CBSE Class 11 Biology Short Answer Questions: Cell – The Unit of Life (NCERT-Based)

Course and Examination Framework

Course: CBSE Class 11 Biology

Board: Central Board of Secondary Education

Unit III: Cell Structure and Function

Chapter 8: Cell – The Unit of Life

Question Type: Short Answer Type Questions

Answer Length: 60–80 Words

Syllabus Compliance: Strictly as per NCERT

Examination Relevance: CBSE Class 11 Annual & School Examinations

Section A: Cell Discovery and Cell Theory (Questions 1–10)

Q1. Describe the discovery of the cell.

Ans:
The cell was discovered by Robert Hooke in 1665 while examining thin slices of cork under a compound microscope. He observed small, box-like structures and named them “cells.” Later, Antonie van Leeuwenhoek observed living cells, providing deeper insight into cell structure and function.

Q2. Explain the cell theory.

Ans:
Cell theory states that all living organisms are composed of cells, the cell is the basic structural and functional unit of life, and new cells arise from pre-existing cells. This theory was proposed by Schleiden and Schwann and later modified by Rudolf Virchow.

Q3. Why is the cell called the basic unit of life?

Ans:
The cell is called the basic unit of life because it performs all essential life functions such as metabolism, respiration, growth, excretion, and reproduction. All multicellular organisms develop from a single cell, highlighting its fundamental importance.

Q4. State the significance of cell theory.

Ans:
Cell theory establishes the cellular basis of life and shows unity among living organisms. It explains growth and reproduction as cellular processes and provides the foundation for understanding heredity, physiology, and development.

Q5. Differentiate between unicellular and multicellular organisms.

Ans:
Unicellular organisms consist of a single cell performing all life functions, such as Amoeba. Multicellular organisms are made up of many specialized cells organized into tissues and organs, as seen in plants and animals.

Section B: Prokaryotic and Eukaryotic Cells (Questions 11–20)

Q6. Describe the general features of prokaryotic cells.

Ans:
Prokaryotic cells lack a true nucleus and membrane-bound organelles. Their genetic material lies in a nucleoid region. They possess 70S ribosomes and are generally small in size. Examples include bacteria and cyanobacteria.

Q7. Explain the structure of a prokaryotic cell.

Ans:
A prokaryotic cell has a cell envelope consisting of glycocalyx, cell wall, and plasma membrane. The cytoplasm contains ribosomes but no organelles. The nucleoid region contains naked circular DNA. Some cells possess flagella and pili.

Q8. Describe the main features of eukaryotic cells.

Ans:
Eukaryotic cells possess a true nucleus enclosed by a nuclear membrane and contain membrane-bound organelles. Their genetic material is linear DNA associated with histones. These cells are larger and more complex than prokaryotic cells.

Q9. Differentiate between prokaryotic and eukaryotic cells.

Ans:
Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells possess both. Prokaryotes have circular DNA and 70S ribosomes, whereas eukaryotes have linear DNA with histones and 80S ribosomes.

Q10. What is the nucleoid region?

Ans:
The nucleoid is an irregular region in prokaryotic cells containing naked circular DNA. It is not surrounded by a nuclear membrane and controls cellular activities.

Section C: Cell Membrane and Cell Wall (Questions 21–30)

Q11. Describe the structure of the plasma membrane.

Ans:
The plasma membrane is composed of a phospholipid bilayer embedded with proteins, carbohydrates, and cholesterol. Its structure is explained by the Fluid Mosaic Model, which allows flexibility and selective permeability.

Q12. Explain the functions of plasma membrane.

Ans:
The plasma membrane regulates the movement of substances in and out of the cell, maintains cellular integrity, enables cell communication, and protects internal components by selective permeability.

Q13. What is selective permeability?

Ans:
Selective permeability is the property of the plasma membrane that allows certain substances like gases and small molecules to pass freely while restricting others, maintaining internal balance.

Q14. Describe diffusion and active transport.

Ans:
Diffusion is the passive movement of molecules from high to low concentration without energy. Active transport moves substances against the concentration gradient using energy and carrier proteins.

Q15. Explain the structure and function of the cell wall.

Ans:
The cell wall is a rigid outer covering found in plant cells, composed mainly of cellulose. It provides shape, protection, and prevents osmotic bursting, maintaining cell rigidity.

Section D: Nucleus and Endomembrane System (Questions 31–40)

Q16. Describe the structure of the nucleus.

Ans:
The nucleus is enclosed by a double-layered nuclear envelope with pores. It contains nucleoplasm, nucleolus, and chromatin. It stores genetic material and regulates cellular activities.

Q17. Explain the function of the nucleolus.

Ans:
The nucleolus is involved in the synthesis of ribosomal RNA and assembly of ribosomes, essential for protein synthesis.

Q18. Describe the endoplasmic reticulum.

Ans:
Endoplasmic reticulum is a network of membranous tubules. RER synthesizes proteins, while SER synthesizes lipids, detoxifies chemicals, and stores calcium ions.

Q19. Explain the structure and function of Golgi apparatus.

Ans:
Golgi apparatus consists of flattened membranous sacs called cisternae. It modifies, packages, and transports proteins and lipids to various cellular destinations.

Q20. Why are lysosomes called suicidal bags?

Ans:
Lysosomes contain hydrolytic enzymes that digest damaged organelles and cellular debris. During cell injury, they may cause self-digestion of the cell.

Section E: Mitochondria, Plastids, and Ribosomes (Questions 41–50)

Q21. Describe the structure of mitochondria.

Ans:
Mitochondria are double-membraned organelles with an outer smooth membrane and an inner folded membrane forming cristae. The inner space is called the matrix.

Q22. State the functions of mitochondria.

Ans:
Mitochondria are the sites of aerobic respiration and ATP synthesis, providing energy for cellular activities. They also regulate apoptosis.

Q23. What are plastids? Explain their types.

Ans:
Plastids are plant cell organelles involved in photosynthesis, storage, and coloration. Types include chloroplasts, chromoplasts, and leucoplasts.

Q24. Describe ribosomes and their functions.

Ans:
Ribosomes are non-membranous organelles composed of rRNA and proteins. They serve as sites for protein synthesis and occur freely or attached to ER.

Q25. Explain the structure and function of vacuoles.

Ans:
Vacuoles are membrane-bound sacs filled with cell sap. In plant cells, they maintain turgidity, store substances, and aid in osmoregulation.