CBSE Class 11 Biology Exemplar: Cell - The Unit of Life NCERT Solutions

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NCERT Solutions PDF Class 11 PDF

This resource provides detailed NCERT Solutions for CBSE Class 11 Biology Exemplar, Chapter 8: Cell - The Unit of Life. It covers various aspects of cell biology, including the characteristics of prokaryotic and eukaryotic cells, the structure and function of ribosomes, and the differences between various cell types like sieve tube cells and erythrocytes. The solutions offer clear explanations for multiple-choice questions, helping students understand concepts like cell size variation, staining techniques for chromosomes, and the fundamental differences that define cell types. These solutions are designed to aid students in grasping complex biological concepts and preparing effectively for their examinations by reinforcing their understanding of the basic unit of life.

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BoardCBSE
ClassClass 11
SubjectBiology Exemplar
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 8

Chapter summary

Chapter 8, 'Cell: The Unit of Life,' focuses on the fundamental building blocks of life. This NCERT Solutions set addresses key concepts through multiple-choice questions, covering topics such as the distinguishing features of prokaryotes and eukaryotes, the role of ribosomes in protein synthesis, and the unique characteristics of plant sieve tube cells and mammalian erythrocytes. It also touches upon cell size variations and staining methods for cellular components, providing a solid foundation for understanding cell biology.

Learning outcomes

  • Understand the differences between prokaryotic and eukaryotic cells.
  • Identify the characteristics and functions of ribosomes.
  • Compare and contrast plant sieve tube cells and mammalian erythrocytes.
  • Recognize the variation in cell sizes and order them appropriately.
  • Differentiate between various cell types based on their structural features.
  • Understand the principles of cell staining techniques.

Topics covered

Paper topics

  • Cell: The Unit of Life
  • Prokaryotic vs. Eukaryotic Cells
  • Ribosomes: Structure and Function
  • Plant Sieve Tube Cells
  • Mammalian Erythrocytes (RBCs)
  • Cell Size Variation
  • Cell Staining Techniques
  • Mycoplasma
  • Bacteria
  • Chromosomes

Important topics

  • Distinguishing features of prokaryotes and eukaryotes
  • Role of ribosomes in protein synthesis
  • Comparison of sieve tube cells and erythrocytes
  • Cell size hierarchy
  • Applications of cell staining

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Questions and Solutions

Q. 1

A common characteristic feature of plant sieve tube cells and most of mammalian erythrocytes is
  1. absence of mitochondria
  2. presence of cell wall
  3. presence of haemoglobin
  4. absence of nucleus
Solution: The correct option is (d) absence of nucleus. Mature sieve tube cells in plants, which are part of the phloem tissue responsible for transporting sugars, lose their nucleus and most organelles to facilitate efficient transport. Similarly, mammalian erythrocytes, or red blood cells (RBCs), also extrude their nucleus during maturation to create more space for hemoglobin, thereby maximizing oxygen-carrying capacity. While sieve tube cells lack mitochondria, most mammalian erythrocytes do possess them. Haemoglobin is characteristic of erythrocytes but not sieve tube cells. Cell walls are present in plant cells but absent in animal cells like erythrocytes.

Q. 2

Select one which is not true for ribosome
  1. Made up of two sub-units
  2. Form polysome
  3. May attach to mRNA
  4. Have no role in protein synthesis
Solution: The statement that is not true for ribosomes is (d) Have no role in protein synthesis. Ribosomes are fundamental cellular machinery and are directly responsible for protein synthesis, acting as the sites where messenger RNA (mRNA) is translated into polypeptide chains. Options (a), (b), and (c) are all true statements about ribosomes. They are composed of two subunits (a large and a small one), they can attach to a single mRNA molecule to form a polysome (multiple ribosomes translating the same mRNA simultaneously), and this attachment to mRNA is a crucial step in initiating protein synthesis.

Q. 3

Which one of these is not a eukaryote?
  1. Euglena
  2. Anabaena
  3. Spirogyra
  4. Agaricus
Solution: The correct option is (b) Anabaena. Anabaena is a type of cyanobacteria, which are prokaryotes. Prokaryotic cells are characterized by the absence of a well-defined, membrane-bound nucleus and other membrane-bound organelles. In contrast, Euglena (a protist), Spirogyra (an alga), and Agaricus (a fungus) are all eukaryotes. Eukaryotic cells possess a true nucleus enclosed by a nuclear envelope and contain various membrane-bound organelles such as mitochondria, chloroplasts (in some), and endoplasmic reticulum.

Q. 4

Which of the following stain is not used for staining chromosomes?
  1. Basic fuschsin
  2. Safranin
  3. Methylene blue
  4. Carmine
Solution: The correct option is (b) Safranin. Safranin is primarily used as a counterstain in techniques like Gram staining for bacteria and endospore staining. While it can stain some cellular components, it is not a primary or common stain for visualizing chromosomes. Basic fuschin, carmine, and methylene blue are all dyes that are frequently used to stain chromosomes and nucleic acids due to their affinity for the negatively charged DNA.

Q. 5

Different cells have different sizes. Arrange the following cells in an ascending order of their size. Choose the correct option among the followings.
  1. Mycoplasma
  2. Ostrich eggs
  3. Human RBC
  4. Bacteria

Options:

  1. I, IV, III, II
  2. I, II, III, IV
  3. II, I, III, IV
  4. III, II, I, IV
Solution: The correct option is (a) I, IV, III, II. Cells exhibit a wide range of sizes. Mycoplasmas are among the smallest known cells, typically around 0.3 micrometers (μm). Bacterial cells are generally larger, ranging from about 0.5 to 5 μm. Human red blood cells (RBCs) are about 7 μm in diameter. Ostrich eggs are exceptionally large, representing a single cell that can measure approximately 15 cm by 13 cm. Therefore, the ascending order of size is Mycoplasma (I), Bacteria (IV), Human RBC (III), and Ostrich eggs (II).

Common mistakes

  • Confusing characteristics of prokaryotes and eukaryotes.
  • Misunderstanding the role of ribosomes in protein synthesis.
  • Incorrectly identifying common features between plant and animal cells.
  • Errors in ordering cells by size.
  • Not recognizing that safranin is not primarily used for staining chromosomes.

Revision tips

  • Focus on the defining characteristics of prokaryotic and eukaryotic cells.
  • Memorize the structure and function of ribosomes, especially their role in protein synthesis.
  • Pay close attention to the unique features of specialized cells like sieve tube elements and RBCs.
  • Review the typical sizes of common cell types to answer ordering questions.
  • Understand why certain stains are used for specific cellular components and others are not.

Practice MCQs

Q1. What is a common characteristic feature shared by plant sieve tube cells and most mammalian erythrocytes?

Q2. Which of the following statements is NOT true regarding ribosomes?

Q3. Which of the following organisms is NOT a eukaryote?

Q4. Which of the following stains is typically NOT used for staining chromosomes?

Q5. Arrange the following cells in ascending order of their size: I. Mycoplasma, II. Ostrich eggs, III. Human RBC, IV. Bacteria

Frequently asked questions

What is the main focus of Chapter 8, 'Cell: The Unit of Life' in the CBSE Class 11 Biology Exemplar?

Chapter 8 focuses on the fundamental concepts of cell biology, including the differences between prokaryotic and eukaryotic cells, the structure and function of ribosomes, and the characteristics of specialized cells like sieve tube cells and erythrocytes.

What common feature do plant sieve tube cells and mammalian erythrocytes share?

A key common feature is the absence of a nucleus in their mature state. This allows for efficient transport in sieve tubes and maximum space for hemoglobin in erythrocytes.

Are ribosomes involved in protein synthesis?

Yes, ribosomes are critically involved in protein synthesis. They are often called the 'protein factories' of the cell and are responsible for translating mRNA into protein chains.

Which type of cell is considered the smallest?

Mycoplasmas are considered the smallest type of cell, with sizes typically around 0.3 micrometers.

How do these NCERT Solutions help in exam preparation?

These solutions provide clear, step-by-step explanations for MCQs, reinforcing understanding of key concepts and helping students identify potential areas of confusion, thus aiding effective revision for exams.

What is the difference between prokaryotic and eukaryotic cells mentioned in the solutions?

The solutions highlight that prokaryotic cells lack a well-defined, membrane-bound nucleus and organelles, while eukaryotic cells possess both a well-defined nucleus and membrane-bound organelles.

Important links

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