A researcher discovers a chemical that locks phospholipids in place, preventing any lateral movement within the membrane. Which aspect of cell membrane function would be most directly impaired?

Membrane fluidity and selective permeability

Scientists believe that calcium carbonate deposits around ancient thermophiles may have contributed to the origin of life by:

Protecting organic molecules and assisting in membrane formation

Supplying energy for metabolism

Forming the first genetic material

Protecting organic molecules and assisting in membrane formation

Creating oxygen for early organisms

Assertion (A): The cell membrane is selectively permeable. Reason (R): It is composed of a lipid bilayer with embedded proteins.

Both A and R are true but R is not the correct explanation of A.

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

Explain the role of the cell membrane in maintaining the internal environment of a cell.

The cell membrane acts as a selectively permeable barrier that controls the movement of substances in and out of the cell, thereby maintaining the appropriate internal conditions necessary for cellular functions.

A plant cell is immersed in a hypertonic salt solution. Predict the changes that will occur in the cell and explain the underlying process.

The cell will lose water and shrink. The cell membrane will pull away from the cell wall, a condition known as plasmolysis. This occurs because water moves out of the cell by osmosis from a region of higher water potential (inside the cell) to a region of lower water potential (the hypertonic solution).

Describe the fluid-mosaic model of the cell membrane. List two key features.

The fluid-mosaic model describes the cell membrane as a lipid bilayer with proteins embedded. The lipids have hydrophilic heads facing outward and hydrophobic tails inward. Key features: (1) The membrane is fluid because the lipids and proteins can move laterally. (2) It is mosaic due to the patchwork of proteins scattered within the lipid bilayer.

A scientist discovers a bacterium in a hypersaline lake that maintains an internal salt concentration much lower than its surroundings. Based on your understanding of osmosis, propose a mechanism that the bacterium might use to prevent water loss and survive. Justify your reasoning.

The bacterium likely accumulates compatible solutes (e.g., amino acids, sugars) inside its cytoplasm to increase internal solute concentration to match or exceed the external osmotic pressure. This prevents net water loss by osmosis. It could also actively pump out toxic ions. This mechanism ensures the cell remains isotonic or slightly hypertonic relative to the environment, thus maintaining cell turgor and survival.

You are given a solution X in which red blood cells (RBCs) are placed. After a few minutes, you observe under the microscope that the RBCs have swollen and some have burst. Based on your knowledge of osmosis, what could you deduce about the concentration of solution X relative to the RBCs' cytoplasm? If a plant cell was placed in the same solution X, what would you expect to happen and why? Explain the role of the cell wall in this context.

RBCs swelling and bursting indicates that solution X is hypotonic relative to the RBCs' cytoplasm; water entered the cells by osmosis, causing them to lyse. If a plant cell is placed in solution X, it would also take in water and swell, but it would not burst because the rigid cell wall exerts an opposing pressure (turgor pressure) that prevents excessive expansion. The cell becomes turgid, and the cell wall provides structural support.

The chapter mentions that scientists from Birbal Sahni Institute studied hot springs in Puga Valley and found calcium carbonate deposits formed around thermophilic bacteria. Assume you are investigating the origin of the first cells. How might these calcium carbonate deposits have contributed to the formation of primitive cells? Also, explain two adaptations that these thermophilic bacteria must have to survive in such extreme temperatures, relating your answer to the structure of their cell membrane and proteins.

Calcium carbonate deposits could have acted as a protective layer, shielding early organic molecules from harmful UV radiation and extreme temperature fluctuations. This mineral encrustation may have formed a primitive boundary, similar to a cell membrane, allowing internal chemistry to develop. Thermophilic bacteria likely possess cell membranes with ether-linked lipids (instead of ester-linked) that remain stable at high temperatures. Additionally, their proteins contain more ionic bonds and hydrophobic interactions, making them resistant to denaturation, and their enzymes are adapted to function optimally at near-boiling points.

In the Puga Valley hot springs of Ladakh, temperatures remain near the boiling point of water. Despite this extreme heat, microorganisms called thermophiles thrive there. Scientists believe that these environments are similar to the conditions on early Earth, around 3.5 billion years ago. The cell membranes of these thermophiles contain special lipids that remain stable at high temperatures, preventing the membrane from becoming too fluid and disintegrating. (1) What is the meaning of the term 'thermophile'? (2) How might the cell membranes of thermophiles be chemically different from those of organisms living in moderate temperatures? (3) Why do scientists consider hot springs as analogues of early Earth environments? Explain their significance in the origin of life.

Thermophiles are heat-loving organisms. Their membranes have adaptations like saturated lipids for stability. Hot springs resemble early Earth's conditions, possibly facilitating the formation of early cells.

Class 9 Science Chapter 2: Cell – The Building Block of Life — Important Questions & Sample Paper

CBSE· 44+ original questions readyहिन्दी में देखें

Practise important & sample questions with answers, see the CBSE marks distribution & blueprint, or generate a full sample paper — free, for 2026-27.

Reviewed by qpaper's CBSE curriculum team · Edited by Mohit · Updated June 2026

Quick answer

Yes — this page has 44+ original Class 9 Science Chapter 2 (“Cell – The Building Block of Life”) important questions with answers (Multiple Choice (MCQ), Assertion–Reason, Short Answer, Short Answer, Long Answer, Case Study). Practise them free, or generate a full CBSE board-pattern sample paper (80 marks) and export it to PDF or Word — in English & Hindi, for 2026-27.

Class 9 Science Chapter 2, ‘Cell – The Building Block of Life,’ introduces students to the fundamental unit of life. This chapter covers the discovery of the cell, cell theory, and the diversity in cell number, shape, and size. Students learn to distinguish between unicellular and multicellular organisms, and between prokaryotic and eukaryotic cells. A major focus is the detailed structure of plant and animal cells, including organelles such as the cell membrane, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, ribosomes, plastids, and vacuoles. The chapter also explains vital processes like diffusion and osmosis, illustrating how substances move across cell membranes. Understanding these concepts builds a strong foundation for biology.

In CBSE exams, questions often test understanding through applications. Common question types include defining terms (osmosis, diffusion), distinguishing between plant and animal cells, explaining the functions of organelles, and predicting outcomes of osmotic experiments. For instance, students might be asked to explain why vegetables shrivel in salty water or why RBCs burst in a hypotonic solution, as seen in our sample questions. Numerical problems, such as calculating cell size using a microscope, also feature. This chapter demands both conceptual clarity and the ability to apply knowledge to real-world scenarios. Our question bank provides ample practice across all these areas, helping teachers generate targeted assessments and students to master the topic.

Generate a full sample paper for this chapter

Pick chapters, set your blueprint and marks distribution, and export a print-ready PDF or editable Word — with an answer key. Free to build.

Generate full paper See a sample paper

Preview: a real paper we generate

This is the actual CBSE board-style layout you export — built from this chapter's own questions, with an answer key.

Science — Cell – The Building Block of Life

Class 9Time: 3 hrsMax Marks: 80

SECTION A

1.
A researcher discovers a chemical that locks phospholipids in place, preventing any lateral movement within the membrane. Which aspect of cell membrane function would be most directly impaired?
(a) Energy production(b) Protein synthesis(c) Membrane fluidity and selective permeability(d) DNA replication
1
2.
A light microscope has an eyepiece of 15X and an objective lens of 40X. A student observes that a cell appears 6 mm long under this microscope. What is the actual length of the cell in micrometres?
(a) 10 µm(b) 0.1 µm(c) 100 µm(d) 6000 µm
1
3.
Unicellular organisms consist of a single cell. Which of the following is an example?
(a) Mushroom(b) Amoeba(c) Earthworm(d) Mosquito
1

+ 41 more questions in the full paper

Generate full paper

Marks distribution & blueprint

In a CBSE exam, this chapter typically contributes questions across the following types. The last column shows how many original questions of each type we have ready in our bank for this chapter:

Question type	Marks each	In our bank
Multiple Choice (MCQ)	1 mark	13
Assertion–Reason	1 mark	6
Short Answer	2 marks	8
Short Answer	3 marks	6
Long Answer	5 marks	5
Case Study	4 marks	6

44 original, exam-style questions in our bank for this chapter — with answers.

Important & sample questions (with answers)

Real, exam-style questions to practise and revise — each with its answer. Generate a full paper for unlimited more.

Q1. A researcher discovers a chemical that locks phospholipids in place, preventing any lateral movement within the membrane. Which aspect of cell membrane function would be most directly impaired?
1 mark
Multiple Choice (MCQ)
(A) Energy production(B) Protein synthesis(C) Membrane fluidity and selective permeability(D) DNA replication
▸ Answer▾ Answer
Membrane fluidity and selective permeability
Q2. A light microscope has an eyepiece of 15X and an objective lens of 40X. A student observes that a cell appears 6 mm long under this microscope. What is the actual length of the cell in micrometres?
1 mark
Multiple Choice (MCQ)
(A) 10 µm(B) 0.1 µm(C) 100 µm(D) 6000 µm
▸ Answer▾ Answer
10 µm
Q3. Unicellular organisms consist of a single cell. Which of the following is an example?
1 mark
Multiple Choice (MCQ)
(A) Mushroom(B) Amoeba(C) Earthworm(D) Mosquito
▸ Answer▾ Answer
Amoeba
Q4. Scientists believe that calcium carbonate deposits around ancient thermophiles may have contributed to the origin of life by:
1 mark
Multiple Choice (MCQ)
(A) Supplying energy for metabolism(B) Forming the first genetic material(C) Protecting organic molecules and assisting in membrane formation(D) Creating oxygen for early organisms
▸ Answer▾ Answer
Protecting organic molecules and assisting in membrane formation
Q5. Assertion (A): The cell membrane is selectively permeable. Reason (R): It is composed of a lipid bilayer with embedded proteins.
1 mark
Assertion–Reason
(A) Both A and R are true and R is the correct explanation of A.(B) Both A and R are true but R is not the correct explanation of A.(C) A is true but R is false.(D) A is false but R is true.
▸ Answer▾ Answer
Both A and R are true but R is not the correct explanation of A.
Q6. Explain the role of the cell membrane in maintaining the internal environment of a cell.
2 marks
Short Answer
▸ Answer▾ Answer
The cell membrane acts as a selectively permeable barrier that controls the movement of substances in and out of the cell, thereby maintaining the appropriate internal conditions necessary for cellular functions.
Q7. A plant cell is immersed in a hypertonic salt solution. Predict the changes that will occur in the cell and explain the underlying process.
2 marks
Short Answer
▸ Answer▾ Answer
The cell will lose water and shrink. The cell membrane will pull away from the cell wall, a condition known as plasmolysis. This occurs because water moves out of the cell by osmosis from a region of higher water potential (inside the cell) to a region of lower water potential (the hypertonic solution).
Q8. Describe the fluid-mosaic model of the cell membrane. List two key features.
3 marks
Short Answer
▸ Answer▾ Answer
The fluid-mosaic model describes the cell membrane as a lipid bilayer with proteins embedded. The lipids have hydrophilic heads facing outward and hydrophobic tails inward. Key features: (1) The membrane is fluid because the lipids and proteins can move laterally. (2) It is mosaic due to the patchwork of proteins scattered within the lipid bilayer.
Q9. A scientist discovers a bacterium in a hypersaline lake that maintains an internal salt concentration much lower than its surroundings. Based on your understanding of osmosis, propose a mechanism that the bacterium might use to prevent water loss and survive. Justify your reasoning.
3 marks
Short Answer
▸ Answer▾ Answer
The bacterium likely accumulates compatible solutes (e.g., amino acids, sugars) inside its cytoplasm to increase internal solute concentration to match or exceed the external osmotic pressure. This prevents net water loss by osmosis. It could also actively pump out toxic ions. This mechanism ensures the cell remains isotonic or slightly hypertonic relative to the environment, thus maintaining cell turgor and survival.
Q10. You are given a solution X in which red blood cells (RBCs) are placed. After a few minutes, you observe under the microscope that the RBCs have swollen and some have burst. Based on your knowledge of osmosis, what could you deduce about the concentration of solution X relative to the RBCs' cytoplasm? If a plant cell was placed in the same solution X, what would you expect to happen and why? Explain the role of the cell wall in this context.
5 marks
Long Answer
▸ Answer▾ Answer
RBCs swelling and bursting indicates that solution X is hypotonic relative to the RBCs' cytoplasm; water entered the cells by osmosis, causing them to lyse. If a plant cell is placed in solution X, it would also take in water and swell, but it would not burst because the rigid cell wall exerts an opposing pressure (turgor pressure) that prevents excessive expansion. The cell becomes turgid, and the cell wall provides structural support.
Q11. The chapter mentions that scientists from Birbal Sahni Institute studied hot springs in Puga Valley and found calcium carbonate deposits formed around thermophilic bacteria. Assume you are investigating the origin of the first cells. How might these calcium carbonate deposits have contributed to the formation of primitive cells? Also, explain two adaptations that these thermophilic bacteria must have to survive in such extreme temperatures, relating your answer to the structure of their cell membrane and proteins.
5 marks
Long Answer
▸ Answer▾ Answer
Calcium carbonate deposits could have acted as a protective layer, shielding early organic molecules from harmful UV radiation and extreme temperature fluctuations. This mineral encrustation may have formed a primitive boundary, similar to a cell membrane, allowing internal chemistry to develop. Thermophilic bacteria likely possess cell membranes with ether-linked lipids (instead of ester-linked) that remain stable at high temperatures. Additionally, their proteins contain more ionic bonds and hydrophobic interactions, making them resistant to denaturation, and their enzymes are adapted to function optimally at near-boiling points.
Q12. In the Puga Valley hot springs of Ladakh, temperatures remain near the boiling point of water. Despite this extreme heat, microorganisms called thermophiles thrive there. Scientists believe that these environments are similar to the conditions on early Earth, around 3.5 billion years ago. The cell membranes of these thermophiles contain special lipids that remain stable at high temperatures, preventing the membrane from becoming too fluid and disintegrating.
4 marks
Case Study
1. (i) What is the meaning of the term 'thermophile'?1 mark
2. (ii) How might the cell membranes of thermophiles be chemically different from those of organisms living in moderate temperatures?1 mark
3. (iii) Why do scientists consider hot springs as analogues of early Earth environments? Explain their significance in the origin of life.2 marks
▸ Answer▾ Answer
Thermophiles are heat-loving organisms. Their membranes have adaptations like saturated lipids for stability. Hot springs resemble early Earth's conditions, possibly facilitating the formation of early cells.

Frequently asked questions

What is the difference between diffusion and osmosis?

Diffusion is the movement of any particles from a region of higher concentration to lower concentration. Osmosis is a special type of diffusion that involves the movement of water molecules through a selectively permeable membrane, such as the cell membrane.

Why do plant cells not burst in a hypotonic solution while animal cells do?

Plant cells have a rigid cell wall that exerts turgor pressure against the cell membrane, preventing it from over-expanding and bursting. Animal cells lack a cell wall, so they swell and may lyse in a hypotonic environment.

How do I calculate the actual size of a cell observed under a microscope?

First, determine the diameter of the field of view. Count the number of cells that fit along that diameter. Divide the field diameter by the number of cells to get the length per cell. Convert to micrometers by multiplying millimeters by 1000. For example, a 4 mm field with 16 cells gives 0.25 mm per cell, or 250 µm.

Generate a full sample paper for this chapter

Preview: a real paper we generate

Marks distribution & blueprint

Important & sample questions (with answers)

Frequently asked questions

More chapters