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Q8:
What are the characteristics of prokaryotic cells?
Solution :
1. Definition and Fundamental Nature
Prokaryotic cells (derived from Greek pro: before; karyon: nucleus) are organisms characterized by the absence of a membrane-bound nucleus and specialized membrane-bound organelles. They constitute the kingdoms Eubacteria and Archaebacteria [Per the Five-Kingdom Classification system].
2. Core Structural Characteristics
The architecture of a prokaryotic cell is defined by high structural efficiency and metabolic versatility. The following table summarizes the key components:
| Component | Description |
|---|---|
| Genetic Material | Single, circular double-stranded DNA molecule located in the nucleoid region. Not enclosed by a nuclear envelope. |
| Ribosomes | $70S$ type, consisting of $50S$ and $30S$ subunits, responsible for protein synthesis [By the principle of sedimentation coefficient]. |
| Cell Envelope | A tripartite structure consisting of the outermost glycocalyx (slime layer or capsule), the cell wall (peptidoglycan), and the plasma membrane. |
| Plasmids | Extrachromosomal, small, circular, self-replicating DNA molecules providing antibiotic resistance or specific metabolic advantages. |
3. Visual Representation of Prokaryotic Organization
4. Physiological and Morphological Attributes
- Absence of Endomembrane System: Prokaryotes lack endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, and chloroplasts.
- Mesosomes: Infoldings of the plasma membrane into the cytoplasm. These structures function similarly to mitochondria in eukaryotes by providing surface area for respiration, DNA replication, and secretion [Per the Invagination Hypothesis].
- Cell Wall Composition: The cell wall provides structural integrity and protection against osmotic pressure. In Bacteria, it is composed of peptidoglycan (murein) [Per biochemical assay].
- Surface Appendages: Prokaryotes possess pili (for attachment and conjugation) and fimbriae (for substrate adhesion). Movement is typically mediated by a flagellum, composed of the protein flagellin, which moves in a propeller-like rotational motion.
- Reproduction: Primarily divide by binary fission, a form of asexual reproduction that does not involve mitosis or meiosis.
Final Solution: Prokaryotic cells are defined by the absence of a true, membrane-bound nucleus and organelles, the presence of a nucleoid containing circular DNA, $70S$ ribosomes, and a complex cell envelope, often including plasmids and specialized membrane invaginations known as mesosomes.
More Questions from Class 11 Biology Cell – The Unit of Life EXERCISES
- Q1: Which of the following is not correct?
- Q2: New cells generate from
- 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.
- 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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