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Cell: Structure and Functions – CBSE NCERT Study Resources

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Cell: Structure and Functions

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8th

8th - Science

Cell: Structure and Functions

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Cell: Structure and Functions

Chapter Overview

This chapter introduces the basic unit of life, the cell. It explains the structure and functions of different cell components, types of cells, and their organization in living organisms. Students will learn about the differences between plant and animal cells, the discovery of the cell, and the significance of cells in biology.

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 and named them "cells." Later, scientists like Anton van Leeuwenhoek observed living cells.

Cell Theory

The cell theory, formulated by Schleiden, Schwann, and Virchow, 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: Simple cells without a well-defined nucleus (e.g., bacteria).
  • Eukaryotic Cells: Complex cells with a well-defined nucleus (e.g., plant and animal cells).

Structure of a Cell

A cell consists of three main parts:

  • Cell Membrane: A thin, flexible outer covering that controls the movement of substances in and out of the cell.
  • Cytoplasm: A jelly-like substance where cell organelles are suspended.
  • Nucleus: The control center of the cell that contains genetic material (DNA).

Cell Organelles

Key organelles in a eukaryotic cell include:

  • Mitochondria: Powerhouse of the cell, produces energy (ATP).
  • Endoplasmic Reticulum (ER): Helps in protein and lipid synthesis.
  • Golgi Apparatus: Packages and transports materials.
  • Lysosomes: Digestive enzymes that break down waste.
  • Chloroplasts: Found in plant cells, site of photosynthesis.
  • Vacuoles: Storage sacs for water and nutrients.

Differences Between Plant and Animal Cells

Feature Plant Cell Animal Cell
Cell Wall Present (made of cellulose) Absent
Chloroplasts Present Absent
Vacuoles Large and central Small and numerous

Functions of the Cell

Cells perform various functions essential for life, including:

  • Growth and reproduction
  • Energy production
  • Protein synthesis
  • Waste elimination
  • Response to stimuli

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 unit of life?
Answer:

The cell is the basic unit of life.

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

Robert Hooke discovered cells.

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 what enters and exits the cell.

Question 5:
Which part of the cell contains genetic material?
Answer:

The nucleus contains genetic material.

Question 6:
Name the process by which cells divide.
Answer:

Cells divide by mitosis or meiosis.

Question 7:
What is the function of chloroplasts in plant cells?
Answer:

Chloroplasts help in photosynthesis.

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

The ribosome helps in protein synthesis.

Question 9:
What is the main difference between plant and animal cells?
Answer:

Plant cells have a cell wall and chloroplasts.

Question 10:
Name the jelly-like substance inside the cell.
Answer:

The cytoplasm is the jelly-like substance.

Question 11:
Which organelle stores water and nutrients in plant cells?
Answer:

The vacuole stores water and nutrients.

Question 12:
What is the function of lysosomes in a cell?
Answer:

Lysosomes digest waste materials.

Question 13:
Which type of cell lacks a nucleus?
Answer:

Prokaryotic cells lack a nucleus.

Question 14:
Name the process by which amoeba captures food.
Answer:

Amoeba captures food by phagocytosis.

Question 15:
Name the organelle 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 16:
Which part of the cell contains chromosomes?
Answer:

The nucleus contains chromosomes, which carry genetic information in the form of DNA.

Question 17:
What is the role of ribosomes in a cell?
Answer:

Ribosomes are responsible for protein synthesis, translating mRNA into proteins.

Question 18:
Name the cell organelle that helps in waste disposal.
Answer:

The lysosome helps in waste disposal by breaking down cellular debris and foreign materials using digestive enzymes.

Question 19:
What is the function of the chloroplast in plant cells?
Answer:

The chloroplast conducts photosynthesis, converting sunlight into chemical energy (glucose) using chlorophyll.

Question 20:
Which structure gives shape and rigidity to a plant cell?
Answer:

The cell wall, made of cellulose, provides shape and rigidity to plant cells.

Question 21:
What is the jelly-like substance inside the cell called?
Answer:

The cytoplasm is the jelly-like substance where organelles are suspended and metabolic reactions occur.

Question 22:
Name the organelle that stores water and nutrients in plant cells.
Answer:

The vacuole stores water, nutrients, and waste products, maintaining turgor pressure in plant cells.

Question 23:
What is the function of the endoplasmic reticulum (ER)?
Answer:

The endoplasmic reticulum (ER) aids in protein and lipid synthesis and transports materials within the cell.
Rough ER has ribosomes for protein synthesis.
Smooth ER helps in lipid production and detoxification.

Question 24:
Which cell structure controls all cellular activities?
Answer:

The nucleus controls all cellular activities by regulating gene expression and DNA replication.

Question 25:
What is the difference between prokaryotic and eukaryotic cells?
Answer:

  • Prokaryotic cells lack a nucleus and membrane-bound organelles (e.g., bacteria).
  • Eukaryotic cells have a nucleus and organelles (e.g., plant and animal cells).

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:
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 energy in the form of ATP through cellular respiration.

Question 2:
Differentiate between prokaryotic and eukaryotic cells based on nucleus.
Answer:

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

Question 3:
What is the function of ribosomes in a cell?
Answer:

Ribosomes are responsible for protein synthesis.
They read RNA instructions to assemble amino acids into proteins.

Question 4:
Why is the cell membrane called a selectively permeable membrane?
Answer:

The cell membrane allows only specific substances to pass through while blocking others.
This selective permeability maintains cellular balance (homeostasis).

Question 5:
List two functions of the Golgi apparatus.
Answer:
  • Modifies, sorts, and packages proteins for secretion.
  • Forms lysosomes for cellular digestion.
Question 6:
What is the role of chloroplasts in plant cells?
Answer:

Chloroplasts contain chlorophyll and perform photosynthesis.
They convert sunlight, CO2, and water into glucose and oxygen.

Question 7:
Name the cell organelle that helps in waste disposal and cellular digestion.
Answer:

The lysosome contains digestive enzymes.
It breaks down waste materials and cellular debris.

Question 8:
Why are vacuoles larger in plant cells compared to animal cells?
Answer:

Plant vacuoles store water, nutrients, and waste, maintaining turgor pressure.
Animal vacuoles are smaller and temporary.

Question 9:
Define plasmolysis and state its cause.
Answer:

Plasmolysis is the shrinking of the cytoplasm away from the cell wall due to water loss.
It occurs when a plant cell is placed in a hypertonic solution.

Question 10:
What is the function of chromosomes in a cell?
Answer:

Chromosomes carry genetic information (DNA) and pass traits to offspring.
They ensure proper inheritance during cell division.

Question 11:
Explain why nerve cells are long and branched.
Answer:

Nerve cells (neurons) transmit electrical signals over long distances.
Their long axons and branched dendrites help in efficient communication.

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:
Explain the difference between prokaryotic and eukaryotic cells with examples.
Answer:

Prokaryotic cells are simpler and smaller, lacking a defined nucleus and membrane-bound organelles. Their genetic material floats freely in the cytoplasm. Example: Bacteria.
Eukaryotic cells are more complex, with a well-defined nucleus and membrane-bound organelles like mitochondria. Example: Plant and animal cells.

Question 2:
Describe the function of the cell membrane in a cell.
Answer:

The cell membrane acts as a protective barrier and regulates the movement of substances in and out of the cell. It is selectively permeable, allowing only certain molecules to pass through. It also provides structural support and helps in cell communication.

Question 3:
What is the role of mitochondria in a cell? Why is it called the 'powerhouse' of the cell?
Answer:

Mitochondria are responsible for producing energy in the form of ATP through cellular respiration. They are called the 'powerhouse' because they generate most of the cell's energy, which is essential for all metabolic activities.

Question 4:
Differentiate between plant cell and animal cell based on their cell wall and vacuoles.
Answer:

Plant cells have a rigid cell wall made of cellulose, providing structural support, while animal cells lack a cell wall.
Plant cells have a large central vacuole for storage and maintaining turgidity, whereas animal cells have smaller, multiple vacuoles.

Question 5:
Explain the significance of chloroplasts in plant cells.
Answer:

Chloroplasts contain the green pigment chlorophyll, which captures sunlight for photosynthesis. This process converts light energy into chemical energy (glucose), providing food for the plant and oxygen for other organisms.

Question 6:
What are chromosomes? Where are they located in a cell?
Answer:

Chromosomes are thread-like structures made of DNA and proteins. They carry genetic information and are located in the nucleus of the cell. Chromosomes become visible during cell division and ensure proper inheritance of traits.

Question 7:
What is the function of the cell membrane in a cell?
Answer:

The cell membrane is a semi-permeable barrier that surrounds the cell. Its main functions are:

  • It protects the cell from external damage.
  • It regulates the movement of substances in and out of the cell, allowing only selective materials to pass.
  • It helps in maintaining the shape of the cell.

Additionally, it plays a role in cell signaling and communication with other cells.

Question 8:
Why are mitochondria called the 'powerhouse of the cell'?
Answer:

Mitochondria are called the powerhouse of the cell because they generate energy in the form of ATP (Adenosine Triphosphate) through cellular respiration.

Here’s how:
1. They break down glucose and other nutrients.
2. Oxygen is used to convert these nutrients into ATP.
3. This energy is then used by the cell for various activities.

Without mitochondria, cells would not have the energy to perform essential functions.

Question 9:
Explain the role of chloroplasts in plant cells.
Answer:

Chloroplasts are organelles found in plant cells that are responsible for photosynthesis.

Their functions include:

  • Containing chlorophyll, a green pigment that captures sunlight.
  • Converting light energy into chemical energy (glucose) using carbon dioxide and water.
  • Releasing oxygen as a byproduct, which is vital for life.

Chloroplasts are unique to plant cells and are absent in animal cells.

Question 10:
What is the significance of vacuoles in plant cells?
Answer:

Vacuoles in plant cells are large and play several critical roles:

  • They store water, nutrients, and waste products.
  • They help maintain turgor pressure, which keeps the plant rigid and upright.
  • They assist in detoxification by isolating harmful substances.

In contrast, animal cell vacuoles are smaller and fewer in number. The central vacuole in plant cells is essential for their survival and growth.

Question 11:
Describe the structure and function of the Golgi apparatus.
Answer:

The Golgi apparatus is a stack of flattened, membrane-bound sacs called cisternae.

Its functions include:

  • Modifying, sorting, and packaging proteins and lipids received from the endoplasmic reticulum.
  • Producing lysosomes for cellular digestion.
  • Forming vesicles to transport materials to other parts of the cell or outside.

It acts like a postal system, ensuring that cellular products reach their correct destinations.

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 of a plant cell with a labeled diagram. How does it differ from an animal cell?
Answer:
Concept Overview

We studied that plant cells have a rigid cell wall, chloroplasts, and a large vacuole, unlike animal cells.

Process Explanation
  • Cell wall provides support.
  • Chloroplasts help in photosynthesis.
  • Vacuole stores water and nutrients.
Real-world Application

Our textbook shows onion peel cells under a microscope, highlighting these features. In real life, plant cells help in food production.

Diagram
[Diagram: Labeled plant cell with cell wall, chloroplast, and vacuole]
Question 2:
Describe the functions of the nucleus in a cell. Why is it called the 'control center'?
Answer:
Concept Overview

The nucleus contains genetic material (DNA) and controls cell activities.

Process Explanation
  • It regulates growth and reproduction.
  • DNA carries hereditary information.
Real-world Application

Our textbook shows cheek cells with a nucleus. In real life, nucleus dysfunction can cause diseases like cancer.

Diagram
[Diagram: Nucleus with chromatin and nuclear membrane]
Question 3:
What are organelles? List the functions of mitochondria and endoplasmic reticulum.
Answer:
Concept Overview

Organelles are tiny structures in cells with specific functions.

Process Explanation
  • Mitochondria produce energy (ATP).
  • Endoplasmic reticulum transports materials.
Real-world Application

Our textbook shows liver cells with many mitochondria for energy. In real life, muscle cells also have more mitochondria.

Diagram
[Diagram: Mitochondria and endoplasmic reticulum in a cell]
Question 4:
Explain the role of cell membrane in a cell. How does it maintain homeostasis?
Answer:
Concept Overview

The cell membrane is selectively permeable and protects the cell.

Process Explanation
  • It controls entry/exit of substances.
  • Maintains internal balance (homeostasis).
Real-world Application

Our textbook shows osmosis in raisins. In real life, cell membranes help in nutrient absorption in intestines.

Diagram
[Diagram: Cell membrane with embedded proteins]
Question 5:
Compare prokaryotic and eukaryotic cells with examples from NCERT.
Answer:
Concept Overview

Prokaryotic cells lack a nucleus, while eukaryotic cells have one.

Process Explanation
  • Prokaryotes (e.g., bacteria) are simpler.
  • Eukaryotes (e.g., plant/animal cells) are complex.
Real-world Application

Our textbook shows bacterial cells (prokaryotic) and onion cells (eukaryotic). In real life, eukaryotes form multicellular organisms.

Diagram
[Diagram: Comparison of prokaryotic and eukaryotic cells]
Question 6:
Explain the structure of a plant cell with a labeled diagram. Highlight the role of cell wall and chloroplast.
Answer:
Concept Overview

A plant cell has a rigid cell wall, cell membrane, cytoplasm, nucleus, and organelles like chloroplasts and mitochondria.

Process Explanation
  • The cell wall provides structural support and protection.
  • Chloroplasts contain chlorophyll for photosynthesis.
Real-world Application

In agriculture, understanding cell structure helps improve crop yield by optimizing photosynthesis.

Diagram
[Diagram: Plant cell with labeled parts like cell wall, chloroplast, nucleus]
Question 7:
Describe the functions of the nucleus in a cell. How does it differ in plant and animal cells?
Answer:
Concept Overview

The nucleus controls cell activities and contains genetic material (DNA).

Process Explanation
  • In animal cells, the nucleus is centrally located.
  • In plant cells, it may be pushed to the side due to the large vacuole.
Real-world Application

Understanding nucleus function aids in genetic engineering, like creating disease-resistant crops.

Question 8:
What is the significance of cell membrane? Explain its selective permeability with an example.
Answer:
Concept Overview

The cell membrane regulates entry and exit of substances, maintaining homeostasis.

Process Explanation
  • It allows only specific molecules to pass (selective permeability).
  • Example: Oxygen enters, and carbon dioxide exits during respiration.
Real-world Application

This property is used in dialysis machines to filter blood.

Question 9:
Explain the role of mitochondria and vacuoles in cells. Give one NCERT example for each.
Answer:
Concept Overview

Mitochondria produce energy (ATP), and vacuoles store nutrients/waste.

Process Explanation
  • Example: Mitochondria are abundant in muscle cells for energy.
  • Plant vacuoles store water, as seen in onion peel cells (NCERT).
Real-world Application

Studying mitochondria helps in understanding diseases like diabetes.

Question 10:
Describe the functions of the nucleus in a cell. Why is it called the control center?
Answer:
Concept Overview

The nucleus contains DNA and controls cell activities. Our textbook calls it the cell's control center.

Process Explanation
  • Stores genetic material.
  • Regulates cell growth.
  • Directs protein synthesis.
Real-world Application

In cloning, the nucleus is transferred to create identical organisms, showing its importance.

Diagram
[Diagram: Nucleus with chromatin and nuclear membrane]
Question 11:
What are plastids? Explain their types and functions with examples.
Answer:
Concept Overview

Plastids are organelles found in plant cells. Our textbook mentions chloroplasts, chromoplasts, and leucoplasts.

Process Explanation
  • Chloroplasts: Photosynthesis.
  • Chromoplasts: Give color to fruits.
  • Leucoplasts: Store food.
Real-world Application

Tomatoes turn red due to chromoplasts, which attract animals for seed dispersal.

Diagram
[Diagram: Types of plastids in a plant cell]
Question 12:
Explain the role of mitochondria in a cell. Why are they called the powerhouse?
Answer:
Concept Overview

Mitochondria produce energy (ATP) through respiration. Our textbook calls them the powerhouse of the cell.

Process Explanation
  • Break down glucose.
  • Release energy as ATP.
  • Have their own DNA.
Real-world Application

Athletes have more mitochondria in muscle cells for extra energy.

Diagram
[Diagram: Mitochondria with inner folds (cristae)]
Question 13:
Compare prokaryotic and eukaryotic cells with examples. Which one is more advanced?
Answer:
Concept Overview

Prokaryotic cells lack a nucleus, while eukaryotic cells have one. Our textbook shows bacteria and human cells as examples.

Process Explanation
  • Prokaryotes: Simpler, smaller.
  • Eukaryotes: Complex, larger.
Real-world Application

Yogurt is made using prokaryotic bacteria, while eukaryotes like yeast are used in baking bread.

Diagram
[Diagram: Prokaryotic vs. eukaryotic cell structure]
Question 14:
Explain the structure and function of a plant cell with a well-labeled diagram. Highlight the roles of cell wall, chloroplast, and vacuole.
Answer:

A plant cell is a eukaryotic cell with distinct structures that perform specialized functions. Below is a detailed explanation of its key components:

  • Cell Wall: A rigid outer layer made of cellulose, providing structural support and protection. It prevents the cell from bursting under osmotic pressure.
  • Chloroplast: Contains chlorophyll, the green pigment responsible for photosynthesis. It converts sunlight into chemical energy (glucose).
  • Vacuole: A large, fluid-filled sac that stores water, nutrients, and waste. It maintains turgor pressure, keeping the cell firm.

Other important organelles include the nucleus (controls cell activities), mitochondria (produces energy), and endoplasmic reticulum (synthesizes proteins and lipids).

Diagram: (Draw a plant cell with labels for cell wall, chloroplast, vacuole, nucleus, mitochondria, and ER.)

Value-added note: Unlike animal cells, plant cells have a fixed shape due to the cell wall and contain plastids like chloroplasts for photosynthesis.

Question 15:
Compare and contrast an animal cell and a plant cell based on their structure and organelles. Provide a tabular representation for clarity.
Answer:

Animal cells and plant cells share some similarities but also have key differences. Below is a detailed comparison:


Tabular Representation:


FeatureAnimal CellPlant Cell
Cell WallAbsentPresent (made of cellulose)
ChloroplastAbsentPresent (for photosynthesis)
VacuoleSmall or absentLarge central vacuole
ShapeIrregularFixed (rectangular)
LysosomesPresentRare or absent

Explanation:


1. Cell Wall: Plant cells have a rigid cell wall for support, while animal cells rely only on a flexible cell membrane.


2. Chloroplast: Exclusive to plant cells, they enable photosynthesis, whereas animal cells obtain energy from food.


3. Vacuole: Plant cells have a large vacuole for storage, while animal cells may have small or temporary vacuoles.


4. Shape: Plant cells are rigid due to the cell wall, while animal cells can change shape.


Both cells share common organelles like the nucleus, mitochondria, and endoplasmic reticulum, but their specialized structures adapt them to different functions.

Question 16:
Explain the structure and functions of a plant cell with a well-labeled diagram. Highlight the roles of cell wall, chloroplast, and vacuole.
Answer:

A plant cell is a eukaryotic cell with a distinct structure adapted for photosynthesis and support. Below is a detailed explanation of its key components:

  • Cell Wall: A rigid outer layer made of cellulose that provides structural support and protection. It prevents the cell from bursting under osmotic pressure.
  • Chloroplast: Contains chlorophyll and is the site of photosynthesis, converting light energy into chemical energy (glucose).
  • Vacuole: A large, membrane-bound organelle storing water, nutrients, and waste. It maintains turgor pressure, keeping the cell firm.

Other important parts include the nucleus (controls cell activities), mitochondria (produces energy), and cytoplasm (site of metabolic reactions).

Diagram: (Draw a plant cell with labels for cell wall, chloroplast, vacuole, nucleus, mitochondria, and cytoplasm.)

Value-add: Unlike animal cells, plant cells have a fixed shape due to the cell wall and can synthesize their own food via chloroplasts.

Question 17:
Compare and contrast prokaryotic and eukaryotic cells with examples. Explain why mitochondria and nucleus are absent in prokaryotes.
Answer:

Prokaryotic and eukaryotic cells differ in structure and complexity:


Prokaryotic Cells:

  • Simpler, smaller (e.g., bacteria).
  • No membrane-bound organelles.
  • Genetic material floats in cytoplasm (no nucleus).
  • Cell wall present (in most).


Eukaryotic Cells:

  • Complex, larger (e.g., plant/animal cells).
  • Have membrane-bound organelles.
  • DNA enclosed in a nucleus.
  • Mitochondria present for energy production.


Why Prokaryotes Lack Mitochondria & Nucleus:
Prokaryotes are primitive cells that evolved before eukaryotes. They rely on mesosomes (folded cell membranes) for respiration instead of mitochondria. Their DNA is circular and freely suspended, eliminating the need for a nucleus.


Value Addition: Prokaryotes reproduce faster due to their simplicity, making them adaptable to extreme environments.

Question 18:
Compare and contrast prokaryotic and eukaryotic cells with examples. Discuss how their structural differences impact their functions.
Answer:

Prokaryotic and eukaryotic cells differ fundamentally in structure and complexity:

  • Prokaryotic Cells: Simpler, smaller (e.g., bacteria).
    Lack a nucleus; DNA floats in the cytoplasm.
    No membrane-bound organelles (e.g., mitochondria).
    Have a cell wall (not made of cellulose) and may have flagella for movement.
  • Eukaryotic Cells: Complex, larger (e.g., plant/animal cells).
    Contain a nucleus housing DNA.
    Have specialized organelles (e.g., Golgi apparatus, endoplasmic reticulum).
    Plant cells have a cellulose cell wall; animal cells do not.

Functional Impact:
Prokaryotes reproduce faster (binary fission) and adapt quickly to environments.
Eukaryotes perform advanced functions (e.g., photosynthesis, multicellular organization) due to compartmentalization.

Value-add: Prokaryotes are often unicellular, while eukaryotes form tissues and organs in higher organisms.

Question 19:
Compare and contrast prokaryotic and eukaryotic cells with examples. Discuss how their structural differences affect their functions.
Answer:

Prokaryotic and eukaryotic cells differ significantly in structure and complexity:

  • Prokaryotic Cells:
    Example: Bacteria (e.g., E. coli).
    Features:
    - No true nucleus (DNA floats in cytoplasm).
    - Lack membrane-bound organelles.
    - Smaller in size (1-10 μm).
    - Have a cell wall (in most cases) and flagella for movement.
  • Eukaryotic Cells:
    Example: Plant and animal cells.
    Features:
    - Have a well-defined nucleus.
    - Contain membrane-bound organelles (e.g., mitochondria, Golgi apparatus).
    - Larger in size (10-100 μm).
    - More complex functions due to compartmentalization.

Functional Impact:
- Prokaryotes reproduce faster (binary fission) but lack specialized functions.
- Eukaryotes perform advanced processes like mitosis and meiosis due to organized organelles.

Value-added note: Prokaryotes are often unicellular, while eukaryotes can be unicellular (e.g., amoeba) or multicellular (e.g., humans).

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 in detail.
Answer:

The plant cell is a eukaryotic cell with distinct structures that perform specialized functions. Below is a detailed explanation along with key components:


Diagram: (Draw a neat, labeled diagram of a plant cell showing cell wall, chloroplast, vacuole, nucleus, cytoplasm, and other organelles.)

1. Cell Wall: It is the outermost rigid layer made of cellulose. It provides structural support, protection, and allows the passage of water and nutrients.


2. Chloroplast: These are green-colored organelles containing chlorophyll. They perform photosynthesis, converting sunlight into chemical energy (glucose).


3. Vacuole: A large, fluid-filled sac that stores water, nutrients, and waste. It maintains turgor pressure, keeping the cell rigid.


Additional Points: The nucleus controls cell activities, while mitochondria produce energy. The cytoplasm houses organelles and facilitates metabolic reactions.

Question 21:
Compare and contrast an animal cell and a plant cell based on their structure and organelles. Provide examples where these differences impact their functions.
Answer:

Comparison between Animal and Plant Cells:


  • Cell Wall: Present in plant cells (made of cellulose), absent in animal cells. This makes plant cells rigid.

  • Chloroplasts: Found only in plant cells for photosynthesis. Animal cells lack them.

  • Vacuoles: Plant cells have a large central vacuole, while animal cells have smaller, temporary vacuoles.

  • Shape: Plant cells are usually rectangular; animal cells are irregular.

Functional Impact:


1. Photosynthesis: Only plant cells can produce food due to chloroplasts.


2. Support: The cell wall helps plants stand upright, while animal cells rely on cytoskeletons.


3. Storage: Large vacuoles in plants store excess water, whereas animal cells store nutrients temporarily.

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:
Riya observed onion peel cells under a microscope and noticed small structures inside. Case Summary: She identified the cell wall, nucleus, and cytoplasm. Explain why plant cells have a cell wall and how it differs from an animal cell.
Answer:
Scientific Principle:

We studied that plant cells have a rigid cell wall made of cellulose for protection and shape. Animal cells lack it.

Solution Approach:
  • Plant cells need cell wall for support (NCERT example: onion peel).
  • Animal cells rely on cell membrane (real-world: human cheek cells).
Question 2:
Amit saw a nerve cell diagram with long extensions. Case Summary: He wondered why its shape differs from a red blood cell. Compare their structures and functions.
Answer:
Scientific Principle:

Our textbook shows nerve cells transmit signals (long axons), while RBCs carry oxygen (biconcave shape).

Solution Approach:
  • Nerve cell: Branched structure (NCERT example: neuron diagram).
  • RBC: No nucleus, flexible (real-world: oxygen transport).
Question 3:
Priya noticed chloroplasts only in plant cells. Case Summary: She asked why animal cells don’t have them. Explain the role of chloroplasts and their absence in animals.
Answer:
Scientific Principle:

Chloroplasts contain chlorophyll for photosynthesis (NCERT: leaf cells). Animals rely on food.

Solution Approach:
  • Plants: Chloroplasts make food (real-world: spinach leaves).
  • Animals: Get energy from mitochondria (NCERT example: muscle cells).
Question 4:
A lab slide showed amoeba changing shape. Case Summary: Rohan questioned how it moves without fixed structures. Describe pseudopodia and its function.
Answer:
Scientific Principle:

We studied amoeba uses pseudopodia (false feet) to move and engulf food (NCERT diagram).

Solution Approach:
  • Pseudopodia extend cytoplasm (real-world: capturing prey).
  • No fixed shape (NCERT: unicellular organisms).
Question 5:
Rahul observed onion peel cells under a microscope and noticed small structures inside.
Case Summary: He identified the cell wall and nucleus but couldn’t see other organelles clearly.
Q1: Why are some organelles not visible? Name one organelle present but unseen and its function.
Answer:
Scientific Principle:

Some organelles are too small to be seen under a basic microscope. Mitochondria, the powerhouse of the cell, is present but often invisible without staining.

Solution Approach:
  • We studied that light microscopes have limited resolution.
  • Our textbook shows mitochondria generate energy (ATP).
Question 6:
Priya compared animal cells and plant cells using diagrams.
Case Summary: She noted plant cells have a cell wall and chloroplasts, while animal cells lack them.
Q2: How do these differences help plants survive?
Answer:
Scientific Principle:

Cell walls provide rigidity, and chloroplasts enable photosynthesis.

Solution Approach:
  • We learned plants need structural support (cell wall) to stand upright.
  • Our textbook shows chloroplasts convert sunlight to food (glucose).
Question 7:
A science experiment showed cheek cells stained with methylene blue.
Case Summary: Only the nucleus and cell membrane were clearly visible.
Q3: Why is staining necessary? Name one other cell part stained and its role.
Answer:
Scientific Principle:

Staining highlights transparent cell parts. The cytoplasm may also absorb dye.

Solution Approach:
  • We studied stains increase contrast under microscopes.
  • Our textbook shows cytoplasm holds organelles and facilitates reactions.
Question 8:
In a lab, students observed amoeba changing shape.
Case Summary: They concluded it lacks a cell wall but has a cell membrane.
Q4: How does the absence of a cell wall help amoeba?
Answer:
Scientific Principle:

Flexible cell membranes allow amoeba to move and engulf food.

Solution Approach:
  • We learned cell walls restrict shape changes.
  • Our textbook shows amoeba uses pseudopodia for locomotion.
Question 9:
Riya observed onion peel cells under a microscope and noticed small structures inside. Case Summary: She identified the cell wall, nucleus, and cytoplasm. Explain why the cell wall is visible but the cell membrane is not, and how the nucleus controls cell activities.
Answer:
Scientific Principle: The cell wall is rigid and visible, while the cell membrane is thin and transparent. Solution Approach:
  • Our textbook shows that plant cells have a thick cell wall for support.
  • The nucleus contains DNA, which directs functions like growth, as seen in NCERT’s cheek cell example.

In real life, onion skin’s toughness comes from its cell wall.

Question 10:
Amit compared animal cells and plant cells using diagrams. Case Summary: He noted chloroplasts and vacuoles differ. Explain why chloroplasts are absent in animal cells and how vacuoles help plants.
Answer:
Scientific Principle: Chloroplasts perform photosynthesis, unnecessary for animals. Solution Approach:
  • NCERT’s amoeba example shows animal cells lack chloroplasts as they don’t make food.
  • Plant vacuoles store water, like in NCERT’s hydrilla experiment, maintaining rigidity.

Real-world example: Leaf cells use chloroplasts to prepare food.

Question 11:
Priya saw amoeba changing shape under a microscope. Case Summary: She learned about pseudopodia and cell membrane flexibility. Explain how pseudopodia help movement and why the cell membrane is flexible.
Answer:
Scientific Principle: Pseudopodia are temporary projections for movement. Solution Approach:
  • NCERT’s amoeba diagram shows pseudopodia extending to capture food.
  • The cell membrane is flexible due to lipids, allowing shape changes, as in white blood cells.

Real-world link: Amoeba uses pseudopodia to avoid predators.

Question 12:
A lab group stained human cheek cells and observed organelles. Case Summary: They saw a nucleus but no cell wall. Compare cheek cells with plant cells and explain the role of the nucleus.
Answer:
Scientific Principle: Animal cells lack cell walls but have a nucleus. Solution Approach:
  • NCERT’s cheek cell experiment confirms no cell wall, unlike onion cells.
  • The nucleus controls traits, as seen in Mendel’s pea plant study.

Real-world example: Cheek cells regenerate faster due to nucleus instructions.

Question 13:

Rahul observed two slides under a microscope: onion peel and human cheek cells. He noticed differences in their shapes and structures.

(a) Identify the cell organelles present in both cells.

(b) Why do onion peel cells have a regular shape while cheek cells appear irregular? Explain.

Answer:

(a) Both onion peel cells and human cheek cells contain the following cell organelles:

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Mitochondria

(b) Onion peel cells have a regular shape because they are plant cells and possess a rigid cell wall made of cellulose, which maintains their structure.
In contrast, human cheek cells are animal cells and lack a cell wall, making their shape irregular and flexible for movement and function.

Question 14:

Priya conducted an experiment to study plasmolysis in Rhoeo leaf cells by placing them in a concentrated salt solution.

(a) What change will she observe in the cells? Explain the reason.

(b) How can she reverse this process? Name the phenomenon involved.

Answer:

(a) Priya will observe the cell membrane shrinking away from the cell wall due to water loss from the cell. This happens because the hypertonic salt solution causes exosmosis, where water moves out of the cell.

(b) She can reverse this by placing the cells in pure water. The phenomenon is called deplasmolysis, where water re-enters the cell, restoring its original shape.

Question 15:

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

  • Identify the type of cells A and B.
  • Give one example of each cell type.
  • State one key difference in their structure.
Answer:

Cell A is a eukaryotic cell because it has a well-defined nucleus and membrane-bound organelles. An example is a human cheek cell.
Cell B is a prokaryotic cell because it lacks a nucleus and membrane-bound organelles. An example is a bacterial cell.

The key structural difference is that eukaryotic cells have a true nucleus enclosed in a nuclear membrane, while prokaryotic cells have a nucleoid region where genetic material is loosely present.

Question 16:

Priya noticed that plant cells have a rigid outer layer, while animal cells do not. Answer the following:

  • Name the rigid outer layer in plant cells and its main component.
  • State two functions of this layer.
  • Explain why animal cells lack this structure.
Answer:

The rigid outer layer in plant cells is called the cell wall, and its main component is cellulose.

Two functions of the cell wall are:

  • It provides structural support and maintains the shape of the cell.
  • It protects the cell from mechanical damage and external threats.

Animal cells lack a cell wall because they need flexibility for movement and specialized functions like forming tissues and organs. Instead, they have a cell membrane for protection and shape maintenance.

Question 17:

Rahul observed two slides under a microscope: one with onion peel cells and another with human cheek cells. He noticed differences in their shapes and structures.

(a) Identify the key structural differences between these two cells.

(b) Why do these differences exist? Explain briefly.

Answer:

(a) The key structural differences are:

  • Onion peel cells are rectangular and have a cell wall, giving them a fixed shape.
  • Human cheek cells are irregularly shaped (rounded) and lack a cell wall, making them flexible.

(b) These differences exist because:

Onion peel cells are plant cells, and the cell wall provides rigidity and support for the plant structure.

Human cheek cells are animal cells, which do not need a cell wall since animals rely on other tissues (like muscles and bones) for support and movement.

Question 18:

Priya prepared a temporary mount of a leaf peel to observe stomata under a microscope. She noticed small pores surrounded by two bean-shaped cells.

(a) Name the bean-shaped cells and state their function.

(b) How does the structure of stomata help in transpiration and gas exchange?

Answer:

(a) The bean-shaped cells are called guard cells. Their function is to control the opening and closing of the stomatal pore to regulate gas exchange and water loss.

(b) The structure of stomata helps in:

  • Transpiration: When guard cells swell (due to water intake), the stomata open, allowing water vapor to escape.
  • Gas exchange: Open stomata allow carbon dioxide to enter for photosynthesis and oxygen to exit as a byproduct.

This adaptation ensures plants balance water loss with the need for photosynthesis.

Question 19:

Rahul observed two slides under a microscope: Onion peel and Human cheek cells. He noted differences in their shapes and structures.

(a) Identify the cell organelles present in both cells.
(b) Why do onion peel cells have a fixed shape while human cheek cells appear irregular?

Answer:

(a) Both onion peel cells and human cheek cells contain the following cell organelles:

  • Cell membrane
  • Cytoplasm
  • Nucleus
  • Mitochondria

(b) Onion peel cells have a fixed shape due to the presence of a rigid cell wall made of cellulose, which provides structural support. Human cheek cells lack a cell wall and only have a flexible cell membrane, making their shape irregular and adaptable.

Question 20:

Priya noticed that amoeba changes its shape frequently, while plant cells maintain a fixed structure.

(a) Name the cell component responsible for the shape difference.
(b) How does the absence of this component help amoeba in movement and feeding?

Answer:

(a) The cell component responsible for the shape difference is the cell wall. Plant cells have a rigid cell wall, while amoeba lacks it.

(b) The absence of a cell wall allows amoeba to form pseudopodia (temporary projections).

  • Movement: Pseudopodia help in crawling by extending and contracting.
  • Feeding: They engulf food particles through phagocytosis, a process enabled by their flexible membrane.

Question 21:
Riya observed a slide of onion peel cells under a microscope. She noticed small, rectangular structures with a prominent boundary.

a) Identify the cell organelle that gives the cell its shape and provides structural support.

b) Why do plant cells have this organelle, but animal cells do not?

Answer:

a) The cell organelle observed is the cell wall. It is a rigid outer layer made of cellulose that gives the cell its shape and structural support.


b) Plant cells have a cell wall because:

  • It provides mechanical strength to withstand environmental pressures like wind or water.
  • It prevents the cell from bursting when water enters by osmosis.
  • Animal cells lack a cell wall because they rely on flexibility for movement and other functions, supported by a cytoskeleton instead.
Question 22:
A student prepared a temporary mount of cheek cells and observed them under a microscope.

a) Name the stain used to make the nucleus visible.

b) Why is the nucleus considered the control center of the cell?

Answer:

a) The stain used is methylene blue or safranin, which highlights the nucleus by binding to DNA.


b) The nucleus is the control center because:

  • It contains chromosomes made of DNA, which carry genetic instructions for cell activities.
  • It regulates cell functions like growth, reproduction, and protein synthesis.
  • Without the nucleus, the cell cannot survive for long as it loses its ability to coordinate vital processes.
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