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GNDU Question Paper-2023
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
BOTANY: Paper-I-A
(Diversity of Microbes)
Time Allowed: Three Hours Max. Marks:50
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. Draw
well labelled neat diagrams wherever required.
SECTION-A
1. Describe in detail the following:
(a) Morphology of Coleochaete.
(b) Sexual Reproduction in Volvox.
2. Describe in detail the habitat, morphology and life cycle of Ectocarpus.
SECTION-B
3. Write a short note on the following:
(a) Mycoplasma
(b) Bacterial Nutrition.
4. Explain in detail the significant characteristics of:
(a) Cyanobacteria
(b) Bacterioids,
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SECTION-C
5. Describe briefly the following:
(a) Reproduction in Phytophthora
(b) Sexual Reproduction in Eurotium.
6. What are the important features of Zygomycetes? Also, explain in detail the life cycle of
Mucor:
SECTION-D
7. Describe briefly the following:
(a) Cercospora
(b) Ecological importance of Lichens.
8. Explain in detail the morphology and reproduction in Agaricus with the help of suitable
diagrams.
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GNDU Answer Paper-2023
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
BOTANY: Paper-I-A
(Diversity of Microbes)
Time Allowed: Three Hours Max. Marks:50
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. Draw
well labelled neat diagrams wherever required.
SECTION-A
1. Describe in detail the following:
(a) Morphology of Coleochaete.
(b) Sexual Reproduction in Volvox.
Ans: Introduction
Coleochaete is a freshwater green alga (Chlorophyceae) that is considered one of the most
advanced green algae. Scientists believe it is closely related to the ancestors of land plants
because it shows several plant-like features. It usually grows attached to stones, aquatic
plants, or submerged wood in ponds, lakes, and slow-moving freshwater.
Think of Coleochaete as a small green carpet spread over underwater surfaces. Even though
it is tiny, its body organization is quite advanced compared to many other algae.
Morphology (Structure of Coleochaete)
1. Plant Body (Thallus)
The body of Coleochaete is called a thallus because it is not differentiated into roots, stems,
or leaves.
There are two common forms:
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Prostrate (disc-shaped) form: Cells grow side by side to form a flat circular disc
attached to a surface.
Cushion-like form: Cells branch upward, giving the thallus a soft cushion
appearance.
The thallus remains firmly attached to the substratum by basal cells.
2. Cells
Each cell is:
Small and polygonal.
Surrounded by a cellulose cell wall.
Living independently but connected with neighboring cells.
Every cell contains:
One large nucleus
Large central vacuole
Cytoplasm
One parietal (side-wall) chloroplast
One or more pyrenoids, which help in starch formation and food storage.
3. Chloroplast
The chloroplast is green due to chlorophyll pigments.
Its functions are:
Photosynthesis
Preparation of food
Storage of starch around pyrenoids
4. Hair (Seta)
One unique feature is the presence of a long colourless hair called a seta.
The seta develops from certain cells and is enclosed at its base by a sheath.
Functions of seta:
Protection
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Prevents small animals from eating the alga
May help reduce the accumulation of dirt on the thallus
5. Habitat
Coleochaete is commonly found:
In ponds
Lakes
Slow-flowing streams
Attached to submerged plants and stones
It prefers clean freshwater.
Simple Diagram
Seta (Hair)
|
|
______
| |
| Cell |
_______|______|_______
| Cell | Cell | Cell |
|______|______|________|
| Cell | Cell | Cell |
|______|______|________|
Disc-shaped thallus
Attached to submerged rock
Easy Points to Remember
Feature
Description
Kingdom
Plantae
Group
Green Algae (Chlorophyceae)
Habitat
Freshwater
Plant body
Disc-shaped or cushion-like thallus
Cell wall
Cellulose
Chloroplast
One parietal chloroplast
Special structure
Long colourless seta
Food reserve
Starch
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Conclusion
Coleochaete is a small freshwater green alga with a disc-shaped or cushion-like thallus,
cellulose cell walls, parietal chloroplasts, and a characteristic seta (hair). Although it lacks
true roots, stems, and leaves, its body organization is more advanced than many algae.
These features make Coleochaete an important organism in understanding the evolution of
land plants.
1(b). Sexual Reproduction in Volvox
Introduction
Volvox is a colonial green alga found in freshwater ponds, lakes, and ditches. Hundreds or
even thousands of tiny cells live together in a hollow spherical colony. Each cell looks similar
to Chlamydomonas and has two flagella, allowing the entire colony to swim through water.
Sexual reproduction in Volvox is an advanced process that helps the organism produce
offspring with greater genetic variation and survive unfavorable conditions.
Sexual Reproduction
Volvox reproduces sexually by oogamy, the most advanced type of sexual reproduction.
In oogamy:
The male gamete is small, motile, and flagellated.
The female gamete (egg) is large, non-motile, and rich in stored food.
The fusion of these two gametes forms a zygote.
1. Formation of Male Gametes (Antheridia)
Some vegetative cells enlarge and become antheridia.
Inside each antheridium:
The cell divides repeatedly.
Many small biflagellate sperm are produced.
When mature:
The antheridium breaks open.
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Sperm are released into the surrounding water.
2. Formation of Female Gamete (Oogonium)
Another vegetative cell enlarges to form an oogonium.
Characteristics:
Produces only one large egg.
The egg is non-motile.
It remains inside the oogonium waiting for fertilization.
3. Fertilization
The released sperm swim through water using their flagella.
One sperm reaches the oogonium and fuses with the egg.
This fusion is called fertilization, producing a diploid zygote.
4. Zygote Formation
The zygote:
Develops a thick protective wall.
Stores food.
Becomes resistant to heat, cold, and drought.
It acts as a resting stage until conditions become favorable.
5. Germination
When environmental conditions improve:
The zygote undergoes meiosis.
Haploid cells are produced.
One survives and divides repeatedly by mitosis.
A new Volvox colony develops.
Thus, the life cycle continues.
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Flow Diagram
Vegetative Cells
│
▼
┌──────────────┐
│ Antheridium │
│ (Male) │
└──────────────┘
│
Produces many sperm
│
▼
Fertilization
▲
│
┌──────────────┐
│ Oogonium │
│ (One Egg) │
└──────────────┘
│
▼
Zygote
│
Thick protective wall
│
▼
Meiosis
│
▼
New Volvox Colony
Characteristics of Sexual Reproduction
Type of reproduction: Oogamy
Male gametes are small, motile, and biflagellate.
Female gamete is large and non-motile.
Fertilization occurs in water.
A diploid zygote is formed.
The zygote survives unfavorable conditions due to its thick wall.
Meiosis during germination restores the haploid phase and gives rise to a new
colony.
Easy Comparison
Male Gamete
Female Gamete
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Small
Large
Motile
Non-motile
Many produced
Only one egg
Has two flagella
No flagella
Formed in antheridium
Formed in oogonium
Conclusion
Sexual reproduction in Volvox occurs through oogamy, where numerous small motile sperm
produced in antheridia swim through water and fertilize a single large non-motile egg
formed in an oogonium. The resulting zygote develops a thick protective wall, helping it
survive unfavorable conditions. When conditions become favorable again, the zygote
undergoes meiosis, producing haploid cells that grow into a new Volvox colony. This process
not only ensures survival but also introduces genetic variation, making the species better
adapted to changing environments.
2. Describe in detail the habitat, morphology and life cycle of Ectocarpus.
Ans: 1. Habitat of Ectocarpus
Ectocarpus mainly grows in marine (sea) water. It is commonly found along the seashores,
where it remains attached to rocks, shells, or larger seaweeds.
Some important points about its habitat are:
It is mainly a marine alga, but a few species are found in freshwater.
It usually grows in cold and temperate coastal regions.
It can grow:
o Attached to rocks (epilithic)
o On larger seaweeds (epiphytic)
o On shells and other submerged objects
It prefers places where sunlight and seawater are available for photosynthesis.
Simple Understanding:
Imagine green moss growing on stones near a river. In the same way, Ectocarpus grows as
soft brown threads on rocks and seaweeds in the ocean.
2. Morphology (Structure) of Ectocarpus
The body of Ectocarpus is called a thallus, meaning it has no true roots, stems, or leaves.
Main Features
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Plant body is small, branched, and filamentous (thread-like).
Usually 1030 cm long.
Brown colour is due to the pigment fucoxanthin, which hides the green chlorophyll.
Attached to the surface by rhizoids or a small holdfast.
Branches are soft and hair-like.
Cellular Structure
Each cell contains:
Cell wall made of cellulose and alginic substances.
One nucleus.
Many chloroplasts.
Brown pigment fucoxanthin.
Food is stored mainly as laminarin and mannitol.
Types of Filaments
The thallus has two parts:
1. Prostrate (creeping) filament
o Lies flat on the surface.
o Helps in attachment.
2. Erect filament
o Grows upward.
o Performs photosynthesis and reproduction.
Simple Understanding:
Think of a small brown plant made of many tiny threads. The lower threads stick to the rock,
while the upper threads stand upright and make food.
Simple Diagram of Ectocarpus
Erect Filaments
/\
/ \
/ /\ \
/ / \ \
/_/____\_\
|
|
Prostrate Filament
-----------------------------
| | | |
Rhizoids / Holdfast
(Attached to Rock)
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3. Life Cycle of Ectocarpus
The life cycle of Ectocarpus is very interesting because it shows alternation of generations.
This means two different plant bodies alternate during the life cycle:
Sporophyte (2n) Diploid generation
Gametophyte (n) Haploid generation
Both generations look almost the same, so the life cycle is called isomorphic alternation of
generations.
Step 1: Sporophyte (Diploid Plant)
The mature sporophyte produces sporangia.
There are two types:
A. Unilocular Sporangia
One chamber
Meiosis occurs.
Produces haploid meiospores.
B. Plurilocular Sporangia
Many chambers
Produces diploid spores by mitosis.
Step 2: Formation of Gametophyte
The haploid meiospores swim in water using two unequal flagella.
They settle on a suitable surface and grow into a haploid gametophyte.
Step 3: Formation of Gametes
The gametophyte develops plurilocular gametangia.
These produce many male and female gametes.
The gametes are:
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Motile
Biflagellate
Similar in size (isogamous)
Step 4: Fertilization
A male gamete fuses with a female gamete.
This process forms a diploid zygote (2n).
Step 5: Formation of New Sporophyte
The zygote settles on a rock or another surface.
It divides repeatedly by mitosis and grows into a new diploid sporophyte.
Thus, the life cycle starts again.
Life Cycle Diagram
Sporophyte (2n)
│
Unilocular Sporangium
(Meiosis)
│
Haploid Spores (n)
│
▼
Gametophyte (n)
│
Plurilocular Gametangia
│
Male + Female Gametes
│
Fertilization
│
Zygote (2n)
│
▼
New Sporophyte (2n)
Important Points for Exams
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Kingdom: Protista (traditionally) / Chromista (modern classification)
Division: Phaeophyta (Brown Algae)
Habitat: Mostly marine
Thallus: Branched and filamentous
Pigment: Fucoxanthin
Stored Food: Laminarin and Mannitol
Attachment: Holdfast or Rhizoids
Reproduction: Vegetative, asexual, and sexual
Life Cycle: Isomorphic alternation of generations
Sexual Reproduction: Usually isogamous
Sporophyte: Diploid (2n)
Gametophyte: Haploid (n)
Conclusion
Ectocarpus is a simple brown marine alga with a thread-like body attached to rocks or
other seaweeds. Its thallus lacks true roots, stems, and leaves but contains pigments like
fucoxanthin that give it a brown colour and help in photosynthesis. One of its most
important characteristics is its isomorphic alternation of generations, where both the
diploid sporophyte and haploid gametophyte are similar in appearance. The sporophyte
produces spores, the spores grow into gametophytes, gametophytes form gametes,
fertilization produces a zygote, and the zygote develops into a new sporophyte. Because of
this clear and complete life cycle, Ectocarpus is an important organism for understanding
the biology and evolution of brown algae.
SECTION-B
3. Write a short note on the following:
(a) Mycoplasma
(b) Bacterial Nutrition.
Ans: (a) Mycoplasma
Introduction
Imagine a tiny living organism that is so small and simple that it can survive without a cell
wall, unlike most bacteria. This unusual organism is called Mycoplasma. It is considered the
smallest free-living organism known in nature. Because it lacks a cell wall, it has no fixed
shape and can change its form easily. This feature makes Mycoplasma unique among
bacteria.
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Mycoplasma was first discovered in diseased cattle and is now known to infect humans,
animals, and plants. Some species cause diseases such as pneumonia in humans, while
others cause diseases in plants known as little leaf disease.
Characteristics of Mycoplasma
It is the smallest living cell capable of independent growth.
It does not have a cell wall; only a flexible plasma membrane surrounds it.
Because there is no cell wall, it is pleomorphic, meaning it can have many different
shapes.
It contains both DNA and RNA.
It reproduces mainly by binary fission (splitting into two cells).
It is resistant to antibiotics like penicillin, because these antibiotics attack the cell
wall, which Mycoplasma does not have.
Importance
Although very tiny, Mycoplasma has great importance in medicine and agriculture.
Scientists study it to understand cell evolution, bacterial infections, and the development of
new antibiotics.
Simple Diagram
Mycoplasma
_______________
/ \
| DNA + RNA |
| Cytoplasm |
| |
\_______________/
Plasma Membrane
(No Cell Wall Present)
Key Points to Remember
Smallest free-living organism.
No cell wall.
Flexible shape (pleomorphic).
Causes diseases in humans, animals, and plants.
Resistant to penicillin.
(b) Bacterial Nutrition
Introduction
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Just like humans need food for energy and growth, bacteria also need nutrients to live,
grow, and reproduce. The process by which bacteria obtain food is called bacterial
nutrition.
Bacteria require:
Carbon (for building cells)
Nitrogen (for proteins)
Water
Minerals
Vitamins
Energy
Different bacteria obtain their food in different ways depending on their environment.
Types of Bacterial Nutrition
1. Autotrophic Nutrition
Autotrophic bacteria prepare their own food.
There are two types:
(a) Photosynthetic Bacteria
Use sunlight as a source of energy.
Convert carbon dioxide and water into food.
Example: Cyanobacteria.
(b) Chemosynthetic Bacteria
Do not need sunlight.
Obtain energy by oxidizing chemicals such as ammonia, sulphur, or iron.
Example: Nitrosomonas.
2. Heterotrophic Nutrition
These bacteria cannot prepare their own food. They depend on other living organisms or
dead organic matter.
There are three main types:
(a) Saprophytic Bacteria
Feed on dead and decaying plants and animals.
Help in decomposition and recycling nutrients.
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Example: Bacillus.
(b) Parasitic Bacteria
Live inside living organisms.
Obtain food from the host and often cause diseases.
Example: Salmonella, Mycobacterium tuberculosis.
(c) Symbiotic Bacteria
Live together with another organism.
Both organisms benefit from each other.
Example: Rhizobium bacteria in the roots of leguminous plants.
Simple Diagram
Bacterial Nutrition
|
--------------------------------
| |
Autotrophic Heterotrophic
| |
------------- -------------------------
| | | | |
Photosynthetic Chemosynthetic Saprophytic Parasitic Symbiotic
Importance of Bacterial Nutrition
Helps bacteria survive and reproduce.
Maintains the balance of nature through decomposition.
Improves soil fertility by nitrogen fixation.
Some bacteria are useful in making curd, cheese, and medicines.
Some harmful bacteria cause diseases in humans, animals, and plants.
Conclusion
Mycoplasma is a unique bacterium because it is the smallest free-living organism and lacks
a cell wall, making it flexible in shape and naturally resistant to certain antibiotics. Despite
its tiny size, it can cause important diseases in humans, animals, and plants.
Bacterial nutrition explains how bacteria obtain the food and energy needed for life. Some
bacteria make their own food (autotrophs) using sunlight or chemical energy, while others
depend on dead matter or living organisms (heterotrophs). Understanding bacterial
nutrition helps us appreciate both the beneficial roles of bacteria, such as recycling nutrients
and improving soil fertility, and their harmful roles in causing diseases.
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Exam Tip (GNDU): Remember these keywords:
Mycoplasma: Smallest organism, no cell wall, pleomorphic, disease-causing,
penicillin-resistant.
Bacterial Nutrition: Autotrophic (photosynthetic, chemosynthetic) and
Heterotrophic (saprophytic, parasitic, symbiotic).
4. Explain in detail the significant characteristics of:
(a) Cyanobacteria
(b) Bacterioids,
Ans: (a) Cyanobacteria
Cyanobacteria are one of the oldest living organisms on Earth. They are often called blue-
green algae, but they are actually bacteria, not true algae. Scientists believe that
cyanobacteria appeared about 3.5 billion years ago and played a major role in producing
oxygen in Earth's atmosphere through photosynthesis. Because of this, they are often called
the "oxygen makers of the planet."
Unlike ordinary bacteria, cyanobacteria contain chlorophyll-a and other pigments that allow
them to prepare their own food using sunlight. This process is called photosynthesis, just
like in green plants.
Significant Characteristics of Cyanobacteria
1. Prokaryotic Nature
Cyanobacteria are prokaryotic organisms, meaning they do not have a true nucleus or
membrane-bound organelles such as mitochondria and chloroplasts. Their DNA floats freely
inside the cell.
Simple Idea:
Think of them as a very simple cell without separate rooms. Everything happens inside one
open space.
2. Photosynthetic Organisms
They contain chlorophyll-a and blue pigments called phycocyanin, which give them their
blue-green color.
Using sunlight, carbon dioxide, and water, they prepare food and release oxygen.
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Photosynthesis Equation:
Sunlight + CO₂ + H₂O → Glucose + Oxygen (O₂)
This oxygen production helped create the Earth's oxygen-rich atmosphere.
3. Nitrogen Fixation
Many cyanobacteria can convert atmospheric nitrogen into ammonia, which plants can use.
This process is called nitrogen fixation.
Examples:
Nostoc
Anabaena
These organisms improve soil fertility naturally and are widely used as biofertilizers,
especially in paddy fields.
4. Presence of Heterocysts
Some cyanobacteria possess special thick-walled cells known as heterocysts.
Function of heterocysts:
Protect nitrogen-fixing enzymes from oxygen.
Carry out nitrogen fixation.
These cells do not perform photosynthesis because oxygen interferes with nitrogen fixation.
5. Different Shapes
Cyanobacteria occur in several forms:
Single-celled
Colonial
Filamentous
Examples include:
Chroococcus (colonial)
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Oscillatoria (filamentous)
Nostoc (filamentous colony)
6. Reproduction
Cyanobacteria reproduce asexually.
Methods include:
Binary fission
Fragmentation
Formation of spores (akinetes)
They do not reproduce sexually.
7. Habitat
They are found almost everywhere:
Freshwater
Oceans
Wet soil
Rocks
Hot springs
Desert crusts
Their ability to survive in extreme environments makes them highly adaptable.
8. Ecological Importance
Cyanobacteria play many important roles:
Produce oxygen
Fix atmospheric nitrogen
Improve soil fertility
Serve as food for aquatic organisms
Help maintain ecological balance
9. Economic Importance
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Humans use cyanobacteria in several ways:
Biofertilizers in agriculture
Production of food supplements like Spirulina
Wastewater treatment
Research in biotechnology
Diagram of Cyanobacterium
Cyanobacterium (Filament)
O──O──O──◎──O──O──O──O
O = Normal photosynthetic cell
◎ = Heterocyst
(Nitrogen Fixation)
Easy Memory Trick
CYANO
C → Chlorophyll
Y → Yields oxygen
A → Ancient organisms
N → Nitrogen fixation
O → Oxygen-producing bacteria
(b) Bacteroids (Bacterioids)
Bacteroids are specialized forms of nitrogen-fixing bacteria found inside the root nodules
of leguminous plants such as pea, gram, soybean, bean, and lentil.
Normally, the bacteria live freely in the soil as Rhizobium. When they enter the roots of
legume plants, they change into a special form called a bacteroid (or bacterioid).
These bacteroids form a symbiotic relationship with the plant. In this relationship, both the
plant and the bacteria benefit.
The plant supplies food (carbohydrates) to the bacteria.
The bacteroids supply usable nitrogen compounds to the plant.
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Significant Characteristics of Bacteroids
1. Derived from Rhizobium
Bacteroids develop from Rhizobium bacteria after entering the root nodules of legumes.
They are not free-living cells but exist only inside plant nodules.
2. Nitrogen Fixation
The main function of bacteroids is nitrogen fixation.
They convert atmospheric nitrogen (N₂) into ammonia (NH₃), which plants use to make
proteins, enzymes, and nucleic acids.
3. Symbiotic Relationship
Bacteroids and plants help each other.
Plant provides:
Sugars
Energy
Safe environment
Bacteroids provide:
Fixed nitrogen
This relationship benefits both partners.
4. Root Nodules
Bacteroids live inside root nodules formed on the roots of leguminous plants.
These nodules are small, rounded swellings visible on the roots.
5. Presence of Leghemoglobin
Root nodules contain a pink-colored pigment called leghemoglobin.
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Its functions are:
Maintains a low oxygen concentration.
Protects the nitrogen-fixing enzyme (nitrogenase).
Gives healthy nodules their pink color.
6. Nitrogenase Enzyme
Bacteroids possess the enzyme nitrogenase.
This enzyme performs nitrogen fixation but is very sensitive to oxygen.
Leghemoglobin protects it by regulating oxygen levels.
7. Improve Soil Fertility
After harvesting legume crops, nitrogen remains in the soil.
This naturally increases soil fertility and reduces the need for chemical fertilizers.
8. Importance in Agriculture
Bacteroids:
Increase crop yield.
Reduce fertilizer costs.
Promote sustainable farming.
Improve soil health.
Formation of Bacteroids
Atmospheric Nitrogen (N₂)
│
▼
Rhizobium bacteria
│
▼
Enter legume root hairs
│
▼
Root nodule forms
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│
▼
Rhizobium changes into
BACTEROID
│
▼
Nitrogen Fixation (NH₃)
│
▼
Plant uses ammonia to
make proteins & grow
Easy Memory Trick
BACTEROID
B → Bacteria
A → Ammonia formation
C → Converts nitrogen
T → Inside root tissue
E → Enzyme (Nitrogenase)
R → Rhizobium origin
O → Oxygen controlled by leghemoglobin
I → Improves soil fertility
D → Develops in root nodules
Difference Between Cyanobacteria and Bacteroids
Feature
Cyanobacteria
Bacteroids
Nature
Free-living photosynthetic
bacteria
Modified Rhizobium inside root
nodules
Food
Make their own food by
photosynthesis
Depend on plant for food
Chlorophyll
Present
Absent
Photosynthesis
Yes
No
Nitrogen
Fixation
Some species (via heterocysts)
Yes (inside root nodules)
Habitat
Water, soil, rocks, hot springs
Root nodules of leguminous plants
Importance
Produce oxygen and improve
soil
Supply nitrogen to plants and
increase soil fertility
Conclusion
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Cyanobacteria are ancient, photosynthetic bacteria that produce oxygen and, in many
species, fix atmospheric nitrogen using specialized heterocysts. They are vital for
ecosystems because they contribute to oxygen production, enrich soil fertility, and are used
as biofertilizers.
Bacteroids, on the other hand, are specialized forms of Rhizobium bacteria that live inside
the root nodules of leguminous plants. Through a mutually beneficial (symbiotic)
relationship, they convert atmospheric nitrogen into ammonia, providing essential nutrients
for plant growth while receiving food and shelter from the plant. This natural process
improves crop productivity and maintains soil fertility, making bacteroids highly important
in sustainable agriculture.
SECTION-C
5. Describe briefly the following:
(a) Reproduction in Phytophthora
(b) Sexual Reproduction in Eurotium.
Ans: (a) Reproduction in Phytophthora
Phytophthora is a fungus-like organism (commonly called a water mold) that causes serious
diseases in plants, such as potato late blight. It reproduces in two ways: asexual
reproduction and sexual reproduction. This dual method helps it survive and spread under
different environmental conditions.
1. Asexual Reproduction
Asexual reproduction is the fastest way for Phytophthora to increase its population.
The fungal body (called mycelium) develops special branches known as
sporangiophores.
At the tip of each sporangiophore, a sporangium is formed.
The sporangium can behave in two different ways, depending on the weather:
o In cool and moist conditions: It releases many tiny, swimming spores called
zoospores. These spores have two flagella (tail-like structures), allowing them
to swim in water and infect new plants.
o In warm and dry conditions: The sporangium itself acts like a spore and
germinates directly by producing a germ tube, which enters the plant.
This method allows Phytophthora to spread rapidly during rainy seasons.
2. Sexual Reproduction
Sexual reproduction occurs when conditions become unfavorable.
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The fungus forms two reproductive organs:
o Oogonium (female organ)
o Antheridium (male organ)
The antheridium attaches to the oogonium and transfers its nucleus.
Fertilization takes place, forming a thick-walled oospore.
The oospore can survive drought, cold, and other harsh conditions.
When favorable conditions return, the oospore germinates and produces new
mycelium or a sporangium.
Simple Diagram
Mycelium
│
Sporangiophore
│
Sporangium
/ \
Cool & Moist Warm & Dry
│ │
Zoospores Germ Tube
│ │
New Plant Infection
Sexual Reproduction
Antheridium (♂)
│
▼
Oogonium (♀)
│
Fertilization
│
Oospore
│
Germination
│
New Mycelium
Key Points to Remember
Phytophthora reproduces asexually and sexually.
Sporangia are the main asexual reproductive structures.
Zoospores swim in water and spread infection.
Oospores are thick-walled resting spores that help the organism survive unfavorable
conditions.
Sexual reproduction increases survival and genetic variation.
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(b) Sexual Reproduction in Eurotium
Eurotium is the sexual stage of certain species of Aspergillus. It belongs to the group
Ascomycetes, also called sac fungi, because their spores are produced inside sac-like
structures called asci.
Sexual reproduction in Eurotium is more complex than asexual reproduction and helps the
fungus produce genetically diverse offspring.
Step 1: Formation of Sex Organs
Two reproductive structures develop on the mycelium:
Ascogonium (female organ)
Antheridium (male organ)
The ascogonium usually has a long extension called the trichogyne, which helps receive the
male nucleus.
Step 2: Fertilization
The antheridium comes in contact with the trichogyne.
Male nuclei move into the ascogonium.
The nuclei pair with female nuclei, but they do not fuse immediately. This stage is
called the dikaryotic stage.
Step 3: Formation of Ascogenous Hyphae
The paired nuclei divide together.
Special hyphae called ascogenous hyphae develop from the ascogonium.
Step 4: Formation of Asci
At the tips of ascogenous hyphae, asci (singular: ascus) are formed.
Inside each ascus, the paired nuclei finally fuse (karyogamy) to form a diploid
nucleus.
This nucleus undergoes meiosis, followed by one mitotic division, producing eight
haploid ascospores.
Step 5: Formation of Cleistothecium
Many asci become enclosed inside a round, closed fruiting body called a
cleistothecium.
When mature, the cleistothecium breaks open and releases the ascospores.
Each ascospore germinates into a new fungal mycelium under favorable conditions.
Simple Diagram
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Ascogonium (♀) Antheridium (♂)
│ │
└────Fertilization─┘
│
Ascogenous Hyphae
│
Ascus
│
Meiosis + Mitosis
│
8 Ascospores
│
Cleistothecium
│
Spore Release
│
New Mycelium
Key Points to Remember
Eurotium belongs to the Ascomycetes (sac fungi).
Sexual organs are ascogonium and antheridium.
Spores are called ascospores.
Ascospores are produced inside an ascus.
Many asci are enclosed in a cleistothecium.
Sexual reproduction creates genetic variation and helps the fungus adapt to
changing environments.
Quick Exam Summary
Phytophthora
Eurotium
Water mold
(Oomycete)
Sac fungus (Ascomycete)
Sporangium
Conidia (mainly in asexual stage)
Oogonium +
Antheridium
Ascogonium + Antheridium
Oospore
Ascospore
Absent
Cleistothecium
Causes plant diseases
Helps fungi survive and produce genetic
variation
Conclusion:
Both Phytophthora and Eurotium reproduce sexually to ensure survival and create genetic
diversity, but they do so in different ways. Phytophthora forms oospores after fertilization
and relies on water for spreading its zoospores, whereas Eurotium produces ascospores
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inside asci, which are enclosed in a cleistothecium. Understanding these reproductive
methods helps explain how these organisms spread, survive adverse conditions, and
continue their life cycle.
6. What are the important features of Zygomycetes? Also, explain in detail the life cycle of
Mucor:
Ans: Introduction
Imagine you leave a piece of bread or fruit in a warm, moist place for a few days. Soon, a
fluffy white cotton-like growth appears on its surface. This growth is usually caused by fungi
belonging to the group Zygomycetes, such as Mucor and Rhizopus. These fungi play an
important role in nature because they break down dead plants and animals, helping recycle
nutrients back into the environment.
One of the most common examples of Zygomycetes is Mucor, also known as the pin mold.
Understanding its characteristics and life cycle helps us learn how fungi reproduce and
survive under different environmental conditions.
Important Features of Zygomycetes
Zygomycetes are a class of simple fungi with several unique characteristics.
1. Body Structure (Thallus)
The body of Zygomycetes consists of long thread-like structures called hyphae.
These hyphae together form a network known as mycelium.
The hyphae are coenocytic (aseptate), meaning they do not have cross walls (septa)
and contain many nuclei in a single continuous cell.
Simple Meaning:
Think of one long tube filled with many nuclei instead of many separate cells.
2. Cell Wall
The cell wall is mainly composed of:
Chitin
Chitosan
These substances provide strength and protection.
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3. Habitat
Zygomycetes commonly grow in:
Moist soil
Decaying fruits
Bread
Vegetables
Animal dung
Organic waste
They prefer warm and humid conditions.
4. Nutrition
They are saprophytic fungi, which means they obtain food from dead and decaying organic
matter.
Some species may also be:
Parasitic (living on living organisms)
Symbiotic (living together with other organisms for mutual benefit)
5. Vegetative Reproduction
Vegetative reproduction occurs by:
Fragmentation of hyphae
Each fragment grows into a new fungus under suitable conditions.
6. Asexual Reproduction
Asexual reproduction takes place through sporangiospores.
Spores are produced inside a sac called sporangium.
When mature, the sporangium bursts.
Spores spread through the air.
Each spore germinates into a new mycelium.
This is the most common method of reproduction.
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7. Sexual Reproduction
Sexual reproduction occurs by gametangial copulation.
Two compatible hyphae (+ and strains) come together.
Their tips fuse.
A thick-walled resting spore called a zygospore is formed.
The zygospore survives harsh environmental conditions.
8. Reserve Food
Food is stored in the form of:
Glycogen
Oil droplets
9. Importance
Useful Effects
Decompose dead organic matter.
Help in nutrient recycling.
Some species are useful in industrial fermentation.
Harmful Effects
Cause food spoilage.
Damage stored fruits and vegetables.
Some species cause infections in humans with weak immune systems.
Life Cycle of Mucor
The life cycle of Mucor includes three stages:
1. Vegetative Phase
2. Asexual Reproduction
3. Sexual Reproduction
1. Vegetative Phase
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The life cycle begins with a haploid spore.
The spore lands on a moist surface.
It absorbs water.
Germinates into hyphae.
Hyphae grow and form a cotton-like mycelium.
This mycelium absorbs nutrients from dead organic matter.
2. Asexual Reproduction
This is the fastest and most common method.
Step 1: Formation of Sporangiophore
A vertical hypha grows upward.
This special stalk is called the sporangiophore.
Step 2: Formation of Sporangium
A round sac develops at the tip.
This sac is called the sporangium.
Inside it, numerous spores are produced.
Step 3: Formation of Spores
The nuclei divide repeatedly.
Thousands of sporangiospores develop.
Step 4: Release of Spores
When mature:
The sporangium bursts.
Spores are released into the air.
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Wind carries them to new places.
Step 5: Germination
If spores land on a moist surface,
they germinate,
forming new hyphae,
which develop into another mycelium.
Thus, the asexual life cycle repeats.
3. Sexual Reproduction
Sexual reproduction usually occurs when environmental conditions become unfavorable.
Step 1: Formation of Opposite Strains
Two compatible mycelia grow near each other.
One is:
Positive (+)
The other is:
Negative (−)
Step 2: Formation of Progametangia
The tips of both hyphae grow toward each other.
These swollen tips are called progametangia.
Step 3: Formation of Gametangia
A wall develops behind each swollen tip.
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The terminal portions become gametangia.
Step 4: Fusion (Plasmogamy)
The walls between gametangia dissolve.
The cytoplasm of both gametangia fuses.
This process is called plasmogamy.
Step 5: Nuclear Fusion (Karyogamy)
Later,
the nuclei fuse.
This process is called karyogamy.
A thick-walled diploid zygospore is formed.
Step 6: Resting Stage
The zygospore remains dormant.
It survives:
Heat
Cold
Dry conditions
This helps the fungus survive unfavorable environments.
Step 7: Germination of Zygospore
When favorable conditions return,
the zygospore germinates.
It produces a germ tube ending in a sporangium.
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Inside this sporangium, meiosis occurs.
Haploid spores are formed.
These spores germinate into new Mucor mycelia.
Thus, the life cycle starts again.
Simple Diagram of the Life Cycle of Mucor
HAPLOID SPORE
│
▼
Germination
│
▼
Hyphae / Mycelium
│
┌───────────┴───────────┐
│ │
▼ ▼
Asexual Reproduction Sexual Reproduction
│ │
Sporangiophore (+) Hypha (-) Hypha
│ │
Sporangium Gametangia
│ │
Sporangiospores Plasmogamy
│ │
▼ Karyogamy
New Mycelium │
▼
Zygospore
│
Resting Stage
│
▼
Germination + Meiosis
│
▼
Haploid Spores
│
▼
New Mycelium
Key Terms to Remember
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Term
Meaning
Hyphae
Thread-like fungal filaments
Mycelium
Network of hyphae
Coenocytic
Hyphae without septa (cross walls)
Sporangium
Sac where spores are formed
Sporangiophore
Stalk bearing the sporangium
Sporangiospores
Asexual spores
Gametangia
Sexual reproductive structures
Plasmogamy
Fusion of cytoplasm
Karyogamy
Fusion of nuclei
Zygospore
Thick-walled resting sexual spore
Conclusion
Zygomycetes are simple fungi that thrive on dead and decaying organic matter. Their body
is made of coenocytic hyphae, and they reproduce both asexually through sporangiospores
and sexually by forming a resistant zygospore. Mucor, a common member of this group, has
a fascinating life cycle that allows it to multiply rapidly under favorable conditions and
survive harsh environments through the formation of zygospores. Because of these
adaptations, Mucor plays an important ecological role as a decomposer while also being
responsible for the spoilage of food in humid conditions.
SECTION-D
7. Describe briefly the following:
(a) Cercospora
(b) Ecological importance of Lichens.
Ans: (a) Cercospora
Introduction
Imagine you have a healthy green plant growing in your garden. After a few days, you notice
small brown or gray spots appearing on its leaves. Gradually, these spots become larger, and
the leaves start drying and falling off. One of the common causes of this disease is a fungus
called Cercospora.
Cercospora is a group of plant-pathogenic fungi that causes Cercospora leaf spot disease in
many crops and ornamental plants. It attacks the leaves, reducing their ability to prepare
food through photosynthesis. This results in poor plant growth and lower crop yield.
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What is Cercospora?
Cercospora is a genus of fungi belonging to the group Deuteromycetes (Imperfect
Fungi).
It mainly infects the leaves of plants.
More than 3,000 species of Cercospora are known.
It is found all over the world, especially in warm and humid climates.
Characteristics
Produces long, thin fungal threads called hyphae.
Reproduces asexually through conidia (spores).
These spores spread through wind, rain splash, insects, and infected plant material.
Infection is more severe during humid and rainy seasons.
Symptoms
The disease caused by Cercospora can be recognized by:
Small circular or irregular leaf spots.
Brown, gray, or black centers with reddish or dark borders.
Yellowing of leaves.
Premature leaf fall.
Reduced photosynthesis.
Poor growth and lower crop production.
Plants Commonly Affected
Some important crops attacked by Cercospora include:
Sugar beet
Groundnut (Peanut)
Soybean
Cotton
Banana
Tomato
Spinach
Beetroot
Control Measures
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To prevent Cercospora disease:
Use disease-free seeds.
Remove infected leaves.
Maintain proper spacing between plants.
Avoid excessive watering on leaves.
Spray recommended fungicides when necessary.
Grow disease-resistant varieties.
Simple Diagram
Wind / Rain
│
Conidia (Spores)
│
▼
Healthy Leaf
│
Infection Begins
│
▼
Brown Leaf Spots
│
▼
Yellow Leaves & Leaf Fall
│
▼
Reduced Crop Yield
Conclusion
Cercospora is an important fungal pathogen that causes leaf spot disease in many
economically valuable crops. Although it mainly attacks leaves, its effect is serious because
damaged leaves cannot perform photosynthesis efficiently. Proper crop management,
sanitation, resistant varieties, and timely fungicide application help control the disease.
(b) Ecological Importance of Lichens
Introduction
Suppose a bare rock has just been exposed after a landslide. At first glance, it looks
impossible for any plant to survive there. Surprisingly, the first living organisms to colonize
such harsh places are often lichens.
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A lichen is not a single organism but a symbiotic association between:
A fungus (mycobiont), and
An alga or cyanobacterium (photobiont).
The fungus provides water, minerals, and protection, while the alga prepares food through
photosynthesis. Because of this cooperation, lichens can survive in deserts, mountains,
forests, and even Arctic regions.
Lichens play a very important role in maintaining ecological balance.
Ecological Importance of Lichens
1. Pioneer Species
Lichens are the first organisms to grow on bare rocks.
They can survive where no other plants can.
They prepare the land for the growth of mosses, grasses, and trees.
This process is called primary succession.
2. Soil Formation
Lichens help in making soil by:
Releasing acids that slowly break rocks.
Mixing rock particles with dead organic matter.
Over time, this forms fertile soil suitable for plant growth.
3. Prevent Soil Erosion
Lichens cover the surface of rocks and soil.
They reduce the impact of wind and rain.
They help hold soil particles together.
Thus, they reduce soil erosion.
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4. Air Pollution Indicators
Lichens are highly sensitive to pollutants, especially sulfur dioxide (SO₂).
They grow well only in clean air.
Their absence often indicates polluted environments.
Because of this, they are called bioindicators of air pollution.
5. Nitrogen Fixation
Some lichens contain cyanobacteria.
These bacteria convert atmospheric nitrogen into usable forms.
This increases soil fertility and benefits nearby plants.
6. Food for Animals
Many animals feed on lichens, especially in cold regions.
Examples include:
Reindeer
Caribou
Deer
Snails
Insects
Thus, lichens are an important part of food chains.
7. Habitat for Small Organisms
Lichens provide shelter for:
Tiny insects
Mites
Small microorganisms
These organisms contribute to ecosystem diversity.
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8. Nutrient Cycling
When lichens die:
They decompose.
Their nutrients return to the soil.
These nutrients become available to plants.
Thus, they help maintain the nutrient cycle.
Simple Diagram
LICHENS
│
┌─────────┼─────────┐
│ │ │
Pioneer Soil Air Pollution
Species Formation Indicator
│ │ │
└─────┬───┴─────────┘
│
Nitrogen Fixation
│
▼
Fertile Soil
│
▼
Growth of Higher Plants
│
▼
Healthy and Balanced Ecosystem
Conclusion
Lichens are unique living organisms formed by the partnership of a fungus and an alga.
Although they grow slowly, their ecological importance is enormous. They begin ecological
succession, help form soil, prevent erosion, enrich the soil through nitrogen fixation, provide
food and shelter to many organisms, recycle nutrients, and act as natural indicators of air
pollution. Because of these valuable roles, lichens are considered one of the most important
organisms in maintaining healthy ecosystems.
Quick Revision (Exam Points)
Cercospora
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Genus of plant-pathogenic fungi.
Causes leaf spot disease.
Reproduces by conidia.
Spreads through wind and rain.
Reduces photosynthesis and crop yield.
Controlled by sanitation, resistant varieties, and fungicides.
Ecological Importance of Lichens
Pioneer species in primary succession.
Help in soil formation.
Prevent soil erosion.
Bioindicators of air pollution.
Fix atmospheric nitrogen (some species).
Provide food and habitat for animals.
Help in nutrient cycling.
Maintain ecological balance.
8. Explain in detail the morphology and reproduction in Agaricus with the help of suitable
diagrams.
Ans: Introduction
Agaricus is a fungus belonging to the kingdom Fungi and the class Basidiomycetes. It is
commonly known as the mushroom. The most familiar example is the edible button
mushroom (Agaricus bisporus), which is widely cultivated and eaten throughout the world.
Unlike green plants, Agaricus does not contain chlorophyll, so it cannot prepare its own
food through photosynthesis. Instead, it obtains nutrients from dead and decaying organic
matter, making it a saprophytic fungus. By decomposing dead plants and animals, it plays a
very important role in recycling nutrients in nature.
The body of Agaricus has two main parts:
1. Vegetative part (mycelium) Hidden underground.
2. Reproductive part (basidiocarp or mushroom) Visible above the ground.
Morphology of Agaricus
Morphology means the external structure and appearance of an organism.
1. Mycelium (Vegetative Body)
The actual plant body of Agaricus is called the mycelium.
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It consists of many thin, white, thread-like structures called hyphae.
These hyphae spread through the soil, wood, or decaying organic matter.
They absorb water and nutrients from the surroundings.
The mycelium remains hidden underground and supports the growth of the
mushroom.
Simple idea:
Think of the mycelium as the roots of the mushroom, although they are not true roots.
2. Basidiocarp (Mushroom)
The visible mushroom is called the basidiocarp or fruiting body. It develops when
environmental conditions such as moisture and temperature become favorable.
The basidiocarp consists of the following parts:
(a) Pileus (Cap)
The umbrella-shaped upper part is called the pileus.
It protects the reproductive structures present underneath.
The upper surface is smooth and fleshy.
Function: Protects the gills where spores are produced.
(b) Gills (Lamellae)
The lower side of the pileus contains many thin plates called gills.
The gills are arranged close together.
They contain the reproductive cells called basidia.
Function: Production of spores.
(c) Stipe (Stalk)
The long cylindrical stem supporting the cap is called the stipe.
It lifts the cap above the ground.
This helps spores spread more easily by wind.
(d) Annulus (Ring)
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A ring-like structure present around the stipe is called the annulus.
It is the remnant of a protective membrane called the partial veil.
(e) Basidia
Basidia are club-shaped microscopic structures found on the gills.
Each basidium produces four basidiospores.
(f) Basidiospores
Basidiospores are the reproductive spores of Agaricus.
They are light in weight and easily carried away by wind.
Under suitable conditions, each spore germinates into a new fungal mycelium.
Diagram of Agaricus
_________
/ \
/ Pileus \
/_____________\
|||||||||||||||| ← Gills (Lamellae)
| |
Annulus (Ring)
|
|
Stipe
|
Underground
Mycelium (Hyphae)
Reproduction in Agaricus
Agaricus reproduces mainly by sexual reproduction through basidiospores. Vegetative
reproduction may occur by fragmentation of mycelium, but sexual reproduction is the
principal method.
A. Vegetative Reproduction
Vegetative reproduction occurs through fragmentation.
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Fragmentation
The mycelium breaks into small pieces.
Each fragment grows independently.
Every fragment develops into a new mycelium under favorable conditions.
Simple Example:
Just as a broken piece of a plant stem can grow into a new plant, a broken piece of fungal
mycelium can form a new fungus.
B. Sexual Reproduction
Sexual reproduction in Agaricus occurs in several stages.
Step 1: Formation of Primary Mycelium
A basidiospore lands on moist soil.
It germinates and produces thread-like hyphae.
This forms the primary mycelium.
The primary mycelium contains only one nucleus in each cell (monokaryotic).
Step 2: Plasmogamy
Two compatible primary mycelia meet.
Their cytoplasm fuses.
This process is called plasmogamy.
Result: Formation of secondary mycelium.
Step 3: Secondary Mycelium
Each cell now contains two nuclei.
This stage is called dikaryotic mycelium.
It is long-lived and vigorous.
It eventually forms the mushroom.
Step 4: Formation of Basidiocarp
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Under favorable environmental conditions such as sufficient moisture, oxygen, and
moderate temperature, the secondary mycelium develops into the basidiocarp
(mushroom).
The gills of the mushroom contain numerous basidia.
Step 5: Karyogamy
Inside each basidium:
The two nuclei fuse together.
This fusion is called karyogamy.
A diploid nucleus is formed.
Step 6: Meiosis
Immediately after karyogamy:
The diploid nucleus undergoes meiosis.
Four haploid nuclei are produced.
Step 7: Formation of Basidiospores
Each nucleus enters a small projection on the basidium.
Four basidiospores are formed.
Mature spores are released into the air by wind.
Step 8: Germination
When basidiospores fall on a suitable surface with enough moisture and nutrients,
they germinate.
New primary mycelium is produced.
Thus, the life cycle repeats.
Diagram of Basidium
Basidiospores
● ● ● ●
\ | | /
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\ | | /
[ Basidium ]
|
Gill Tissue
Life Cycle of Agaricus
Basidiospore
│
▼
Primary Mycelium
(Monokaryotic)
│
▼
Plasmogamy
│
▼
Secondary Mycelium
(Dikaryotic)
│
▼
Basidiocarp
(Mushroom)
│
▼
Basidium
│
Karyogamy
│
Meiosis
│
▼
Four Basidiospores
│
▼
Germination
│
▼
New Primary Mycelium
Importance of Agaricus
It is an edible mushroom rich in proteins, vitamins, and minerals.
It decomposes dead organic matter and helps in nutrient recycling.
It improves soil fertility by breaking down organic waste.
It has economic importance because it is cultivated commercially and provides
income to farmers.
It is widely used in cooking due to its high nutritional value and taste.
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Key Points for Exam
Agaricus is a saprophytic fungus belonging to Basidiomycetes.
The vegetative body is made of mycelium consisting of hyphae.
The fruiting body is called the basidiocarp (mushroom).
Main parts are pileus, gills, stipe, annulus, basidia, and basidiospores.
Reproduction occurs mainly by sexual reproduction through basidiospores.
Important stages include plasmogamy → dikaryotic mycelium → basidiocarp →
karyogamy → meiosis → basidiospore formation.
Agaricus is economically important as an edible mushroom and ecologically
important as a decomposer.
Conclusion
Agaricus is one of the best-known fungi because of its edible mushroom and unique method
of reproduction. Its hidden mycelium absorbs nutrients from dead organic matter, while the
visible basidiocarp produces spores for reproduction. The life cycle involves plasmogamy,
formation of a dikaryotic mycelium, development of the mushroom, karyogamy, meiosis,
and production of basidiospores. Besides being a nutritious food, Agaricus plays a vital role
in nature by decomposing organic matter and maintaining the balance of ecosystems.
Understanding its morphology and reproduction helps students appreciate both its
biological importance and its practical value in agriculture and human nutrition.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
have suggestions, feel free to share your feedback.