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GNDU Question Paper-2022
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
BOTANY: Paper-I-B
(Diversity of Cryptogams)
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Define Alternation of Generations. Explain the phenomenon taking an example of any
Bryophytic plant.
2. Write short notes on:
(a) Bryophytes as amphibians of plant kingdom.
(b) Types of thallus types in Bryophytes,
SECTION-B
3. Discuss the pattern of reproduction in Anthocerotopsida by taking any example.
4. Write short notes on:
(a) Structure of Funaria capsule.
(b) Draw T S of Marchantia thallus.
SECTION-C
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5. Differentiate the important characteristics of Sphenopsida and Pteropsida.
6. Write short notes on:
(a) Sporangia of Rhynia.
(b) Stele evolution in Pteridophytes.
SECTION-D
7. Describe the life history of Marsilea duly supported by diagrams.
8. Write short notes on:
(a) Typical sporophyte structure of Equisetum.
(b) Gametophyte in Ferns.
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GNDU Answer Paper-2022
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
BOTANY: Paper-I-B
(Diversity of Cryptogams)
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Define Alternation of Generations. Explain the phenomenon taking an example of any
Bryophytic plant.
Ans: Definition of Alternation of Generations
Alternation of generations is a natural life cycle found in plants in which two different
stages occur one after another. One stage produces gametes (sex cells) and is called the
gametophyte, while the other stage produces spores and is called the sporophyte. These
two generations keep alternating, which is why the process is called alternation of
generations.
In simple words, a bryophyte plant spends its life in two forms:
Gametophyte (n): Produces male and female sex cells.
Sporophyte (2n): Produces spores that grow into new gametophytes.
This cycle continues again and again, helping the plant reproduce and survive.
Alternation of Generations in Bryophytes (Example: Moss Funaria)
Let us understand this concept through the example of Funaria, a common moss.
1. Gametophyte Stage (Haploid n)
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The life of a moss begins with a spore. When the spore falls on moist soil, it germinates and
forms a green thread-like structure called the protonema.
The protonema later develops into the leafy moss plant, which is the gametophyte. This is
the main, green, photosynthetic, and independent plant body in bryophytes.
The gametophyte bears two reproductive organs:
Antheridium Male reproductive organ that produces antherozoids (male
gametes).
Archegonium Female reproductive organ that produces the egg (female gamete).
Since bryophytes usually grow in moist places, water is essential. The male gametes swim
through a thin film of water to reach the egg inside the archegonium.
2. Fertilization
When the male gamete fuses with the egg, fertilization takes place.
This fusion forms a zygote (2n), which is the first cell of the sporophyte generation.
Thus, the life cycle changes from the haploid (n) gametophyte to the diploid (2n)
sporophyte.
3. Sporophyte Stage (Diploid 2n)
The zygote remains attached to the female gametophyte and develops into the sporophyte.
The sporophyte has three main parts:
Foot Absorbs food from the gametophyte.
Seta A stalk that supports the capsule.
Capsule Produces spores.
Unlike the gametophyte, the sporophyte cannot live independently. It depends on the
gametophyte for water and nutrients.
Inside the capsule, special cells undergo meiosis, producing many haploid spores (n).
4. Formation of New Gametophyte
When the capsule becomes mature, it releases the spores into the air.
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If the spores land on a moist surface, each spore germinates into a protonema, which
develops into a new leafy gametophyte.
This completes one life cycle, and the entire process begins again.
Why is it called Alternation of Generations?
It is called alternation of generations because two different generations alternate
regularly:
The gametophyte generation (n) produces gametes.
The sporophyte generation (2n) produces spores.
One generation gives rise to the other, forming a continuous life cycle.
Simple Flow Diagram
Spores (n)
│
▼
Protonema (n)
│
▼
Leafy Gametophyte (n)
│ │
▼ ▼
Antheridium Archegonium
(Male gametes) (Female egg)
\ /
\ /
Fertilization
│
▼
Zygote (2n)
│
▼
Sporophyte (2n)
(Foot → Seta → Capsule)
│
Meiosis in Capsule
│
▼
Spores (n)
│
Cycle Repeats
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Important Features of Alternation of Generations in Bryophytes
The gametophyte is the dominant, green, and independent generation.
The sporophyte remains attached to and depends on the gametophyte for
nourishment.
Water is necessary for fertilization because the male gametes must swim to the egg.
Spores help in reproduction and dispersal.
The life cycle alternates regularly between haploid (n) and diploid (2n) stages.
Conclusion
Alternation of generations is one of the most important characteristics of bryophytes. In
Funaria (moss), the life cycle alternates between a haploid gametophyte, which produces
gametes, and a diploid sporophyte, which produces spores. The gametophyte is the
dominant plant body, while the sporophyte depends on it for nutrition. Through the
continuous formation of gametes, fertilization, spores, and new plants, bryophytes
successfully complete their life cycle and ensure the survival of the species.
2. Write short notes on:
(a) Bryophytes as amphibians of plant kingdom.
(b) Types of thallus types in Bryophytes,
Ans: Bryophytes are called the "amphibians of the plant kingdom" because they can live on
land, but they still need water to complete their life cycle, especially for reproduction. This
is very similar to amphibian animals like frogs, which live on land but must return to water
to lay eggs. Because of this similarity, bryophytes have been given this special name.
Bryophytes are the simplest land plants and include three main groups: mosses, liverworts,
and hornworts. They usually grow in cool, damp, and shady places, such as on moist soil,
rocks, tree trunks, or near streams. They are generally small because they do not have true
roots, stems, leaves, or vascular tissues (xylem and phloem) for transporting water and
food.
The main reason bryophytes are called amphibians is their dependence on water for sexual
reproduction. The male reproductive organ produces motile sperm (antherozoids). These
sperm cannot move through air, so they swim through a thin film of water to reach the
female reproductive organ (archegonium), where fertilization takes place. Without water,
fertilization cannot occur, and the plant cannot produce the next generation.
Although bryophytes require water for reproduction, they are land plants because they
grow on land, absorb water from the soil, and perform photosynthesis like other green
plants. This shows that bryophytes represent an important evolutionary link between
aquatic algae and higher land plants.
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Bryophytes also play an important role in nature. They help in soil formation, prevent soil
erosion, retain moisture, and provide shelter for small organisms. Some mosses, such as
Sphagnum, are used as peat, fuel, and in gardening because they can store large amounts of
water.
Simple Diagram
Bryophytes
│
Live on Land
│
▼
Need Water for Reproduction
│
▼
Sperm swims to egg for fertilization
│
▼
Called "Amphibians of Plant Kingdom"
Key Points
Bryophytes are the simplest land plants.
They grow in moist and shady places.
They lack true roots, stems, leaves, and vascular tissues.
Water is essential for fertilization because the sperm must swim to the egg.
Hence, they are called the amphibians of the plant kingdom.
2(b) Types of Thallus in Bryophytes
The plant body of bryophytes is called a thallus. A thallus is a simple plant body that is not
clearly divided into true roots, stems, and leaves. Depending on its structure, bryophytes
have different types of thallus.
1. Flat (Thalloid) Thallus
This type is flat, green, ribbon-like, and spreads over the ground. It usually grows close to
moist soil or rocks. Rhizoids are present on the lower side to attach the plant to the surface
and absorb water.
Example: Marchantia, Riccia
Flat Thallus
_____________
/ \
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/ \
\_______________/
|||||||
Rhizoids
2. Leafy Thallus
In this type, the plant body looks like a small leafy plant. It has a stem-like axis with leaf-like
structures, but these are not true stems or true leaves because they lack vascular tissue.
Example: Mosses such as Funaria and Polytrichum
Leaf-like Parts
/\/\
/\/\/\
||
||
||
Stem-like Axis
||
Rhizoids
3. Simple Thallus
This is the most primitive type. It is small, undivided, and simple without any branching. It is
commonly found in primitive liverworts.
Example: Riccia
4. Branched Thallus
The plant body is branched repeatedly, increasing the surface area for photosynthesis and
growth.
Example: Marchantia
Y-shaped Branching
/\
/ \
/ \
/\ /\
/ \ / \
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Importance of Different Thallus Types
The different thallus forms help bryophytes survive in different environments.
Flat thallus absorbs water efficiently from moist surfaces.
Leafy thallus provides a larger surface area for photosynthesis.
Branched thallus allows better growth and spread.
Simple thallus represents the earliest and most primitive body structure.
These variations show the gradual evolution of plant body organization from simple forms
to more complex land plants.
Conclusion
Bryophytes are called the amphibians of the plant kingdom because they live on land but
depend on water for reproduction. Their simple plant body, known as the thallus, occurs in
different forms such as flat, leafy, simple, and branched. These thallus types help
bryophytes adapt to moist environments and perform essential functions like
photosynthesis, water absorption, and growth. Bryophytes represent an important stage in
the evolution of plants from aquatic ancestors to higher land plants.
SECTION-B
3. Discuss the pattern of reproduction in Anthocerotopsida by taking any example.
Ans: Anthocerotopsida, commonly known as Hornworts, is one of the three main groups of
bryophytes. These are small, green, non-vascular plants that usually grow in moist and
shady places, such as wet soil, rocks, or near streams. The name hornwort comes from the
long, horn-like sporophyte that grows from the plant.
The pattern of reproduction in Anthocerotopsida is interesting because it includes both
sexual and asexual reproduction, and the plant also shows alternation of generations. Let
us understand each step in a simple way by taking Anthoceros as an example.
1. Vegetative (Asexual) Reproduction
Vegetative reproduction means the plant produces new plants without the formation of
seeds or spores through fertilization.
In Anthoceros, vegetative reproduction occurs mainly by:
a) Fragmentation
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The plant body (called the thallus) may break into several pieces because of aging, injury, or
drying. Each fragment grows into a new hornwort plant when it gets favorable conditions
like moisture and sunlight.
b) Tubers
Some species produce tubers, which are thick, food-storing structures. During unfavorable
conditions like drought, the tubers remain alive. When rain returns, they germinate and
produce new plants.
Thus, vegetative reproduction helps the plant multiply quickly and survive difficult
environmental conditions.
2. Sexual Reproduction
Sexual reproduction involves the formation of male and female reproductive organs.
The plant body that produces these organs is called the gametophyte, which is the
dominant generation in Anthocerotopsida.
Male Reproductive Organ Antheridium
Produces male gametes (antherozoids or sperms).
Found inside chambers on the upper surface of the thallus.
The sperms are motile (they can swim) because they have two flagella.
Female Reproductive Organ Archegonium
Produces a single egg cell.
Embedded inside the thallus.
Protected by surrounding tissues.
3. Fertilization
Fertilization occurs only when water is available.
During rain or heavy moisture:
The antheridia release sperms.
The sperms swim through a thin film of water.
They reach the archegonium.
One sperm fuses with the egg.
This fusion forms a zygote (2n).
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Therefore, hornworts are called water-dependent plants because water is essential for
fertilization.
4. Development of Sporophyte
The zygote does not leave the parent plant.
Instead, it develops into the sporophyte, which remains attached to the gametophyte.
The sporophyte has three important parts:
Foot absorbs food from the gametophyte.
Meristematic region continuously produces new cells, allowing the sporophyte to
grow for a long time.
Capsule long and horn-shaped, where spores are formed.
The horn-like capsule is the most distinctive feature of Anthocerotopsida.
5. Formation of Spores
Inside the capsule:
Certain cells undergo meiosis.
Meiosis produces haploid spores (n).
The capsule also contains pseudoelaters, which help in the dispersal of spores by changing
shape as they dry.
When the capsule becomes mature, it splits open from the tip downward, releasing the
spores into the air.
6. Germination of Spores
When spores fall on moist soil:
They germinate.
They directly develop into a young thallus (gametophyte).
The new gametophyte again forms male and female reproductive organs.
Thus, the life cycle continues.
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Alternation of Generations
Anthocerotopsida shows alternation of generations, meaning two stages occur one after
another.
1. Gametophyte (n) Produces gametes (sperms and eggs).
2. Sporophyte (2n) Produces spores by meiosis.
The spores grow into new gametophytes, completing the life cycle.
Simple Life Cycle Diagram
Mature Gametophyte (n)
│
┌────────────┴────────────┐
│ │
Antheridium Archegonium
(Male Organ) (Female Organ)
│ │
Sperms Egg Cell
└──────────┬──────────────┘
│
Fertilization (Water Needed)
│
Zygote (2n)
│
Sporophyte (2n)
(Foot + Meristem + Capsule)
│
Meiosis
│
Haploid Spores (n)
│
Germination
│
New Gametophyte (n)
Important Characteristics of Reproduction in Anthocerotopsida
Plant body is a thallus.
Gametophyte is dominant and independent.
Sporophyte remains attached to the gametophyte.
Fertilization requires water.
Sporophyte is horn-shaped and grows continuously because of the basal meristem.
Pseudoelaters help in spore dispersal.
Reproduction occurs by both vegetative and sexual methods.
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The life cycle shows alternation of generations.
Conclusion
The reproduction in Anthocerotopsida, represented by Anthoceros, is a well-organized
process involving both vegetative and sexual methods. Vegetative reproduction helps the
plant survive and multiply quickly, while sexual reproduction increases genetic variation.
The life cycle alternates between the haploid gametophyte and the diploid sporophyte,
with the unique horn-shaped sporophyte being the most characteristic feature of this
group. Since fertilization depends on water, hornworts are commonly found in moist
habitats. This reproductive pattern ensures the survival, growth, and continuation of the
species across generations.
4. Write short notes on:
(a) Structure of Funaria capsule.
(b) Draw T S of Marchantia thallus.
Ans: The capsule of Funaria is the spore-producing part of the moss plant. It is found at the
top of a long stalk called the seta. You can think of the capsule as a small box or container
filled with tiny spores, just like a seed box stores seeds. These spores help the moss
reproduce and spread to new places.
The capsule is divided into three main parts:
1. Apophysis (Basal Region)
The apophysis is the swollen green base of the capsule. It contains chlorophyll, so it can
prepare food through photosynthesis. It also has tiny openings called stomata, which help in
the exchange of gases. Because of its green color and food-making ability, it acts like a mini
leaf attached to the capsule.
2. Theca (Middle Region)
The theca is the largest and most important part of the capsule. It contains a central sterile
column called the columella. Around the columella lies the spore sac, where numerous
spores are formed through meiosis. These spores are very light and are later dispersed by
wind to grow into new moss plants.
3. Operculum (Upper Region)
The operculum is the cap-like lid present at the top of the capsule. It protects the spores
while they are developing. When the spores become mature, the operculum falls off.
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After the operculum falls, a ring of 16 pairs of peristome teeth becomes visible. These teeth
are highly sensitive to moisture. In dry weather, they bend outward and gradually release
the spores. During humid weather, they close again. This controlled release helps the spores
travel farther with the wind, increasing the chances of successful germination.
Another important structure is the calyptra, a hood-like covering that protects the young
capsule during its development. It falls off when the capsule matures.
Simple Diagram of Funaria Capsule
Calyptra
/\
/ \
___________
| Operculum | ← Lid
|-----------|
| Peristome | ← Teeth
|-----------|
| |
| Theca | ← Spore sac around columella
| (Spores) |
| | |
| Columella |
|___________|
| Apophysis | ← Green base with stomata
|___________|
||
Seta
Key Points for Exams
Capsule is the spore-producing organ of Funaria.
It consists of Apophysis, Theca, and Operculum.
Apophysis performs photosynthesis.
Theca contains the spore sac and columella.
Operculum protects the spores.
Peristome teeth help in gradual spore dispersal.
4(b) T.S. (Transverse Section) of Marchantia Thallus
The thallus of Marchantia is a flat, green, ribbon-like plant body that grows on moist soil,
rocks, or damp walls. Unlike higher plants, it does not have true roots, stems, or leaves.
When we cut the thallus across its width and observe it under a microscope, we get a
Transverse Section (T.S.), which shows how its internal tissues are arranged.
The T.S. of Marchantia is divided into two major regions:
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1. Upper Photosynthetic Region
The upper portion is responsible for preparing food. It contains many air chambers arranged
in rows. These chambers contain green cells rich in chloroplasts called photosynthetic
filaments.
The upper surface has tiny air pores, which allow gases like carbon dioxide and oxygen to
move in and out. Unlike stomata of higher plants, these pores remain permanently open.
This region acts like the leaf of a flowering plant, carrying out photosynthesis.
2. Lower Storage Region
The lower portion is made of colorless parenchymatous cells. These cells store food and
water for the plant. This region provides support and nourishment.
From the lower surface arise two important structures:
Rhizoids Hair-like structures that anchor the plant to the soil and absorb water.
Scales Small protective structures that help retain moisture and protect the
growing region.
Simple Diagram of T.S. of Marchantia Thallus
Upper Surface
___________________
| Air Pore |
|--------------------|
| Air Chamber |
| Photosynthetic |
| Filaments |
|--------------------|
| |
| Storage Tissue |
| (Parenchyma) |
|____________________|
| | | |
Rhizoids Scales
Easy Way to Remember
Imagine Marchantia as a two-storey building:
The upper floor has windows (air pores) and green workers (photosynthetic
filaments) making food using sunlight.
The ground floor is a storage room where food and water are kept safely.
Under the building are rhizoids, acting like ropes that hold the plant firmly to the
ground, while scales work like protective mats to prevent water loss.
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Key Points for Exams
Marchantia has a dorsiventral thallus.
The upper region contains air pores, air chambers, and photosynthetic filaments.
The lower region consists of storage parenchyma.
Rhizoids absorb water and fix the plant.
Scales protect the thallus and conserve moisture.
These structures together enable Marchantia to survive in moist habitats while efficiently
performing photosynthesis, storing food, and reproducing successfully.
SECTION-C
5. Differentiate the important characteristics of Sphenopsida and Pteropsida.
Ans: Differentiate the Important Characteristics of Sphenopsida and Pteropsida
Plants are divided into different groups based on their structure, method of reproduction,
and way of growing. Two important groups of pteridophytes (seedless vascular plants) are
Sphenopsida and Pteropsida. Although both reproduce by spores instead of seeds and have
true roots, stems, and leaves, they differ in many important characteristics. Let us
understand these differences in a very simple and interesting way.
Imagine two students in the same class. Both wear the same school uniform, but one is tall
with thin branches while the other has broad leaves and a different style of growth. In the
same way, Sphenopsida and Pteropsida belong to the same plant group (Pteridophytes),
but their appearance and characteristics are quite different.
1. What is Sphenopsida?
Sphenopsida is a class of pteridophytes represented today mainly by the genus Equisetum,
commonly called the horsetail plant.
Main Characteristics
The stem is green, hollow, jointed, and rough.
Leaves are very small, scale-like, and arranged in a ring (whorl) around each joint.
The stem performs most of the photosynthesis because the leaves are too small.
Spores are produced in cone-like structures called strobili at the tips of the stems.
These plants usually grow in moist and damp places.
2. What is Pteropsida?
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Pteropsida includes the true ferns, which are the most common pteridophytes.
Main Characteristics
The stem is usually an underground rhizome.
Leaves are large, green, and divided into many leaflets. These leaves are called
fronds.
Young leaves are coiled like a spring, a condition called circinate vernation.
Spores develop in clusters called sori, which are present on the lower surface of the
leaves.
Ferns are also found in cool, shady, and moist places.
Diagram (Simple Comparison)
SPHENOPSIDA PTEROPSIDA
(Equisetum) (Fern)
/\
/ \ /\/\/\/\/\
|----| ← Cone (Strobilus) (Large Fronds)
| || | \\/\/\/\/\/
| || | ||
==||== ← Whorled leaves ||
| || | Underground Rhizome
| || |
Difference Between Sphenopsida and Pteropsida
Sphenopsida
Pteropsida
Represented mainly by Equisetum
(Horsetail)
Represented mainly by Ferns
Stem is jointed, hollow, and green
Stem is usually an underground rhizome
Leaves are small and scale-like
Leaves are large and compound (fronds)
Photosynthesis occurs mainly in the stem
Photosynthesis occurs mainly in the leaves
Spores are produced in strobili (cones)
Spores are produced in sori on leaf
undersides
Young leaves are not coiled
Young leaves show circinate vernation
Plant looks like a brush or horse's tail
Plant has broad, feather-like leaves
Similarities
Although they are different, both groups have some common features:
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Both are vascular plants with xylem and phloem.
Both possess true roots, stems, and leaves.
Both reproduce by spores, not by seeds.
Both require water for fertilization.
Both show alternation of generations in their life cycle.
Conclusion
In simple words, Sphenopsida and Pteropsida are two important groups of pteridophytes,
but they can be easily identified by their appearance. Sphenopsida (horsetails) have jointed
green stems, tiny scale-like leaves, and cone-like strobili for spore production. In contrast,
Pteropsida (ferns) have large green fronds, underground rhizomes, and sori on the
underside of leaves where spores are formed. Both groups are seedless vascular plants and
usually grow in moist environments, but their structure, leaves, stems, and reproductive
organs clearly distinguish them. Understanding these differences makes it easy to identify
each group in nature and is very useful for examinations.
6. Write short notes on:
(a) Sporangia of Rhynia.
(b) Stele evolution in Pteridophytes.
Ans: (a) Sporangia of Rhynia
Introduction
Rhynia is one of the oldest and simplest land plants known to science. It lived about 400
420 million years ago during the Devonian Period. Scientists consider it a connecting link
between primitive algae and modern vascular plants. Although Rhynia had no true roots or
leaves, it possessed sporangia, which were responsible for producing spores for
reproduction.
What is a Sporangium?
A sporangium is a spore-producing organ found in lower plants such as ferns, mosses, and
early vascular plants. Instead of producing seeds like flowering plants, Rhynia reproduced by
forming tiny spores inside these sporangia.
Think of a sporangium as a small capsule filled with reproductive cells (spores). When the
spores became mature, the capsule opened and released them into the air. These spores
later germinated under suitable conditions to form new plants.
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Structure of the Sporangium in Rhynia
The sporangia of Rhynia had several unique features:
They were terminal, meaning they were present at the tips of aerial branches.
Each branch ended in one spindle-shaped (elongated oval) sporangium.
The sporangium had a thick outer wall made of several layers of cells for protection.
Inside the sporangium were many spore mother cells, which underwent meiosis to
produce haploid spores.
Mature spores were released after the sporangium split open.
Unlike modern ferns, Rhynia had no clusters of sporangia (sori). Each branch carried only
one sporangium.
Functions of the Sporangium
The sporangium performed several important functions:
Produced spores for reproduction.
Protected developing spores from drying and damage.
Helped the species spread by releasing spores into the wind.
Ensured survival of the plant in different environments.
Simple Diagram of Sporangium in Rhynia
Sporangium
__________
/ \
/ Spores \
/______________\
|
|
Aerial Stem
|
|
Dichotomous Branch
Importance of Sporangia in Rhynia
The sporangia of Rhynia provide evidence that early land plants had already developed
specialized reproductive organs. They represent one of the earliest examples of vascular
plant reproduction and help scientists understand how modern ferns and seed plants
evolved.
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(b) Stele Evolution in Pteridophytes
Introduction
The stele is the central vascular cylinder of a plant stem or root. It contains the xylem,
phloem, and supporting tissues. These tissues transport water, minerals, and food
throughout the plant.
The evolution of the stele is one of the most important events in plant evolution because it
made plants stronger, taller, and better adapted to life on land.
What is a Stele?
Imagine a plant stem as a building.
The outer tissues are like the walls.
The stele is like the building's plumbing and wiring system, carrying water and food
to every part of the plant.
As plants evolved, the stele became more advanced and efficient.
Evolution of Stele in Pteridophytes
Scientists believe that the stele evolved through several stages.
1. Protostele (Most Primitive)
This is the simplest type of stele.
Characteristics:
Solid central core of xylem.
Phloem surrounds the xylem.
No pith in the centre.
Found in primitive plants like Rhynia.
Importance:
It provided basic support and water conduction in early land plants.
2. Actinostele
This is a modified protostele.
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Characteristics:
Xylem becomes star-shaped.
Phloem lies between the arms of the star.
Advantage:
The star shape increases the conducting surface.
3. Plectostele
Characteristics:
Xylem is divided into parallel plates.
Phloem lies between the plates.
Found in plants such as Lycopodium.
Advantage:
Better flexibility and more efficient transport.
4. Siphonostele
As plants became larger, a pith appeared in the centre.
Characteristics:
Central pith is present.
Vascular tissue forms a hollow cylinder around it.
Types:
Ectophloic siphonostele phloem only outside xylem.
Amphiphloic siphonostele phloem on both sides of xylem.
Advantage:
Allowed plants to become taller and stronger.
5. Dictyostele
Characteristics:
Leaf gaps divide the vascular cylinder into separate strands.
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Each strand is called a meristele.
Found in many ferns.
Advantage:
Provides better transport and flexibility.
6. Polycyclic Stele
Characteristics:
Two or more rings of vascular tissue are present.
Found in some advanced ferns.
Advantage:
Supports very large plants with efficient transport.
Simple Diagram Showing Stele Evolution
Evolution of Stele
Protostele
●
Actinostele
✶
Plectostele
|| || ||
Siphonostele
( ○ )
Dictyostele
(● ● ● ●)
Polycyclic Stele
((● ●))
((● ●))
Why Did the Stele Evolve?
The evolution of the stele helped plants in many ways:
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Better transport of water and food.
Greater mechanical strength.
Growth of taller stems.
Formation of larger leaves.
Better adaptation to land conditions.
Increased efficiency of vascular tissues.
Conclusion
The sporangia of Rhynia were simple terminal spore-producing structures that helped one
of the earliest vascular plants reproduce successfully on land. They mark an important stage
in the evolution of plant reproduction.
The evolution of the stele in Pteridophytes shows how plants gradually developed from a
simple protostele to advanced forms like dictyostele and polycyclic stele. These changes
improved water transport, food conduction, mechanical support, and overall survival.
Together, the development of efficient sporangia and vascular steles played a crucial role in
the evolution of modern vascular plants and their successful colonization of terrestrial
environments.
SECTION-D
7. Describe the life history of Marsilea duly supported by diagrams.
Ans: The life history of Marsilea explains how this plant grows, reproduces, and completes
its life cycle from one generation to another. Marsilea is commonly known as the water
clover because its leaves look like a four-leaf clover. It is an aquatic or semi-aquatic fern
that grows in ponds, marshes, and wet soil. Like all ferns, Marsilea shows alternation of
generations, meaning its life cycle has two different stages:
1. Sporophyte (Diploid, 2n) the main green plant.
2. Gametophyte (Haploid, n) a small stage that produces sex cells.
1. Sporophyte Stage (Main Plant)
The sporophyte is the plant that we normally see. It has:
A creeping rhizome (underground stem).
Roots growing from the rhizome.
Long stalks ending in four leaflets, giving it the appearance of a clover.
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This stage is diploid (2n) and performs photosynthesis to prepare food.
2. Formation of Sporocarps
Instead of producing spores directly on the leaves like many ferns, Marsilea forms special
bean-shaped structures called sporocarps.
Sporocarp Characteristics:
Hard and drought-resistant.
Attached near the base of the leaf stalk.
Protects spores for many years.
Opens only when placed in water.
Inside each sporocarp are many sori, and each sorus contains two kinds of sporangia.
3. Heterospory
Marsilea is heterosporous, meaning it produces two different types of spores.
(A) Microspores
Small in size.
Produced inside microsporangia.
Develop into the male gametophyte.
(B) Megaspores
Large in size.
Produced inside megasporangia.
Develop into the female gametophyte.
4. Development of Gametophytes
When the sporocarp comes in contact with water, it opens and releases the spores.
Male Gametophyte
Develops from a microspore.
Produces antheridia.
Antheridia produce many motile sperm (antherozoids).
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Female Gametophyte
Develops from a megaspore.
Produces one archegonium.
The archegonium contains a single egg cell.
5. Fertilization
Water is essential for fertilization.
The motile sperm swims through water and reaches the archegonium. One sperm fuses
with the egg to form a zygote (2n). This process is called fertilization.
6. Embryo Formation
The zygote divides repeatedly and develops into an embryo. The embryo gradually grows
into a young sporophyte, which develops roots, leaves, and a rhizome.
Finally, it becomes a mature Marsilea plant, completing the life cycle.
Life Cycle Diagram
Mature Marsilea Plant
(Sporophyte - 2n)
│
▼
Produces Sporocarps
│
▼
┌──────────────────────────┐
│ Sporocarps │
└──────────────────────────┘
│
┌─────────────┴─────────────┐
▼ ▼
Microsporangia Megasporangia
│ │
▼ ▼
Microspores (n) Megaspores (n)
│ │
▼ ▼
Male Gametophyte Female Gametophyte
│ │
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Produces Sperm Produces Egg
└──────────┬───────────────┘
▼
Fertilization
│
Zygote (2n)
│
Embryo
│
▼
Young Sporophyte (2n)
│
▼
Mature Marsilea Plant
Important Features of Marsilea
It is an aquatic fern.
The plant body is the sporophyte (2n).
It has a creeping rhizome, roots, and four-leaflet leaves.
Reproduction occurs through sporocarps.
It is heterosporous, producing microspores and megaspores.
Fertilization requires water.
It shows alternation of generations, where the sporophyte and gametophyte
alternate during the life cycle.
Conclusion
The life history of Marsilea is a clear example of alternation of generations. The dominant
green sporophyte forms protective sporocarps, which produce microspores and
megaspores. These spores develop into male and female gametophytes. After fertilization
in water, a zygote is formed, which grows into an embryo and finally develops into a new
sporophyte. This continuous cycle ensures the survival and reproduction of Marsilea in
aquatic and marshy habitats.
8. Write short notes on:
(a) Typical sporophyte structure of Equisetum.
(b) Gametophyte in Ferns.
Ans: (a) Typical Sporophyte Structure of Equisetum (Horsetail)
Equisetum, commonly known as the Horsetail Plant, is one of the oldest living vascular
plants on Earth. It belongs to the group Pteridophytes, which are plants that have roots,
stems, and leaves but do not produce flowers or seeds. Instead, they reproduce through
spores.
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The sporophyte is the main, green, and independent stage of the life cycle. This is the plant
that we normally see growing in fields, near rivers, or in moist places.
What is a Sporophyte?
A sporophyte is the diploid (2n) generation of the plant that develops after fertilization. Its
main function is to produce spores, which later grow into the gametophyte generation.
In Equisetum, the sporophyte is well-developed, photosynthetic, and independent.
Structure of the Sporophyte
1. Roots
Equisetum has adventitious roots, meaning they arise from the underground stem
instead of from the embryo.
These roots are thin, branched, and grow into the soil.
Their main functions are:
o Absorbing water and minerals.
o Anchoring the plant firmly in the soil.
Although they are small, they play an important role in keeping the plant alive.
2. Rhizome (Underground Stem)
The plant has an underground horizontal stem called a rhizome.
Functions of the rhizome:
Stores food.
Produces roots.
Produces new aerial shoots every season.
Helps in vegetative reproduction.
The rhizome allows the plant to survive unfavorable conditions like drought or winter.
3. Aerial Stem
The aerial stem is the most noticeable part of Equisetum.
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Characteristics:
Green in colour because it contains chlorophyll.
Hollow from the inside.
Jointed with distinct nodes and internodes.
Rough surface due to silica deposits.
Branched in a regular whorl (ring-like arrangement).
Since the leaves are very small, the stem performs most of the photosynthesis.
The silica present in the stem makes it rough, which is why people in the past used it for
polishing utensils. Because of this, Equisetum is sometimes called "Scouring Rush."
4. Leaves
The leaves are:
Very small.
Scale-like.
Green or brownish.
Arranged in whorls around each node.
They are fused together at the base, forming a small sheath around the stem.
Since these leaves are tiny, they perform very little photosynthesis.
5. Branches
Branches arise in whorls from the nodes.
They:
Look similar to the main stem.
Increase the surface area for photosynthesis.
Give the plant its characteristic "horse-tail" appearance.
6. Cone (Strobilus)
The tip of the fertile shoot bears a cone, called a strobilus.
This is the reproductive part of the sporophyte.
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Inside the cone are many sporangiophores, each carrying several sporangia.
The sporangia produce haploid spores through meiosis.
When mature, the spores are released into the air.
7. Spores
The spores possess four ribbon-like structures called elaters.
Functions of elaters:
Help spores spread easily by wind.
Prevent spores from sticking together.
Improve chances of successful germination.
After reaching moist soil, these spores develop into the gametophyte.
Simple Diagram of Equisetum Sporophyte
Cone (Strobilus)
▲
__________
/ \
/ \
Stem
|----Node----|
| |
Whorled Branches
| |
Scale-like Leaves
|
|
Underground Rhizome
----------------------
/ / \ \
Roots Roots Roots Roots
Important Features to Remember
Main plant body is the sporophyte.
Has true roots, stem, and leaves.
Stem is green, hollow, jointed, and performs photosynthesis.
Leaves are small and scale-like.
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Cone (strobilus) produces spores.
Spores contain elaters for wind dispersal.
(b) Gametophyte in Ferns
The gametophyte is the second generation in the life cycle of a fern. While the sporophyte
is large and leafy, the gametophyte is small, delicate, and short-lived.
It develops from a spore that is produced by the sporophyte.
Although tiny, the gametophyte is extremely important because it produces the male and
female sex organs, making sexual reproduction possible.
Development of the Gametophyte
The life cycle begins when a haploid spore lands on moist soil.
If the conditions are suitable:
The spore germinates.
It divides repeatedly.
It develops into a small green structure called the prothallus.
This prothallus is the gametophyte.
Structure of the Prothallus
The fern gametophyte is:
Heart-shaped.
Flat.
Green.
Thin.
Photosynthetic.
About 310 mm wide.
Because it contains chlorophyll, it prepares its own food.
It grows independently on moist soil.
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Rhizoids
On the lower surface of the prothallus are tiny hair-like structures called rhizoids.
Functions:
Anchor the gametophyte.
Absorb water.
Absorb minerals.
Rhizoids are not true roots.
Sex Organs
The gametophyte bears both male and female reproductive organs.
1. Antheridia (Male)
Small and round.
Found near the rhizoids.
Produce many motile sperms.
These sperms require water to swim.
2. Archegonia (Female)
Flask-shaped.
Present near the notch of the heart-shaped prothallus.
Each archegonium contains one egg.
Fertilization
During rainy or moist conditions:
Water forms a thin film on the surface.
Sperms swim towards the archegonium.
One sperm fuses with the egg.
Fertilization occurs.
This produces a zygote (2n).
The zygote develops into a young sporophyte while still attached to the gametophyte.
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Eventually, the young sporophyte grows larger and becomes independent, while the
gametophyte gradually dies.
Importance of Water
One of the most important features of ferns is that water is essential for fertilization.
Without water:
Sperms cannot swim.
Fertilization cannot occur.
New sporophytes cannot develop.
This is why ferns usually grow in moist and shady places.
Simple Diagram of Fern Gametophyte (Prothallus)
Heart-shaped Prothallus
Notch
▼
___________
/ \
/ Archegonia \
/ \
| |
| |
\ /
\ /
\_____________/
Rhizoids (Lower Surface)
||||||||||||||||||||||||
Antheridia near Rhizoids
Important Features to Remember
The fern gametophyte is called the prothallus.
It is small, green, heart-shaped, and independent.
It develops from a haploid spore.
Rhizoids absorb water and anchor the plant.
Antheridia produce sperms.
Archegonia contain eggs.
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Water is essential for fertilization.
The fertilized egg develops into the new sporophyte.
Conclusion
The sporophyte of Equisetum is the dominant, green, and independent plant body with
roots, a rhizome, jointed stems, reduced leaves, and a cone (strobilus) that produces spores.
These spores disperse with the help of elaters and give rise to the next generation.
The gametophyte of ferns, called the prothallus, is a small, heart-shaped, photosynthetic
structure that bears antheridia and archegonia. In the presence of water, sperm reaches
the egg, fertilization takes place, and a new sporophyte is formed. Thus, the alternation
between sporophyte and gametophyte ensures the continuation of the life cycle in
pteridophytes.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
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