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GNDU Question Paper-2023
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:75
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. Bryophytes are amphibians of plant kingdom. Justify this statement by giving general
characteristics of bryophytes.
2. Give an account of life cycle of bryophytes.
SECTION-B
3. Give an account of general characteristics and classification of Hepaticopsida.
4. Draw a diagram to show different stages of the development of sporophyte in
Marchantia. Discuss in brief.
SECTION-C
5. Give an account of Important characteristics of Lycopsida.
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6. With the help of suitable diagrams, discuss in detail the structure and reproduction of
Rhynia.
SECTION-D
7. With the help of suitable diagram, discuss organization of strobilus in Selaginella.
8. Give an account of 'Sporophyte of Marsilea. Support your answer with diagrams.
GNDU Answer Paper-2023
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:75
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. Bryophytes are amphibians of plant kingdom. Justify this statement by giving general
characteristics of bryophytes.
Ans: Introduction
Imagine a small green plant growing on a damp rock, near a pond, or on the bark of a tree
after rain. It looks simple, soft, and delicate. This tiny plant is called a Bryophyte. Bryophytes
are among the earliest plants that appeared on Earth. They are often called the
"amphibians of the plant kingdom" because, just like amphibian animals (such as frogs),
they live on land but depend on water to complete their life cycle, especially for
reproduction.
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A frog spends part of its life on land and part in water. Similarly, bryophytes grow on land
but need a thin layer of water for the male reproductive cells (sperm) to swim and reach the
female reproductive cells (egg). Because of this unique feature, bryophytes are known as
the amphibians of the plant kingdom.
Why are Bryophytes called the Amphibians of the Plant Kingdom?
Bryophytes are called amphibians because they show characteristics of both aquatic and
terrestrial (land) plants.
They grow on land, usually in moist and shady places.
However, water is essential for sexual reproduction.
The male gametes (antherozoids) can swim only through water to reach the egg
present inside the female organ (archegonium).
Without water, fertilization cannot occur.
Therefore, bryophytes cannot complete their life cycle in completely dry conditions.
Simple Example:
Just as a frog cannot reproduce without water, bryophytes also cannot reproduce without
water. Hence, they are called the amphibians of plants.
General Characteristics of Bryophytes
1. They are simple, non-vascular plants
Bryophytes do not have special tissues called xylem and phloem.
Xylem carries water.
Phloem carries food.
Since these tissues are absent, water and nutrients move slowly from one cell to another.
Examples: Mosses and Liverworts.
2. They grow in moist and shady places
Bryophytes prefer places where water is available.
They commonly grow on:
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Damp soil
Wet rocks
Tree trunks
Walls
River banks
Forest floors
They avoid dry environments because they easily lose water.
3. They have no true roots, stems, or leaves
Bryophytes possess simple structures instead of real plant organs.
Rhizoids → Root-like structures that absorb water and anchor the plant.
Stem-like axis
Leaf-like structures
These are not true roots, stems, or leaves because they lack vascular tissues.
4. Small in size
Most bryophytes are only a few centimeters tall.
Since they lack vascular tissues, they cannot transport water over long distances, limiting
their height.
5. Reproduce by spores
Bryophytes do not produce flowers, fruits, or seeds.
Instead, they reproduce using spores.
Spores are tiny reproductive units that can develop into new plants under suitable
conditions.
6. Water is essential for fertilization
This is their most important feature.
The male reproductive cell swims through water to reach the egg.
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Without water:
Fertilization cannot happen.
No new bryophyte plant is formed.
This is the main reason they are called amphibians.
7. Alternation of Generations
Bryophytes have two stages in their life cycle.
Gametophyte Stage
Green
Independent
Produces male and female sex organs.
This is the dominant stage.
Sporophyte Stage
Develops after fertilization.
Produces spores.
Depends on the gametophyte for food.
8. Dominant Gametophyte
Unlike higher plants, the gametophyte is the main visible plant in bryophytes.
The sporophyte remains attached to it and receives nutrition from it.
9. Lack of flowers and seeds
Bryophytes are very primitive plants.
They do not produce:
Flowers
Fruits
Seeds
Their reproduction occurs only through spores.
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10. Ecological Importance
Bryophytes play several important roles in nature.
They:
Prevent soil erosion.
Retain moisture.
Help in soil formation.
Provide habitat for tiny organisms.
Maintain ecological balance.
Some mosses, like Sphagnum, form peat, which is used as fuel and in gardening.
Diagram: Structure of a Moss Plant
Capsule
│
Seta
│
------------------
Leaf-like Structures
------------------
│
Stem-like Axis
│
Rhizoids
(Root-like structures)
Diagram: Life Cycle of Bryophytes
Spores
│
▼
Gametophyte Plant
│
Male Organ Female Organ
(Antheridium) (Archegonium)
\ /
\ Water /
\ /
Fertilization
│
▼
Sporophyte
│
Produces Spores
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│
▼
New Bryophyte
Examples of Bryophytes
Riccia (Liverwort)
Marchantia (Liverwort)
Funaria (Moss)
Sphagnum (Peat Moss)
Anthoceros (Hornwort)
Why are Bryophytes Important?
Bryophytes are considered the connecting link between algae and higher plants because:
They are among the first plants to live on land.
They show simple body organization.
They require water for reproduction like algae.
They helped in the evolution of more advanced land plants.
Conclusion
Bryophytes are called the amphibians of the plant kingdom because they grow on land but
cannot complete sexual reproduction without water. Their dependence on water for
fertilization is similar to amphibian animals like frogs, which also require water for
reproduction. They are small, simple, non-vascular plants that reproduce by spores and
possess rhizoids instead of true roots. The gametophyte is the dominant stage, while the
sporophyte depends on it for nourishment. Besides their biological importance, bryophytes
help conserve soil, retain moisture, and play a vital role in maintaining ecological balance.
Thus, their unique combination of terrestrial life and aquatic reproductive requirements
fully justifies the statement that bryophytes are the amphibians of the plant kingdom.
2. Give an account of life cycle of bryophytes.
Ans: 2. Give an Account of the Life Cycle of Bryophytes
The life cycle of bryophytes is one of the most important topics in botany. Bryophytes
include mosses, liverworts, and hornworts. They are known as the "amphibians of the
plant kingdom" because they live on land but need water for reproduction.
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The most special feature of bryophytes is that they show alternation of generations, which
means their life cycle has two different stages that occur one after another:
1. Gametophyte (Haploid - n) Produces sex cells (gametes).
2. Sporophyte (Diploid - 2n) Produces spores.
Let's understand the complete life cycle step by step in a simple story.
Step 1: Formation of Spores
The life cycle begins with spores, which are tiny, lightweight reproductive cells produced
inside the capsule (sporangium) of the sporophyte.
These spores are haploid (n).
They are released into the air when the capsule matures.
Wind carries the spores to suitable moist places.
If the conditions are favourable (water, moisture, and shade), the spores begin to grow.
Step 2: Germination of Spore
Each spore germinates and develops into a protonema.
The protonema is a green, thread-like structure.
It absorbs water and minerals from the soil.
It is the first stage of the gametophyte in mosses.
Small buds arise from the protonema.
These buds gradually develop into mature leafy plants called gametophytes.
Step 3: Formation of Gametophyte (Main Plant Body)
The gametophyte is the dominant and independent stage of bryophytes.
It is green because it contains chlorophyll and can prepare its own food through
photosynthesis.
The gametophyte produces two reproductive organs:
1. Antheridium (Male Reproductive Organ)
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Produces antherozoids (male gametes).
These male gametes are motile (they can swim).
2. Archegonium (Female Reproductive Organ)
Produces a single egg (female gamete).
It is flask-shaped.
Step 4: Fertilization
This is the reason bryophytes need water.
When rain or dew provides water:
The male gametes swim through the water.
They reach the archegonium.
One male gamete fuses with the egg.
This fusion is called fertilization.
The result is the formation of a zygote (2n).
Step 5: Development of Sporophyte
The zygote remains inside the archegonium.
It divides repeatedly by mitosis and develops into a sporophyte.
The sporophyte usually has three parts:
Foot Absorbs nutrients from the gametophyte.
Seta A stalk supporting the capsule.
Capsule (Sporangium) Produces spores.
Unlike the gametophyte, the sporophyte depends on the gametophyte for food and water.
Step 6: Meiosis and Formation of New Spores
Inside the capsule, special cells undergo meiosis.
Meiosis reduces the chromosome number from 2n to n, producing haploid spores.
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When the capsule bursts open, these spores are released.
The spores spread by wind, land on moist soil, germinate, and the life cycle starts again.
Alternation of Generations
Bryophytes exhibit alternation of generations, where two generations alternate in the life
cycle:
Gametophyte (n) → Produces gametes.
Sporophyte (2n) → Produces spores.
This continuous alternation ensures the survival and reproduction of bryophytes.
Simple Life Cycle Diagram
Spores (n)
│
Germination
│
Protonema
│
▼
Mature Gametophyte (n)
┌────────────┴────────────┐
│ │
Antheridium Archegonium
(Male) (Female)
│ │
└────── Fertilization ─────┘
│
Zygote (2n)
│
▼
Sporophyte (2n)
(Foot → Seta → Capsule)
│
Meiosis
│
Spores (n)
│
Life Cycle Repeats
Key Points to Remember
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Bryophytes are called the amphibians of the plant kingdom because they need
water for fertilization.
The gametophyte (n) is the dominant, green, and independent plant body.
The sporophyte (2n) remains attached to and depends on the gametophyte.
Antheridium produces male gametes, while archegonium produces the female
gamete (egg).
Fertilization forms the zygote (2n).
The sporophyte forms spores by meiosis.
The life cycle shows alternation of generations between the gametophyte and
sporophyte.
Conclusion
The life cycle of bryophytes is a beautiful example of how nature alternates between two
different generations to complete reproduction. The gametophyte is the main,
photosynthetic plant that produces male and female gametes. With the help of water,
fertilization takes place, forming a zygote, which develops into a sporophyte. The
sporophyte produces haploid spores through meiosis, and these spores grow into new
gametophytes. This continuous cycle of spore → protonema → gametophyte →
fertilization → sporophyte → spores is called the life cycle of bryophytes, ensuring the
survival and spread of these simple yet fascinating plants.
SECTION-B
3. Give an account of general characteristics and classification of Hepaticopsida.
Ans: Hepaticopsida, commonly known as liverworts, are one of the oldest and simplest
groups of land plants. They belong to the division Bryophyta, which includes non-vascular
plants. The name "liverwort" comes from their flat, liver-shaped body, which ancient people
believed could cure liver diseases. Although this belief was incorrect, the name has
remained.
Imagine walking through a damp forest after rainfall. If you look closely at wet rocks, tree
trunks, or moist soil, you may notice tiny green plants spreading like a soft carpet. Many of
these are liverworts. Despite their small size, they play an important role in nature by
preventing soil erosion, helping in soil formation, and maintaining moisture.
General Characteristics of Hepaticopsida
1. Small and Non-Vascular Plants
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Hepaticopsida are very small plants that do not have vascular tissues (xylem and phloem).
Since they lack these tissues, they cannot transport water and food efficiently like higher
plants. Therefore, they remain short and usually grow only in moist places.
2. Moist Habitat
These plants are commonly found in shady, cool, and damp environments, such as river
banks, wet rocks, tree bark, and forest floors. Water is essential for their growth and
reproduction.
3. Gametophyte is the Dominant Plant Body
The main plant body that we see is called the gametophyte. It is green and performs
photosynthesis to prepare food. The gametophyte is independent, while the sporophyte
depends on it for nutrition.
4. Plant Body
The body may be of two types:
Thalloid Flat, ribbon-like structure without true roots, stems, or leaves (Example:
Marchantia).
Leafy Has small leaf-like structures arranged around a stem-like axis (Example:
Porella).
5. Rhizoids
Instead of true roots, liverworts possess unicellular rhizoids. These help the plant attach
firmly to the soil and absorb water.
6. Reproduction
Liverworts reproduce in three different ways:
Vegetative Reproduction By fragmentation or gemmae.
Asexual Reproduction Through spores produced in capsules.
Sexual Reproduction By male and female reproductive organs called antheridia
and archegonia.
7. Water is Necessary for Fertilization
The male gametes are motile and swim through a thin layer of water to reach the female
egg. Therefore, reproduction can occur only when water is available.
8. Sporophyte
The sporophyte remains attached to the gametophyte and usually consists of:
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Foot
Seta
Capsule
Inside the capsule, spores are produced, which germinate into new gametophytes.
Classification of Hepaticopsida
Hepaticopsida is mainly divided into two important groups:
1. Thallose Liverworts
Characteristics:
Plant body is flat and ribbon-like (thallus).
No distinct stem or leaves.
Usually grows on moist soil.
Rhizoids are present on the lower surface.
Examples:
Marchantia
Riccia
2. Leafy Liverworts
Characteristics:
Plant body has stem-like and leaf-like structures.
Leaves are arranged in two or three rows.
Mostly found on tree bark and rocks.
Examples:
Porella
Frullania
Simple Classification Chart
Hepaticopsida (Liverworts)
│
┌───────────────┴───────────────┐
│ │
Thallose Liverworts Leafy Liverworts
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│ │
Flat thallus body Stem-like axis with
No true leaves leaf-like structures
│ │
Marchantia, Riccia Porella, Frullania
Simple Diagram of a Liverwort (Marchantia)
Gemma Cup
○
____________
/ \
/ Thallus \
/________________\
| |
| |
|__________________|
| | | |
Rhizoids (Unicellular)
Importance of Hepaticopsida
Help in soil formation by breaking down rocks.
Prevent soil erosion by covering the ground.
Retain moisture in forest ecosystems.
Provide shelter for tiny organisms.
Used by scientists to study the evolution of land plants.
Conclusion
Hepaticopsida are simple, non-vascular plants that mostly grow in moist and shady places.
Their dominant gametophyte, unicellular rhizoids, and dependence on water for
fertilization are their most important characteristics. They are broadly classified into
Thallose liverworts (such as Marchantia and Riccia) and Leafy liverworts (such as Porella
and Frullania). Although they are small, liverworts play a vital role in maintaining ecological
balance, protecting soil, and helping scientists understand the early evolution of plants.
Their simple structure and unique life cycle make them an important topic in the study of
bryophytes.
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4. Draw a diagram to show different stages of the development of sporophyte in
Marchantia. Discuss in brief.
Ans: Introduction
Marchantia is a small, green, liverwort (Bryophyte) that grows in moist and shady places.
Like all bryophytes, it has two stages in its life cycle: the gametophyte (green, dominant
plant body) and the sporophyte (spore-producing stage). The sporophyte develops only
after fertilization and remains attached to the female gametophyte throughout its life. It
depends completely on the gametophyte for water and nutrients because it cannot prepare
enough food on its own.
The development of the sporophyte is an interesting process because it begins from a single
fertilized egg (zygote) and gradually changes into a mature structure that produces spores
for reproduction.
Development of Sporophyte in Marchantia
1. Formation of Zygote
The process starts when the male gamete (antherozoid) reaches the egg inside the
archegonium with the help of water.
Fertilization takes place inside the archegonium.
The male and female gametes fuse.
This fusion forms a diploid zygote (2n).
The zygote is the first cell of the sporophyte generation.
2. First Division of the Zygote
The zygote does not leave the archegonium. Instead, it starts dividing by mitosis.
The first division forms two cells.
Continuous cell divisions produce a small embryo.
This embryo is the beginning of the young sporophyte.
3. Embryo Development
As cell division continues, the embryo becomes larger and differentiates into different
regions.
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Three important parts are formed:
Foot
Seta
Capsule
Each part performs a specific function.
4. Formation of the Foot
The lower part of the embryo develops into the foot.
Functions of Foot:
Anchors the sporophyte to the female gametophyte.
Absorbs water and nutrients.
Keeps the sporophyte attached throughout its life.
The foot acts like the root of the sporophyte, although it is not a true root.
5. Formation of the Seta
The middle part develops into the seta.
Functions of Seta:
It is a short stalk.
Pushes the capsule upward during maturity.
Helps in better spore dispersal.
6. Formation of Capsule
The upper portion develops into the capsule, which is the most important reproductive
part.
Inside the capsule:
Some cells become spore mother cells.
Other cells become elaters.
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7. Formation of Spores
Each spore mother cell (2n) undergoes meiosis.
As a result:
Four haploid spores (n) are produced.
These spores later germinate into new gametophyte plants.
Thus, meiosis restores the haploid generation.
8. Role of Elaters
Elaters are long, spiral-shaped sterile cells.
Their functions are:
Help in drying of the capsule.
Twist and untwist with changes in humidity.
Assist in dispersing spores into the air.
They ensure spores spread to suitable places for germination.
9. Mature Sporophyte
A mature sporophyte has three clearly visible parts:
Foot absorbs food from the gametophyte.
Seta stalk supporting the capsule.
Capsule produces spores.
The capsule eventually bursts open and releases spores.
Simple Diagram of Sporophyte Development
Fertilization
│
Zygote (2n)
│
Repeated Mitosis
│
Young Embryo
│
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┌────────┼────────┐
│ │ │
Foot Seta Capsule
│
┌──────────────┴─────────────┐
│ │
Spore Mother Cells Elaters
│
Meiosis
│
Haploid Spores (n)
│
Germination
│
New Marchantia Gametophyte
Structure of Mature Sporophyte
Capsule
______________
/ \
| Spores + |
| Elaters |
\______________/
│
Seta
│
Foot
│
Female Gametophyte
Functions of Different Parts
Part
Function
Foot
Anchors the sporophyte and absorbs nutrients from the
gametophyte.
Seta
Lifts the capsule upward for efficient spore release.
Capsule
Produces spores through meiosis.
Spore Mother
Cells
Undergo meiosis to form haploid spores.
Elaters
Help in dispersing spores by twisting in dry conditions.
Key Points for Exam
The sporophyte develops from the diploid zygote.
Development occurs inside the archegonium.
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The sporophyte is completely dependent on the female gametophyte for nutrition.
It is divided into foot, seta, and capsule.
Meiosis occurs in the capsule to produce haploid spores.
Elaters help in efficient spore dispersal.
Released spores germinate to form a new gametophyte, completing the life cycle.
Conclusion
The development of the sporophyte in Marchantia is a gradual transformation from a single
fertilized zygote into a mature spore-producing structure. The embryo differentiates into
the foot, seta, and capsule, each with a specific role in growth and reproduction. Although
the sporophyte depends entirely on the female gametophyte for nourishment, it plays a
vital role in the life cycle by producing haploid spores through meiosis. These spores
disperse with the help of elaters, germinate under favorable conditions, and develop into
new Marchantia gametophytes. This alternation between gametophyte and sporophyte
ensures the continuation of the species and is a characteristic feature of all bryophytes.
SECTION-C
5. Give an account of Important characteristics of Lycopsida.
Ans: Lycopsida is one of the oldest groups of vascular plants (Pteridophytes) found on
Earth. These plants first appeared about 400 million years ago and are often called club
mosses, although they are not true mosses. Unlike mosses, they have well-developed roots,
stems, and leaves, along with vascular tissues (xylem and phloem) that transport water and
food throughout the plant.
The most common examples of Lycopsida are Lycopodium (Club Moss), Selaginella (Spike
Moss), and Isoetes (Quillwort). Some ancient Lycopsida formed huge forests during the
Carboniferous period, and their remains later turned into coal deposits.
Simple Definition
Lycopsida is a class of vascular, seedless plants that reproduce through spores instead of
seeds. They possess true roots, stems, and small leaves called microphylls.
Important Characteristics of Lycopsida
1. Seedless Vascular Plants
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Lycopsida plants have vascular tissues (xylem and phloem) that help transport water and
nutrients. However, they do not produce flowers, fruits, or seeds. Instead, they reproduce
by spores.
Easy Example:
Think of Lycopsida as a plant that has its own "water pipes" but does not produce seeds like
mango or sunflower plants.
2. Dominant Sporophyte Plant
The main plant that we usually see is called the sporophyte, which is large, green, and
independent.
The gametophyte generation is much smaller and depends on suitable environmental
conditions for survival.
Remember:
Large visible plant = Sporophyte
Small reproductive stage = Gametophyte
3. True Roots, Stems, and Leaves
Unlike mosses, Lycopsida has:
True roots for absorbing water.
True stems for support.
True leaves for photosynthesis.
These organs make the plant stronger and more advanced than bryophytes.
4. Microphyll Leaves
One of the most unique characteristics is the presence of microphylls.
A microphyll is:
A very small leaf.
Contains only one unbranched vein.
Helps in photosynthesis.
This feature clearly distinguishes Lycopsida from many other vascular plants.
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5. Reproduction by Spores
Lycopsida reproduces by producing spores inside structures called sporangia.
When spores mature, they are released and can grow into a new gametophyte if
environmental conditions are favorable.
No flowers or seeds are formed.
6. Sporangia are Present on Sporophylls
The sporangia develop on special leaves called sporophylls.
Many sporophylls are arranged together to form a cone-like structure known as a strobilus.
This cone protects the sporangia until the spores mature.
7. Homosporous or Heterosporous
Lycopsida may produce:
Homospores only one type of spore.
o Example: Lycopodium
Heterospores two different types of spores:
o Microspores (male)
o Megaspores (female)
o Example: Selaginella and Isoetes
Heterospory is considered an important evolutionary step toward the development of
seeds.
8. Mostly Terrestrial Plants
Most Lycopsida grow on land, especially in moist and shaded forests.
Some species may grow in wetlands or shallow water, but the majority are terrestrial.
They require moisture because water helps the sperm reach the egg during fertilization.
9. Fertilization Requires Water
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The male gametes (sperm) are motile (they can swim).
Therefore, water is essential for fertilization because the sperm must swim to reach the
female egg.
This is why Lycopsida commonly grow in damp environments.
10. Alternation of Generations
Lycopsida show alternation of generations, meaning they have two stages in their life cycle:
Sporophyte (dominant stage) → Produces spores.
Gametophyte → Produces male and female gametes.
After fertilization, a new sporophyte develops, completing the life cycle.
Diagram of Lycopsida
Lycopsida Plant (Sporophyte)
▲ Strobilus (Cone)
/ \
Sporophylls
│
Sporangia
│
Spores
│
Germination
│
Gametophyte
(Male & Female)
│
Fertilization
│
Young Sporophyte
│
Mature Lycopsida Plant
Roots ─ Stem ─ Microphyll Leaves
Examples of Lycopsida
Plant
Special Feature
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Lycopodium
Homosporous club moss
Selaginella
Heterosporous spike moss
Isoetes
Aquatic or semi-aquatic quillwort
Why is Lycopsida Important?
Lycopsida represents an important stage in plant evolution because it was among the first
vascular plants to develop true roots, stems, and leaves. Some members evolved
heterospory, which later contributed to the evolution of seed plants. Ancient Lycopsida
forests also played a major role in the formation of coal deposits, making them important
both biologically and economically.
Conclusion
Lycopsida are ancient vascular, seedless plants characterized by true roots, stems,
microphyll leaves, vascular tissues, and reproduction through spores. Their sporangia are
arranged on sporophylls, often forming strobili, and they exhibit alternation of generations
with a dominant sporophyte stage. Some species are homosporous, while others are
heterosporous, making Lycopsida a significant group in understanding the evolution of
modern vascular plants.
6. With the help of suitable diagrams, discuss in detail the structure and reproduction of
Rhynia.
Ans: Introduction
Rhynia is one of the oldest known land plants in the history of Earth. It lived about 400
million years ago during the Devonian Period. Fossils of Rhynia were first discovered in
Rhynie, Scotland, which is why the plant was given this name.
Scientists consider Rhynia a primitive vascular plant because it had simple water-
conducting tissues but lacked true leaves and roots. It acts as a connecting link between
simple non-vascular plants (Bryophytes) and advanced vascular plants (Pteridophytes). By
studying Rhynia, scientists understand how plants first adapted from living in water to
surviving on land.
Structure of Rhynia
1. General Appearance
Rhynia was a small, upright plant that usually grew 2050 cm tall.
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Its body was very simple and consisted of:
A horizontal underground stem called a rhizome.
Upright green branches.
No true roots.
No true leaves.
Dichotomous branching (every branch divides into two equal branches).
This simple structure made Rhynia one of the earliest land plants.
2. Rhizome (Underground Stem)
The lower part of the plant was a creeping rhizome.
Functions:
Anchored the plant in the soil.
Absorbed water and minerals.
Produced rhizoids for attachment.
Unlike modern plants, Rhynia had rhizoids instead of true roots.
3. Stem
The aerial stem was:
Green
Cylindrical
Smooth
Leafless
Dichotomously branched
Since there were no leaves, the stem itself carried out photosynthesis.
4. Internal Structure of Stem
The stem had three main layers.
(a) Epidermis
Outermost protective layer.
Covered with a cuticle to reduce water loss.
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Contained stomata for gas exchange.
(b) Cortex
Located below the epidermis.
Functions:
Food storage.
Photosynthesis.
Mechanical support.
(c) Vascular Tissue
At the center was a simple vascular cylinder called protostele.
It contained:
Xylem transports water.
Phloem transports food.
The presence of vascular tissue allowed Rhynia to grow taller than bryophytes.
Simple Diagram of Rhynia
Sporangium
▲
( )
|
/\ |
/ \|
/ \
/ \
/ \
| |
| Stem |
| |
| |
| |
---Rhizome---
\ | /
\ | /
Rhizoids
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Internal Structure of Stem
-------------------------
| Epidermis |
|--------------------------|
| Cortex |
|--------------------------|
| Phloem |
|--------------------------|
| Xylem |
-------------------------
Reproduction in Rhynia
Rhynia reproduced mainly by spores.
It did not produce flowers, fruits, or seeds.
Reproduction occurred through sporangia.
1. Sporangia
At the tip of each branch, there was a single sporangium.
Characteristics:
Oval or elongated.
Thick-walled.
Terminal in position.
Produced numerous spores.
The spores were all of the same type (homosporous).
2. Formation of Spores
Inside the sporangium:
Special spore mother cells were formed.
These cells underwent meiosis.
Meiosis produced many haploid spores.
When mature, the sporangium split open and released the spores.
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3. Germination of Spores
After falling onto moist soil:
Each spore germinated.
It developed into a gametophyte.
Although fossil gametophytes are rare, scientists believe they were small and independent.
4. Formation of Sex Organs
The gametophyte produced two reproductive organs:
Antheridia (Male Organ)
Produced motile sperm.
Archegonia (Female Organ)
Contained the egg.
5. Fertilization
During rainy or moist conditions:
Sperm swam through a thin film of water.
Reached the egg inside the archegonium.
Fertilization produced a zygote.
6. Formation of New Sporophyte
The zygote divided repeatedly.
It developed into a young sporophyte, which later became the mature Rhynia plant.
Thus, the life cycle showed alternation of generations, where:
Gametophyte produces gametes.
Sporophyte produces spores.
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Life Cycle Diagram
Mature Sporophyte
│
▼
Sporangium
│
Meiosis
│
▼
Spores
│
Germination
│
▼
Gametophyte
│ │
Antheridia Archegonia
│ │
└──┬──┘
▼
Fertilization
│
Zygote
│
▼
Young Sporophyte
│
▼
Mature Rhynia
Importance of Rhynia
It is one of the earliest vascular land plants.
It helps scientists understand the evolution of land plants.
It possessed xylem and phloem, showing the beginning of vascular tissues.
It lacked true roots and leaves, indicating an early stage of plant evolution.
It forms an important evolutionary link between Bryophytes and Pteridophytes.
Conclusion
Rhynia was a simple but highly important primitive land plant. Its body consisted of a
rhizome, green leafless stem, rhizoids, and terminal sporangia. It had a protostele with
xylem and phloem, making it one of the first vascular plants. Reproduction occurred by
homospores produced in terminal sporangia. After germination, the spores formed a
gametophyte, which produced male and female sex organs. Fertilization led to the
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formation of a new sporophyte, completing the alternation of generations. Because of
these characteristics, Rhynia is regarded as a key plant in understanding how early plants
successfully adapted to life on land.
SECTION-D
7. With the help of suitable diagram, discuss organization of strobilus in Selaginella.
Ans: Introduction
Selaginella is a small, green, vascular plant belonging to the group Pteridophytes (club
mosses). It is commonly found in moist and shady places. One of its most important
reproductive structures is the strobilus, also called a cone. The strobilus is a compact
arrangement of leaves and sporangia that helps the plant reproduce efficiently.
Think of a strobilus as a miniature tower or pine-cone-like structure where all the
reproductive organs are neatly arranged. Instead of flowers or fruits like flowering plants,
Selaginella produces spores inside this cone.
What is a Strobilus?
A strobilus is a compact cone-like reproductive structure formed at the tip of the stem or
branches. It consists of many special leaves called sporophylls arranged closely around a
central axis.
Strobilus = Central Axis + Sporophylls + Sporangia
It protects the reproductive organs and ensures proper spore production.
Organization of the Strobilus
1. Central Axis
The strobilus has a central upright axis.
It acts as the main supporting structure.
All the sporophylls are attached around this axis in a spiral or opposite arrangement.
2. Sporophylls
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Sporophylls are modified leaves that bear sporangia.
They are usually smaller than normal leaves.
They are closely packed to form a cone.
Each sporophyll bears one sporangium on its upper (adaxial) side near the base.
Their main function is to protect and support the sporangia.
3. Sporangia
A sporangium is a sac-like structure where spores are produced.
In Selaginella, there are two types of sporangia, making it a heterosporous plant.
(A) Microsporangium
Small in size.
Produces many tiny microspores.
Microspores develop into the male gametophyte.
(B) Megasporangium
Larger in size.
Produces only a few large megaspores (usually four).
Megaspores develop into the female gametophyte.
Heterospory in Selaginella
One of the most important features of Selaginella is heterospory, meaning it produces two
different kinds of spores.
Type of Spore
Produced in
Function
Microspores
Microsporangium
Form the male gametophyte
Megaspores
Megasporangium
Form the female gametophyte
This is considered an important evolutionary step because it eventually led to the
development of seed plants.
Arrangement of Sporangia
Different species of Selaginella show different arrangements.
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In many species, microsporangia are present in the upper part of the strobilus.
Megasporangia are present in the lower part.
In some species, both may occur alternately.
This arrangement helps in efficient reproduction.
Simple Diagram of Strobilus
Tip of Strobilus
▲
│
┌────────────────┐
│ Sporophyll │
│ Microsporangium│
└────────────────┘
│
┌────────────────┐
│ Sporophyll │
│ Microsporangium│
└────────────────┘
│
┌────────────────┐
│ Sporophyll │
│ Megasporangium │
└────────────────┘
│
┌────────────────┐
│ Sporophyll │
│ Megasporangium │
└────────────────┘
│
Central Axis
Functions of the Strobilus
Produces reproductive spores.
Protects developing sporangia.
Arranges sporophylls in a compact cone.
Helps in efficient spore dispersal.
Supports sexual reproduction.
Shows heterospory, an advanced evolutionary feature.
Importance of the Strobilus
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The strobilus is important because it:
Serves as the reproductive organ of Selaginella.
Produces both male and female spores.
Protects spores until they mature.
Increases reproductive efficiency.
Represents an evolutionary stage between simple spore-producing plants and seed
plants.
Conclusion
The strobilus of Selaginella is a compact cone-like reproductive structure made up of a
central axis bearing numerous sporophylls. Each sporophyll carries either a
microsporangium or a megasporangium. The production of two different types of spores
(heterospory) is the most distinctive feature of Selaginella and marks an important step in
plant evolution toward the origin of seeds. Thus, the well-organized strobilus ensures
protection, efficient spore formation, and successful reproduction, making it one of the
most significant structures in the life cycle of Selaginella.
8. Give an account of 'Sporophyte of Marsilea. Support your answer with diagrams.
Ans: Introduction
Marsilea is a small aquatic or amphibious fern commonly known as the Water Clover
because its leaves look like a four-leaf clover. Like all ferns, it has two generations in its life
cycle:
1. Sporophyte (Diploid) the main green plant body.
2. Gametophyte (Haploid) a small stage that develops from spores.
The sporophyte is the dominant, independent, and long-living stage. It performs
photosynthesis, absorbs water and minerals, and produces spores for reproduction.
Structure of the Sporophyte
1. Rhizome (Stem)
The rhizome is the underground or creeping stem of Marsilea.
It grows horizontally in mud or shallow water.
It has nodes and internodes.
At each node, roots and leaves are produced.
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The rhizome stores food and helps the plant spread to new areas.
Simple idea:
Think of the rhizome as the main pipeline of the plant from which roots and leaves grow.
2. Roots
The roots are adventitious roots, meaning they arise from the nodes of the rhizome instead
of from a primary root.
Functions:
Absorb water and minerals.
Anchor the plant firmly in muddy soil.
Help the plant survive in aquatic habitats.
3. Leaves
The leaves are one of the most attractive parts of Marsilea.
Each leaf has:
A long stalk called the petiole.
Four leaflets attached at the top.
This makes the leaf resemble a four-leaf clover.
Functions:
Prepare food through photosynthesis.
Exchange gases.
Lose excess water through transpiration.
4. Sporocarp (Reproductive Organ)
The most important reproductive structure of the sporophyte is the sporocarp.
It is a hard, bean-shaped structure.
It develops near the base of the leaf stalk.
It protects spores during unfavorable conditions.
When water becomes available, the sporocarp opens and releases spores.
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Inside the sporocarp are two kinds of sporangia:
Microsporangia → produce microspores (male spores).
Megasporangia → produce megaspores (female spores).
Because it produces two different types of spores, Marsilea is called a heterosporous fern.
Why is the Sporophyte Important?
The sporophyte is responsible for:
Making food through photosynthesis.
Absorbing water and minerals.
Storing food.
Producing sporocarps.
Forming spores for the next generation.
Thus, it is the main visible plant that completes almost all life activities.
Simple Diagram of Sporophyte
Leaf
(4 Leaflets)
|
Petiole
|
-------------------------------
| Rhizome |
-------------------------------
| | | |
Roots Roots Roots Roots
|
Sporocarp
(Bean-shaped)
|
-------------------------
| |
Microsporangia Megasporangia
(Microspores) (Megaspores)
Key Features of the Sporophyte
Part
Function
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Rhizome
Creeping stem, stores food, produces roots and leaves
Roots
Absorb water and anchor the plant
Leaves
Photosynthesis and gas exchange
Petiole
Connects leaf to stem
Sporocarp
Protects and produces spores
Microsporangia
Produce male spores
Megasporangia
Produce female spores
Conclusion
The sporophyte of Marsilea is the dominant and independent green plant. It consists of a
creeping rhizome, adventitious roots, long-stalked four-lobed leaves, and bean-shaped
sporocarps. The rhizome helps in growth and storage, the roots absorb water, the leaves
prepare food, and the sporocarps produce microspores and megaspores for reproduction.
Since Marsilea produces two different kinds of spores, it is called a heterosporous fern. The
sporophyte is therefore the most important stage in the life cycle of Marsilea, ensuring its
survival, growth, and reproduction.
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