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GNDU Question Paper-2022
Bachelor of Computer Application (BCA) (Hons.)
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. Write a note on:
(a) Fixatives.
(b) Stains and staining techniques.
II. Discuss principle of phasee contrast microscopy.
SECTION-B
III. Explain how transportation of materials occurs across the plasma 7 membrane.
IV. Write functions of smooth and rough endoplasmic reticulum.
SECTION-C
V. Which organelle is called Recycling centre ? Give its functions.
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VI. Describe the ultra-structure of ribosome and write its functions.
SECTION-D
VII. Define immunity and immune response. Explain briefly different types of immunity.
VIII. Differentiate between chormatin and chromosome. Describe nuclear envelop and
structure of its pores.
GNDU Question Paper-2022
Bachelor of Computer Application (BCA) (Hons.)
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. Write a note on:
(a) Fixatives.
(b) Stains and staining techniques.
Ans: (a) Fixatives
(b) Stains and Staining Techniques
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In biology, scientists often study very small structures such as cells, tissues, bacteria, and
microorganisms under a microscope. However, these living materials begin to decay soon
after they are removed from the body. Also, many cells are almost transparent, making it
difficult to see their internal parts. To solve these problems, scientists use fixatives and
staining techniques.
Think of it like taking a photograph. Before clicking a picture, the object should remain still;
otherwise, the image becomes blurry. Similarly, before studying a cell, it must be preserved
in its original condition. After that, if the object is too light to see, we use colors to make it
visible. This is exactly what fixatives and stains do.
(a) Fixatives
What are Fixatives?
Fixatives are special chemical substances used to preserve cells and tissues in their natural
condition before microscopic examination.
Their main purpose is to stop decomposition, prevent bacterial attack, and preserve the
shape and internal structure of cells.
Without fixation, cells lose their original shape, enzymes start breaking them down, and
bacteria may destroy them. Therefore, fixation is the first and most important step in
preparing microscope slides.
Why are Fixatives Needed?
Fixatives perform several important functions:
Preserve the natural shape of cells and tissues.
Stop decay caused by enzymes.
Kill bacteria and microorganisms.
Harden tissues, making them easier to cut into thin sections.
Prevent changes in cell structure during staining.
Maintain the chemical composition of cells.
Common Fixatives
1. Formalin (Formaldehyde)
Most commonly used fixative.
Preserves tissues for a long time.
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Widely used in hospitals and research laboratories.
2. Alcohol (Ethanol or Methanol)
Removes water from cells.
Fixes blood smears and microorganisms.
Quick and inexpensive.
3. Acetic Acid
Preserves chromosomes and nuclei.
Often mixed with other fixatives.
4. Bouin's Fluid
Contains:
Picric acid
Formaldehyde
Acetic acid
It is mainly used for preserving soft tissues.
5. Carnoy's Fixative
Contains:
Ethanol
Chloroform
Acetic acid
Used mainly for chromosome studies.
Characteristics of an Ideal Fixative
A good fixative should:
Preserve tissues without shrinking them.
Prevent decomposition.
Maintain cell shape.
Work quickly.
Allow easy staining afterward.
Be safe and easy to use.
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Simple Diagram of Fixation
Fresh Tissue
│
▼
Apply Fixative
(Formalin/Alcohol)
│
▼
Stops Decay
Kills Bacteria
Preserves Shape
│
▼
Ready for Staining
(b) Stains and Staining Techniques
What are Stains?
Most cells are colorless and transparent, so their internal structures cannot be seen clearly
under a microscope.
A stain is a colored chemical dye used to increase the contrast between different parts of a
cell so they become clearly visible.
Staining helps scientists identify the nucleus, cytoplasm, cell wall, bacteria, and many other
structures.
Why is Staining Necessary?
Staining helps to:
Make transparent cells visible.
Differentiate different cell parts.
Identify bacteria and microorganisms.
Observe cell shape and arrangement.
Detect diseases.
Study tissue structure.
Common Biological Stains
1. Methylene Blue
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Stains nuclei blue.
Used for cheek cells and bacteria.
2. Safranin
Gives a red color.
Commonly used in plant tissues.
3. Crystal Violet
Used in Gram staining.
Colors Gram-positive bacteria purple.
4. Eosin
Stains cytoplasm pink.
Used with Hematoxylin.
5. Hematoxylin
Stains nuclei deep blue or purple.
Widely used in histology.
6. Iodine Solution
Stains starch blue-black.
Helps identify plant cell structures.
Types of Staining Techniques
1. Simple Staining
Only one stain is used.
Purpose:
Observe the size, shape, and arrangement of cells.
Example:
Methylene Blue
Crystal Violet
2. Differential Staining
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Uses two or more stains to distinguish between different types of cells.
Example:
Gram staining
Acid-fast staining
This technique helps identify bacterial species.
3. Negative Staining
Instead of staining the cell, the background is stained.
Result:
Cell appears clear against a dark background.
Used for delicate bacteria and capsules.
4. Special Staining
Used to stain specific structures like:
Spores
Capsules
Flagella
Cell wall
Simple Flow Diagram of Staining
Transparent Cell
│
▼
Add Biological Stain
│
▼
Cell Parts Absorb Dye
│
▼
Nucleus, Cytoplasm,
Cell Wall Become Visible
│
▼
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Observation Under Microscope
Difference Between Fixatives and Stains
Fixatives
Stains
Preserve cells and tissues
Color cells and tissues
Used before staining
Used after fixation
Prevent decomposition
Increase visibility
Maintain natural structure
Highlight different cell parts
Example: Formalin, Alcohol
Example: Methylene Blue, Safranin
Everyday Example
Imagine you want to preserve an old flower for a school project.
First, you dry and preserve the flower so it does not rot. This is like using a fixative.
Then, if you want to highlight its petals for a display, you may color or decorate it.
This is similar to staining.
Thus, fixation preserves, while staining makes structures easy to see.
Conclusion
Fixatives and staining techniques are two essential steps in microscopic studies. Fixatives
preserve the natural structure of cells and tissues by preventing decay and maintaining their
original form. After fixation, stains add color to different cell components, making them
clearly visible under the microscope. Different stains and staining techniques are chosen
depending on what scientists want to observe, such as nuclei, cytoplasm, bacteria, or
specific cell structures. Together, fixation and staining enable researchers, doctors, and
students to study cells accurately, diagnose diseases, identify microorganisms, and
understand the organization of living tissues. Without these techniques, microscopic
examination would be difficult because cells would either decompose or remain nearly
invisible.
II. Discuss principle of phasee contrast microscopy.
Ans: Introduction
A phase contrast microscope is a special type of microscope that allows us to observe living,
transparent, and unstained cells clearly. Normally, many biological cells are almost
colorless, so they are difficult to see under an ordinary light microscope without staining.
However, staining often kills the cells, making it impossible to study their natural activities.
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To solve this problem, Dutch physicist Frits Zernike developed the phase contrast
microscope in the 1930s. This invention made it possible to observe living cells without
using any dyes or stains.
What is the Principle of Phase Contrast Microscopy?
The principle of phase contrast microscopy is based on the fact that different parts of a cell
have different thicknesses and refractive indices (optical densities).
When light passes through a transparent specimen:
Some light passes through thin regions without much change.
Some light passes through thicker or denser regions, where it slows down.
Because of this difference in speed, the light waves become slightly out of step with
each other. This difference is called a phase difference.
The human eye cannot detect these phase differences directly.
A phase contrast microscope converts these invisible phase differences into visible
differences in brightness (light and dark areas). As a result, transparent cells become
clearly visible without staining.
How Does It Work? (Step by Step)
Step 1: Light Enters the Microscope
A beam of light passes through a special ring called the annular diaphragm, producing a
hollow cone of light.
Step 2: Light Passes Through the Specimen
When the light reaches the specimen:
Some light passes straight through without changing.
Some light bends or slows down because different cell parts have different densities.
This creates a phase shift.
Step 3: Phase Plate
The light then reaches a special phase plate placed inside the objective lens.
The phase plate changes the phase of one set of light rays.
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Step 4: Image Formation
When the two light rays combine:
Some areas become brighter.
Some areas become darker.
Thus, invisible phase differences become visible contrast, allowing us to see the internal
structures of living cells.
Simple Diagram
Light Source
│
▼
Annular Diaphragm
│
▼
Transparent Specimen
(Living Cell)
│
┌──────────────┐
│ │
Direct Light Diffracted Light
│ │
└──────┬───────┘
▼
Phase Plate
│
▼
Bright & Dark Image
│
▼
Eye / Camera
Why Is It Called "Phase Contrast"?
The word Phase refers to the position of a light wave.
When light travels through different parts of a cell, its phase changes slightly.
The microscope converts this phase difference into contrast, producing light and dark
regions.
Hence, the name Phase Contrast Microscopy.
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Main Parts Involved
1. Light Source Provides illumination.
2. Annular Diaphragm Produces a ring-shaped beam of light.
3. Objective Lens Magnifies the specimen.
4. Phase Plate Converts phase differences into brightness differences.
5. Eyepiece Allows observation of the final image.
Advantages
No staining is required.
Living cells can be observed.
Cell division and movement can be studied.
Internal cell structures become visible.
Cells remain alive and undamaged.
Quick and easy observation.
Limitations
Not suitable for thick specimens.
Produces halo (bright ring) around objects.
Equipment is more expensive than a simple light microscope.
Image quality decreases for very dense samples.
Applications
Phase contrast microscopy is widely used in:
Studying living bacteria.
Observing protozoa and algae.
Examining tissue culture cells.
Watching cell division (mitosis).
Medical and microbiology laboratories.
Biological and research laboratories.
Conclusion
The principle of phase contrast microscopy is based on converting the invisible phase
differences produced when light passes through transparent specimens into visible
differences in brightness. This enables scientists to observe living, unstained cells in their
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natural state without harming them. Because it reveals structures that are invisible under a
normal light microscope, phase contrast microscopy has become one of the most important
tools in biology, microbiology, medicine, and cell research.
SECTION-B
III. Explain how transportation of materials occurs across the plasma 7 membrane.
Ans: The plasma membrane is a thin, flexible covering that surrounds every living cell. It
acts like a security gate or border checkpoint of a city. Its main job is to control what enters
and what leaves the cell. It allows useful substances like oxygen, water, and nutrients to
enter while allowing waste materials to leave. Because it selects what can pass through it,
the plasma membrane is called a selectively permeable membrane.
Imagine a house with a smart door. Family members and invited guests can enter easily, but
strangers need permission. Similarly, the plasma membrane decides which substances can
cross it.
Why is transportation across the plasma membrane necessary?
Every cell needs a continuous supply of nutrients and oxygen to stay alive and perform its
functions. At the same time, harmful substances and waste products produced inside the
cell must be removed. Therefore, materials constantly move across the plasma membrane.
There are two main types of transportation:
1. Passive Transport (No energy required)
2. Active Transport (Energy required)
1. Passive Transport
Passive transport means substances move without using cellular energy (ATP). They
naturally move from an area of higher concentration (where there are more molecules) to
an area of lower concentration (where there are fewer molecules).
Think of it like a crowd leaving a packed stadium. People naturally move from the crowded
area to the less crowded area without anyone pushing them.
Passive transport includes three important processes:
(A) Diffusion
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Diffusion is the movement of molecules from high concentration to low concentration.
Example:
Oxygen enters our body cells from the blood because there is more oxygen in the
blood.
Carbon dioxide moves out of the cells because its concentration is higher inside the
cells.
This process continues until the concentration becomes equal on both sides.
(B) Osmosis
Osmosis is the movement of water molecules through a selectively permeable membrane
from a region of higher water concentration to lower water concentration.
Example:
Plant roots absorb water from the soil by osmosis.
Our body cells also gain and lose water through osmosis.
(C) Facilitated Diffusion
Some large molecules like glucose or charged particles (ions) cannot pass directly through
the membrane.
They use special transport proteins or channel proteins present in the plasma membrane.
Even though helper proteins are involved, no energy is required because substances still
move from high concentration to low concentration.
2. Active Transport
Sometimes the cell needs to move substances against the concentration gradient, that is,
from low concentration to high concentration.
This cannot happen naturally.
Therefore, the cell uses energy in the form of ATP (Adenosine Triphosphate).
This process is called Active Transport.
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Example:
Plant roots absorb important minerals from the soil even when the mineral
concentration is lower in the soil than inside the root cells.
Human cells absorb essential ions such as sodium and potassium using active
transport.
Special carrier proteins in the plasma membrane help perform this process.
Bulk Transport
Very large materials cannot pass through the membrane by diffusion or active transport.
The cell transports them through vesicles (small membrane-bound sacs).
(A) Endocytosis
In Endocytosis, the plasma membrane folds inward and surrounds the material, forming a
vesicle that brings the material inside the cell.
Example:
White blood cells engulf bacteria through endocytosis.
Amoeba captures food using this process.
(B) Exocytosis
In Exocytosis, vesicles carrying materials move to the plasma membrane, fuse with it, and
release their contents outside the cell.
Example:
Hormones and digestive enzymes are released by exocytosis.
Waste products are also removed through this process.
Simple Diagram
OUTSIDE THE CELL
│
Oxygen, Water, Nutrients
↓
┌──────────────────────────┐
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│ Plasma Membrane │
│ (Selectively Permeable) │
└──────────────────────────┘
│
CELL INSIDE
│
Waste, CO₂, Harmful Products
↑
-------------------------------------------------------
Passive Transport
High Concentration ─────────► Low Concentration
(No ATP Required)
Diffusion
Osmosis
Facilitated Diffusion
-------------------------------------------------------
Active Transport
Low Concentration ──(ATP Energy)──► High Concentration
-------------------------------------------------------
Endocytosis
Outside → (Membrane folds inward) → Inside Cell
Exocytosis
Inside Cell → (Vesicle fuses with membrane) → Outside
Key Differences Between Passive and Active Transport
Passive Transport
Active Transport
No energy (ATP) required
Energy (ATP) is required
Moves from high to low concentration
Moves from low to high
concentration
Includes diffusion, osmosis, and facilitated
diffusion
Uses carrier proteins and ATP
Natural movement of molecules
Cell forces molecules to move
Conclusion
The plasma membrane plays a vital role in maintaining the life of a cell by carefully
regulating the movement of substances. Materials move across it through passive transport
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(diffusion, osmosis, and facilitated diffusion), which does not require energy, and active
transport, which uses ATP to move substances against the concentration gradient. Larger
substances are transported through endocytosis and exocytosis using vesicles. Together,
these transport mechanisms ensure that the cell receives essential nutrients and oxygen,
maintains water balance, removes waste products, and functions efficiently.
IV. Write functions of smooth and rough endoplasmic reticulum.
Ans: Functions of Smooth and Rough Endoplasmic Reticulum (ER)
The Endoplasmic Reticulum (ER) is one of the most important parts of a cell. It is a network
of tiny tubes and flattened sacs that spreads throughout the cytoplasm. Think of it as the
transport system and manufacturing factory of the cell. It helps in making, processing, and
transporting different materials that the cell needs to survive.
There are two types of Endoplasmic Reticulum:
1. Rough Endoplasmic Reticulum (RER)
2. Smooth Endoplasmic Reticulum (SER)
Although both are connected to each other, they perform different functions.
Simple Diagram of Endoplasmic Reticulum
Nucleus
│
┌─────────────────────┐
│ │
Rough ER Smooth ER
(With Ribosomes) (Without Ribosomes)
● ● ● ● ───────
● ● ● ● ───────
● ● ● ● ───────
↓ ↓
Makes Proteins Makes Lipids (Fats),
Detoxifies Poisons,
Stores Calcium
1. Rough Endoplasmic Reticulum (RER)
The Rough Endoplasmic Reticulum is called "rough" because its outer surface is covered
with tiny particles called ribosomes. Under a microscope, these ribosomes make it look
rough.
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Imagine this...
Think of a bakery where many workers are making bread. Here:
The bakery building is the Rough ER.
The workers (ribosomes) are making bread.
Instead of bread, they make proteins.
Since proteins are very important for growth, repair, enzymes, hormones, and muscles, the
Rough ER works continuously in many cells.
Functions of Rough Endoplasmic Reticulum
1. Protein Synthesis
Its main function is to manufacture proteins with the help of ribosomes.
These proteins are needed for:
Growth
Repair of damaged tissues
Formation of enzymes
Hormones
Antibodies
2. Protein Processing
After proteins are made, they are folded into the correct shape.
If proteins are not folded properly, they cannot work correctly.
3. Protein Transport
The Rough ER sends proteins to the Golgi apparatus, where they are packed and sent to
different parts of the cell or outside the cell.
4. Cell Membrane Formation
The Rough ER also helps produce proteins that become part of the cell membrane.
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5. Production of Secretory Proteins
Many glands release proteins outside the cell.
Examples:
Insulin
Digestive enzymes
Saliva proteins
These proteins are first made in the Rough ER.
Summary of Rough ER Functions
Produces proteins.
Modifies proteins.
Transports proteins.
Helps form the cell membrane.
Makes proteins for secretion.
2. Smooth Endoplasmic Reticulum (SER)
The Smooth Endoplasmic Reticulum has no ribosomes attached to its surface, so it looks
smooth.
Instead of making proteins, it performs many other important jobs.
Imagine the Smooth ER as a chemical factory inside the cell.
It prepares fats, removes harmful chemicals, and stores important minerals.
Functions of Smooth Endoplasmic Reticulum
1. Lipid (Fat) Synthesis
The Smooth ER manufactures:
Fats
Lipids
Phospholipids
Cholesterol
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These substances are essential for building cell membranes and producing certain
hormones.
2. Steroid Hormone Production
Cells of the adrenal glands and reproductive organs use the Smooth ER to produce steroid
hormones such as:
Testosterone
Estrogen
Cortisol
These hormones regulate growth, reproduction, and metabolism.
3. Detoxification of Harmful Substances
The Smooth ER removes harmful chemicals from the body.
It detoxifies:
Alcohol
Medicines
Drugs
Other poisonous substances
This function is especially important in liver cells, where detoxification protects the body
from damage.
4. Carbohydrate Metabolism
The Smooth ER helps convert stored glycogen into glucose whenever the body needs
energy, helping maintain blood sugar levels.
5. Calcium Storage
In muscle cells, a specialized Smooth ER called the sarcoplasmic reticulum stores calcium
ions.
When muscles need to contract, calcium is released.
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Without this function, muscles cannot move properly.
6. Formation of Cell Membrane
The Smooth ER also produces lipids that become part of the cell membrane.
Summary of Smooth ER Functions
Produces fats and lipids.
Makes steroid hormones.
Detoxifies harmful substances.
Helps in carbohydrate metabolism.
Stores calcium.
Helps build the cell membrane.
Difference Between Rough ER and Smooth ER
Feature
Rough ER
Smooth ER
Ribosomes
Present
Absent
Appearance
Rough
Smooth
Main Product
Proteins
Lipids (Fats)
Main
Function
Protein synthesis and
transport
Lipid synthesis and detoxification
Found in
Protein-producing cells
Liver cells, muscle cells, steroid-producing
cells
Easy Trick to Remember
Rough = Ribosomes = Proteins
Smooth = No Ribosomes = Fats + Detoxification
Or remember:
RER → "R" for Ribosomes and Repair proteins
SER → "S" for Smooth, Steroids, and Safety (detoxification)
Conclusion
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The Endoplasmic Reticulum acts like the factory and transportation network of the cell.
The Rough Endoplasmic Reticulum (RER) specializes in making, modifying, and transporting
proteins because it contains ribosomes. In contrast, the Smooth Endoplasmic Reticulum
(SER) produces lipids and steroid hormones, detoxifies harmful chemicals, helps in
carbohydrate metabolism, stores calcium for muscle contraction, and contributes to cell
membrane formation. Together, the Rough ER and Smooth ER ensure that the cell has the
proteins, fats, energy, and chemical balance it needs to grow, function, and survive.
SECTION-C
V. Which organelle is called Recycling centre ? Give its functions.
Ans: Lysosome The Recycling Centre of the Cell
Imagine your home. Every day, waste is producedold newspapers, broken toys, food
leftovers, and damaged items. If no one cleaned the house, it would soon become dirty and
unhealthy. We usually throw waste into a dustbin or recycle useful materials to keep our
home clean.
The same thing happens inside every living cell. Cells continuously produce waste materials,
old cell parts become damaged, and harmful substances may enter the cell. If this waste is
not removed, the cell cannot function properly.
This is where lysosomes come into action. They work like the cleaning staff, recycling plant,
and garbage disposal system of the cell. Because they break down waste and recycle useful
materials, lysosomes are called the "Recycling Centre of the Cell."
What is a Lysosome?
A lysosome is a small, round, membrane-bound organelle found mainly in animal cells. It
contains many powerful digestive enzymes.
These enzymes can break down:
Waste materials
Worn-out cell parts
Germs like bacteria and viruses
Large food particles
The useful substances released after digestion are reused by the cell, while the remaining
waste is removed.
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Why is Lysosome Called the Recycling Centre?
Lysosomes do much more than destroy waste.
When they digest old or damaged cell parts, many useful molecules such as amino acids,
sugars, and fatty acids are released. Instead of throwing these materials away, the cell uses
them again to build new cell structures.
This process is called recycling, which is why lysosomes are known as the recycling centre of
the cell.
Simple Example:
Imagine an old bicycle.
Metal parts are melted and reused.
Rubber is recycled.
Useful screws and bolts are kept for future use.
Similarly, lysosomes break old cell parts into smaller molecules, and the cell uses these
materials again.
Structure of Lysosome
Lysosomes have several important features:
Small, spherical sacs.
Surrounded by a single membrane.
Filled with nearly 50 different digestive enzymes.
The membrane protects the rest of the cell from these powerful enzymes.
Enzymes work best in an acidic environment inside the lysosome.
Functions of Lysosome
1. Digests Waste Materials
Lysosomes remove unnecessary waste produced during cell activities.
Without lysosomes, waste would keep accumulating and damage the cell.
Example: Removing leftover materials after chemical reactions.
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2. Recycles Old Cell Parts
Old mitochondria, ribosomes, and other worn-out organelles are broken down.
Their useful materials are reused to build new organelles.
This saves both energy and resources.
3. Destroys Harmful Germs
When bacteria or viruses enter the cell, lysosomes surround and digest them.
This helps protect the cell from infection.
They are therefore an important part of the body's defense system.
4. Digests Food Particles
Food particles entering the cell are broken into simpler substances.
These nutrients can then be used for energy and growth.
5. Removes Damaged Organelles
Cells constantly inspect their organelles.
If an organelle becomes damaged or stops working, lysosomes destroy it before it harms the
cell.
6. Helps During Starvation
When food is unavailable, lysosomes digest some non-essential cell materials.
This releases nutrients that help the cell survive until more food becomes available.
7. Helps in Cell Renewal
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By removing old structures and replacing them with new ones, lysosomes help cells stay
healthy and function efficiently.
8. Causes Autolysis (Self-Destruction)
If a cell becomes severely damaged or dies, lysosomes release their enzymes.
These enzymes digest the entire cell.
Because of this, lysosomes are sometimes called the "Suicide Bags of the Cell."
This process prevents damaged cells from harming nearby healthy cells.
Simple Flow Diagram
Old Organelles / Waste / Germs
│
▼
Lysosome
(Digestive enzymes break them down)
│
┌───────────────┐
▼ ▼
Useful Materials Waste
(Reused by Cell) (Removed)
Easy Way to Remember
Everyday Object
Cell Organelle
Recycling Plant
Lysosome
Garbage Collector
Lysosome
Cleaning Worker
Lysosome
Waste Disposal Unit
Lysosome
Key Points for Exams
Organelle: Lysosome
Also Called: Recycling Centre of the Cell
Other Name: Suicide Bag of the Cell
Found Mainly In: Animal cells
Contains: Digestive enzymes
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Main Work: Digests waste, recycles useful materials, destroys germs, removes
damaged organelles, and keeps the cell clean.
Conclusion
Lysosomes are one of the most important organelles in a cell because they act as its
cleaning and recycling system. They digest waste materials, destroy harmful microbes,
remove damaged organelles, and recycle useful substances so the cell can use them again.
This recycling process keeps the cell healthy, efficient, and free from unnecessary waste.
Since they continuously clean and reuse cellular materials, lysosomes are rightly called the
"Recycling Centre of the Cell."
VI. Describe the ultra-structure of ribosome and write its functions.
Ans: Introduction
Imagine a large factory where thousands of different products are made every day. In our
body, every cell is like that factory, and the most important products are proteins. Proteins
help build muscles, repair tissues, make enzymes, hormones, antibodies, and perform
countless other jobs.
But where are these proteins made?
The answer is ribosomes. Ribosomes are often called the "protein factories of the cell."
They are tiny cell organelles found in both prokaryotic (bacteria) and eukaryotic (plants and
animals) cells. Although they are extremely small, they perform one of the most essential
functions necessary for life.
What is a Ribosome?
A ribosome is a small, non-membrane-bound cell organelle made of ribosomal RNA (rRNA)
and proteins. Its main function is to manufacture proteins by joining amino acids according
to the instructions carried by messenger RNA (mRNA).
Ribosomes may be:
Free in the cytoplasm (make proteins used inside the cell)
Attached to the Rough Endoplasmic Reticulum (RER) (make proteins that are
secreted or transported outside the cell)
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Ultra-Structure of Ribosome
The term ultra-structure means the detailed internal structure of a ribosome that can only
be seen with an electron microscope.
Ribosomes are made of two unequal subunits:
Large Subunit
Small Subunit
These two subunits remain separate when not making proteins and join together only
during protein synthesis.
Types of Ribosomes
1. 70S Ribosome (Prokaryotes)
Found in:
Bacteria
Blue-green algae
Mitochondria
Chloroplasts
Composition:
50S Large Subunit
30S Small Subunit
Remember: 50S + 30S = 70S (not 80 because S stands for Svedberg unit, which measures
sedimentation rate rather than simple size.)
2. 80S Ribosome (Eukaryotes)
Found in:
Plants
Animals
Fungi
Protists
Composition:
60S Large Subunit
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40S Small Subunit
Detailed Structure of Each Subunit
Large Subunit
The large subunit contains:
Ribosomal RNA (rRNA)
Ribosomal proteins
Peptidyl transferase enzyme
Function
Joins amino acids together.
Forms peptide bonds.
Helps build the growing protein chain.
Small Subunit
The small subunit contains:
rRNA
Ribosomal proteins
Function
Reads the genetic message on mRNA.
Ensures the correct tRNA enters.
Decodes the genetic information.
Composition of Ribosome
Every ribosome is made of:
1. Ribosomal RNA (rRNA)
Makes up about 60% of the ribosome.
Provides structural support.
Catalyzes peptide bond formation.
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2. Ribosomal Proteins
Make up about 40%.
Stabilize the ribosome.
Help in assembling the ribosome.
Diagram of Ribosome
Ribosome
______________________
| Large Subunit |
|_______________________|
↑
Peptide bond formation
│
Growing Protein Chain
│
-------------------- ← mRNA
A P E
(tRNA)(tRNA)(tRNA)
--------------------
___________________
| Small Subunit |
|___________________|
Labels:
Large Subunit
Small Subunit
mRNA
tRNA
A Site (Aminoacyl site)
P Site (Peptidyl site)
E Site (Exit site)
Important Sites Present on Ribosome
1. A Site (Aminoacyl Site)
New tRNA carrying an amino acid enters here.
2. P Site (Peptidyl Site)
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Holds the growing protein chain.
Peptide bond formation occurs here.
3. E Site (Exit Site)
Empty tRNA leaves the ribosome after donating its amino acid.
Functions of Ribosomes
Ribosomes perform several essential functions:
1. Protein Synthesis
This is the main function of ribosomes.
They join amino acids together to form proteins according to the instructions in mRNA.
2. Formation of Enzymes
Many enzymes are proteins. Ribosomes synthesize these enzymes needed for digestion,
metabolism, and other cellular activities.
3. Cell Growth
New proteins produced by ribosomes help cells grow and develop.
4. Repair of Damaged Cells
When tissues are injured, ribosomes produce repair proteins that help heal damaged cells.
5. Production of Hormones
Several hormones, such as insulin, are proteins synthesized by ribosomes.
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6. Production of Antibodies
Immune cells use ribosomes to make antibodies that protect the body from harmful
microorganisms.
7. Muscle Formation
Muscle fibers are rich in proteins like actin and myosin, both produced by ribosomes.
8. Helps in Cell Division
During cell division, many new proteins are needed. Ribosomes supply these proteins for
successful cell reproduction.
Difference Between 70S and 80S Ribosomes
Feature
70S Ribosome
80S Ribosome
Found in
Prokaryotes
Eukaryotes
Large Subunit
50S
60S
Small Subunit
30S
40S
Size
Smaller
Larger
Examples
Bacteria, mitochondria, chloroplasts
Plant and animal cells
Easy Way to Remember
Think of a ribosome as a protein-making machine in a factory:
mRNA = Instruction manual
tRNA = Delivery truck carrying amino acids
Ribosome = Factory machine
Amino acids = Raw materials
Protein = Finished product
Just as a factory follows instructions to assemble products, the ribosome follows the genetic
code on mRNA to assemble amino acids into proteins.
Conclusion
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Ribosomes are tiny but indispensable organelles found in every living cell. They are
composed of two subunits made of rRNA and proteins, and they work together to translate
genetic information into proteins. Their ultra-structure, including the large and small
subunits and the A, P, and E sites, is specially designed for efficient protein synthesis.
Because proteins are required for growth, repair, metabolism, immunity, and countless
cellular activities, ribosomes are rightly known as the "protein factories of the cell."
Understanding their structure and functions helps explain how cells grow, survive, and carry
out the processes essential for life.
SECTION-D
VII. Define immunity and immune response. Explain briefly different types of immunity.
Ans: Our body is surrounded by millions of tiny organisms every day. Some are harmless,
while others can cause diseases. Yet, we do not fall sick every time because our body has a
powerful defense system called the immune system. This system works like a team of
soldiers guarding a country. Whenever harmful bacteria, viruses, fungi, or parasites enter
the body, these "soldiers" immediately recognize them, fight them, and protect us from
illness.
To understand this topic easily, let us first learn the meaning of immunity and immune
response, and then study the different types of immunity.
What is Immunity?
Immunity is the natural or acquired ability of the body to protect itself from disease-
causing organisms (pathogens) such as bacteria, viruses, fungi, and parasites.
In simple words:
Immunity is the body's shield or defense system that protects us from infections and
diseases.
For example:
When a virus enters your body, your immune system attacks and destroys it.
After recovering from diseases like chickenpox, the body usually becomes immune to
that disease because it "remembers" the virus.
What is an Immune Response?
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An immune response is the reaction of the body's immune system against harmful foreign
substances called antigens.
Simple Definition
Immune response is the process by which the body identifies, attacks, and removes harmful
microorganisms or foreign substances.
Steps of Immune Response
1. Recognition
o The immune system detects harmful germs (antigens).
2. Activation
o White blood cells become active.
3. Attack
o Antibodies and immune cells destroy the invading germs.
4. Memory Formation
o Memory cells remain in the body.
o If the same germ attacks again, the immune system responds much faster.
Diagram of Immune Response
Disease-causing Germ Enters Body
│
▼
Immune System Detects Germ
│
▼
White Blood Cells Become Active
│
▼
Antibodies Attack and Destroy Germs
│
▼
Memory Cells Remain
│
▼
Faster Protection in Future
Types of Immunity
Immunity is mainly divided into two major types:
1. Innate (Natural) Immunity
2. Acquired (Adaptive) Immunity
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Immunity
│
┌─────────────┴─────────────┐
│ │
Innate Immunity Acquired Immunity
(Natural) (Adaptive)
│
┌────────────┴────────────┐
│ │
Active Passive
Immunity Immunity
│ │ │ │
Natural Artificial Natural Artificial
1. Innate (Natural) Immunity
Innate immunity is the protection that we are born with.
It is the body's first line of defense and acts immediately whenever germs enter the body.
Characteristics
Present from birth
Works immediately
Non-specific (attacks all harmful germs)
No memory of previous infections
Examples
Skin prevents germs from entering.
Tears wash away bacteria.
Saliva kills many germs.
Stomach acid destroys harmful microorganisms.
White blood cells eat bacteria (phagocytosis).
Example
If dust containing bacteria enters your nose, mucus traps the bacteria before they reach the
lungs.
2. Acquired (Adaptive) Immunity
Acquired immunity develops after birth when the body is exposed to diseases or receives
vaccines.
Unlike innate immunity, it is specific and remembers previous infections.
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Characteristics
Develops after birth
Specific to particular germs
Forms memory cells
Gives long-lasting protection
Example:
After recovering from measles, the body usually develops immunity against measles for
many years.
Types of Acquired Immunity
Acquired immunity is divided into two types:
A. Active Immunity
Active immunity develops when the person's own immune system produces antibodies.
It usually lasts for a long time.
Types of Active Immunity
(i) Natural Active Immunity
Occurs after recovering from an infection.
Example:
Chickenpox
Measles
The body naturally produces antibodies.
(ii) Artificial Active Immunity
Occurs after vaccination.
Vaccines contain weakened or inactive germs that stimulate the immune system without
causing serious disease.
Examples:
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Polio vaccine
COVID-19 vaccine
Hepatitis B vaccine
BCG vaccine
B. Passive Immunity
Passive immunity occurs when a person receives ready-made antibodies from another
source.
The body does not produce these antibodies itself.
It provides immediate but temporary protection.
Types of Passive Immunity
(i) Natural Passive Immunity
Antibodies pass from the mother to the baby.
Examples:
Through the placenta during pregnancy.
Through breast milk after birth.
These antibodies protect newborn babies during the first few months of life.
(ii) Artificial Passive Immunity
Ready-made antibodies are given through injections.
Examples:
Anti-rabies injection
Anti-snake venom
Tetanus immunoglobulin
These provide immediate protection but only for a short period.
Difference Between Innate and Acquired Immunity
Innate Immunity
Acquired Immunity
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Present from birth
Develops after birth
Acts immediately
Takes time to develop
Non-specific
Specific to a particular germ
No memory
Has memory cells
Same response every time
Faster response after repeated exposure
Importance of Immunity
Immunity is essential because it:
Protects the body from harmful microorganisms.
Prevents infections and diseases.
Helps the body recover faster after illness.
Reduces the severity of many diseases.
Makes vaccination effective by creating memory cells.
Improves overall health and survival.
Conclusion
Immunity is the body's natural defense mechanism that protects us from disease-causing
organisms. An immune response is the process by which the immune system detects
harmful germs, destroys them, and remembers them for future protection. Immunity is of
two main types: Innate (Natural) Immunity, which provides immediate protection from
birth, and Acquired (Adaptive) Immunity, which develops after infection or vaccination.
Acquired immunity is further divided into Active Immunity, where the body produces its
own antibodies, and Passive Immunity, where ready-made antibodies are received from
another source. Together, these defense mechanisms keep our body healthy and protect us
from many infectious diseases throughout life.
VIII. Differentiate between chormatin and chromosome. Describe nuclear envelop and
structure of its pores.
Ans: The nucleus is the control center of the cell because it stores the genetic material
(DNA) and controls all cellular activities such as growth, metabolism, reproduction, and
protein synthesis. Inside the nucleus are several important structures, including chromatin,
chromosomes, the nuclear envelope, and nuclear pores. To understand how the nucleus
works, we first need to know the difference between chromatin and chromosomes, and
then study the nuclear envelope and its pores.
1. Difference Between Chromatin and Chromosome
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Although chromatin and chromosomes are made of the same material (DNA and proteins),
they differ in their structure, appearance, and function.
Chromatin
Chromosome
Chromatin is a thin, long, thread-like
network of DNA and proteins.
Chromosomes are short, thick, condensed
rod-like structures.
Found in the nucleus during the resting
stage (Interphase).
Visible during cell division (Mitosis and
Meiosis).
DNA is loosely packed.
DNA is tightly packed.
Not clearly visible under a light microscope.
Easily visible under a light microscope
during cell division.
Helps in protein synthesis and normal cell
activities.
Helps in equal distribution of genetic
material to daughter cells.
Appears like a tangled thread.
Appears like an "X"-shaped or rod-shaped
structure.
Simple Analogy
Imagine you have a long rope.
When the rope is loosely spread on the floor, it looks like chromatin.
When you roll and tie the rope tightly, it becomes compact, just like a chromosome.
So,
Chromatin = Loose DNA
Chromosome = Condensed DNA
Chromatin
Chromatin is made of:
DNA
Histone proteins
Non-histone proteins
The DNA wraps around histone proteins, forming small bead-like structures called
nucleosomes. These nucleosomes coil together to form chromatin fibers.
Functions of Chromatin
Stores genetic information.
Controls protein synthesis.
Regulates gene expression.
Converts into chromosomes during cell division.
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Chromosome
When a cell prepares to divide, chromatin becomes highly condensed and forms
chromosomes.
Each chromosome contains:
One DNA molecule
Proteins
Genes
A duplicated chromosome has:
Two sister chromatids
Centromere
Telomeres at both ends
Functions of Chromosomes
Carry hereditary information.
Transfer genes from parents to offspring.
Ensure equal distribution of DNA during cell division.
Control inherited characteristics.
Diagram: Chromatin and Chromosome
Chromatin (Resting Cell)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~ DNA Thread Network ~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
↓ Cell Division
Chromosome
\ /
\ /
\ /
||
/ \
/ \
/ \
2. Nuclear Envelope
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The nuclear envelope is a double-layered membrane that surrounds the nucleus.
It separates the nucleus from the cytoplasm and protects the genetic material.
It is also called the nuclear membrane.
The space between the two membranes is known as the perinuclear space.
Structure of Nuclear Envelope
The nuclear envelope consists of:
1. Outer Membrane
Faces the cytoplasm.
Connected with the rough endoplasmic reticulum (RER).
May contain ribosomes.
2. Inner Membrane
Faces the nucleoplasm.
Attached to a protein layer called the nuclear lamina.
Gives support to the nucleus.
3. Perinuclear Space
Narrow space between the inner and outer membranes.
Usually about 2040 nm wide.
4. Nuclear Pores
Many tiny openings are present in the nuclear envelope.
These openings are called nuclear pores.
They allow materials to move between the nucleus and cytoplasm.
Functions of Nuclear Envelope
Protects DNA from damage.
Separates nuclear contents from the cytoplasm.
Maintains the shape of the nucleus.
Controls movement of molecules through nuclear pores.
Helps organize chromatin.
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3. Structure of Nuclear Pores
The nuclear envelope is not completely closed.
It contains thousands of tiny openings called nuclear pores.
Each pore is filled by a large protein structure called the Nuclear Pore Complex (NPC).
The NPC is one of the largest protein complexes in the cell and acts like a security gate,
allowing only the correct molecules to enter or leave the nucleus.
Parts of a Nuclear Pore
1. Cytoplasmic Ring
Located on the cytoplasm side.
Helps recognize incoming molecules.
2. Central Channel
Main passage through which molecules move.
Small molecules pass freely.
Large molecules require transport proteins.
3. Nuclear Ring
Faces the inside of the nucleus.
Supports the pore structure.
4. Nuclear Basket
Basket-like protein structure extending into the nucleus.
Helps regulate transport and gene activity.
5. Cytoplasmic Filaments
Hair-like projections extending into the cytoplasm.
Capture proteins that need to enter the nucleus.
Functions of Nuclear Pores
Nuclear pores regulate the movement of substances between the nucleus and cytoplasm.
Materials entering the nucleus
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Proteins
DNA polymerase
RNA polymerase
Histone proteins
Enzymes
Materials leaving the nucleus
mRNA
tRNA
Ribosomal subunits
Regulatory proteins
Thus, nuclear pores ensure that only the right molecules move in and out of the nucleus,
maintaining proper cell function.
Diagram of Nuclear Envelope and Nuclear Pore
Cytoplasm
↑
Cytoplasmic Filaments
|
==================================== Outer Membrane
○ ○ ○ ○ ○
| Nuclear Pores |
------------------------------------ Perinuclear Space
==================================== Inner Membrane
Nuclear Basket
|
Nucleoplasm
Easy Memory Trick
Chromatin = Loose DNA = Resting Cell
Chromosome = Condensed DNA = Cell Division
Nuclear Envelope = Double protective membrane
Nuclear Pores = Gatekeepers controlling transport
Conclusion
Chromatin and chromosomes are two forms of the same genetic material. Chromatin is the
loose, thread-like form present during the normal functioning of the cell, while
chromosomes are the tightly packed form that appears during cell division to ensure
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accurate distribution of DNA. The nuclear envelope is a protective double membrane
surrounding the nucleus, and its nuclear pores act as highly selective gateways, regulating
the movement of proteins, RNA, and other molecules between the nucleus and the
cytoplasm. Together, these structures protect the cell's genetic information and ensure that
all cellular activities are properly controlled.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
have suggestions, feel free to share your feedback.
