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GNDU Question Paper-2021
Ba/BSc
1
st
Semester (Batch 2024-28) (CBGS)
BOTANY: Paper-I-A
(Diversity of Microbes)
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. Give the general characters, classification and economic importance of Algae.
2. Write a note on important features and life history of Oedogonium.
SECTION-B
3. Give structure, nutrition and reproduction of bacteria.
4. Give general characters of Viruses.
SECTION-C
5. Write a detailed note on important features and life history of Pythium.
6. Write details about the reproduction and life cycle of Mucor.
SECTION-D
7. Give details of morphology and life cycle of Agricus.
8. Give general account of lichens. Give its economic importance.
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GNDU Answer Paper-2021
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: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. Give the general characters, classification and economic importance of Algae.
Ans: General Characters, Classification, and Economic Importance of Algae
Algae are among the oldest and simplest living organisms on Earth. If you have ever seen a
green layer floating on the surface of a pond, or long seaweeds attached to rocks on a
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beach, then you have already seen algae. Although they look like ordinary plants, algae are
not true plants because they do not have real roots, stems, leaves, or vascular tissues
(xylem and phloem).
Algae play a very important role in nature. They prepare their own food by the process of
photosynthesis using sunlight, carbon dioxide, and water. During this process, they also
release oxygen into the atmosphere. In fact, scientists estimate that about 5070% of the
oxygen on Earth is produced by algae and other microscopic aquatic organisms. Because of
this, algae are often called the "lungs of the oceans."
General Characters (Characteristics) of Algae
The main characteristics of algae are:
1. Simple Plant Body
The body of algae is called a thallus.
It is not divided into true roots, stems, and leaves.
Example: Spirogyra, Ulva, Chlamydomonas.
2. Mostly Aquatic
Most algae live in freshwater, seawater, ponds, lakes, rivers, and oceans.
Some grow on moist soil, rocks, tree bark, or even in snow.
3. Photosynthetic Organisms
They contain chlorophyll, which gives them a green color.
They prepare their own food by photosynthesis.
Equation:
Sunlight + Carbon dioxide + Water → Glucose + Oxygen
This process makes algae important producers in aquatic ecosystems.
4. Cell Structure
Algae may be:
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o Unicellular (single-celled) Chlamydomonas
o Colonial Volvox
o Filamentous Spirogyra
o Large multicellular seaweeds Laminaria
5. Reproduction
Algae reproduce in three ways:
Vegetative reproduction by fragmentation.
Asexual reproduction by spores.
Sexual reproduction by fusion of male and female gametes.
6. Cell Wall
Usually made of cellulose.
Some algae also contain pectin, silica, or algin.
7. Food Storage
Different algae store food in different forms.
Type of Algae
Stored Food
Green algae
Starch
Brown algae
Laminarin and Mannitol
Red algae
Floridean starch
Classification of Algae
Algae are mainly classified according to their pigments, food storage material, and cell wall
composition.
1. Green Algae (Chlorophyceae)
Characteristics
Green due to abundant chlorophyll.
Mostly found in freshwater.
Store food as starch.
Cell wall mainly consists of cellulose.
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Examples
Spirogyra
Chlamydomonas
Volvox
Ulva
2. Brown Algae (Phaeophyceae)
Characteristics
Brown color due to the pigment fucoxanthin.
Mostly marine (sea).
Usually large seaweeds.
Store food as laminarin and mannitol.
Examples
Laminaria
Sargassum
Fucus
3. Red Algae (Rhodophyceae)
Characteristics
Red due to the pigment phycoerythrin.
Mostly marine.
Found in deeper water because red pigments absorb light efficiently.
Store food as Floridean starch.
Examples
Gelidium
Gracilaria
Polysiphonia
Simple Classification Diagram
ALGAE
│
┌──────────────┼──────────────┐
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│ │ │
Green Algae Brown Algae Red Algae
(Chlorophyceae) (Phaeophyceae) (Rhodophyceae)
│ │ │
Spirogyra Laminaria Gelidium
Volvox Sargassum Gracilaria
Economic Importance of Algae
Algae are extremely useful in everyday life, industries, agriculture, medicine, and the
environment.
1. Source of Food
Many seaweeds are eaten as food, especially in countries like Japan, China, and Korea.
Examples:
Porphyra (Nori)
Ulva (Sea lettuce)
Laminaria
They are rich in proteins, vitamins, minerals, and iodine.
2. Animal Feed
Some algae are used as nutritious food for:
Fish
Poultry
Cattle
Microalgae such as Spirulina are also used as dietary supplements because they are rich in
protein.
3. Production of Oxygen
Algae release large amounts of oxygen through photosynthesis, helping maintain
atmospheric oxygen levels and supporting aquatic life.
4. Fertilizers and Biofertilizers
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Seaweeds are used as natural fertilizers because they improve soil fertility and increase crop
yield.
Blue-green algae (cyanobacteria) also help fix nitrogen in paddy fields, improving soil health.
5. Industrial Uses
Algae provide important substances used in industries:
Agar obtained from red algae; used in microbiology laboratories to grow bacteria
and in food products like jellies.
Alginates obtained from brown algae; used in textiles, cosmetics, paper, paints,
toothpaste, and ice cream.
Carrageenan extracted from red algae; used as a thickening and stabilizing agent in
dairy products, desserts, and medicines.
6. Medicines
Some algae produce compounds with:
Antibacterial properties
Antiviral properties
Antioxidant effects
These are being researched for making new medicines.
7. Environmental Importance
Algae:
Form the base of aquatic food chains.
Absorb carbon dioxide, helping reduce greenhouse gases.
Provide shelter and food for many aquatic organisms.
8. Biofuel Production
Some algae contain large amounts of oil and can be used to produce biodiesel, making them
a promising renewable energy source.
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Easy Way to Remember the Classification
Group
Color
Stored Food
Example
Green Algae
Green
Starch
Spirogyra, Volvox
Brown Algae
Brown
Laminarin, Mannitol
Laminaria, Sargassum
Red Algae
Red
Floridean starch
Gelidium, Gracilaria
Conclusion
Algae are simple, chlorophyll-containing organisms that mostly live in water and prepare
their own food through photosynthesis. They may be microscopic or large seaweeds and are
classified into Green (Chlorophyceae), Brown (Phaeophyceae), and Red (Rhodophyceae)
based on their pigments and stored food. Besides producing a major share of Earth's
oxygen, algae are valuable as food, animal feed, fertilizers, industrial raw materials,
medicines, and even renewable biofuels. Their ecological and economic importance makes
them one of the most beneficial groups of organisms for both humans and the environment.
2. Write a note on important features and life history of Oedogonium.
Ans:
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Introduction
Oedogonium is a freshwater green alga belonging to the group Chlorophyceae. It
commonly grows in ponds, lakes, ditches, and other slow-moving freshwater bodies. It
appears as long, green, unbranched threads (filaments) that are often attached to aquatic
plants or stones. Scientists study Oedogonium because it has a unique method of cell
division and an advanced type of sexual reproduction among algae.
Important Features of Oedogonium
1. Habitat
It is mainly found in freshwater ponds, lakes, canals, and slow-flowing streams.
It may float freely or remain attached to submerged objects using a special holdfast.
2. Structure of the Plant Body
The body is filamentous, meaning it consists of a long chain of cells.
The filament is unbranched, so no side branches are formed.
At the base is a holdfast, which anchors the alga to stones or aquatic plants.
3. Cell Structure
Each cell contains:
A cell wall made mainly of cellulose.
A large central vacuole filled with cell sap.
A single nucleus.
A network-like (reticulate) chloroplast containing many pyrenoids, which help in
storing food as starch.
4. Unique Cell Division
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One of the most special characteristics of Oedogonium is its unusual method of cell division.
Instead of dividing normally like many other algae, each dividing cell forms a ring-like cap at
its upper end. Every time the cell divides, another cap is added. Therefore, the number of
caps tells how many times the cell has divided. This is a distinctive feature of Oedogonium.
5. Nutrition
It prepares its own food by photosynthesis because it contains chlorophyll.
The stored food is mainly starch.
6. Reproduction
Oedogonium reproduces by three methods:
Vegetative reproduction
Asexual reproduction
Sexual reproduction
Life History of Oedogonium
The life cycle of Oedogonium is mainly haplontic, which means the main plant body is
haploid (n). The only diploid stage is the zygote (2n).
1. Vegetative Reproduction
This is the simplest method.
The filament breaks into small pieces due to injury or natural causes.
Each fragment grows into a complete new filament under suitable conditions.
This process is called fragmentation.
2. Asexual Reproduction
Asexual reproduction occurs through zoospores.
Formation of Zoospores
A vegetative cell changes into a zoosporangium.
Inside it, one large multiflagellate zoospore is formed.
The zoospore has many flagella arranged in a ring.
Germination
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The zoospore swims freely in water.
After some time, it settles on a suitable surface.
It develops a holdfast and grows into a new filament.
This method helps the alga spread quickly.
3. Sexual Reproduction
Sexual reproduction in Oedogonium is oogamous, which is considered the most advanced
type among algae.
This means:
The female gamete (egg) is large and non-motile.
The male gamete (antherozoid) is small and motile.
(a) Formation of Oogonium (Female Organ)
Certain vegetative cells enlarge to form an oogonium.
Each oogonium contains one large egg.
(b) Formation of Antheridium (Male Organ)
Some cells become antheridia.
Each antheridium produces small motile male gametes called antherozoids.
(c) Fertilization
The mature oogonium develops a small opening.
Antherozoids swim through water and enter the oogonium.
One antherozoid fuses with the egg to form a zygote (oospore).
(d) Germination of the Zygote
The zygote develops a thick protective wall and remains dormant during unfavorable
conditions.
When conditions become favorable, it undergoes meiosis, producing four haploid
zoospores.
Usually, only one zoospore survives and develops into a new haploid filament.
Thus, the life cycle is completed.
Life Cycle (Simple Flow)
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Adult Oedogonium Filament (n)
│
┌─────────┴──────────┐
│ │
Fragmentation Zoospore Formation
│ │
New Filament New Filament
│
Sexual Reproduction
│
Egg + Antherozoid
│
Fertilization
│
Zygote (2n / Oospore)
│
Meiosis
│
Haploid Zoospore (n)
│
New Oedogonium Filament
Key Points to Remember
Oedogonium is a freshwater, filamentous green alga.
It has an unbranched filament with a holdfast.
Cells contain a reticulate chloroplast with pyrenoids.
It shows a unique cap formation during cell division.
It reproduces by fragmentation, zoospores, and oogamous sexual reproduction.
The zygote is the only diploid stage, making the life cycle haplontic.
Sexual reproduction involves oogonium (female) and antheridium (male), producing
a thick-walled oospore that undergoes meiosis to form new haploid plants.
Exam Tip (23 Marks)
Remember these five words: Freshwater Filamentous Holdfast Cap Formation
Oogamous Reproduction. These are the most important features examiners expect in
answers about Oedogonium.
SECTION-B
3. Give structure, nutrition and reproduction of bacteria.
Ans: 3. Structure, Nutrition and Reproduction of Bacteria
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Bacteria are tiny, single-celled microorganisms that are so small they can only be seen with
a microscope. They are among the oldest living organisms on Earth and are found almost
everywherein soil, water, air, food, and even inside the human body. Some bacteria are
harmful and cause diseases like typhoid and tuberculosis, but many are useful. For example,
bacteria help in making curd, cheese, medicines, and improving soil fertility.
To understand bacteria better, we will study three important topics:
1. Structure of bacteria
2. Nutrition in bacteria
3. Reproduction of bacteria
1. Structure of Bacteria
Although bacteria are very small, each bacterial cell has different parts that help it survive
and perform its functions.
Simple Diagram of a Bacterial Cell
Flagellum
|
|
______________________
/ \
/ Capsule (Outer) \
|--------------------------|
| Cell Wall |
|--------------------------|
| Plasma Membrane |
| |
| Cytoplasm |
| o o o Ribosomes |
| |
| DNA (Nucleoid) |
| (No nucleus) |
| |
| Plasmid (small DNA) |
\________________________/
Parts of a Bacterial Cell
1. Capsule
It is the outermost protective covering.
Protects bacteria from drying and from the body's immune system.
Helps bacteria stick to surfaces.
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2. Cell Wall
Gives the bacterium its shape.
Protects the cell from damage.
Made mainly of peptidoglycan, a strong material found only in bacteria.
3. Plasma Membrane
Located inside the cell wall.
Controls what enters and leaves the cell.
Helps in respiration and energy production.
4. Cytoplasm
Jelly-like fluid inside the cell.
Contains water, enzymes, nutrients, and ribosomes.
Most metabolic activities occur here.
5. Ribosomes
Tiny particles present in the cytoplasm.
They make proteins needed for growth and repair.
6. Nucleoid (DNA)
Bacteria do not have a true nucleus.
Their genetic material (DNA) floats freely in the cytoplasm.
DNA controls all activities of the bacterial cell.
7. Plasmid
Small circular DNA molecules.
Carry extra genes, such as antibiotic resistance.
8. Flagellum
Long whip-like structure.
Helps bacteria move from one place to another.
2. Nutrition in Bacteria
Nutrition means how bacteria obtain food and energy to survive and grow.
Bacteria show different types of nutrition.
A. Autotrophic Nutrition
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Autotrophic bacteria prepare their own food.
There are two types:
(i) Photosynthetic Bacteria
Use sunlight to prepare food.
Similar to plants but do not produce oxygen like green plants.
Example: Purple sulfur bacteria.
(ii) Chemosynthetic Bacteria
Obtain energy from chemical reactions instead of sunlight.
They oxidize substances like ammonia or sulfur compounds.
Example: Nitrosomonas.
B. Heterotrophic Nutrition
These bacteria cannot prepare their own food.
They obtain food from other organisms.
(i) Saprophytic Bacteria
Feed on dead and decaying organic matter.
Help in decomposition and recycling nutrients.
Example: Lactobacillus in compost.
(ii) Parasitic Bacteria
Live inside living organisms.
Cause diseases by taking nutrients from the host.
Examples:
o Tuberculosis bacteria
o Cholera bacteria
(iii) Symbiotic Bacteria
Live with another organism and both benefit.
Example:
o Rhizobium bacteria live in the roots of leguminous plants.
o They fix nitrogen in the soil while receiving food from the plant.
3. Reproduction in Bacteria
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Reproduction is the process by which bacteria produce new bacteria.
Most bacteria reproduce asexually, meaning only one parent is needed.
A. Binary Fission (Most Common Method)
Binary fission is the simplest and fastest method of reproduction.
Steps:
1. The bacterial DNA duplicates.
2. The cell becomes longer.
3. A partition develops in the middle.
4. The cell divides into two identical daughter cells.
Diagram
Parent Cell
(DNA)
●
_______
| |
| |
|_______|
↓
DNA duplicates
● ●
_________
| |
| |
|_________|
↓
Cell divides
_______ _______
| ● | | ● |
|_______| |_______|
Two identical daughter cells
Under suitable conditions, one bacterium can divide every 2030 minutes, leading to a very
rapid increase in population.
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B. Spore Formation
When conditions become unfavorable (lack of food, high temperature, or dryness), some
bacteria form endospores.
Spores are thick-walled protective structures.
They remain inactive for a long time.
When conditions improve, the spore germinates into a new bacterial cell.
This helps bacteria survive harsh environments.
C. Genetic Exchange (Not True Reproduction)
Although bacteria mainly reproduce by binary fission, they can exchange genetic material to
increase variation through:
Conjugation transfer of DNA from one bacterium to another through a connecting
bridge.
Transformation uptake of free DNA from the surroundings.
Transduction transfer of DNA by viruses (bacteriophages).
These processes do not increase the number of bacteria, but they help bacteria adapt and
evolve.
Importance of Bacteria
Useful Bacteria
Help in making curd, cheese, and yogurt.
Fix nitrogen in the soil, improving crop growth.
Produce antibiotics and vitamins.
Decompose dead plants and animals.
Help in sewage treatment.
Harmful Bacteria
Cause diseases such as cholera, typhoid, tuberculosis, pneumonia, and food
poisoning.
Spoil food and contaminate water.
Conclusion
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Bacteria are microscopic, single-celled organisms with a simple structure consisting of a
capsule, cell wall, plasma membrane, cytoplasm, ribosomes, DNA, plasmids, and sometimes
flagella. Depending on how they obtain food, bacteria can be autotrophic (making their own
food through sunlight or chemical energy) or heterotrophic (obtaining food from dead
matter, living hosts, or through symbiotic relationships). Their most common method of
reproduction is binary fission, where one bacterial cell divides into two identical daughter
cells. Under unfavorable conditions, some bacteria form protective spores to survive.
Despite their tiny size, bacteria play a huge role in nature, industry, agriculture, and human
health, making them one of the most important groups of microorganisms on Earth.
4. Give general characters of Viruses.
Ans: 4. General Characters of Viruses
Viruses are among the smallest and most unique infectious agents found in nature. They
are so tiny that they cannot be seen with the naked eye or even with an ordinary
microscope. A virus can only be seen using an electron microscope. Unlike plants, animals,
fungi, or bacteria, viruses are not considered completely living organisms because they
cannot carry out life processes on their own. They become active only after entering the
body of a living organism. This is why viruses are often called obligate intracellular
parasites, meaning they can live and reproduce only inside the cells of a host.
Imagine a virus as a USB drive without a computer. A USB drive stores information, but it
cannot do anything by itself. It needs a computer to function. Similarly, a virus carries
genetic information but needs a living cell to multiply.
Simple Diagram of a Virus
_____________
/ \
/ Protein \
| Coat | ← Capsid
| (Capsid) |
| |
| DNA or RNA | ← Genetic Material
\ /
\_____________/
Some viruses also have an outer envelope made of lipids, which helps them enter the host
cell.
General Characters of Viruses
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1. Extremely Small in Size
Viruses are microscopic particles ranging from 20 to 300 nanometers (nm) in size. They are
much smaller than bacteria and can only be observed with an electron microscope.
Example: Coronavirus, Influenza virus, HIV.
2. Acellular Organisms
Viruses are acellular, meaning they are not made of cells. Unlike plants and animals, they
do not have a cell membrane, cytoplasm, nucleus, mitochondria, or other cell organelles.
This is one of the main reasons why viruses are placed separately from living organisms.
3. Contain Only One Type of Genetic Material
Every virus contains either DNA or RNA, but never both together.
DNA viruses: Adenovirus, Herpes virus
RNA viruses: Coronavirus, HIV, Influenza virus
The genetic material carries all the instructions needed to make new viruses inside the host.
4. Covered by a Protein Coat (Capsid)
The genetic material is surrounded by a protective protein coat called the capsid.
Functions of the capsid:
Protects the genetic material.
Gives shape to the virus.
Helps the virus attach to host cells.
Some viruses also possess an additional lipid envelope outside the capsid.
5. Obligate Intracellular Parasites
Viruses cannot reproduce on their own.
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They must enter a living host cell and use the host's machinery to make copies of
themselves.
Outside the host:
They remain inactive.
Inside the host:
They become active and multiply rapidly.
6. No Independent Metabolism
Viruses do not:
Breathe
Eat food
Produce energy
Grow independently
They completely depend on the host cell for energy and nutrients.
7. Can Infect All Living Organisms
Viruses are capable of infecting almost every type of living organism.
They infect:
Humans
Animals
Plants
Bacteria (called bacteriophages)
Fungi
Different viruses are specialized for different hosts.
8. Show Both Living and Non-Living Characteristics
This is one of the most interesting features of viruses.
Living characteristics:
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Reproduce inside living cells.
Contain genetic material.
Undergo mutation and evolution.
Non-living characteristics:
Can be crystallized like chemicals.
No cellular structure.
No metabolism.
Cannot reproduce outside a host.
Because of these mixed features, viruses are considered to lie between living and non-living
things.
9. Host Specific
Most viruses infect only particular hosts or specific tissues.
For example:
Rabies virus mainly infects mammals.
Tobacco Mosaic Virus infects tobacco and related plants.
HIV mainly attacks human immune cells.
This property is called host specificity.
10. Cause Many Diseases
Viruses are responsible for numerous diseases in humans, animals, and plants.
Examples:
Common cold
Influenza (Flu)
COVID-19
Measles
Chickenpox
Rabies
Dengue
AIDS
Plant viruses reduce crop production, while animal viruses can affect livestock and pets.
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11. Rapid Multiplication
Once inside a suitable host cell, viruses reproduce very quickly.
A single virus can produce hundreds or even thousands of new virus particles, which then
infect nearby cells and spread the infection.
12. Different Shapes
Viruses occur in many different shapes.
Common shapes include:
Spherical Coronavirus
Rod-shaped Tobacco Mosaic Virus
Helical Rabies virus
Icosahedral (polyhedral) Adenovirus
Complex Bacteriophage
Easy Trick to Remember the General Characters
"S-A-D-P-H-M-I-L-H-D-R-S"
S Small size
A Acellular
D DNA or RNA only
P Protein coat (Capsid)
H Host-dependent
M No metabolism
I Infect all living organisms
L Living and non-living characteristics
H Host specific
D Cause diseases
R Rapid multiplication
S Different shapes
Conclusion
Viruses are extremely small, acellular infectious particles that contain either DNA or RNA
enclosed within a protein coat called the capsid. They cannot perform any life activities on
their own and therefore depend completely on a living host cell for reproduction. Viruses
possess both living characteristics (such as reproduction and mutation inside host cells)
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and non-living characteristics (such as lacking cellular structure and metabolism). They
infect humans, animals, plants, and even bacteria, causing many important diseases. Their
unique nature makes viruses one of the most fascinating subjects in biology and medicine.
SECTION-C
5. Write a detailed note on important features and life history of Pythium.
Ans: Introduction
Pythium is a fungus-like organism that belongs to the group Oomycetes (water molds).
Although it looks like a fungus, scientists now know that it is more closely related to algae
than to true fungi. Pythium usually lives in moist soil, stagnant water, and decaying organic
matter. Some species are harmless, but many are plant pathogens, meaning they cause
diseases in crops. One of the most common diseases caused by Pythium is damping-off
disease, which kills young seedlings before or just after they emerge from the soil.
Think of Pythium as an invisible enemy living in wet soil. When a seed begins to grow,
Pythium attacks its soft tissues, causing the seedling to rot and die.
Important Features of Pythium
1. Fungus-like Organism
Although Pythium resembles fungi, it belongs to the kingdom Chromista under the class
Oomycetes. Therefore, it is called a water mold rather than a true fungus.
2. Habitat
It is commonly found in:
Wet soil
Freshwater ponds
Irrigation water
Decaying leaves and plant debris
It grows best in cool and moist conditions.
3. Body Structure (Mycelium)
The body of Pythium is made up of long thread-like structures called hyphae.
Characteristics of hyphae:
Colourless (hyaline)
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Branched
Aseptate (without cross walls)
These hyphae absorb nutrients from dead organic matter or from living plants.
4. Cell Wall
Unlike true fungi, whose cell walls contain chitin, the cell wall of Pythium mainly contains:
Cellulose
Glucans
This is one of the major differences between Pythium and true fungi.
5. Nutrition
Pythium shows two types of nutrition:
Saprophytic feeds on dead and decaying organic matter.
Parasitic infects living plants and causes diseases.
6. Plant Diseases
It causes several important diseases such as:
Damping-off of seedlings
Root rot
Stem rot
Fruit rot in some crops
These diseases reduce crop production and cause heavy economic losses.
Life History (Life Cycle) of Pythium
The life cycle of Pythium includes both asexual and sexual reproduction.
Asexual Reproduction
This is the fastest method of reproduction.
Step 1: Formation of Sporangium
Special swollen structures called sporangia develop at the tips of hyphae.
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Step 2: Formation of Zoospores
Inside the sporangium, many tiny zoospores are formed.
Zoospores are:
Microscopic
Kidney-shaped
Biflagellate (have two flagella)
Able to swim in water
Step 3: Germination
The zoospores swim in water until they find a suitable host.
They then:
Lose their flagella.
Form a protective wall (becoming a cyst).
Germinate by producing a germ tube.
The germ tube develops into new hyphae, forming another Pythium plant.
When water is absent, the sporangium may directly produce a germ tube without forming
zoospores.
Sexual Reproduction
Sexual reproduction occurs when conditions become unfavorable.
Step 1: Formation of Sex Organs
Two reproductive organs are formed:
Oogonium (Female organ) round and contains one or more eggs.
Antheridium (Male organ) transfers male nuclei to the oogonium.
Step 2: Fertilization
The antheridium sends a fertilization tube into the oogonium.
The male nucleus fuses with the female egg.
This process is called fertilization.
Step 3: Formation of Oospore
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After fertilization, a thick-walled oospore is formed.
The oospore:
Acts as a resting spore.
Survives drought, cold, and other unfavorable conditions.
Germinates later when conditions become favorable.
The oospore produces new hyphae or a sporangium, completing the life cycle.
Simple Diagram of the Life Cycle
Pythium Mycelium
│
┌───────────────┴───────────────┐
│ │
Asexual Reproduction Sexual Reproduction
│ │
Sporangium Oogonium + Antheridium
│ │
Zoospores formed Fertilization
│ │
Swim in water Thick-walled Oospore
│ │
Germination Germination in favorable
conditions
│ │
└───────────────► New Mycelium ◄───────────────┘
Importance of Pythium
Harmful Effects
Causes damping-off disease in nurseries.
Damages roots and stems of many crops.
Reduces seed germination.
Leads to heavy agricultural losses.
Beneficial Role
Helps decompose dead organic matter.
Recycles nutrients back into the soil ecosystem.
Easy Way to Remember
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Remember the word "PYTHIUM":
P Plant pathogen
Y Young seedlings affected
T Thrives in wet conditions
H Hyphae are aseptate
I Infects roots and stems
U Uses zoospores for asexual reproduction
M Makes thick-walled oospores during sexual reproduction
Conclusion
Pythium is a fungus-like water mold that grows mainly in moist environments. It has
aseptate, cellulose-containing hyphae and reproduces by zoospores (asexual reproduction)
and oospores (sexual reproduction). While it helps decompose organic matter, it is best
known for causing damping-off disease, root rot, and stem rot in many crop plants.
Understanding its life history helps farmers and scientists develop effective methods to
prevent crop diseases and improve agricultural productivity.
6. Write details about the reproduction and life cycle of Mucor.
Ans: Reproduction and Life Cycle of Mucor
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Mucor is a common fungus that grows on bread, fruits, vegetables, dung, and other moist
organic materials. It belongs to a group of fungi called Zygomycetes. If you have ever seen a
piece of bread covered with soft white cotton-like growth that later turns black, you have
probably seen Mucor. The body of Mucor is made up of long, thread-like structures called
hyphae. These hyphae are non-septate (without cross walls) and together form a network
known as the mycelium.
The life cycle of Mucor mainly includes two types of reproduction:
1. Asexual reproduction (takes place under favourable conditions)
2. Sexual reproduction (takes place under unfavourable conditions)
1. Asexual Reproduction
This is the most common and fastest method of reproduction in Mucor. It occurs when
food, moisture, and temperature are suitable.
Step 1: Formation of Sporangiophore
Some hyphae grow upward into the air. These special upright hyphae are called
sporangiophores.
Step 2: Formation of Sporangium
At the tip of each sporangiophore, a round sac develops. This sac is called a sporangium.
Step 3: Formation of Spores
Inside the sporangium, the nucleus divides many times, producing thousands of tiny
sporangiospores. These spores are protected inside the sac until they mature.
Step 4: Release of Spores
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When the spores become fully mature, the wall of the sporangium bursts open. The
lightweight spores are carried away by wind, insects, or air currents.
Step 5: Germination
If a spore lands on a moist surface with enough food, it germinates. It forms new hyphae,
which develop into a new mycelium. Thus, a new Mucor fungus is produced.
Importance:
Asexual reproduction helps Mucor multiply very quickly, allowing it to spread over food
materials in a short time.
2. Sexual Reproduction
Sexual reproduction occurs when environmental conditions become unfavourable, such as
lack of food, dryness, or extreme temperatures.
Step 1: Fusion of Two Hyphae
Two compatible hyphae, known as positive (+) and negative (−) strains, grow toward each
other.
Step 2: Formation of Gametangia
The tips of these hyphae swell and form structures called gametangia, which contain nuclei.
Step 3: Plasmogamy and Karyogamy
The walls between the gametangia dissolve, and their cytoplasm fuses (plasmogamy). Later,
the nuclei also fuse (karyogamy) to form a zygote.
Step 4: Formation of Zygospore
The zygote develops a thick, dark, protective wall, becoming a zygospore. This structure
can survive harsh environmental conditions for a long time.
Step 5: Germination of Zygospore
When conditions become favourable again, the zygospore germinates and produces a new
sporangiophore with a sporangium.
Step 6: Formation of New Spores
The sporangium releases spores, which germinate into new Mucor plants, completing the
life cycle.
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Importance:
Sexual reproduction increases genetic variation, helping Mucor adapt better to changing
environments.
Life Cycle of Mucor (Simple Flow Diagram)
Favourable Conditions
│
Mature Mycelium
│
Sporangiophore
│
Sporangium
│
Sporangiospores
│
Spores Dispersed by Wind
│
Germination
│
New Mycelium
│
────────────────────────────────────────
Unfavourable Conditions
│
+ Hypha − Hypha
\ /
Gametangia
│
Plasmogamy + Karyogamy
│
Zygospore
│
Favourable Conditions Return
│
Germinating Zygospore
│
New Sporangium
│
Spores Released
│
New Mycelium
Key Differences Between Asexual and Sexual Reproduction
Asexual Reproduction
Occurs in favourable conditions
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Uses only one parent
Produces sporangiospores
Fast process
Produces genetically similar offspring
Helps rapid multiplication
Conclusion
The life cycle of Mucor is simple yet highly efficient. During favourable conditions, it
reproduces rapidly through asexual spores, allowing the fungus to spread quickly on food
and other organic matter. When environmental conditions become unfavourable, Mucor
switches to sexual reproduction, forming a thick-walled zygospore that protects it until
conditions improve. Once the environment becomes suitable again, the zygospore
germinates and produces new spores, restarting the cycle. This ability to reproduce in two
different ways ensures both rapid growth and long-term survival, making Mucor one of the
most successful and widespread fungi.
SECTION-D
7. Give details of morphology and life cycle of Agricus.
Ans:
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Simple Explanation
Agaricus is the common mushroom that we often see growing on moist soil, grasslands,
gardens, and forests, especially during the rainy season. It belongs to the kingdom Fungi and
reproduces through spores instead of seeds. The mushroom that we eat is actually only the
fruiting body of the fungus. The main body remains hidden underground as a network of
thread-like structures called mycelium.
To understand Agaricus, we need to study two things:
1. Morphology (Structure of the Mushroom)
2. Life Cycle (How it Grows and Reproduces)
1. Morphology (Structure of Agaricus)
The visible mushroom is called the Basidiocarp (fruiting body). It has several important
parts:
A. Pileus (Cap)
The broad umbrella-shaped upper part of the mushroom.
It protects the gills present underneath.
It may be white, brown, or cream in color.
B. Gills (Lamellae)
Thin plate-like structures found below the cap.
They contain millions of tiny reproductive cells called basidia.
Basidia produce spores known as basidiospores.
C. Stipe (Stalk)
The stem-like structure supporting the cap.
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It keeps the cap above the ground so spores can spread easily by wind.
D. Annulus (Ring)
A ring present on the stalk.
It is the remains of a protective covering called the partial veil.
E. Mycelium
The actual body of the fungus.
It remains hidden in the soil.
It absorbs water and nutrients from dead organic matter.
Labeled Diagram of Agaricus
_________
/ \
/ Pileus \ ← Cap
/_____________\
||||||||||||||| ← Gills (Lamellae)
||
---====--- ← Annulus (Ring)
||
|| ← Stipe (Stalk)
||
_____||_____
/ \
Mycelium (Underground)
Thread-like fungal network
2. Life Cycle of Agaricus
The life cycle of Agaricus mainly involves spore formation and germination.
Step 1: Formation of Basidiospores
Inside the gills are tiny club-shaped cells called basidia. Each basidium produces four
basidiospores through meiosis.
Step 2: Dispersal of Spores
When the spores become mature, they are released into the air. Wind carries them to
suitable moist places.
Step 3: Germination
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If a spore lands on a moist and nutrient-rich surface, it germinates and forms thin fungal
threads called hyphae.
Step 4: Primary Mycelium
The hyphae produced from a single spore form a primary (monokaryotic) mycelium. Each
cell contains one nucleus.
Step 5: Secondary Mycelium
When two compatible primary mycelia meet, they fuse in a process called plasmogamy.
This produces a secondary (dikaryotic) mycelium, where each cell has two nuclei. This stage
is long-lived and forms the main fungal body.
Step 6: Formation of Basidiocarp
Under favorable conditions such as moisture, suitable temperature, and sufficient nutrients,
the secondary mycelium develops into a basidiocarp, the mushroom we see above the
ground.
Step 7: Nuclear Fusion and Meiosis
Inside each basidium:
The two nuclei fuse (karyogamy) to form one diploid nucleus.
This diploid nucleus undergoes meiosis, producing four haploid nuclei.
Each nucleus develops into a basidiospore.
These spores are released, and the entire life cycle starts again.
Life Cycle Diagram
Basidiospores
│
▼
Germination
│
▼
Primary Mycelium
(Monokaryotic)
│
▼
Fusion of Compatible Mycelia
(Plasmogamy)
│
▼
Secondary Mycelium
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(Dikaryotic)
│
▼
Basidiocarp
(Mushroom)
│
▼
Basidia in Gills
│
Karyogamy + Meiosis
│
▼
Four Basidiospores
│
▼
Life Cycle Repeats
Key Points for Exams
Agaricus is a saprophytic fungus that feeds on dead and decaying organic matter.
The underground body is called mycelium.
The visible mushroom is the basidiocarp.
The cap is called the pileus, and the spore-producing plates are the gills (lamellae).
Basidia present on the gills produce four basidiospores.
Reproduction occurs mainly through basidiospores.
The life cycle includes spore → primary mycelium → secondary mycelium →
basidiocarp → basidiospores.
Conclusion
Agaricus is one of the best-known fungi because it demonstrates the typical structure and
reproduction of Basidiomycetes. Although we usually recognize only the mushroom above
the ground, its real body is the hidden mycelium beneath the soil. Through the production
of basidiospores and the formation of new mycelia, Agaricus completes its life cycle and
continues to grow in nature, where it plays an important role in decomposing dead organic
matter and recycling nutrients in the ecosystem.
8. Give general account of lichens. Give its economic importance.
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Ans: Introduction
Lichens are one of the most interesting organisms found in nature because they are not a
single plant or fungus. Instead, they are a combination of two different living organisms
that live together and help each other survive. This type of relationship is called symbiosis
or mutualism.
A lichen is made up of:
A fungus (mycobiont) provides protection, absorbs water and minerals, and gives
the lichen its shape.
An alga or cyanobacterium (photobiont) prepares food by photosynthesis using
sunlight.
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Think of a lichen like two best friends sharing one house. One friend cooks the food (alga),
while the other builds and protects the house (fungus). Since both help each other, they
survive even in places where most plants cannot grow.
Lichens are commonly found on rocks, tree bark, old walls, soil, roofs, and even in deserts
and snowy mountains. They grow very slowly but can live for many years.
General Account of Lichens
1. Structure of Lichens
The body of a lichen is called the thallus. It has no true roots, stems, or leaves like ordinary
plants.
The thallus usually has four layers:
1. Upper Cortex A protective outer layer made of fungal cells.
2. Algal Layer Contains algae that prepare food through photosynthesis.
3. Medulla A loose layer of fungal threads that stores water and air.
4. Lower Cortex The bottom protective layer. Some lichens also have root-like
structures called rhizines that help them attach to rocks or tree bark.
Simple Diagram of a Lichen
LICHEN (Thallus)
-------------------------
| Upper Cortex |
-------------------------
| Algal Layer | ← Makes food
-------------------------
| Medulla | ← Stores water & air
-------------------------
| Lower Cortex |
-------------------------
|| ||
Rhizines
(Help in attachment)
2. Types of Lichens
Lichens are mainly divided into three types based on their shape:
a) Crustose Lichens
Thin and crust-like.
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Firmly attached to rocks or tree bark.
Cannot be removed without damaging them.
b) Foliose Lichens
Flat and leaf-like.
Loosely attached to the surface.
Easy to remove.
c) Fruticose Lichens
Shrub-like or hanging in appearance.
Grow upright or hang from tree branches.
Highly branched.
A simple way to remember them is:
Crustose = Crust
Foliose = Leaf
Fruticose = Bush
3. Reproduction
Lichens reproduce in different ways:
Vegetative reproduction by fragmentation, soredia, and isidia.
Asexual reproduction through fungal spores.
Sexual reproduction occurs only through the fungal partner. After the fungal spores
germinate, they must find the correct alga to form a new lichen.
4. Habitat
Lichens can survive in places where most plants cannot.
They are found on:
Rocks
Tree bark
Soil
Old walls
Roofs
Mountains
Arctic and desert regions
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They require very little water and can tolerate extreme heat and cold.
Economic Importance of Lichens
Lichens are useful in many ways.
1. Food
Some lichens are eaten by humans during times of famine after proper processing.
Animals like reindeer and caribou depend on lichens as their main winter food.
2. Medicine
Many lichens contain natural chemicals that kill bacteria and fungi.
They are used in:
Antibiotics
Wound healing
Herbal medicines
Traditional treatments
3. Dyes and Indicators
Certain lichens are used to prepare natural dyes for wool and cloth.
They are also used to make litmus, which is a natural indicator used in laboratories to test
whether a solution is acidic or basic.
4. Perfume Industry
Some lichens produce pleasant-smelling compounds.
These are used in:
Perfumes
Cosmetics
Soaps
Air fresheners
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5. Environmental Indicators
Lichens are highly sensitive to air pollution.
They absorb substances directly from the atmosphere.
Many lichens = Clean air
Few or no lichens = Polluted air
Because of this, scientists use them as bioindicators to measure air quality.
6. Soil Formation
Lichens slowly break down rocks by producing weak acids.
Over many years:
Rocks break into small particles.
Soil begins to form.
Other plants can then grow.
Thus, lichens are called pioneer organisms because they are among the first living
organisms to colonize bare rocks.
7. Ecological Importance
Lichens help maintain ecological balance by:
Preventing soil erosion.
Providing shelter for small insects.
Recycling nutrients.
Supporting biodiversity.
Conclusion
Lichens are unique living organisms formed by the symbiotic association of a fungus and an
alga (or cyanobacterium). The fungus provides water, minerals, and protection, while the
alga prepares food through photosynthesis. Their simple body, called a thallus, lacks true
roots, stems, and leaves. Lichens are classified into crustose, foliose, and fruticose types
based on their shape. Although they grow slowly, they are extremely hardy and survive in
harsh environments where most plants cannot.
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Economically, lichens are very valuable. They are used as food, medicines, natural dyes,
perfumes, and laboratory indicators such as litmus. They also play an important
environmental role by acting as bioindicators of air pollution, helping in soil formation, and
maintaining ecological balance. Because of these numerous benefits, lichens are considered
one of the most important symbiotic organisms in nature.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
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