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GNDU Question Paper-2021
BA/BSc
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-A
(Cell Biology)
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
I. Explain the principle of working of an electron microscope and give a comparative
account of light microscopy and electron microscopy.
II. Discuss in detail different types of staining techniques.
SECTION-B
III. Enlist different methods of cellular transportation. Describe endocytosis and its types.
IV. Discuss the structure and functions of mitochondria.
SECTION-C
V. Why lysosomes are called suicidal bags? Write functions of lysosomes.
VI. Draw and describe the structure of Golgi complex and write its functions.
SECTION-D
VII. Explain briefly active and passive immunity.
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VIII. Discuss in detail the structure of nucleus with the help of well labelled diagram.
GNDU Answer Paper-2021
Ba/Bsc
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-A
(Cell Biology)
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
I. Explain the principle of working of an electron microscope and give a comparative
account of light microscopy and electron microscopy.
Ans: Electron Microscope: Principle of Working and Comparison with Light Microscope
The electron microscope is a powerful scientific instrument used to observe objects that are
too small to be seen with the naked eye or even with an ordinary light microscope. It helps
scientists study tiny structures such as viruses, bacteria, cell organelles (mitochondria,
ribosomes), and even atoms.
To understand it easily, imagine you are trying to see a tiny ant from a long distance. Your
eyes cannot see it clearly, so you use binoculars. If you want to see something even smaller,
like a bacterium, binoculars are not enoughyou need a microscope. But even a light
microscope has limits, so scientists developed the electron microscope, which gives a much
higher magnification and a much clearer image.
Principle of Working of an Electron Microscope
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The working principle of an electron microscope is based on the fact that electrons have a
much shorter wavelength than visible light. According to physics, shorter wavelengths
produce higher resolution, allowing us to see much smaller objects in great detail.
How does it work?
1. Electron Gun
An electron gun produces a beam of high-speed electrons instead of light rays.
This beam acts like the light in a normal microscope.
2. Electromagnetic Lenses
Instead of glass lenses, the microscope uses electromagnetic lenses.
These magnetic lenses focus the electron beam onto the specimen.
3. Specimen
The specimen must be very thin because electrons cannot easily pass through thick
materials.
It is placed inside a vacuum chamber because electrons can collide with air
molecules.
4. Formation of Image
When electrons strike the specimen, some pass through while others are scattered.
These electrons form an enlarged image on a fluorescent screen or digital camera.
5. Magnification
The final image is highly magnified and displayed on a monitor.
Electron microscopes can magnify objects up to 12 million times, much greater
than light microscopes.
Simple Working Diagram
Electron Gun
│
▼
Electromagnetic Lens
│
▼
Specimen
(Inside Vacuum)
│
▼
Objective Lens
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│
▼
Projector Lens
│
▼
Screen / Camera
│
▼
Magnified Image
Why is a Vacuum Needed?
Electrons are very small particles. If air is present inside the microscope, electrons collide
with air molecules and lose their energy. Therefore, the entire system is kept in a vacuum so
the electrons can travel freely and produce a clear image.
Light Microscope vs Electron Microscope
Feature
Light Microscope
Electron Microscope
Source of
illumination
Visible light
Electron beam
Type of lenses
Glass lenses
Electromagnetic lenses
Medium
Works in air
Requires vacuum
Magnification
Up to about 10002000×
Up to 12 million×
Resolution
Around 0.2 µm
Around 0.2 nm (much higher)
Specimen
Living or dead specimens
Only dead specimens
Image
Colored (natural)
Black and white (can be colorized
digitally)
Cost
Less expensive
Very expensive
Maintenance
Easy
Complex
Main use
Cells, tissues,
microorganisms
Viruses, organelles, proteins, atoms
Advantages of Electron Microscope
Produces extremely high magnification.
Gives very high resolution.
Can observe viruses and cell organelles clearly.
Helps in medical research, microbiology, nanotechnology, and material science.
Limitations of Electron Microscope
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Very expensive to purchase and maintain.
Requires a vacuum chamber.
Living organisms cannot be observed because specimens must be dead and specially
prepared.
Produces only black-and-white images (originally).
Conclusion
An electron microscope is one of the most important inventions in modern science. It works
by using a beam of electrons instead of light, and because electrons have a much shorter
wavelength, they produce images with far greater magnification and resolution than a light
microscope. While a light microscope is suitable for observing living cells and simple
laboratory work, an electron microscope is used for studying extremely tiny structures such
as viruses, bacteria, cell organelles, and even atoms. Although it is costly and requires
complex preparation, its ability to reveal the microscopic world in extraordinary detail
makes it an indispensable tool in biological, medical, and scientific research.
II. Discuss in detail different types of staining techniques.
Ans: Staining is one of the most important techniques used in microbiology. Most
microorganisms, especially bacteria, are colorless and transparent, so they cannot be seen
clearly under a microscope. To make them visible, scientists use stains (dyes). These stains
color the bacteria and highlight different parts of the cell, making it easier to study their
shape, size, arrangement, and internal structures.
You can think of staining like using a highlighter on important text in a book. Without
highlighting, the important lines are difficult to notice. Similarly, without staining, bacteria
are difficult to observe under the microscope.
Why is Staining Important?
Staining helps scientists and doctors to:
Observe microorganisms clearly.
Identify different types of bacteria.
Study the shape and arrangement of cells.
Detect special structures like capsules, spores, and flagella.
Diagnose diseases accurately.
Types of Staining Techniques
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Staining techniques are mainly divided into four major types.
1. Simple Staining
Simple staining is the easiest and quickest staining method. Only one stain (dye) is used.
Common dyes include:
Methylene Blue
Crystal Violet
Safranin
Procedure
1. Prepare a bacterial smear on a glass slide.
2. Heat-fix the smear.
3. Add the stain for about one minute.
4. Wash with water.
5. Dry and observe under a microscope.
Result
All bacteria appear in one single color.
Uses
Determines the shape of bacteria.
Measures bacterial size.
Studies bacterial arrangement.
Example
A round bacterium (coccus) appears completely blue after staining with methylene blue.
Simple Diagram
Without Staining
○ ○ ○
(Hard to see)
↓
After Simple Staining
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(All cells appear in one color)
2. Differential Staining
Differential staining uses more than one stain to separate bacteria into different groups.
It is mainly of two types:
(A) Gram Staining
This is the most widely used staining technique.
It divides bacteria into:
Gram-positive bacteria
Gram-negative bacteria
Principle
Gram-positive bacteria have a thick cell wall, so they retain the crystal violet stain.
Gram-negative bacteria have a thin cell wall, so they lose the first stain during washing and
take up the counterstain.
Steps
1. Crystal Violet (Primary stain)
2. Iodine (Mordant)
3. Alcohol (Decolorizer)
4. Safranin (Counter stain)
Results
Gram-positive → Purple/Violet
Gram-negative → Pink/Red
Uses
Identification of bacteria.
Selection of correct antibiotics.
Diagnosis of infections.
Gram Staining Diagram
Gram-Positive
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█████████
Purple
↓
Gram-Negative
▒▒▒▒▒▒▒▒
Pink
(B) Acid-Fast Staining
Some bacteria have a waxy cell wall that does not allow ordinary stains to enter.
These bacteria are called Acid-fast bacteria.
Example:
Mycobacterium tuberculosis (causes Tuberculosis)
Stains Used
Carbol Fuchsin
Acid Alcohol
Methylene Blue
Results
Acid-fast bacteria → Red
Non-acid-fast bacteria → Blue
Uses
Diagnosis of Tuberculosis (TB)
Detection of Leprosy bacteria
3. Negative Staining
In this technique, the background is stained instead of the bacteria.
Acidic dyes such as Nigrosin or India Ink are used.
Since bacteria repel the acidic dye, they remain colorless, while the background becomes
dark.
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Result
██████████████
██ ○ ○ ○ ██
██████████████
Dark Background
Colorless Cells
Uses
Observing bacterial size.
Studying capsules.
Viewing delicate bacteria without heat fixing.
Advantage
The bacteria remain undamaged because heat fixing is not required.
4. Special (Structural) Staining
Special stains are used to observe specific structures inside or outside bacterial cells.
(A) Capsule Staining
A capsule is a protective covering around some bacteria.
Purpose
Detect bacterial capsules.
Identify disease-causing bacteria.
Appearance
Background = Dark
( Halo )
●
Capsule appears as a clear ring.
(B) Endospore Staining
Some bacteria produce endospores to survive harsh conditions.
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Example:
Bacillus
Clostridium
Stains Used
Malachite Green
Safranin
Result
Endospores → Green
Bacterial cells → Red
Uses
Detect spore-forming bacteria.
Food industry testing.
Medical diagnosis.
(C) Flagella Staining
Flagella are long, thin structures used for movement.
Since they are extremely thin, ordinary staining cannot show them.
A special stain coats and thickens the flagella so they become visible.
Uses
Observe bacterial movement.
Identify motile bacteria.
Summary Table
Staining
Technique
Main Purpose
Result
Simple Staining
Study shape, size, and
arrangement
Cells appear in one color
Gram Staining
Differentiate bacteria
Gram-positive: Purple, Gram-
negative: Pink
Acid-Fast
Staining
Detect acid-fast bacteria
Acid-fast: Red, Others: Blue
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Negative
Staining
Observe true size and capsules
Dark background, clear cells
Capsule Staining
Detect capsules
Clear halo around bacteria
Endospore
Staining
Detect spores
Green spores, Red cells
Flagella Staining
Observe flagella
Flagella become visible
Conclusion
Staining techniques are essential tools in microbiology because they make otherwise
invisible microorganisms easy to observe under a microscope. Different staining methods
serve different purposes. Simple staining helps study the basic shape and arrangement of
bacteria. Differential staining, including Gram staining and Acid-fast staining, helps classify
bacteria into different groups for accurate diagnosis. Negative staining reveals the natural
size and delicate structures of bacteria without damaging them, while special staining
techniques such as capsule, endospore, and flagella staining highlight specific bacterial
structures. Together, these techniques enable scientists and doctors to identify
microorganisms, diagnose infectious diseases, select appropriate treatments, and carry out
microbiological research effectively.
SECTION-B
III. Enlist different methods of cellular transportation. Describe endocytosis and its types.
Ans: III. Enlist Different Methods of Cellular Transportation. Describe Endocytosis and Its
Types.
Every cell in our body is surrounded by a thin outer covering called the cell membrane
(plasma membrane). Think of the cell membrane as the security gate of a house. It decides
what can enter the cell and what must leave it. This movement of substances in and out of
the cell is called cellular transportation.
Without cellular transportation, a cell cannot get nutrients, remove waste, or communicate
with its surroundings. Therefore, it is essential for the survival of every living cell.
Different Methods of Cellular Transportation
Cellular transportation is mainly divided into two types:
1. Passive Transport
Passive transport is the movement of substances without using cellular energy (ATP).
Molecules move from an area of higher concentration to lower concentration.
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Types of Passive Transport:
a) Diffusion
Movement of molecules from a region of high concentration to low concentration.
No energy is required.
Example: Oxygen moves from the lungs into the blood.
b) Osmosis
Movement of water molecules through a selectively permeable membrane.
Water moves from an area with more water to an area with less water.
Example: Plant roots absorb water from the soil.
c) Facilitated Diffusion
Some large or charged molecules cannot cross the membrane directly.
They move through special protein channels or carrier proteins.
No energy is required.
Example: Glucose entering many body cells.
2. Active Transport
Active transport requires energy in the form of ATP.
Here, substances move against the concentration gradient, meaning from low
concentration to high concentration.
Example:
Sodium-Potassium Pump in nerve cells.
Mineral absorption by plant roots.
What is Endocytosis?
Endocytosis is a type of active transport in which the cell takes substances inside by folding
its cell membrane inward.
Instead of substances passing through the membrane, the membrane surrounds the
material, forms a small sac called a vesicle, and brings it into the cell.
Since the cell has to change the shape of its membrane, ATP energy is required.
Simple Example
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Imagine the cell is like a person holding a shopping bag.
Instead of passing groceries through a tiny window, the person opens the bag, puts the
groceries inside, and closes it.
Similarly, the cell membrane wraps around materials and brings them inside.
Steps of Endocytosis
1. A substance comes close to the cell membrane.
2. The membrane bends inward.
3. It surrounds the substance.
4. The edges of the membrane join together.
5. A small vesicle is formed inside the cell.
6. The vesicle carries the substance where it is needed.
Diagram of Endocytosis
Outside Cell
● Particle
↓
_______________
| |
| \ ● / |
| \ / | ← Cell membrane folds inward
| V |
| (●) | ← Vesicle formed
|_______________|
Inside Cell
Types of Endocytosis
Endocytosis is mainly of three types.
1. Phagocytosis ("Cell Eating")
The word Phagocytosis means cell eating.
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In this process, the cell takes in large solid particles such as bacteria, dead cells, or food
particles.
The cell extends finger-like projections called pseudopodia, which surround the particle and
form a vesicle.
Example
White blood cells engulf bacteria to protect the body.
Amoeba captures food by phagocytosis.
Importance
Protects the body from harmful microorganisms.
Helps in nutrition in some single-celled organisms.
Diagram
Bacteria
●
\ /
\ /
\ /
\ /
[ Cell ]
↓
(Bacteria)
2. Pinocytosis ("Cell Drinking")
The word Pinocytosis means cell drinking.
Instead of solid particles, the cell absorbs liquids and dissolved nutrients.
Small droplets of fluid are enclosed inside tiny vesicles.
Example
Intestinal cells absorb nutrients.
Kidney cells absorb dissolved substances.
Importance
Helps cells obtain nutrients from surrounding fluids.
Maintains the internal environment of the cell.
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Diagram
Liquid Droplets
○ ○ ○
↓
_____________
| |
| \ ○○ / |
| \ / |
| (○) |
|_____________|
3. Receptor-Mediated Endocytosis
This is the most selective type of endocytosis.
The cell membrane contains special receptor proteins that recognize only specific
molecules.
Only substances that fit these receptors are taken into the cell.
It works like a lock-and-key system.
Example
Uptake of cholesterol (LDL).
Absorption of certain hormones and vitamins.
Importance
Highly efficient and selective.
Prevents unnecessary substances from entering the cell.
Diagram
Outside
▲ ▲ ▲
| | |
[Receptors]
_____________
| ▲ ▲ ▲ |
| \___/ |
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| (Vesicle) |
|_____________|
Importance of Endocytosis
Endocytosis is important because it:
Helps cells absorb nutrients and food.
Removes harmful bacteria and foreign particles.
Allows the uptake of important hormones and proteins.
Supports the immune system.
Helps cells communicate with each other.
Maintains normal cell growth and repair.
Difference Between the Types of Endocytosis
Type
Material Taken In
Example
Phagocytosis
Large solid particles
White blood cells engulf
bacteria
Pinocytosis
Liquids and dissolved substances
Intestinal cells absorb
nutrients
Receptor-mediated
Endocytosis
Specific molecules recognized by
receptors
Cholesterol and hormone
uptake
Conclusion
Cellular transportation is the process by which substances move into and out of cells. It
includes passive transport (diffusion, osmosis, and facilitated diffusion), which does not
require energy, and active transport, which uses ATP. Endocytosis is an important form of
active transport where the cell membrane folds inward to bring substances into the cell by
forming vesicles. It occurs in three forms: phagocytosis (cell eating), pinocytosis (cell
drinking), and receptor-mediated endocytosis (selective uptake). Together, these
processes help cells obtain nutrients, fight infections, remove unwanted materials, and
maintain normal cellular functions.
IV. Discuss the structure and functions of mitochondria.
Ans: Introduction
Have you ever wondered how your body gets the energy to walk, run, think, study, or even
breathe? Every activity we perform requires energy. This energy is produced inside tiny
structures present in almost every living cell called mitochondria. Because they produce
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most of the cell's energy, mitochondria are popularly known as the "Powerhouse of the
Cell."
Think of a cell as a city. Just as a city needs a power station to provide electricity, a cell
needs mitochondria to supply energy. Without mitochondria, cells would not have enough
energy to perform their daily activities.
Diagram of Mitochondrion
Mitochondrion
___________________________
/ \
/ Outer Membrane \
|-------------------------------|
| Intermembrane Space |
|-------------------------------|
| /\/\/\/\/\/\/\/\/\/\/\/\ |
| Inner Membrane (Cristae) |
| |
| Matrix |
| ○ DNA Ribosomes |
|_______________________________|
Labels
Outer Membrane
Intermembrane Space
Inner Membrane
Cristae (folds)
Matrix
Mitochondrial DNA
Ribosomes
Structure of Mitochondria
Mitochondria are small, rod-shaped or oval-shaped organelles found in the cytoplasm of
eukaryotic cells (plants, animals, fungi, and protists). Their size generally ranges from 0.51
micrometer in width and 110 micrometers in length.
The structure of a mitochondrion consists of several important parts.
1. Outer Membrane
The outer membrane is the smooth outer covering of the mitochondrion.
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It protects the organelle.
It contains special proteins that allow small molecules to pass in and out.
It acts as a protective barrier.
Simple Example:
Just like the outer wall of a house protects everything inside, the outer membrane protects
the mitochondrion.
2. Intermembrane Space
This is the narrow space between the outer and inner membranes.
It stores hydrogen ions (H⁺).
These ions help produce ATP during cellular respiration.
Think of it as a storage area that temporarily collects materials needed to make energy.
3. Inner Membrane
The inner membrane is highly folded.
These folds are called Cristae.
Unlike the outer membrane, the inner membrane is selective and contains many important
enzymes involved in energy production.
Its main functions are:
Carrying out cellular respiration
Producing ATP
Holding proteins needed for electron transport
4. Cristae
Cristae are the inward folds of the inner membrane.
These folds increase the surface area.
More surface area means:
More enzymes can be present.
More ATP can be produced.
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Energy production becomes much more efficient.
Simple Example:
Imagine folding a large bedsheet. Folding allows more cloth to fit into a smaller space.
Similarly, cristae provide more working space for energy production.
5. Matrix
The matrix is the fluid-filled central part of the mitochondrion.
It contains:
Enzymes
Mitochondrial DNA
Ribosomes
Minerals
Proteins
Many important reactions of cellular respiration occur here.
6. Mitochondrial DNA (mtDNA)
One unique feature of mitochondria is that they contain their own DNA.
This DNA:
Is circular
Is different from the DNA in the nucleus
Helps mitochondria make some of their own proteins
This is why mitochondria are called semi-autonomous organelles.
7. Ribosomes
Mitochondria also contain small ribosomes.
These ribosomes help manufacture proteins required inside the mitochondrion.
Functions of Mitochondria
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Mitochondria perform many important functions besides producing energy.
1. Production of ATP (Energy)
This is the most important function.
Mitochondria convert glucose and oxygen into ATP (Adenosine Triphosphate) through
cellular respiration.
ATP is the energy currency of the cell.
Every activity such as:
Walking
Running
Thinking
Heart beating
Muscle movement
Cell growth
depends on ATP.
2. Cellular Respiration
Cellular respiration occurs mainly inside mitochondria.
It includes:
Krebs Cycle (Matrix)
Electron Transport Chain (Inner Membrane)
These reactions release a large amount of energy from food.
3. Regulation of Cell Death (Apoptosis)
Old or damaged cells must be removed from the body.
Mitochondria help control programmed cell death (apoptosis).
This keeps tissues healthy and prevents abnormal cell growth.
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4. Storage of Calcium
Mitochondria store calcium ions.
Calcium is important for:
Muscle contraction
Nerve signaling
Cell communication
5. Heat Production
In brown fat tissue, mitochondria help generate heat instead of ATP.
This keeps the body warm, especially in newborn babies and animals living in cold climates.
6. Protein and Lipid Metabolism
Mitochondria participate in:
Breakdown of fatty acids
Formation of certain proteins
Energy release from fats
7. Formation of Some Molecules
Mitochondria help produce substances needed for:
Hormone synthesis
Amino acid metabolism
Cell growth
Why are Mitochondria Called the Powerhouse of the Cell?
Mitochondria produce about 90% of the ATP required by most cells.
Since ATP provides energy for nearly every cellular activity, mitochondria act like power
stations supplying electricity to a city.
Without mitochondria:
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Cells cannot produce enough energy.
Organs cannot function properly.
Life cannot continue.
Therefore, mitochondria are called the Powerhouse of the Cell.
Interesting Facts About Mitochondria
They have two membranes (outer and inner).
They contain their own DNA and ribosomes.
They can grow and divide independently inside the cell.
Cells that require more energy (such as muscle, heart, liver, and brain cells) contain
a larger number of mitochondria.
The number of mitochondria varies depending on the energy needs of the cell.
Conclusion
Mitochondria are one of the most important organelles in living cells because they provide
the energy needed for life. Their unique double-membrane structure, folded cristae,
enzyme-rich matrix, and their own DNA make them highly specialized for energy
production. Besides producing ATP, they also help regulate cell death, store calcium,
produce heat, and support many metabolic activities. For these reasons, mitochondria are
rightly known as the "Powerhouse of the Cell." Understanding their structure and functions
helps us appreciate how every cell in our body stays alive and performs its vital activities.
SECTION-C
V. Why lysosomes are called suicidal bags? Write functions of lysosomes.
Ans: Lysosomes are small, round, membrane-bound cell organelles that are found mainly in
animal cells. They were discovered by the Belgian scientist Christian de Duve in 1955.
Lysosomes act as the cleaning and recycling center of the cell because they contain many
powerful digestive enzymes. These enzymes can break down unwanted materials, damaged
cell parts, bacteria, viruses, and even old organelles.
Imagine a cell as a house. Just as every house has a dustbin and cleaning staff to remove
waste, the cell also needs a system to remove garbage. Lysosomes perform this job. They
collect unwanted substances, digest them into simpler materials, and recycle useful
components so the cell can use them again.
Why are lysosomes called "Suicidal Bags"?
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Lysosomes are called suicidal bags because they contain very strong digestive enzymes.
Normally, these enzymes remain safely enclosed inside the lysosome by its membrane.
However, if a cell becomes old, severely damaged, or infected, the lysosome membrane
may break open. When this happens, the digestive enzymes are released into the cell and
begin to digest the cell itself. This process is called autolysis (self-digestion).
This is similar to a building that is too damaged to repair. Instead of leaving it unsafe, it is
carefully demolished. Likewise, lysosomes destroy damaged cells so they do not harm the
surrounding healthy cells. Therefore, they are known as "suicidal bags" or "suicide sacs" of
the cell.
Functions of Lysosomes
Lysosomes perform several important functions that help keep the cell healthy.
1. Digestion of Food
When food enters the cell, lysosomes release digestive enzymes to break complex food
molecules into simpler substances that the cell can use for energy and growth.
2. Removal of Cell Waste
Lysosomes digest and remove unwanted waste materials, keeping the inside of the cell
clean.
3. Destruction of Harmful Microorganisms
If bacteria or viruses enter the cell, lysosomes surround and digest them, protecting the cell
from infection.
4. Recycling of Old Organelles
Old or damaged cell organelles are broken down by lysosomes. Their useful parts are
recycled to make new cell components.
5. Autolysis (Self-Destruction)
When a cell is badly damaged or no longer useful, lysosomes release their enzymes to
destroy the entire cell. This prevents damaged cells from affecting healthy tissues.
6. Helping in Tissue Development
During the growth and development of the body, lysosomes help remove unnecessary cells,
allowing proper formation of tissues and organs.
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Simple Diagram of a Lysosome
Animal Cell
___________________________
/ \
| Nucleus |
| ○ |
| |
| Mitochondrion |
| () |
| |
| _________ |
| / \ |
| | Lysosome | |
| | Digestive| |
| | Enzymes | |
| \_________/ |
| |
\___________________________/
Lysosome = Cleans waste + Destroys germs +
Recycles old parts + Can digest
the whole cell (Autolysis)
Key Points to Remember
Lysosomes are membrane-bound organelles found mainly in animal cells.
They contain digestive enzymes.
They are called suicidal bags because they can digest the entire cell during autolysis.
They help in digestion, waste removal, recycling old organelles, destroying bacteria
and viruses, tissue development, and self-destruction of damaged cells.
Exam Definition
Lysosomes are called suicidal bags because they contain powerful digestive enzymes that
can digest the entire cell when released during cell damage or old age. Their main
functions are intracellular digestion, waste removal, destruction of harmful
microorganisms, recycling of worn-out organelles, and self-digestion (autolysis).
VI. Draw and describe the structure of Golgi complex and write its functions.
Ans: The Golgi Complex (also called the Golgi Apparatus or Golgi Body) is an important cell
organelle found in the cytoplasm of both plant and animal cells. It acts like the post office,
packaging center, and delivery service of the cell. Just as a post office receives parcels,
packs them properly, labels them, and sends them to the correct destination, the Golgi
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complex receives proteins and fats from another cell organelle called the Endoplasmic
Reticulum (ER), modifies them, packages them, and sends them to different parts of the cell
or outside the cell.
Because of this important role, the Golgi complex is often called the "Packaging and
Dispatching Unit of the Cell."
Simple Diagram of Golgi Complex
Transport Vesicles
↓
___________________
/ \
| Cis Face | (Receiving Side)
|=====================|
| |
| Flattened Sacs |
| (Cisternae) |
|=====================|
| |
|=====================|
| Trans Face | (Shipping Side)
\___________________/
↓
Secretory Vesicles
↓
To Cell Membrane / Lysosome /
Other Organelles / Outside Cell
Structure of the Golgi Complex
The Golgi complex has a unique structure that helps it perform its work efficiently.
1. Flattened Sacs (Cisternae)
The Golgi complex is made up of a stack of flat, membrane-bound sacs called
cisternae.
Usually, 48 cisternae are stacked one above another like a pile of plates.
These sacs are surrounded by a single membrane.
2. Cis Face (Receiving Face)
The cis face is the side of the Golgi complex that faces the Endoplasmic Reticulum
(ER).
It receives newly made proteins and lipids from the ER through small transport
vesicles.
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This side is also called the forming face because new cisternae are continuously
formed here.
3. Trans Face (Shipping Face)
The trans face is the opposite side.
After proteins and lipids are modified and packed, they leave through this side.
It is called the maturing face because finished products are released from here in
secretory vesicles.
4. Vesicles
Tiny membrane-bound sacs called vesicles surround the Golgi complex.
These vesicles carry materials into the Golgi and transport finished products to
different parts of the cell or outside the cell.
How Does the Golgi Complex Work?
The working of the Golgi complex can be understood in four simple steps:
1. Receives proteins and lipids from the Endoplasmic Reticulum.
2. Modifies them by adding carbohydrates or other molecules.
3. Packages them into small vesicles.
4. Sends them to their correct destination inside or outside the cell.
Think of it like an online shopping warehouse:
The ER manufactures the products.
The Golgi complex checks, labels, packs, and dispatches them.
Vesicles act like delivery trucks carrying the packages.
Functions of the Golgi Complex
1. Packaging of Proteins
The Golgi complex packages proteins produced by the rough Endoplasmic Reticulum into
vesicles so they can be transported safely.
2. Modification of Proteins and Lipids
It modifies proteins and fats by adding sugars or other molecules, making them ready for
their specific functions.
3. Transport of Materials
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It sends proteins and lipids to different parts of the cell or outside the cell wherever they are
needed.
4. Formation of Lysosomes
The Golgi complex produces lysosomes, which contain digestive enzymes that break down
waste materials, old cell parts, and foreign substances.
5. Secretion of Cell Products
It helps in the secretion of substances such as enzymes, hormones, mucus, and other useful
materials outside the cell.
6. Cell Membrane Formation
The Golgi complex contributes membrane material that helps in the formation and repair of
the cell membrane.
7. Formation of Cell Wall Materials (Plants)
In plant cells, it synthesizes and transports substances like pectin and hemicellulose, which
help build the cell wall.
8. Storage and Sorting
The Golgi complex sorts different molecules and stores them temporarily before sending
them to their correct destinations.
Importance of the Golgi Complex
Without the Golgi complex, proteins and lipids made by the cell would not reach their
proper locations. Important substances such as hormones, enzymes, and digestive proteins
would not be packaged or transported correctly. Therefore, the Golgi complex is essential
for the normal growth, maintenance, communication, and survival of the cell.
Key Points for Exam
Golgi complex is known as the Packaging and Dispatching Unit of the cell.
It is made of flattened membrane-bound sacs called cisternae.
Cis face receives materials from the Endoplasmic Reticulum.
Trans face sends modified materials to their destinations.
It modifies, packages, stores, and transports proteins and lipids.
It forms lysosomes.
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It helps in secretion, cell membrane formation, and cell wall material formation in
plants.
Conclusion
The Golgi complex is one of the most important organelles in a cell because it works like a
post office or courier service. It receives proteins and lipids from the Endoplasmic
Reticulum, modifies them, packs them into vesicles, and delivers them to the correct
location. It also forms lysosomes, helps in secretion, and contributes to cell membrane and
cell wall formation. Due to these vital roles, the Golgi complex is essential for the proper
functioning, growth, and survival of both plant and animal cells.
SECTION-D
VII. Explain briefly active and passive immunity.
Ans: Our body is constantly exposed to harmful microorganisms such as bacteria, viruses,
fungi, and parasites. To protect us from these disease-causing organisms, the body has a
powerful immune system. Immunity is the body's natural ability to fight infections and
diseases. It helps us stay healthy by recognizing harmful germs and destroying them before
they can cause serious illness.
Immunity is mainly divided into two types: Active Immunity and Passive Immunity.
1. Active Immunity
Active immunity is the type of immunity in which our own body produces antibodies after
coming into contact with a disease-causing organism (antigen). Since the body prepares its
own defense, this protection is usually strong and long-lasting.
Think of it like learning to ride a bicycle. Once you learn it yourself, you remember it for
many years. Similarly, once your immune system learns to fight a disease, it remembers it
and can fight the same disease quickly in the future.
How Active Immunity Works
1. A germ (bacteria or virus) enters the body or a vaccine is given.
2. The immune system recognizes the germ as harmful.
3. White blood cells produce antibodies to destroy the germ.
4. The body also creates memory cells.
5. If the same germ attacks again, memory cells quickly produce antibodies, preventing
illness.
Types of Active Immunity
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A. Natural Active Immunity
Occurs when a person gets infected naturally and then recovers.
The immune system remembers the infection.
Example: A person who recovers from chickenpox usually does not get it again.
B. Artificial Active Immunity
Occurs through vaccination.
Vaccines contain weakened or dead germs (or parts of germs).
They stimulate the immune system without causing the actual disease.
Examples: Polio vaccine, Measles vaccine, Hepatitis B vaccine, COVID-19 vaccine.
Advantages
Long-lasting protection.
Produces memory cells.
Prevents future infections.
Can protect for many years or even a lifetime.
Disadvantages
Takes several days or weeks to develop.
Not useful when immediate protection is needed.
2. Passive Immunity
Passive immunity is the type of immunity in which ready-made antibodies are received
from another person or another source. In this case, the body does not make its own
antibodies.
Think of it like borrowing an umbrella during heavy rain. It protects you immediately, but
once you return the umbrella, the protection is gone. Similarly, passive immunity provides
quick protection but only for a short time.
How Passive Immunity Works
1. Ready-made antibodies are introduced into the body.
2. These antibodies immediately fight the harmful germs.
3. Since the body does not produce them itself, no memory cells are formed.
4. Protection disappears after the antibodies break down.
Types of Passive Immunity
A. Natural Passive Immunity
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Antibodies pass from the mother to the baby.
During pregnancy, antibodies cross the placenta.
After birth, antibodies are also provided through breast milk (colostrum).
These antibodies protect the baby during the first few months of life.
B. Artificial Passive Immunity
Ready-made antibodies are injected into a person.
Used when immediate protection is required.
Examples:
o Anti-rabies injection after a dog bite.
o Tetanus immunoglobulin after a serious wound.
o Snake antivenom after a poisonous snake bite.
Advantages
Provides immediate protection.
Useful during emergencies.
Helps people with weak immune systems.
Disadvantages
Protection lasts only for a short period (weeks or months).
No memory cells are formed.
The body does not learn to fight the disease itself.
Difference Between Active and Passive Immunity
Active Immunity
Passive Immunity
Body produces its own antibodies.
Ready-made antibodies are received from
another source.
Protection develops slowly.
Protection is immediate.
Long-lasting immunity.
Short-term immunity.
Memory cells are formed.
Memory cells are not formed.
Examples: Vaccines, recovery from
infection.
Mother's antibodies, anti-rabies injection,
antivenom.
Simple Diagram
IMMUNITY
│
┌──────────────┴──────────────┐
│ │
Active Immunity Passive Immunity
│ │
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Body makes antibodies Ready-made antibodies
│ │
Memory cells formed No memory cells formed
│ │
Long-lasting protection Temporary protection
│ │
Vaccines / Natural infection Mother's milk / Antiserum
Easy Trick to Remember
Active = "Act Yourself"
Your own body acts and makes antibodies.
Slow but long-lasting protection.
Passive = "Pass to You"
Antibodies are passed from another person or source.
Fast but temporary protection.
Conclusion
Active and passive immunity are both essential for protecting the human body from
diseases. Active immunity develops when the body's immune system produces its own
antibodies after infection or vaccination, giving long-lasting protection and creating memory
cells. Passive immunity provides immediate protection by supplying ready-made antibodies
from another source, such as the mother or medical injections, but the protection is
temporary because no memory cells are formed. Together, these two types of immunity
play an important role in preventing infections and maintaining good health.
VIII. Discuss in detail the structure of nucleus with the help of well labelled diagram.
Ans: Introduction
The nucleus is the control center of the cell. It is the largest and one of the most important
organelles found in most plant and animal cells. Just as a principal controls a school or a
captain leads a team, the nucleus controls all the activities of the cell. It stores the cell's
genetic material (DNA), which carries all the instructions needed for growth, reproduction,
repair, and normal functioning of the organism.
The nucleus was first discovered by Robert Brown in 1831 while studying plant cells.
Well-Labelled Diagram of the Nucleus
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STRUCTURE OF NUCLEUS
___________________________
/ \
/ Nuclear Envelope \
/_______________________________\
| |
| ○ Nucleolus |
| |
| ~~~~~ Chromatin Network ~~~~ |
| ~~~~~ (DNA + Proteins) ~~~~ |
| |
| Nucleoplasm |
| |
\_______________________________/
Nuclear Pores Nuclear Pores
Structure of the Nucleus
The nucleus is made up of the following main parts:
1. Nuclear Envelope (Nuclear Membrane)
The nuclear envelope is the outer covering of the nucleus. It consists of two membranes
(double membrane) that protect the nucleus from the rest of the cell.
Functions:
Protects the genetic material (DNA).
Separates the nucleus from the cytoplasm.
Maintains the shape of the nucleus.
Controls the movement of substances in and out of the nucleus through nuclear
pores.
Simple Example:
Think of the nuclear envelope as the walls of a classroom. The walls protect the students
inside while the doors allow people to enter and leave.
2. Nuclear Pores
Small openings called nuclear pores are present in the nuclear envelope.
Functions:
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Allow RNA, proteins, enzymes, and nutrients to move between the nucleus and
cytoplasm.
Regulate what enters and leaves the nucleus.
Simple Example:
Nuclear pores work like security gates at an airport. Only approved materials can pass
through them.
3. Nucleoplasm
The nucleoplasm is a clear, jelly-like fluid present inside the nucleus.
Functions:
Supports all nuclear components.
Provides nutrients to chromatin and nucleolus.
Acts as the medium where many chemical reactions occur.
Simple Example:
Just as fish swim in water, all parts of the nucleus remain suspended in the nucleoplasm.
4. Chromatin Network
The chromatin network is made of DNA and proteins (histones). During cell division,
chromatin condenses to form chromosomes.
Functions:
Stores hereditary information.
Controls cell activities through genes.
Transfers genetic information from parents to offspring.
Helps in protein synthesis.
Simple Example:
Imagine chromatin as a huge library of instruction books. Every book contains information
on how the body should grow, function, and repair itself.
5. Nucleolus
The nucleolus is a dense, round structure inside the nucleus.
Functions:
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Produces ribosomes.
Helps in protein synthesis.
Disappears during cell division and reappears afterwards.
Simple Example:
The nucleolus is like a factory that manufactures ribosomes, which later produce proteins
for the cell.
Functions of the Nucleus
The nucleus performs many important functions:
1. Controls Cell Activities
It regulates growth, metabolism, movement, and all other activities of the cell.
2. Stores Genetic Material
DNA present inside the nucleus contains hereditary information.
3. Protein Synthesis
It controls protein production by sending genetic instructions to ribosomes.
4. Cell Division
The nucleus plays an important role during mitosis and meiosis, ensuring that genetic
information is passed correctly to new cells.
5. Heredity
Genes present on chromosomes transfer characteristics from parents to offspring.
6. Regulation of Cell Growth
The nucleus controls when cells should grow, divide, repair themselves, or die.
Why is the Nucleus Called the Control Centre?
The nucleus is called the control centre of the cell because:
It contains DNA, the cell's instruction manual.
It controls all metabolic activities.
It regulates cell division.
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It directs protein synthesis.
It coordinates communication between different parts of the cell.
Without a nucleus, a cell cannot properly control its activities and usually cannot survive for
long.
Easy Way to Remember (Real-Life Analogy)
Imagine a company:
Nucleus → Company Head Office
DNA (Chromatin) → Company Records and Important Documents
Nucleolus → Factory producing workers (ribosomes)
Nuclear Envelope → Office Building Walls
Nuclear Pores → Entry and Exit Gates
Nucleoplasm → Office Working Space
Just as the head office controls the entire company, the nucleus controls the entire cell.
Conclusion
The nucleus is the most important organelle of a eukaryotic cell because it controls all
cellular activities and stores hereditary information in the form of DNA. Its main parts
nuclear envelope, nuclear pores, nucleoplasm, chromatin network, and nucleoluswork
together to regulate growth, protein synthesis, cell division, and inheritance. Therefore, the
nucleus is rightly known as the "brain" or "control centre" of the cell.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
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