This MCQ module is based on: Cell — NCERT Exercises and Summary
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Cell — NCERT Exercises and Summary
🎓 Class 9
Science
CBSE
Theory
Ch 2 — Cell: The Building Block of Life
⏱ ~15 min
🌐 Language: [gtranslate]
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Cell — NCERT Exercises and Summary
Class 9 Science · Chapter 2 · Part 4 — Summary, Key Terms & NCERT Exercises
Chapter Summary
- Life on Earth is believed to have begun in water; thermophiles found in hot springs (e.g., Puga Valley, Ladakh, studied by the Birbal Sahni Institute of Palaeosciences) hint at how the first cells survived.
- Robert Hooke (1665) discovered cells in cork; Leeuwenhoek (1674) first saw living cells; Robert Brown (1831) identified the nucleus.
- Cell Theory: All organisms are made of cells; the cell is the basic unit of life; all cells arise from pre-existing cells (Schleiden, Schwann, Virchow).
- The plasma membrane is selectively permeable; the cell wall (cellulose) gives plant cells shape.
- The nucleus contains chromatin (DNA + protein) which condenses into chromosomes during division.
- Major organelles: ER (rough/smooth), Golgi apparatus, ribosomes, mitochondria (powerhouse — make ATP), plastids (chloroplasts/chromoplasts/leucoplasts), lysosomes (suicide bags), vacuoles.
- Prokaryotes (bacteria) lack a true nucleus; eukaryotes (plants, animals) have one.
- Plant cells have cell wall, plastids, large central vacuole; animal cells do not.
- Mitosis = body cells → 2 identical daughter cells; Meiosis = reproductive cells → 4 daughter cells with halved chromosome number.
- Uncontrolled cell division leads to tumours and cancer.
Key Terms at a Glance
CellBasic unit of life
Plasma membraneSelectively permeable boundary
Cell wallCellulose; only in plants
CytoplasmJelly-like fluid inside cell
NucleusControl centre with DNA
ChromatinLoose DNA + protein network
ChromosomesCondensed DNA rods
ERTubular transport network
Golgi apparatusPackaging and dispatch
RibosomeProtein synthesis
MitochondriaPowerhouse — ATP
ChloroplastPhotosynthesis
LysosomeSuicide bag — digestion
VacuoleStorage sac
ProkaryoteNo true nucleus
EukaryoteTrue nucleus + organelles
MitosisBody-cell division
MeiosisGamete formation
OsmosisWater movement across membrane
DiffusionHigh → low concentration
NCERT Exercises (with Solutions)
1Who discovered the cell and how?
Robert Hooke discovered the cell in 1665. He cut a thin slice of cork (the bark of an oak tree) and observed it under a self-made compound microscope. He saw tiny, hollow box-like compartments resembling the small rooms of a monastery and named them "cellulae" (Latin for little rooms) — from which the term cell originates.
2Why is the cell called the structural and functional unit of life?
Structural unit: Every organism, whether unicellular or multicellular, is built up from cells — they are the bricks of the body. Functional unit: All life processes such as nutrition, respiration, excretion, growth and reproduction are carried out at the cell level. Hence the cell is both the smallest unit of structure and the smallest unit capable of performing the activities of life.
3How do substances like CO2 and water move in and out of the cell?
CO2: moves by diffusion — from a region of higher concentration to lower concentration through the plasma membrane. Inside cells CO2 builds up as a waste product of respiration; outside the concentration is lower, so it diffuses out.
Water: moves by osmosis — across the selectively permeable membrane from a region of higher water concentration to lower water concentration.
Water: moves by osmosis — across the selectively permeable membrane from a region of higher water concentration to lower water concentration.
4Why is the plasma membrane called a selectively permeable membrane?
Because it allows only certain substances (like O2, CO2, water, glucose) to pass through it freely while restricting the movement of others (like large proteins or harmful ions). This selectivity gives the cell control over what enters and leaves, helping maintain a stable internal environment.
5Differentiate between prokaryotic and eukaryotic cells.
Prokaryotic cells: small (1–10 µm), no membrane-bound nucleus (DNA in nucleoid), no membrane-bound organelles, 70S ribosomes, divide by binary fission. Examples: bacteria, blue-green algae.
Eukaryotic cells: larger (10–100 µm), true nucleus with nuclear membrane, several membrane-bound organelles (mitochondria, ER, Golgi), 80S ribosomes, divide by mitosis/meiosis. Examples: plant, animal, fungal cells.
Eukaryotic cells: larger (10–100 µm), true nucleus with nuclear membrane, several membrane-bound organelles (mitochondria, ER, Golgi), 80S ribosomes, divide by mitosis/meiosis. Examples: plant, animal, fungal cells.
6What is the function of the cell wall? Why don't animal cells have one?
The cell wall is a thick, non-living covering of cellulose found outside the plasma membrane in plant cells. It (i) gives the cell a definite shape, (ii) provides mechanical strength and protection, and (iii) allows the cell to withstand large changes in surrounding water concentration without bursting. Animal cells move, change shape and require flexibility (e.g., to crawl, contract, or change form during development), which a rigid cell wall would not permit.
7Why is mitochondria called the powerhouse of the cell?
Because mitochondria release energy from food during cellular respiration and store it in molecules of ATP (adenosine triphosphate). ATP acts as the energy currency that powers almost every activity of the cell — muscle contraction, nerve impulses, biosynthesis. Since mitochondria run this energy-supply system, they are called the powerhouse of the cell.
8Where are proteins synthesised inside the cell?
Proteins are synthesised on ribosomes. Ribosomes may float freely in the cytoplasm or attach to the rough endoplasmic reticulum. The mRNA carrying genetic instructions from the nucleus binds to the ribosome, which then assembles amino acids in the correct order to build the protein.
9What are the consequences of the following conditions?
(a) A cell containing higher water concentration than the surrounding medium.
(b) A cell with a lower water concentration than the surrounding medium.
(c) A cell at the same water concentration as its surroundings.
(a) A cell containing higher water concentration than the surrounding medium.
(b) A cell with a lower water concentration than the surrounding medium.
(c) A cell at the same water concentration as its surroundings.
(a) Water will move out of the cell by exosmosis — the cell shrinks (plasmolysis in plant cells).
(b) Water will move into the cell by endosmosis — the cell swells; an animal cell may burst (cytolysis), a plant cell becomes turgid.
(c) No net movement of water — the cell remains in osmotic equilibrium.
(b) Water will move into the cell by endosmosis — the cell swells; an animal cell may burst (cytolysis), a plant cell becomes turgid.
(c) No net movement of water — the cell remains in osmotic equilibrium.
10Name any two organelles that contain their own genetic material.
Mitochondria and chloroplasts. Both also have their own ribosomes, allowing them to synthesise some of their own proteins. This supports the endosymbiotic theory that they evolved from ancient free-living bacteria.
11What would happen if the Golgi apparatus is removed from a cell?
Without the Golgi apparatus, the cell would lose its packaging and dispatch system. Proteins and lipids made in the ER would not be properly modified, sorted or shipped to their destinations. Lysosomes — which are formed by the Golgi — would also not be produced, so cellular waste cleanup would fail. The cell would soon become disorganised and die.
12Which organelle is known as the suicide bag and why?
The lysosome. It contains powerful digestive enzymes capable of breaking down almost any biological material. When a cell is damaged or dying, the lysosomal membrane breaks down and the released enzymes digest the entire cell — leading to the cell's own destruction. This self-destructive role is why lysosomes are called the suicide bags of the cell.
13Compare mitosis and meiosis.
Mitosis: occurs in body (somatic) cells; produces 2 daughter cells; chromosome number is preserved (diploid → diploid); responsible for growth, repair and asexual reproduction.
Meiosis: occurs only in reproductive cells; produces 4 daughter cells; chromosome number is halved (diploid → haploid); responsible for the formation of gametes (sperm/egg, pollen/ovule) and introduces genetic variation.
Meiosis: occurs only in reproductive cells; produces 4 daughter cells; chromosome number is halved (diploid → haploid); responsible for the formation of gametes (sperm/egg, pollen/ovule) and introduces genetic variation.
14What is cancer? How is it linked to cell division?
Cancer is a disease characterised by uncontrolled cell division. Normally, cell division is tightly regulated — cells divide only when needed and stop when sufficient cells are made. Mutations in the DNA can damage these control mechanisms, causing certain cells to divide endlessly and form a mass called a tumour. If the tumour spreads to other organs through blood or lymph (metastasis), it is called cancer.
15Why was the discovery of the electron microscope important for cell biology?
Light microscopes can magnify only up to about 1500x and cannot resolve very tiny structures inside the cell. The electron microscope, invented by Ernst Ruska in 1931, uses electron beams instead of light and can magnify more than 1,000,000 times. This allowed biologists to see — for the first time — internal organelles like ribosomes, ER membranes, mitochondrial cristae and even viruses, opening up the modern field of cell biology.
Frequently Asked Questions — NCERT Exercises & Intext Questions
How do I solve NCERT Class 9 Science Chapter 2 (Cell: The Building Block of Life) exercise questions for the CBSE board exam?
Solve NCERT Chapter 2 — Cell: The Building Block of Life — exercise questions by first reading the question carefully, writing down the given data, recalling the relevant concepts like cell theory, cell organelles, prokaryote, and applying them step by step. This Part 4 covers every intext and end-of-chapter exercise from the NCERT textbook. Write balanced equations, label diagrams clearly and show each step — CBSE Class 9 examiners award step marks even if the final answer has a small slip. Practising these solutions strengthens conceptual clarity and builds speed for both the school exam and the upcoming Class 10 board exam.
Are the NCERT intext questions from Cell: The Building Block of Life important for the Class 9 Science exam?
Yes, NCERT intext questions for Chapter 2 Cell: The Building Block of Life are highly important for the CBSE Class 9 Science exam. Many questions in school and competitive papers are directly lifted or only slightly modified from these intext questions, and they test the foundational concepts — cell theory, cell organelles, prokaryote — that chapter-end questions and the Class 10 board build on. Attempt every intext question first, then move on to the exercises. This practice ensures complete NCERT coverage, which is the CBSE syllabus's primary source.
What types of questions from Cell: The Building Block of Life are asked in the Class 9 Science exam?
The Class 9 Science paper (CBSE pattern) asks a mix of question types from Cell: The Building Block of Life: 1-mark MCQ and assertion-reason, 2-mark short answers, 3-mark explanations, 5-mark long answers with diagrams or derivations, and 4-mark competency-based / case-study questions. These test understanding of cell theory, cell organelles, prokaryote, eukaryote. Practising every NCERT exercise and intext question prepares you to answer all of these formats with confidence.
How many marks does Chapter 2 — Cell: The Building Block of Life — typically carry in the Class 9 Science paper?
Chapter 2 — Cell: The Building Block of Life — is part of the CBSE Class 9 Science syllabus and typically contributes 5–9 marks in the annual paper, depending on the year's weightage. Questions are drawn from definitions, reasoning, numerical/descriptive problems and diagrams on topics like cell theory, cell organelles, prokaryote. Solving the NCERT exercises in this part is essential because CBSE directly references the NCERT Exploration textbook for question design.
Where can I find step-by-step NCERT solutions for Chapter 2 Cell: The Building Block of Life Class 9 Science?
You can find complete, step-by-step NCERT solutions for Chapter 2 Cell: The Building Block of Life Class 9 Science on MyAiSchool. Every intext and end-of-chapter exercise question is solved with full working, labelled diagrams and CBSE-aligned mark distribution. Solutions highlight key points about cell theory, cell organelles, prokaryote that examiners look for. This makes revision quick and exam-focused for Class 9 CBSE students.
What is the best way to revise Cell: The Building Block of Life for the Class 9 Science exam?
The best way to revise Cell: The Building Block of Life for the CBSE Class 9 Science exam is a three-pass approach. First pass: skim the chapter and note down key terms like cell theory, cell organelles, prokaryote in a one-page mind map. Second pass: solve every NCERT intext and exercise question without looking at the solution, then self-check. Third pass: attempt sample papers and competency-based questions under timed conditions. This structured revision secures full marks for this chapter.
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