UNIT 17: SEXUAL REPRODUCTION IN PLANTS
UNIT 17: SEXUAL REPRODUCTION IN PLANTS
Key Unit Competence
Describe sexual reproduction in plants.
Learning objectives
By the end of this unit, I should be able to:– Explain the meaning of the term alternation of generations.Introductory activity
– Describe the types and structure of flowers.
– Describe pollination and fertilization in flowering plants.
– Explaining the events that takes place in a flower after fertilization.
– Describe the types and structure of seeds and fruits.
– Discuss the modes of dispersal of fruits and seeds.
– Observe and draw pollen grains.
– Draw and interpret floral formulae and diagrams.
– Relate the floral structures to the mode of pollination.
– Draw and label structures of fruits and seeds.– Appreciate the role of pollinating agents in flowering plants.
1. Observe the following pictures and suggest what is going on.2. How are the pictures below related to reproduction in flowering plants?
17.1. Alternation of generations in bryophytes and
pteridophytes
Activity 17.1
Using different resources to compare the life cycles of mosses and ferns.
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. This unit concerns 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. Thisphenomenon 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
ensures that both generations exist at any given time. This prevents extinctionof the plant species
The life cycle in mosses involves alternation of generations between the diploid
(2n) sporophyte and haploidgametophyte. In bryophytes, the gametophyte
is a dominant 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
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.
Checkpoint: why bryophytes grow in habitats where water is available constantly:
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.
17.1.1. 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 bear 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.
Sporophyte is 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 insporangia (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
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.
17.1.2. Differences between the mosses and fernsTable 17.1: Comparison between moss and fern.
Self-Assessment 17.1
1. Explain the meaning of the term alternation of generation17.2. Types and structures of flowers
2. Why is water essential in the life cycle of a bryophyte?
3. What are the archegonium and antheridium?
4. Why 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 between gametophyte and sporophyte phases of
the fern.
7. Compare gametophyte and sporophyte stages of the plant cycle. Which is
haploid? Which is diploid?8. How do bryophytes reproduce asexually?
Activities 17.2
Collect different forms of flowers from the school compound or around the school,
such as hibiscus, morning glory, sweet potato, or maize flower:
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 the flower.
17.2.1. Structure of a typical complete flowerA flower is a reproductive organ of a plant, which produces fruits and seeds.
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 form a 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 ofthe flower.
– Androecium: 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: 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: maintains the stigma in a good position to receive pollen grains.
c. Ovary: a sac where ovules are produced. Ovules become seeds afterfertilization.
17.2.2. Types of flowers
1. According to absence of some reproductive parts of the flower, we can
distinguish:
a. Unisexual flower: is 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.
b. Bisexual or hermaphrodite flower: a flower with 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:
a. A flower with inferior ovary: it is when the ovary is located below the point of
insertion of calyx, corolla and stamens.
b. A flower with superior ovary: it is when the ovary is located over the point of
insertion of calyx, corolla and stamens.
c. The semi-infer or semi-super flower: when ovary is neither inferior nor superior
but in the middle of receptacle which is hollowed.– When sepals are joined together, the flowers are called gamosepal, and where3. According to the shape and symmetry of the flower, we can distinguish:
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 dial petal. When they are absent,the flower is called apetal.
i. Zygomorphic or irregular flower: a flower with a bilateral symmetry.Dichogany: it is when male and female organs of the flower mature at different
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.
times. We can distinguish:1. Protandry: when stamens mature before pistil.Inflorescence is when two or more flowers are borne on a common stalk.
2. Protogyny: when pistil matures before stamen.
17.2.3. Representation of the number and characteristics of a flower
There are two ways by which we can present the number and characteristics ofdifferent parts of the flower. These ways include: floral diagram and floral formula.
Floral formula
The floral 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 free 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, G (2): two fused carpels, G0: carpels
absent, G (2): Bicarpellary, syncarpous semi-inferior ovary.
Representation of the symmetry of flower: zygomorphic or irregularflower:
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– (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.– K (5) + C (5) + A5 + G-2(2) ∞
Self-assessment 17.21. What are the male and female structures of a flower?17.3. Pollination and double fertilization in flowering plants
2. What is the 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.
Activity 17.3
Use various resources to identify different pollinating agents and describe the
process of double fertilization in flowering plants.
Pollination is transfer of pollen grains from anther to the stigma.
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 plant. It involves two plants. E.g. flowers ofpawpaw
17.3.1. 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.Characteristics of wind-pollinated flowers: (anemophilous flowers)
– Flowers have a 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.– The flowers have large stigma to hold pollen grains.17.3.2. Double fertilization and events after fertilization in flowering
– 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 reachthe stigmas.
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 (sperms).
Development of pollen grains and plant ovules.
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 orapertures in the wall through which a pollen tube may emerge.
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 center 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 generativenucleus, 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: It 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 nourishesthe 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 fertilized by separate pollen
grain and hence the fruit will have many seeds genetically different from each other.
a. 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.
Table 17.2: Floral parts and their fate after fertilization
Self-assessment 17.31. Are angiosperms typically wind or animal pollinated? How does this process17.4. Structures and types of fruits and seeds
occur?
2. What is meant by the term endosperm?
3. What is the importance of brightly coloured petals to the plant?
4. What is double fertilization?
5. What happens to the antipodal cells and synergids cells after fertilization?
Activity 17.4
Observe slides containing micrographs of different fruits and seeds. According to
their characteristics:a. Differentiate fruits.
b. Draw and show a structure of seed as seen on microscopeBelow are some examples of fruits:
A fruit is a structure formed from the ovary of a flower, usually after the ovules have
been fertilized. It 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. Indehiscent
fruits do not open. Seeds remain inside of the fruits. E.g. fruits of coconuts. Dehiscent
fruits open and release seeds. They 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 examples 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 of fruits.
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 integumentsof the ovule.
The main components of the embryo are: seed 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. Maizeis 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 they 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: It is located at the tip of the epicotyl and has a feathery appearance
due to the presence of young leaf primordial at the apex. It 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 and it 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 adventitious roots
form from the sides. Here the hypocotyl is a rudimentary axis between radicle andplumule.
Self-Assessment 17.4
1. Describe the structure of a drupe17.5. Fruits and seeds dispersal with their adaptations
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.
Activity 17.5
Use books and internet and to answer to the following questions:1. Suggest the ways of fruits and seeds dispersal.
2. Explain adaptation of fruits dispersed by animals.
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 dispersed 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
and 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. These seeds will germinate where the faeces will be deposited.
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 at a considerable distance away from the mother plant. Such
fruits are called explosive fruits.
The dispersal of seeds is important for the survival of the plant species because:– It minimises overcrowding of plants growing around the parent plant thatSelf-assessment 17.5
could then result in too much competition for nutrients and light;
– It allows the plant species to colonise new habitats which can offer suitableconditions.
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.
End of unit assessment 17
1. Answer by true or falsea. Mosses have life cycle that depends on water for reproduction.2. Choose the letter that best answers the question or complete the statement.
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 anthers.
a. Which of the following is not part of a flower?i. Stamensb. Which is the structure of a flower that includes all parts listed below?
ii. Petals
iii. Carpels
iv. Stem
v. Sepalsi. Stigmac. The thickened ovary wall of a plant may join with other parts of the flower to
ii. Carpel
iii. Ovary
iv. Stylev. Ovule
become thei. Cotyledond. In angiosperms, the structures that produce the male gametophyte are called
ii. Fruit
iii. Endosperm
iv. Seed
thei. Pollen tubese. The small and multicellular structures by which liverworts reproduce
ii. Stigma
iii. Anthers
iv. Sepals
asexually arei. Archegoniaf. In angiosperms, the mature seed is surrounded by a
ii. Gemmae
iii. Protonema
iv. Rhizoidsi. Flowerg. The leaves of ferns are called
ii. Fruit
iii. Cotyledon
iv. Conei. Sporesh. The most recognizable stage of a moss is the
ii. Fronds
iii. Sori
iv. Rhizomesi. Gametophyte3. Which are more likely to be dispersed by animals- the seeds of angiosperms or
ii. Archegonium
iii. Protonema
iv. Sporophyte
the spores of a fern? Explain your answer.
4. Pollination is a process that occurs only in seed plants. What is the process in
seedless plants is that is equivalent to pollination?
5. What is the dominant stage of the ferns life cycle? Explain the relationship
between gametophyte and sporophyte phases of the fern
6. Why is water essential in the life cycle of a bryophyte?
7. What is the characteristic responsible for the small size of bryophytes? 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 life cycle of a moss, what are the environmental conditions
necessary for fertilization to occur?
11. Describe the dominant stage in the life cycle 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. How
does your answer illustrate a major characteristic of the plant kingdom?14. Study the structure of the seed bellow
a. Name the parts 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-colored
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 corresponding to the following to the letters: from A to J. Explainthe 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 currentsd. A gluey substance which sticks the seed to an animal.