fruits with many carpels.

The major function of a fruit is the protection of developing seeds. In many
plants, the fruit also aids in seed distribution (dispersal).

Food value
Fruits are eaten raw or cooked, dried, canned, or preserved. Carbohydrates,
including starches and sugars, constitute the principal nutritional material.
Citrus fruits, tomatoes, and strawberries are primary sources of vitamin C,
and most fruits contain considerable quantities of vitamin A and vitamin B.
In general, fruits contain little protein or fat. Exceptions are avocados, nuts,
and olives, which contain large quantities of fat, and grains and legumes,
which contain considerable protein.

A seed is an embryonic plant enclosed in a protective outer covering. The
formation of the seed is part of the process of reproduction in seed plants,
the spermatophytes, including the gymnosperm and angiosperm plants.
Seeds are the product of the ripened ovule, after fertilization by pollen and
some growth within the mother plant. The embryo is developed from the
zygote and the seed coat from the integuments of the ovule

The main components of the embryo are:A seed is made up of a seed coat
(testa), one or two cotyledons and an embryonic axis. The embryonic axis is
made up of a plumule, an epicotyl, a hypocotyl and a radical. A seed which
has one seed-leaf is described as monocotyledonous, and one which has
two, as dicotyledonous. Maize is monocotyledonous seed while bean is a
dicotyledonous seed.

• The cotyledons, the seed leaves, attached to the embryonic axis. There
may be one (Monocotyledons), or two (Dicotyledons). The cotyledons
are also the source of nutrients in the non-endospermic Dicotyledons,
in this case they replace the endosperm, and are thick and leathery. In
endospermic seeds the cotyledons are thin and papery.

• The epicotyl, the embryonic axis above the point of attachment of the
cotyledon(s).

• The plumule, the tip of the epicotyl, and has a feathery appearance due
to the presence of young leaf primordia at the apex, and will become
the shoot upon germination.

• The hypocotyl, the embryonic axis below the point of attachment of
the cotyledon(s), connecting the epicotyl and the radicle, being the
stem-root transition zone.

• The radicle, the basal tip of the hypocotyl, grows into the primary root.
Monocotyledonous plants have two additional structures in the form of
sheaths. The plumule is covered with a coleoptile that forms the first leaf
while the radicle is covered with a coleorhiza that connects to the primary
root and adventitiousroots form from the sides. Here the hypocotyl is a
rudimentary axis between radicle and plumule.

Application activity 14.3.4
1. Describe the structure of a drupe
2. Differentiate between a drupe and a berry
3. What would happen to the fruit if ovules in the flower did not develop?
4. Compare the typical structure of seeds that are dispersed by animals
to those dispersed by wind and water.

14.3.5. Fruits and seeds dispersal with their adaptations

Activity 14.3.5
A man visited a lake and he found around the lake some grown plants of
maize, beans and other variety plants meanwhile nobody has cultivated
any seed or fruit. Suggest ways of those variety of (plants) have been
reached on that lake.

Dispersal of fruits and seeds is the scattering of fruits and seeds from their
mother plants. They are four methods of seeds and fruits dispersal such as:
1. Dispersal by Wind
2. Dispersal by Water
3. Dispersal by Animals and
4. Mechanical Dispersal.

Seeds disperses by wind or water are typically lightweight, allowing them
to be carried in air or to float on the surface of water. The wind carries also
small seeds that have wing-like structure. Seeds dispersed by animals
are typically contained in sweet, nutritious flesh fruits. They can be carried
externally on their feet, fur, feathers, or beaks.

Those seeds with hooks or sticky substances rely on the chance that they will
attach themselves to a passing animal. Other seeds are eaten by animals
and passed out in the faeces.

With mechanical Dispersal: All dehiscent fruits scatter the seeds when
they burst. This dehiscence is accompanied by the expression of great force
in many fruits so that seeds are jerked a considerable distance away from
the mother plant. Such fruits are called explosive fruits.

These seeds will germinate where the faeces will be deposited. The dispersal
of seeds is important for the survival of the plant species because:

• It minimises overcrowding of plants growing around the parent plant
that could then result in too much competition for nutrients and light;

• It allows the plant species to colonise new habitats which can offer
suitable conditions.

Application activity 14.3.5
1. Why is it adaptive for some seeds to remain dormant before they
germinate?
2. The seeds of a bishop pine germinate only after they have undergone
a forest fire. Evaluate the significance of this structural adaptation.
3. Evaluate the importance of seed dispersal.

Skills lab 14
After studies, and completion of this unit 14, student-teachers will use the
acquired knowledge to increase the crop productivity using different modes
of vegetative and artificial propagation. They will also improve the quality of
fruit plants by using forexample grafting method.

End unit assessment 14

PART A

A. Multiple choice questions (choose the best answers)
1. In cutting method of vegetative propagation, cuttings are mainly taken
from
a). Leaves of parent plant.
b). Roots or stems of parent plant.
c). Shoots of parent plant.
d). Buds of parent plant.

2. Artificial methods of vegetative propagation includes
a). Cloning
b). Grafting
c). Cuttings
d). Both b and c

3. Example of plant in which vegetative propagation is occurred by
leaves is called __________
a). Cannabis
b). Chrysanthemum
c). Bryophyllum
d). Brassica

4. Which of the following is NOT an advantage of asexual reproduction?
a). Rapid reproduction.
b). High genetic diversity.
c). No need for a mate.
d). Low resource investment in offspring.

B. PART B
1. Answer by true or false.
a). Mosses have life cycles that depend on water for reproduction.
b). In ferns the gametophyte depends on sporophyte.
c). In mosses the sporophyte dominates over the gametophyte.
d). Seeds that are dispersed by animals are not contained in a flesh-
sweet tissue.
e). During pollination, pollen grains move from stigma to anther.

2. Chose the letter that best answers the question or complete the
statement.
a). Which of the following is not part of a flower?
i. Stamens
ii. Petals
iii. Carpels
iv. Stem
v. Sepals.
b). Which flower structure that includes all the others listed below?
i. Stigma
ii. Carpel
iii. Ovary
iv. Style
v. Ovule
c). The thickened ovary wall of a plant may join with other parts of the
flower stem to become the _______________
i. Cotyledon
ii. Fruit
iii. Endosperm
iv. Seed
d). In angiosperms the structures that produce the male gametophyte
are called the _______________
i. Pollen tubes
ii. Stigma
iii. Anthers
iv. Sepals

e). The small, multicellular structures by which liverworts reproduce
asexually are ______________
i. Archegonia
ii. Gemmae
iii. Protonema
iv. Rhizoids

f). The small, multicellular structures by which liverworts reproduce
asexually are __________________
i. Archegonia
ii. Gemmae
iii. Protonema
iv. Rhizoids

g). In angiosperms, the mature seed is surrounded by a __________
i. Flower
ii. Fruit
iii. Cotyledon
iv. Cone

h). The leaves of ferns are called ______________
i. Spores
ii. Fronds
iii. Sori
iv. Rhizomes

i). The most recognizable stage of a moss is the _____________
i. Gametophyte
ii. Archegonium
iii. Protonema
iv. Sporophyte

3. Which are more likely to be dispersed by animals- the seeds of
angiosperms or the spores of a fern? Explain your reasoning.

4. Pollination is a process that occurs only in seed plants. What process
in seedless plants is analogous to pollination?

5. What is the dominant stage of the ferns life cycle? Explain the
relationship of the fern gametophyte and sporophyte.

6. How is water essential in the life cycle of a bryophyte?

7. What characteristic of bryophytes is responsible for their small size?
Explain.

8. Briefly explain why a seed may remain dormant even when the
environmental conditions are favorable for germination.

9. Describe the relationship between the gametophyte and sporophyte
in mosses.

10. During the lifecycle of a moss, what environmental conditions are
necessary for fertilization to occur?

11. Describe the dominant stage in the lifecycle of a fern.

12. Propose a hypothesis to explain why angiosperms have become the
dominant type of plant on the earth.

13. Moss plants are small. Ferns can grow as tall as small tree. Explain
why this is so. How does your answer illustrate a major characteristic
of the plant kingdom?

14. Study the structure of the seed below.

a). Name the parts labelled by: A, B and C

b). What is the importance of the part C for a growing seedling?

15. Many flowers have bright patterns of coloration that directly surround
the reproductive structures. Evaluate the importance of those bright-
coloured patterns to plants.

16. What is the function of endosperm?

17. Some plants form flowers that produce stamens but no carpels. Could
fruit form on one of these flowers? Explain your answer.

18. Distinguish between pollination and fertilization.

19. Give names of letters from A to J, and explain the function of the parts
represented by: B, G, and E.

20. Explain why the relationship between bees and flowers is described
as mutually beneficial.

21. What is the main advantage of cross-pollination?

22. Why are the stamens of wind-pollinated plants and insect-pollinated
plants different?

23. Differentiate wind-pollinated flowers from insect-pollinated flowers.

24. Give one example of a plant that uses each of the following dispersal
mechanism:

a). An explosive device which works by being inflated with water.
b). A winged seed lifted by air currents.
c). A buoyant seed carried by sea currents.
d). A gluey substance which sticks the seed to an animal.