Cell the Building Block of Life — Class 9 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 9 Science chapter "Cell the Building Block of Life" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Cell the Building Block of Life" — 8 important questions with detailed answers for CBSE…
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NCERT Solutions for Class 9 Science — Cell the Building Block of Life. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Cell the Building Block of Life — All 8 Questions Solved
Q1. What is the cell?
The cell is the fundamental unit of life. It is the smallest unit of living organisms that can carry out all life processes independently. All living organisms are made of one or more cells.
Q2. Distinguish between prokaryotic and eukaryotic cells.
Prokaryotic cells lack a membrane-bound nucleus and organelles (e.g., bacteria).
Eukaryotic cells have a true membrane-bound nucleus and membrane-bound organelles (e.g., animal and plant cells).
Prokaryotes are generally smaller than eukaryotes.
Q3. Name the three main parts of the cell.
1. Cell membrane (plasma membrane) - controls passage of materials
2. Cytoplasm - gel-like substance containing organelles
3. Nucleus - contains genetic material (DNA), controls cell activities
Q4. What is the function of the plasma membrane?
The plasma membrane is a semipermeable barrier that controls the passage of substances in and out of the cell. It allows useful materials to enter and prevents harmful substances from entering while removing waste products.
Q5. What is the function of mitochondria?
Mitochondria are the powerhouses of the cell. They generate energy (ATP) through cellular respiration, breaking down glucose and other nutrients to release energy that the cell uses for various activities.
Q6. Name two differences between plant and animal cells.
1. Plant cells have a cell wall (rigid) outside the membrane; animal cells do not.
2. Plant cells have large vacuoles for storage; animal cells have small vacuoles.
3. Plant cells have chloroplasts for photosynthesis; animal cells do not.
4. Plant cells are rectangular; animal cells are round.
Q7. What is the role of the nucleus in the cell?
The nucleus stores genetic information (DNA) in the form of chromosomes. It controls all cellular activities by directing protein synthesis and regulating cell division, growth, and metabolism through gene expression.
Q8. What is the function of ribosomes?
Ribosomes are the sites of protein synthesis. They read mRNA instructions from the nucleus and assemble amino acids in the correct sequence to build proteins required for cellular functions.
Cell the Building Block of Life — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Who was the first scientist to observe and describe living cells?
- A. Robert Hooke
- B. Antonie van Leeuwenhoek
- C. Robert Brown
- D. Rudolf Virchow
Answer: B. Antonie van Leeuwenhoek — Robert Hooke observed dead cork cells. Antonie van Leeuwenhoek was the first to observe and describe living cells, such as bacteria and protozoa, using his improved microscope.
MCQ 2. Which of the following cell organelles is known as the 'powerhouse of the cell'?
- A. Nucleus
- B. Mitochondria
- C. Ribosome
- D. Lysosome
Answer: B. Mitochondria — Mitochondria are responsible for cellular respiration, a process that generates ATP (adenosine triphosphate), the primary energy currency of the cell.
MCQ 3. The statement 'Omnis cellula e cellula', meaning 'all cells arise from pre-existing cells', was added to the cell theory by:
- A. Matthias Schleiden
- B. Theodor Schwann
- C. Rudolf Virchow
- D. Robert Hooke
Answer: C. Rudolf Virchow — While Schleiden and Schwann proposed the initial cell theory, Rudolf Virchow later formalized the idea that new cells originate only from existing cells through division.
MCQ 4. In plant cells, which organelle is primarily responsible for storing water, nutrients, and waste products, and maintains turgor pressure?
- A. Chloroplast
- B. Vacuole
- C. Mitochondria
- D. Nucleus
Answer: B. Vacuole — Plant cells typically have a large central vacuole that performs multiple functions including storage, waste disposal, and contributing to the cell's turgidity by maintaining internal pressure.
MCQ 5. The plasma membrane is selectively permeable. This means it:
- A. Allows all substances to pass through freely
- B. Prevents all substances from entering or leaving the cell
- C. Allows only water molecules to cross it
- D. Regulates the movement of specific substances into and out of the cell
Answer: D. Regulates the movement of specific substances into and out of the cell — A selectively permeable membrane controls which molecules can pass through it, ensuring that essential nutrients enter and waste products exit, while maintaining the cell's internal environment.
MCQ 6. If a plant cell is placed in a hypertonic solution (a solution with higher solute concentration than the cell), what will be the most likely outcome?
- A. It will swell and burst due to water intake.
- B. It will remain unchanged in size and shape.
- C. It will shrink and its protoplast will pull away from the cell wall (plasmolysis).
- D. It will absorb more water and become more turgid.
Answer: C. It will shrink and its protoplast will pull away from the cell wall (plasmolysis). — In a hypertonic solution, water moves out of the plant cell by osmosis. Due to the rigid cell wall, the cell itself doesn't burst, but the protoplast shrinks and detaches from the wall, a process called plasmolysis.
MCQ 7. Which of the following is a characteristic feature of prokaryotic cells?
- A. Presence of a well-defined nucleus
- B. Presence of membrane-bound organelles
- C. Genetic material is not enclosed by a nuclear membrane
- D. Always larger in size compared to eukaryotic cells
Answer: C. Genetic material is not enclosed by a nuclear membrane — Prokaryotic cells lack a true nucleus and other membrane-bound organelles. Their genetic material, typically a single circular chromosome, is located in a region called the nucleoid, without a surrounding membrane.
MCQ 8. Rough Endoplasmic Reticulum (RER) is primarily involved in the synthesis and folding of:
- A. Lipids
- B. Carbohydrates
- C. Proteins
- D. Nucleic acids
Answer: C. Proteins — The RER is studded with ribosomes, which are the sites of protein synthesis. These proteins are often destined for secretion, insertion into membranes, or delivery to other organelles.
MCQ 9. Lysosomes are often referred to as 'suicidal bags' of the cell because they:
- A. Produce energy for the cell's activities
- B. Are involved in synthesizing essential cellular proteins
- C. Contain powerful digestive enzymes that can break down cellular components
- D. Store excess water and nutrients for the cell
Answer: C. Contain powerful digestive enzymes that can break down cellular components — Lysosomes contain a variety of hydrolytic enzymes that can digest worn-out cell parts, waste materials, and even engulf foreign invaders. If the lysosomal membrane ruptures, these enzymes can digest the entire cell, leading to its death.
MCQ 10. Which of these components is present in plant cells but absent in animal cells?
- A. Cell membrane
- B. Cytoplasm
- C. Cell wall
- D. Nucleus
Answer: C. Cell wall — Plant cells possess a rigid cell wall, located outside the plasma membrane, which provides structural support, protection, and prevents excessive water uptake. Animal cells lack this structure.
MCQ 11. Chromosomes, which carry the genetic information in the form of DNA, are located within which part of a eukaryotic cell?
- A. Cytoplasm
- B. Mitochondria
- C. Nucleus
- D. Ribosomes
Answer: C. Nucleus — The nucleus is the control center of the eukaryotic cell and contains the cell's genetic material organized into chromosomes, which are made of DNA and proteins.
MCQ 12. Which organelle is responsible for modifying, sorting, and packaging proteins and lipids synthesized in the endoplasmic reticulum for secretion or delivery to other organelles?
- A. Endoplasmic Reticulum
- B. Mitochondria
- C. Golgi Apparatus
- D. Lysosomes
Answer: C. Golgi Apparatus — The Golgi apparatus (or Golgi complex) acts as the cell's post office, processing and packaging macromolecules like proteins and lipids into vesicles for targeted delivery.
MCQ 13. What is the primary function of chloroplasts in plant cells?
- A. Cellular respiration
- B. Protein synthesis
- C. Photosynthesis
- D. Waste storage
Answer: C. Photosynthesis — Chloroplasts contain the pigment chlorophyll and are the sites where light energy is captured and converted into chemical energy (sugars) through the process of photosynthesis.
MCQ 14. The fluid mosaic model best describes the structure of the:
- A. Cell wall
- B. Nucleus
- C. Plasma membrane
- D. Mitochondria
Answer: C. Plasma membrane — The fluid mosaic model depicts the plasma membrane as a fluid bilayer of phospholipids with various proteins embedded in or associated with it, allowing for dynamic movement.
MCQ 15. If the ribosomes of a cell were to be completely destroyed, what would be the most immediate and significant consequence for the cell?
- A. Energy production would cease immediately.
- B. Waste materials would accumulate rapidly.
- C. Protein synthesis would be severely inhibited.
- D. The cell would lose its structural integrity and burst.
Answer: C. Protein synthesis would be severely inhibited. — Ribosomes are the cellular machinery responsible for synthesizing proteins from messenger RNA. Without functional ribosomes, the cell would be unable to produce essential proteins necessary for its survival and function.
MCQ 16. An organism that consists of only a single cell is known as a(n):
- A. Multicellular organism
- B. Unicellular organism
- C. Colonial organism
- D. Tissue
Answer: B. Unicellular organism — Unicellular organisms, such as bacteria and Amoeba, perform all life functions within a single cell.
MCQ 17. The process of osmosis specifically involves the movement of:
- A. Solute molecules across a permeable membrane
- B. Water molecules across a selectively permeable membrane
- C. Solute molecules against a concentration gradient
- D. Water molecules through a fully permeable membrane
Answer: B. Water molecules across a selectively permeable membrane — Osmosis is the net movement of water (solvent) molecules from a region of higher water concentration to a region of lower water concentration across a partially permeable membrane.
MCQ 18. Which of the following statements about mitochondria is INCORRECT?
- A. They have their own circular DNA.
- B. They can synthesize some of their own proteins.
- C. They are the primary sites for anaerobic respiration.
- D. They have a double membrane structure, with the inner membrane folded into cristae.
Answer: C. They are the primary sites for anaerobic respiration. — Mitochondria are the primary sites for aerobic respiration, which requires oxygen. Anaerobic respiration, which does not require oxygen, mainly occurs in the cytoplasm.
MCQ 19. The jelly-like fluid that fills the cell and surrounds the organelles, excluding the nucleus, is called:
- A. Protoplasm
- B. Cytoplasm
- C. Nucleoplasm
- D. Cell sap
Answer: B. Cytoplasm — Cytoplasm refers to all the contents within the cell membrane, except for the nucleus. It includes the cytosol (the jelly-like substance) and the organelles suspended within it.
MCQ 20. Which cell organelle plays a crucial role in the detoxification of drugs and poisons, as well as the synthesis of lipids?
- A. Rough Endoplasmic Reticulum
- B. Smooth Endoplasmic Reticulum
- C. Golgi apparatus
- D. Lysosomes
Answer: B. Smooth Endoplasmic Reticulum — The Smooth Endoplasmic Reticulum (SER) lacks ribosomes and is primarily involved in lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons in liver cells.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.