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Q2:
New cells generate from
New cells generate from
Solution :
Theoretical Foundation: The Concept of Cell Lineage
The biological principle governing the origin of new cells is defined by the theory of Omnis cellula-e cellula. This axiom establishes that the continuity of life is maintained through the division of pre-existing units rather than spontaneous generation.
Step 1: Historical Context and Proof
In 1855, Rudolf Virchow formulated the concept that all cells arise from pre-existing cells. This countered the earlier 19th-century misconceptions regarding spontaneous generation. This principle is a cornerstone of the Cell Theory, which asserts:
- All living organisms are composed of one or more cells.
- The cell is the basic unit of structure and organization in organisms.
- All cells arise from pre-existing cells through the process of cell division (Mitosis and Meiosis).
Step 2: Biological Mechanism of Generation
The generation of new cells occurs through Cell Division. The sequence involves:
- Interphase: DNA replication and organelle duplication [Ref: Cell Cycle phases $G_1$, $S$, and $G_2$].
- Karyokinesis: The organized segregation of replicated chromosomes.
- Cytokinesis: The physical division of the cytoplasm, resulting in two distinct daughter cells.
Visual Representation of Cell Lineage
Comparative Analysis of Generation Models
| Model | Premise | Scientific Validity |
|---|---|---|
| Spontaneous Generation | Life arises from non-living matter | Disproven (Pasteur's Experiment) |
| Cell Lineage (Virchow) | Life arises from pre-existing cells | Universally Accepted |
Final Solution: New cells generate from pre-existing cells.
More Questions from Class 11 Biology Cell – The Unit of Life EXERCISES
- Q1: Which of the following is not correct?
- Q3: Match the following Column I Column II (a) Cristae (i) Flat membranous sacs in stroma (b) Cisternae (ii) Infoldings in mitochondria (c) Thylakoids (iii) Disc-shaped sacs in Golgi apparatus
- Q4: Which of the following is correct:
- Q5: What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
- Q6: How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
- Q7: Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
- Q8: What are the characteristics of prokaryotic cells?
- Q9: Multicellular organisms have division of labour. Explain.
- Q10: Cell is the basic unit of life. Discuss in brief.
- Q11: What are nuclear pores? State their function.
- Q12: Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
- Q13(i): Describe the structure of the following with the help of labelled diagrams. (i) Nucleus
- Q13(ii): Describe the structure of the following with the help of labelled diagrams. (ii) Centrosome
- Q14: What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.
CBSE Solutions for Class 11 Biology Cell – The Unit of Life
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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