Online Self Test
Learn & Practice Quizzes & Challenges Competitive Exams
 

The Fundamental Unit of Life – CBSE NCERT Study Resources

Previous ChapterNext Chapter
Previous Chapter Next Chapter
The Fundamental Unit of Life

Study Materials

9th

9th - Science

The Fundamental Unit of Life

Jump to Question Sets

The Fundamental Unit of Life

Chapter Overview

This chapter introduces the basic structural and functional unit of life, the cell. It covers the discovery of the cell, the cell theory, types of cells, cell organelles, and their functions. The chapter also explains the differences between plant and animal cells and the concept of cell division.

Cell: The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.

Discovery of the Cell

The cell was first discovered by Robert Hooke in 1665 when he observed a thin slice of cork under a microscope. He noticed small compartments resembling honeycomb structures, which he called 'cells'. Later, Anton van Leeuwenhoek observed living cells for the first time.

Cell Theory

The cell theory, formulated by Schleiden and Schwann, states:

  • All living organisms are composed of cells.
  • The cell is the basic unit of life.
  • All cells arise from pre-existing cells.

Types of Cells

Cells can be classified into two types based on their structure:

  • Prokaryotic Cells: Cells without a well-defined nucleus or membrane-bound organelles (e.g., bacteria).
  • Eukaryotic Cells: Cells with a well-defined nucleus and membrane-bound organelles (e.g., plant and animal cells).

Cell Organelles and Their Functions

Eukaryotic cells contain various organelles, each with specific functions:

  • Cell Membrane: A selectively permeable membrane that regulates the entry and exit of substances.
  • Nucleus: Controls all cellular activities and contains genetic material (DNA).
  • Cytoplasm: A jelly-like substance where organelles are suspended.
  • Mitochondria: Powerhouse of the cell, produces energy (ATP).
  • Endoplasmic Reticulum (ER): Involved in protein and lipid synthesis.
  • Golgi Apparatus: Packages and transports materials within the cell.
  • Lysosomes: Contain digestive enzymes to break down waste.
  • Vacuoles: Storage sacs for water, nutrients, and waste.
  • Plastids (in plant cells): Includes chloroplasts for photosynthesis.
  • Cell Wall (in plant cells): Provides rigidity and protection.

Differences Between Plant and Animal Cells

Feature Plant Cell Animal Cell
Cell Wall Present Absent
Plastids Present Absent
Vacuole Large and central Small and numerous

Cell Division

Cell division is the process by which a parent cell divides into two or more daughter cells. It is essential for growth, repair, and reproduction. There are two types of cell division:

  • Mitosis: Produces two identical daughter cells with the same number of chromosomes.
  • Meiosis: Produces four daughter cells with half the number of chromosomes (gametes).

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
What is the basic structural and functional unit of life?
Answer:

The cell is the basic unit of life.

Question 2:
Name the scientist who discovered the cell.
Answer:

Robert Hooke discovered the cell.

Question 3:
Which cell organelle is called the powerhouse of the cell?
Answer:

The mitochondria is the powerhouse.

Question 4:
What is the function of the cell membrane?
Answer:

It controls entry and exit of substances.

Question 5:
Which cell component contains chromosomes?
Answer:

The nucleus contains chromosomes.

Question 6:
Name the process by which Amoeba obtains food.
Answer:

Amoeba uses endocytosis for feeding.

Question 7:
What is the main difference between prokaryotic and eukaryotic cells?
Answer:

Prokaryotes lack a nucleus.

Question 8:
Which organelle helps in protein synthesis?
Answer:

Ribosomes help in protein synthesis.

Question 9:
What is the function of lysosomes?
Answer:

They digest cellular waste.

Question 10:
Name the fluid present inside the cell membrane.
Answer:

Cytoplasm fills the cell.

Question 11:
Which cell structure provides rigidity to plant cells?
Answer:

The cell wall provides rigidity.

Question 12:
What is the role of chloroplasts?
Answer:

They perform photosynthesis.

Question 13:
Name the process by which cells divide.
Answer:

Cells divide by mitosis.

Question 14:
What is plasmolysis?
Answer:

Shrinking of cytoplasm from the cell wall.

Question 15:
Name the scientist who discovered the cell.
Answer:
Robert Hooke discovered the cell in 1665 while observing a thin slice of cork under a microscope.
Question 16:
Define plasmolysis.
Answer:

Plasmolysis is the process where the cytoplasm shrinks away from the cell wall due to water loss in a hypertonic solution. This occurs in plant cells when they lose water through osmosis.

Question 17:
Which organelle is known as the powerhouse of the cell?
Answer:

The mitochondrion is called the powerhouse of the cell because it generates energy (ATP) through cellular respiration.

Question 18:
What is the role of ribosomes in a cell?
Answer:

Ribosomes are responsible for protein synthesis. They read the genetic code from mRNA and assemble amino acids into proteins.

Question 19:
Differentiate between prokaryotic and eukaryotic cells.
Answer:
  • Prokaryotic cells lack a nucleus and membrane-bound organelles (e.g., bacteria).
  • Eukaryotic cells have a well-defined nucleus and membrane-bound organelles (e.g., plant and animal cells).
Question 20:
Why is the nucleus called the control center of the cell?
Answer:

The nucleus contains genetic material (DNA) that regulates all cellular activities, including growth, metabolism, and reproduction, making it the control center.

Question 21:
What happens to a cell when placed in a hypotonic solution?
Answer:

In a hypotonic solution, water enters the cell by osmosis, causing it to swell. Animal cells may burst (lysis), while plant cells become turgid due to their rigid cell wall.

Question 22:
Name the process by which amoeba obtains its food.
Answer:

Amoeba obtains food through phagocytosis, a type of endocytosis where the cell engulfs solid particles by forming pseudopodia.

Question 23:
Why are vacuoles larger in plant cells compared to animal cells?
Answer:

Plant cells have larger vacuoles to store water, nutrients, and waste products, helping maintain turgor pressure and structural support.

Question 24:
What is the significance of chromosomes?
Answer:

Chromosomes carry genetic information in the form of DNA, ensuring inheritance of traits and proper functioning of the cell through protein synthesis.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
What is the basic structural and functional unit of life?
Answer:

The cell is the basic structural and functional unit of life. Cells are the building blocks of all living organisms, performing essential functions like growth, reproduction, and energy production.

Question 2:
Name the scientist who discovered the cell and in which year?
Answer:

Robert Hooke discovered the cell in 1665. He observed cork cells under a primitive microscope and coined the term cell.

Question 3:
Differentiate between prokaryotic and eukaryotic cells.
Answer:
  • Prokaryotic cells lack a nucleus and membrane-bound organelles (e.g., bacteria).
  • Eukaryotic cells have a well-defined nucleus and membrane-bound organelles (e.g., plant and animal cells).
Question 4:
Why is the mitochondria called the powerhouse of the cell?
Answer:

Mitochondria are called the powerhouse of the cell because they generate ATP (energy currency) through cellular respiration.

Question 5:
What is the role of chloroplasts in plant cells?
Answer:

Chloroplasts contain chlorophyll and are responsible for photosynthesis, converting sunlight into chemical energy (glucose).

Question 6:
Name two cell organelles that contain their own DNA.
Answer:

Mitochondria and chloroplasts contain their own DNA, supporting the endosymbiotic theory.

Question 7:
What is osmosis? Give one example.
Answer:

Osmosis is the movement of water molecules across a semi-permeable membrane from a dilute to a concentrated solution.
Example: Absorption of water by plant roots.

Question 8:
Why do plant cells have a large central vacuole?
Answer:

The central vacuole stores water, nutrients, and waste, maintaining turgor pressure for structural support in plants.

Question 9:
What happens when a plant cell is placed in a hypertonic solution?
Answer:

Water moves out of the cell, causing plasmolysis (shrinkage of cytoplasm away from the cell wall).

Question 10:
Name the process by which Amoeba obtains food.
Answer:

Amoeba obtains food through phagocytosis, where it engulfs food particles using pseudopodia.

Question 11:
What is the function of the cell membrane in a cell?
Answer:

The cell membrane acts as a selectively permeable barrier, controlling the movement of substances in and out of the cell. It allows nutrients to enter and waste products to exit while maintaining the cell's internal environment.

Question 12:
Name the organelle known as the powerhouse of the cell and state its function.
Answer:

The mitochondrion is called the powerhouse of the cell. It generates ATP (adenosine triphosphate) through cellular respiration, providing energy for various cellular activities.

Question 13:
Differentiate between prokaryotic and eukaryotic cells based on nucleus presence.
Answer:

Prokaryotic cells lack a true nucleus; their genetic material floats freely in the cytoplasm. Eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane.

Question 14:
Why is the Golgi apparatus important in a cell?
Answer:

The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or use within the cell. It also forms lysosomes, which help in digestion.

Question 15:
What is the role of ribosomes in protein synthesis?
Answer:

Ribosomes are the sites of protein synthesis. They read mRNA and assemble amino acids into polypeptide chains, forming proteins essential for cell functions.

Question 16:
Explain why plastids are found only in plant cells.
Answer:

Plastids, like chloroplasts, are specialized for photosynthesis, storing pigments or starch. Since animals do not perform photosynthesis, they lack plastids.

Question 17:
Define osmosis and give one example of its importance in plants.
Answer:

Osmosis is the movement of water molecules across a selectively permeable membrane from a dilute to a concentrated solution. In plants, it helps in water absorption by roots.

Question 18:
List two functions of the endoplasmic reticulum.
Answer:
  • Rough ER synthesizes proteins due to attached ribosomes.
  • Smooth ER detoxifies chemicals and produces lipids.
Question 19:
How does an amoeba obtain its food?
Answer:

An amoeba uses pseudopodia (false feet) to engulf food particles via phagocytosis, forming a food vacuole where digestion occurs.

Question 20:
Why are lysosomes called 'suicide bags' of the cell?
Answer:

Lysosomes contain digestive enzymes that break down worn-out organelles or pathogens. If ruptured, they can digest the cell itself, hence the name.

Question 21:
Name the scientist who first observed cells under a microscope.
Answer:

Robert Hooke was the first scientist to observe cells in 1665.
He examined a thin slice of cork under a microscope and noticed tiny compartments, which he called cells.

Question 22:
Define osmosis with an example.
Answer:

Osmosis is the movement of water molecules from a region of higher concentration to lower concentration through a semi-permeable membrane.
Example: Absorption of water by plant roots from the soil.

Question 23:
What is the function of ribosomes?
Answer:

Ribosomes are responsible for protein synthesis.
They read mRNA and assemble amino acids into polypeptide chains.

Question 24:
Why are lysosomes known as suicide bags?
Answer:

Lysosomes contain digestive enzymes that break down worn-out organelles or pathogens.
During cell damage, they release enzymes, causing self-destruction, hence called suicide bags.

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Differentiate between prokaryotic and eukaryotic cells based on their nucleus.
Answer:

The key difference lies in the structure of the nucleus:

  • Prokaryotic cells lack a true nucleus. Their genetic material (DNA) is scattered in the cytoplasm without a nuclear membrane.
  • Eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane, which separates the genetic material from the cytoplasm.

This difference makes eukaryotic cells more complex and organized compared to prokaryotic cells.

Question 2:
Why are mitochondria called the 'powerhouse of the cell'?
Answer:

Mitochondria are called the powerhouse of the cell because they generate ATP (Adenosine Triphosphate), the energy currency of the cell. Here's how:
1. They perform cellular respiration, breaking down glucose.
2. This process releases energy stored in ATP molecules.
3. The energy is used for various cellular activities.

Mitochondria have their own DNA and ribosomes, suggesting they might have evolved from independent organisms.

Question 3:
Explain the role of lysosomes in a cell.
Answer:

Lysosomes are membrane-bound organelles containing digestive enzymes. Their roles include:
1. Digesting worn-out cell parts, foreign particles, and pathogens.
2. Breaking down large molecules into simpler ones for reuse (autophagy).
3. Acting as the cell's waste disposal system.

They are also called suicidal bags because, if ruptured, their enzymes can digest the entire cell.

Question 4:
What is plasmolysis? Describe its significance.
Answer:

Plasmolysis is the shrinkage of the cytoplasm away from the cell wall when a plant cell loses water in a hypertonic solution.
Significance:
1. It helps in understanding osmosis and water movement in cells.
2. Farmers use this concept to prevent excessive fertilizer use, which can cause plasmolysis and harm crops.
3. It demonstrates the importance of turgor pressure in maintaining plant rigidity.

Question 5:
What is plasmolysis? Describe a situation where it occurs.
Answer:

Plasmolysis is the shrinkage of cytoplasm away from the cell wall due to water loss in a hypertonic solution.
For example, when a plant cell is placed in a concentrated salt solution, water moves out, causing the cell membrane to detach from the cell wall.

Question 6:
How does an amoeba obtain its food? Explain the process.
Answer:

An amoeba obtains food through phagocytosis, a type of endocytosis.
It extends pseudopodia (false feet) to surround and engulf food particles.
The food is then enclosed in a food vacuole, where digestive enzymes break it down for absorption.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the structure and functions of a plasma membrane with reference to its selective permeability.
Answer:
Concept Overview

The plasma membrane is a thin, flexible barrier made of lipids and proteins. It controls the movement of substances in and out of the cell.

Process Explanation

Due to its selective permeability, it allows only certain molecules (like oxygen) to pass while blocking others (like large proteins). Our textbook shows how it maintains cell homeostasis.

Real-world Application

In dialysis, a semi-permeable membrane mimics the plasma membrane to filter waste from blood.

Question 2:
Describe the role of lysosomes as the suicidal bags of the cell with an example.
Answer:
Concept Overview

Lysosomes are membrane-bound organelles containing digestive enzymes. They break down waste and foreign particles.

Process Explanation

When a cell is damaged, lysosomes burst and digest their own cell, earning the name suicidal bags. Our textbook explains this in tadpole tail degeneration.

Real-world Application

In autoimmune diseases, lysosomes mistakenly attack healthy cells, causing tissue damage.

Question 3:
Compare prokaryotic and eukaryotic cells based on their nucleus and organelles.
Answer:
Concept Overview

Prokaryotic cells lack a true nucleus, while eukaryotic cells have a well-defined nucleus.

Process Explanation

Prokaryotes (e.g., bacteria) have free-floating DNA, whereas eukaryotes (e.g., plant cells) store DNA in the nucleus. Our textbook highlights mitochondria as eukaryotic organelles absent in prokaryotes.

Real-world Application

Antibiotics target prokaryotic ribosomes, sparing human (eukaryotic) cells.

Question 4:
Explain how diffusion and osmosis help in the absorption of water by roots.
Answer:
Concept Overview

Diffusion moves particles from high to low concentration, while osmosis is water diffusion across a membrane.

Process Explanation

Root hair cells absorb water via osmosis due to higher soil water concentration. Our textbook shows mineral uptake through diffusion.

Real-world Application

Wilting plants recover when watered as osmosis restores cell turgidity.

Question 5:
Illustrate the importance of Golgi apparatus in protein packaging with a NCERT example.
Answer:
Concept Overview

The Golgi apparatus modifies, sorts, and packages proteins for secretion.

Process Explanation

It receives proteins from the ER, tags them, and dispatches them to target sites. Our textbook describes its role in lysosome formation.

Real-world Application

Pancreatic cells use Golgi to package digestive enzymes like amylase.

Question 6:
Explain the structure and functions of plasma membrane with reference to its selective permeability.
Answer:
Concept Overview

The plasma membrane is a thin, flexible barrier made of lipids and proteins. It controls the movement of substances in and out of the cell.

Process Explanation

Due to its selective permeability, it allows only certain molecules (like oxygen) to pass while blocking others (like large proteins). Our textbook shows how this maintains cell homeostasis.

Real-world Application

In dialysis, a semi-permeable membrane mimics this function to filter blood.

[Diagram: Fluid mosaic model of plasma membrane]
Question 7:
Describe the role of lysosomes as suicide bags of the cell with an example.
Answer:
Concept Overview

Lysosomes are membrane-bound organelles containing digestive enzymes that break down waste.

Process Explanation

During cellular damage, they burst and digest their own cell, earning the name suicide bags. Our textbook mentions tadpole tail disappearance during metamorphosis.

Real-world Application

In autoimmune diseases, this process sometimes malfunctions, causing cell damage.

[Diagram: Lysosome digesting cellular debris]
Question 8:
Compare plant cell and animal cell based on three structural differences.
Answer:
Concept Overview

While both have nuclei and organelles, key differences exist.

Process Explanation
  • Plant cells have cell walls (absent in animals)
  • Chloroplasts present only in plants
  • Large vacuoles in plants vs small ones in animals
Real-world Application

This explains why plant cells maintain rigid shapes (like in NCERT's onion peel experiment) while animal cells are flexible.

[Diagram: Side-by-side comparison]
Question 9:
Explain how diffusion and osmosis help in gaseous exchange in plants.
Answer:
Concept Overview

Diffusion moves gases while osmosis regulates water balance during this process.

Process Explanation

CO₂ enters leaves via diffusion through stomata (shown in NCERT's leaf experiment). Water moves by osmosis to maintain turgidity for opening stomata.

Real-world Application

This explains why plants wilt in drought - lack of water disrupts osmosis and closes stomata.

[Diagram: Stomatal opening showing gas exchange]
Question 10:
Why is the mitochondria called the powerhouse of the cell? Support with one NCERT activity.
Answer:
Concept Overview

Mitochondria generate ATP, the cell's energy currency, through respiration.

Process Explanation

Their folded inner membrane (cristae) increases surface area for ATP production. Our textbook's activity shows more mitochondria in muscle cells which need constant energy.

Real-world Application

This explains why athletes train at high altitudes - to increase mitochondrial efficiency for oxygen use.

[Diagram: Mitochondrial structure with labeled cristae]
Question 11:
Explain the structure and functions of a plasma membrane in a cell. How does it maintain the homeostasis of the cell?
Answer:

The plasma membrane is a thin, flexible barrier that surrounds the cell and separates its internal environment from the external surroundings. It is primarily composed of phospholipids, proteins, and carbohydrates arranged in a fluid mosaic model.

Structure:
The plasma membrane consists of:

  • A phospholipid bilayer with hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails facing inward.
  • Proteins embedded in the bilayer, which act as channels, carriers, or receptors.
  • Cholesterol molecules that provide stability and flexibility.
  • Carbohydrate chains attached to proteins or lipids, forming glycoproteins or glycolipids, which help in cell recognition.

Functions:

  • Selective permeability: It regulates the entry and exit of substances, allowing only specific molecules to pass.
  • Protection: It shields the cell from external threats.
  • Cell signaling: Proteins in the membrane help in communication between cells.
  • Structural support: It maintains the shape of the cell.

Homeostasis:
The plasma membrane maintains homeostasis by:

  • Controlling the movement of nutrients and waste products via diffusion, osmosis, and active transport.
  • Preventing harmful substances from entering the cell.
  • Balancing water and ion concentrations to keep the cell stable.

Thus, the plasma membrane is vital for the survival and proper functioning of the cell.

Question 12:
Differentiate between prokaryotic and eukaryotic cells based on their structure and organization. Provide examples of each.
Answer:

Prokaryotic and eukaryotic cells differ significantly in their structure and organization. Below is a detailed comparison:

1. Cell Type:

  • Prokaryotic Cells: Primitive, simpler cells without a defined nucleus.
  • Eukaryotic Cells: Advanced cells with a well-defined nucleus.

2. Nucleus:

  • Prokaryotic: Genetic material (DNA) floats freely in the cytoplasm (no nuclear membrane).
  • Eukaryotic: DNA is enclosed in a nuclear membrane.

3. Organelles:

  • Prokaryotic: Lack membrane-bound organelles (e.g., mitochondria, Golgi apparatus).
  • Eukaryotic: Contain membrane-bound organelles.

4. Size:

  • Prokaryotic: Generally smaller (1-10 micrometers).
  • Eukaryotic: Larger (10-100 micrometers).

5. Examples:

  • Prokaryotic: Bacteria (e.g., E. coli), Archaea.
  • Eukaryotic: Plant cells, animal cells (e.g., human cheek cells).

Eukaryotic cells are more complex due to compartmentalization, allowing specialized functions.

Question 13:
Explain the structure and functions of a plasma membrane with a well-labeled diagram. How does it maintain the homeostasis of the cell?
Answer:

The plasma membrane is a selectively permeable barrier that surrounds the cell, composed of a phospholipid bilayer with embedded proteins. Here’s its structure and functions:

  • Structure:
    1. Phospholipid bilayer: Forms the basic framework with hydrophilic (water-loving) heads facing outward and hydrophobic (water-hating) tails inward.
    2. Proteins: Integral proteins span the membrane, while peripheral proteins attach superficially for transport and signaling.
    3. Cholesterol: Provides stability and fluidity.
    4. Carbohydrates: Attached to proteins/lipids for cell recognition.
  • Functions:
    1. Selective permeability: Allows essential substances (like oxygen, glucose) in and waste (like CO2) out.
    2. Cell signaling: Proteins act as receptors for hormones.
    3. Protection: Shields the cell from external damage.

Homeostasis maintenance: The plasma membrane regulates the internal environment by:
1. Osmosis: Balances water content.
2. Active/passive transport: Controls ion and nutrient levels.
3. Endocytosis/exocytosis: Engulfs or expels materials as needed.

Diagram requirement: A labeled sketch showing the phospholipid bilayer, proteins, cholesterol, and carbohydrates.

Question 14:
Compare and contrast prokaryotic and eukaryotic cells based on their structure, organelles, and genetic material. Provide examples of each.
Answer:

Prokaryotic and eukaryotic cells differ significantly in complexity and organization:

  • Prokaryotic Cells:
    1. Structure: Smaller (1-10 µm), lack membrane-bound organelles.
    2. Genetic Material: Single circular DNA in the nucleoid region; no nucleus.
    3. Organelles: Only ribosomes (70S) present.
    4. Examples: Bacteria (e.g., E. coli), Archaea.
  • Eukaryotic Cells:
    1. Structure: Larger (10-100 µm), have a defined nucleus and organelles.
    2. Genetic Material: Linear DNA enclosed in a nuclear membrane.
    3. Organelles: Mitochondria, Golgi apparatus, ER, etc.; ribosomes (80S).
    4. Examples: Plant cells (e.g., onion peel), animal cells (e.g., human cheek cells).

Key Contrasts:
1. Nucleus: Absent in prokaryotes, present in eukaryotes.
2. Cell Division: Prokaryotes divide by binary fission; eukaryotes by mitosis/meiosis.
3. Complexity: Eukaryotes are more advanced with compartmentalized functions.

Similarity: Both have a plasma membrane, cytoplasm, and ribosomes for protein synthesis.

Question 15:
Explain the structure and functions of a plasma membrane with a labeled diagram. How does it maintain the selective permeability of the cell?
Answer:

The plasma membrane is a thin, flexible barrier surrounding the cell, composed of a phospholipid bilayer with embedded proteins. Its structure includes:

  • Phospholipids: Form the basic framework with hydrophilic heads facing outward and hydrophobic tails inward.
  • Proteins: Act as channels, receptors, or enzymes for transport and signaling.
  • Cholesterol: Provides stability to the membrane.
  • Carbohydrates: Attached to proteins/lipids for cell recognition.

Functions:

  • Protects the cell and maintains its shape.
  • Regulates the entry/exit of substances (selective permeability).
  • Facilitates cell communication via receptor proteins.

Selective permeability is maintained by:


1. Size of molecules: Small molecules (e.g., oxygen) diffuse freely, while large ones require proteins.
2. Charge: Non-polar molecules pass easily; polar/charged ones need assistance.
3. Protein channels/carriers: Enable active/passive transport of specific substances.

A labeled diagram would show the bilayer, proteins, cholesterol, and carbohydrates.

Question 16:
Compare and contrast plant and animal cells based on their organelles and functions. Support your answer with a table.
Answer:

Plant and animal cells share common organelles like the nucleus, mitochondria, and Golgi apparatus, but differ in key aspects:


Comparison Table:
FeaturePlant CellAnimal Cell
Cell WallPresent (cellulose)Absent
ChloroplastsPresent (for photosynthesis)Absent
VacuoleLarge, centralSmall, temporary
LysosomesRareCommon
ShapeFixed (rectangular)Irregular

Key Differences:

  • Plant cells store energy as starch; animal cells store glycogen.
  • Plant cells lack centrioles (except in lower plants), while animal cells have them for cell division.
  • Plant cells rely on turgor pressure for support; animal cells use cytoskeleton.
Question 17:
Explain the structure and functions of a plant cell with a well-labelled diagram. Highlight the differences between a plant cell and an animal cell.
Answer:

The plant cell is a eukaryotic cell with a distinct structure that enables it to perform specialized functions. Below is a detailed explanation along with key differences from an animal cell:


Structure of a Plant Cell:

  • Cell Wall: A rigid outer layer made of cellulose, providing structural support and protection.
  • Cell Membrane: A semi-permeable membrane inside the cell wall that regulates the movement of substances.
  • Nucleus: Contains DNA and controls cellular activities.
  • Cytoplasm: A jelly-like substance where organelles are suspended.
  • Chloroplasts: Contain chlorophyll for photosynthesis, converting sunlight into energy.
  • Mitochondria: Powerhouse of the cell, producing ATP through respiration.
  • Vacuole: A large, central storage space for water, nutrients, and waste.
  • Golgi Apparatus: Modifies and packages proteins and lipids.
  • Endoplasmic Reticulum (ER): Rough ER (with ribosomes) synthesizes proteins, while smooth ER aids in lipid synthesis.

Differences Between Plant and Animal Cells:

  • Cell Wall: Present in plant cells, absent in animal cells.
  • Chloroplasts: Found in plant cells for photosynthesis; absent in animal cells.
  • Vacuole: Large and central in plant cells; small or absent in animal cells.
  • Shape: Plant cells are rigid and rectangular; animal cells are flexible and round.

Diagram: (Draw a well-labelled diagram of a plant cell, highlighting all the above structures.)


Value-Added Information: Plant cells also contain plasmodesmata, tiny channels that allow communication between adjacent cells, which animal cells lack. This adaptation helps in the transport of nutrients and signals.

Question 18:
Explain the structure and functions of a plasma membrane in a cell. How does it maintain the homeostasis of the cell? Support your answer with a labeled diagram.
Answer:

The plasma membrane is a semi-permeable barrier that surrounds the cell, separating its internal environment from the external surroundings. It is primarily composed of phospholipids, proteins, and carbohydrates arranged in a fluid mosaic model.

Structure:
The phospholipids form a bilayer with hydrophilic (water-loving) heads facing outward and hydrophobic (water-hating) tails facing inward. Proteins are embedded in the bilayer, acting as channels or pumps for transport. Cholesterol provides stability, and carbohydrates on the outer surface help in cell recognition.

Functions:

  • Selective permeability: Allows only specific substances to enter or exit the cell.
  • Protection: Shields the cell from external threats.
  • Cell signaling: Proteins act as receptors for communication.
  • Transport: Facilitates active and passive transport of molecules.

Maintaining Homeostasis:
The plasma membrane regulates the movement of substances to maintain a stable internal environment. For example:
- Osmosis: Balances water levels.
- Diffusion: Ensures nutrients enter and waste exits.
- Active transport: Pumps ions against concentration gradients.

Diagram: (A labeled sketch should show the phospholipid bilayer, proteins, cholesterol, and carbohydrate chains with clear annotations.)

Value-added: The membrane's flexibility allows cells to change shape (e.g., red blood cells squeezing through capillaries), and its repair mechanisms prevent leaks, ensuring cell survival.

Question 19:
Explain the structure and functions of a plasma membrane in a cell. How does it maintain the homeostasis of the cell?
Answer:

The plasma membrane is a thin, flexible barrier surrounding the cell, made up of a phospholipid bilayer with embedded proteins. It plays a crucial role in protecting the cell and regulating the movement of substances in and out.

Structure:
1. The membrane consists of two layers of phospholipids, where the hydrophilic (water-loving) heads face outward and the hydrophobic (water-hating) tails face inward.
2. Proteins are scattered throughout the membrane, acting as channels or pumps for transport.
3. Cholesterol molecules provide stability to the membrane.

Functions:
1. Selective Permeability: It allows only specific molecules (like oxygen, glucose) to pass while blocking others (like large ions).
2. Cell Signaling: Proteins in the membrane help cells communicate with their environment.
3. Protection: It acts as a barrier against harmful substances.

Maintaining Homeostasis:
The plasma membrane ensures a stable internal environment by:
1. Osmosis: Regulating water balance to prevent cell bursting or shrinking.
2. Active Transport: Using energy (ATP) to move substances against their concentration gradient.
3. Diffusion: Allowing passive movement of small molecules to maintain equilibrium.

Thus, the plasma membrane is vital for the survival and proper functioning of the cell.

Question 20:
Explain the structure and functions of a plant cell with a well-labeled diagram. Highlight the roles of cell wall, chloroplast, and vacuole.
Answer:

The plant cell is a eukaryotic cell with a distinct structure that enables it to perform specialized functions. Below is a detailed explanation along with a diagram (described in words):

Diagram Description: A rectangular-shaped cell with a thick outer cell wall, a cell membrane inside it, a large central vacuole, green chloroplasts, a nucleus, cytoplasm, mitochondria, and other organelles.

Key Components and Their Functions:

  • Cell Wall: Made of cellulose, it provides rigidity, protection, and structural support to the plant cell. It also prevents bursting under hypotonic conditions.
  • Chloroplast: Contains chlorophyll for photosynthesis, converting sunlight into chemical energy (glucose). It has stacked structures called grana and a fluid-filled stroma.
  • Vacuole: A large, membrane-bound sac storing water, nutrients, and waste. It maintains turgor pressure, keeping the cell firm and aiding in growth.

Additional Notes: Unlike animal cells, plant cells have a fixed shape due to the cell wall and lack centrioles. The presence of chloroplasts makes them autotrophic.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A student observed onion peel cells under a microscope and noticed small structures. Case Summary: The cells had a distinct boundary and a dense round structure.

Q1. Identify the structures observed and explain their functions.
Answer:
Case Summary: Onion peel cells show a cell wall and nucleus.

Scientific Principle: We studied that plant cells have a cell wall for rigidity and a nucleus controlling activities.

Solution Approach:
  • The boundary is the cell wall, providing shape.
  • The dense structure is the nucleus, storing genetic material.

Our textbook shows similar cells in Figure 5.5.

Question 2:
A red blood cell placed in a hypertonic solution shrivels. Case Summary: The cell lost water due to osmosis.

Q2. Define osmosis and predict what happens if the cell is placed in pure water.
Answer:
Case Summary: RBC shrinks in hypertonic solution.

Scientific Principle: Osmosis is water movement across a membrane. We learned it from NCERT Figure 5.8.

Solution Approach:
  • In pure water, water enters the cell.
  • The RBC swells and may burst (hemolysis).

This matches our experiment with raisins.

Question 3:
Case Summary: A plant cell has chloroplasts but an animal cell lacks them.

Q3. Compare their roles and link this to the autotrophic nutrition of plants.
Answer:
Case Summary: Chloroplasts are only in plant cells.

Scientific Principle: We studied that chloroplasts contain chlorophyll for photosynthesis.

Solution Approach:
  • Chloroplasts make food (glucose) using sunlight.
  • Animals depend on plants for food, showing autotrophic vs. heterotrophic nutrition.

NCERT Page 66 explains this.

Question 4:
Case Summary: A cell’s lysosome ruptures, releasing enzymes.

Q4. Explain why lysosomes are called suicide bags and their importance in worn-out cells.
Answer:
Case Summary: Lysosome enzymes digest cell contents.

Scientific Principle: We learned lysosomes break down waste (NCERT Page 65).

Solution Approach:
  • They digest damaged organelles, earning the name suicide bags.
  • In worn-out cells, they clean up debris for recycling.

Example: Tadpole tail disappearance.

Question 5:
A student observed onion peel cells under a microscope and noticed small structures. Case Summary: The cells had a distinct boundary and a dense round structure.
Scientific Principle: Identify the structures and explain their functions.
Answer:
Case Summary: Onion peel cells show a cell wall (boundary) and nucleus (dense structure).
Scientific Principle: The cell wall provides rigidity, while the nucleus controls cell activities.
Solution Approach:
  • We studied in NCERT that plant cells have a cell wall.
  • The nucleus contains DNA, as seen in cheek cells too.

This helps understand basic cell structure.

Question 6:
A drop of iodine solution was added to potato cells, turning them blue-black. Case Summary: The color change indicates a chemical reaction.
Scientific Principle: What does this test confirm? Explain with an NCERT example.
Answer:
Case Summary: Iodine tests for starch, turning blue-black.
Scientific Principle: Starch is a stored food in plants, like in potato tubers.
Solution Approach:
  • Our textbook shows starch storage in leucoplasts.
  • Real-world application: Testing food for starch content.

This confirms starch presence, as in NCERT Activity 5.1.

Question 7:
RBCs placed in a hypertonic solution shrivel. Case Summary: The cells lose water due to osmosis.
Scientific Principle: Define osmosis and relate it to this observation.
Answer:
Case Summary: Osmosis causes water to move out of RBCs in hypertonic solutions.
Scientific Principle: Osmosis is water movement across a semi-permeable membrane.
Solution Approach:
  • NCERT explains osmosis using raisins in water.
  • Application: Salty foods cause dehydration similarly.

This aligns with cell behavior in different solutions.

Question 8:
A cell lacked mitochondria but had other organelles. Case Summary: The cell couldn’t produce enough energy.
Scientific Principle: Why is mitochondria called the powerhouse? Give an NCERT example.
Answer:
Case Summary: Mitochondria generate ATP, the energy currency.
Scientific Principle: They perform cellular respiration, releasing energy.
Solution Approach:
  • NCERT shows muscle cells have more mitochondria for energy.
  • Real-world: Athletes need more mitochondria-rich cells.

This explains the cell’s energy deficiency.

Question 9:
A student observed onion peel cells under a microscope and noticed small structures. Case Summary: The cells had a distinct boundary and contained a darker region.
Identify the structures and explain their functions.
Answer:
Case Summary: Onion peel cells show a cell wall and nucleus.
Scientific Principle: We studied that plant cells have a rigid cell wall for protection and a nucleus controlling activities.
Solution Approach: The boundary is the cell wall, and the darker region is the nucleus. Our textbook shows the nucleus contains DNA, and the wall provides shape.
Question 10:
Case Summary: A leaf cell has green organelles. Identify them and explain their role in a real-world example like food production.
Answer:
Case Summary: The green organelles are chloroplasts.
Scientific Principle: We learned chloroplasts contain chlorophyll for photosynthesis.
Solution Approach: They trap sunlight to make food (glucose). Our textbook shows spinach leaves use them. In farms, crops rely on chloroplasts for growth.
Question 11:
Case Summary: A cell swells in water but shrinks in salt solution. Explain the phenomenon using osmosis and an NCERT example.
Answer:
Case Summary: Water moves in/out due to osmosis.
Scientific Principle: We studied osmosis is water movement across a membrane.
Solution Approach: In water, cells swell (like raisins in NCERT). In salt, water exits, shrinking cells (like Rhoeo leaf in hypertonic solution).
Question 12:
Case Summary: A cell lacks mitochondria. Predict the consequences and relate it to a daily activity like running.
Answer:
Case Summary: Mitochondria are the powerhouse.
Scientific Principle: We learned they produce energy (ATP).
Solution Approach: Without them, cells can’t release energy. Our textbook shows muscle cells need ATP. Running would be impossible without mitochondria.
Question 13:

Rahul observed two cells under a microscope. Cell A had a well-defined nucleus and membrane-bound organelles, while Cell B lacked these features. Based on this observation:

  • Identify the type of cells A and B.
  • State one key structural difference between them.
  • Give an example of each cell type.
Answer:

Cell A is a eukaryotic cell because it has a well-defined nucleus and membrane-bound organelles.
Cell B is a prokaryotic cell as it lacks these features.

Key structural difference: Eukaryotic cells have a true nucleus enclosed in a nuclear membrane, while prokaryotic cells have a nucleoid region without a membrane.

Examples:
Eukaryotic cell: Human cheek cell (Animal cell)
Prokaryotic cell: Bacteria (like E. coli)

Question 14:

Priya noticed that when a plant cell is placed in a hypertonic solution, it shrinks. However, an animal cell bursts in a hypotonic solution. Explain:

  • Why does the plant cell shrink but not burst?
  • What happens to an animal cell in a hypertonic solution?
  • Define osmosis in this context.
Answer:

Plant cell behavior: The plant cell shrinks due to plasmolysis (water moves out in a hypertonic solution), but it does not burst because of the rigid cell wall that provides structural support.

Animal cell in hypertonic solution: It shrinks (crenation) as water moves out due to osmosis.

Osmosis: It is the movement of water molecules from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution) through a semi-permeable membrane.

Question 15:

Rohan observed a cell under a microscope and noticed that it lacked a well-defined nucleus and membrane-bound organelles. However, the cell had a cell wall and could perform photosynthesis.

a) Identify the type of cell observed by Rohan.
b) Name two organelles present in such cells that aid in photosynthesis.
c) Why do these cells have a cell wall? Explain its function.

Answer:

a) The cell observed by Rohan is a prokaryotic cell, specifically a cyanobacterium (blue-green alga), as it lacks a well-defined nucleus and membrane-bound organelles but can perform photosynthesis.

b) Two organelles present in such cells that aid in photosynthesis are:

  • Thylakoids: These contain chlorophyll and are the sites of photosynthesis.
  • Ribosomes: They help in protein synthesis required for photosynthetic enzymes.

c) These cells have a cell wall to provide structural support and protection.
The cell wall:

  • Prevents the cell from bursting in hypotonic conditions.
  • Maintains cell shape and rigidity.
  • Protects against mechanical damage and pathogens.

Question 16:

Priya conducted an experiment where she placed a plant cell and an animal cell in a hypotonic solution. She observed that the plant cell became turgid, while the animal cell burst.

a) Why did the plant cell not burst like the animal cell?
b) What would happen if the plant cell was placed in a hypertonic solution?
c) Differentiate between osmosis and diffusion based on this experiment.

Answer:

a) The plant cell did not burst because it has a rigid cell wall that prevents over-expansion.
The cell wall exerts turgor pressure, balancing the inward osmotic pressure, while the animal cell lacks a cell wall and bursts due to excessive water intake.

b) If the plant cell was placed in a hypertonic solution, water would move out of the cell, causing plasmolysis.
The cell membrane would shrink away from the cell wall, making the cell flaccid.

c) Differences between osmosis and diffusion:

  • Osmosis is the movement of water across a semi-permeable membrane (like in this experiment).
  • Diffusion is the movement of any substance (solid, liquid, gas) from high to low concentration without a membrane.

Question 17:
Rahul observed a temporary mount of onion peel under a microscope. He noticed small, box-like structures.
(a) Identify the structures observed.
(b) Why are these structures referred to as the 'basic unit of life'?
(c) State one function of the part labeled in the diagram (if provided).
Answer:

(a) The small, box-like structures observed are cells, specifically plant cells from the onion peel.
(b) Cells are called the basic unit of life because they are the smallest structural and functional units that perform all life processes like respiration, nutrition, and reproduction.
(c) If the diagram shows the cell wall, its function is to provide rigidity and protection to the cell. If it shows the nucleus, it controls cell activities and contains genetic material.

Question 18:
Priya prepared a slide of human cheek cells and stained it with methylene blue. She observed irregularly shaped structures under the microscope.
(a) Name the stain used and its purpose.
(b) Why do cheek cells lack a cell wall?
(c) Differentiate between prokaryotic and eukaryotic cells based on her observation.
Answer:

(a) The stain used is methylene blue, which helps highlight the nucleus and other cell organelles for better visibility.
(b) Cheek cells (animal cells) lack a cell wall because they need flexibility for movement and adaptation, unlike plant cells which require rigidity.
(c)

  • Prokaryotic cells (e.g., bacteria) lack a well-defined nucleus and membrane-bound organelles.
  • Eukaryotic cells (e.g., cheek cells) have a distinct nucleus and organelles like mitochondria.
Priya observed eukaryotic cells.

Question 19:
Rahul observed a temporary mount of an onion peel under a microscope. He noticed small, box-like structures.

(a) Identify these structures and explain their function.
(b) Why did Rahul need to stain the peel before observation?
Answer:

(a) The small, box-like structures observed are cells. They are the basic structural and functional units of life. Each cell consists of:

  • A cell wall for protection and shape.
  • A cell membrane controlling substance movement.
  • Cytoplasm containing organelles for various functions.
Their primary function is to carry out life processes like respiration, nutrition, and growth.

(b) Rahul stained the onion peel to enhance visibility. The stain (e.g., iodine) highlights cell components like the nucleus and cell wall by binding to them, making structures clearer under the microscope.

Question 20:
Priya placed a drop of pond water on a slide and observed moving organisms under a microscope.

(a) Name two unicellular organisms she might have seen and describe their locomotion.
(b) How do these organisms differ from multicellular organisms in terms of structure and function?
Answer:

(a) Priya might have observed:

  • Amoeba: Moves using pseudopodia (temporary extensions of cytoplasm).
  • Paramecium: Swims using cilia (hair-like projections).

(b) Differences:

  • Structure: Unicellular organisms have a single cell performing all functions, while multicellular organisms have specialized cells grouped into tissues/organs.
  • Function: In unicellular organisms, one cell handles digestion, respiration, etc., whereas multicellular organisms have division of labor among cells.

Question 21:
Rahul observed a temporary mount of an onion peel under a microscope and noticed small compartments.

(a) What are these compartments called?
(b) Why is the cell called the structural and functional unit of life?
(c) How do plant cells differ from animal cells in terms of structure?
Answer:

(a) The small compartments observed are called cells. They are the basic building blocks of all living organisms.


(b) The cell is called the structural and functional unit of life because:

  • All living organisms are made up of cells.
  • All life processes like respiration, digestion, and reproduction occur within cells.
  • Cells can independently perform essential functions to sustain life.


(c) Plant cells differ from animal cells in the following ways:

  • Plant cells have a rigid cell wall made of cellulose, while animal cells lack it.
  • Plant cells contain chloroplasts for photosynthesis, which are absent in animal cells.
  • Plant cells have a large central vacuole, whereas animal cells have smaller vacuoles or none.

Question 22:
Priya placed a drop of pond water on a slide and observed it under a microscope. She saw tiny organisms moving.

(a) Name the process by which these organisms move.
(b) What is the function of the cell membrane in these organisms?
(c) Why are some cells, like those of Amoeba, irregular in shape?
Answer:

(a) The tiny organisms move using pseudopodia (false feet), cilia, or flagella, depending on the organism.


(b) The cell membrane functions as:

  • A protective barrier that controls the entry and exit of substances.
  • A structure that maintains the cell's shape and integrity.
  • A medium for cellular communication and transport.


(c) Cells like those of Amoeba are irregular in shape because:

  • They lack a rigid cell wall, allowing flexibility.
  • Their shape changes due to the formation of pseudopodia for movement and feeding.
  • This adaptability helps them survive in diverse environments.

Chat on WhatsApp