Chapter 8: Cell — Structure and Functions
कोशिका - संरचना एवं प्रकार्य (पादप व जंतु कोशिका तुलना, कोशिका भित्ति, केंद्रक, रसधानी, लवक)
Don't Let a 20-Minute Bubbling Delay Cost You CTET Qualification
In offline CTET exams, bubbling 150 bubbles takes 18 to 22 minutes of mechanical time. A single misaligned row can trigger an 8-question domino error. Practice bubble-filling this chapter's solved MCQs inside Mentora's official OMR simulator.
- Discovery of Cell: Robert Hooke in 1665 observed thin slices of cork under a self-designed microscope and coined the term 'cell' (compartments).
- Organism Complexity: Unicellular (single cell performs all life functions: Amoeba, Paramecium) vs Multicellular (specialized tissues, organs, systems: Humans, Trees).
- Fundamental Parts of a Cell:
- - Cell Membrane (Plasma Membrane): Selectively permeable boundary enclosing cytoplasm; controls inbound and outbound molecular transport.
- - Cytoplasm: Jelly-like matrix between cell membrane and nucleus containing organelles (mitochondria, ribosomes, Golgi bodies).
- - Nucleus: Spherical master control center bounded by a porous double Nuclear Membrane; contains gelatinous Nucleoplasm, dense spherical Nucleolus, and thread-like Chromosomes carrying genes (units of genetic inheritance made of DNA).
- Prokaryotes vs Eukaryotes:
- - Prokaryotic Cells: Lack a well-defined nuclear membrane; genetic material lies naked in nucleoid region. Examples: Bacteria, Blue-green algae.
- - Eukaryotic Cells: Possess a true membrane-bound nucleus and organized membrane-bound organelles. Examples: Onion peel cells, human cheek cells, plant and animal cells.
- Plant Cell vs Animal Cell (Guaranteed CTET Question):
- - Cell Wall (कोशिका भित्ति): Present ONLY in plant cells; made of rigid cellulose located outside plasma membrane to provide structural rigidity and withstand high osmotic pressure, temperature, moisture shifts, and high wind speeds.
- - Chloroplasts / Plastids (लवक): Found ONLY in plant cells. Chloroplasts contain chlorophyll required for photosynthesis.
- - Vacuoles (रसधानी): Plant cells have ONE HUGE CENTRAL VACUOLE occupying 90% of cell volume. Animal cells have multiple small, temporary vacuoles.
- Trap: Do animal cells have a cell wall? Correct: NEVER. Cell walls exist only in plants, fungi, and bacteria.
- Trap: Which organelles are present in plant cells but completely absent in human cheek cells? Correct: CELL WALL and PLASTIDS (Chloroplasts). Large central vacuole is also characteristic of plant cells.
- Trap: Bacteria have a well-defined nuclear membrane. FALSE: Bacteria are PROKARYOTES, lacking a nuclear membrane.
NCERT Core Facts: Comparative Cytology (Plant vs. Animal Cells)
Cell organelle identification and eukaryotic vs prokaryotic distinctions appear annually in CTET:
1. Plant Cell vs. Animal Cell Distinction Matrix
| Cellular Component | Plant Cell (पादप कोशिका) | Animal Cell (जंतु कोशिका) | Functional Significance |
|---|---|---|---|
| Cell Wall (कोशिका भित्ति) | PRESENT (Cellulose) | ABSENT | Rigid defense against wind, rain, pressure |
| Cell Membrane | Present (inner to cell wall) | Present (outermost layer) | Selectively permeable barrier |
| Plastids / Chloroplasts | PRESENT | ABSENT | Pigment synthesis and photosynthesis |
| Vacuole Architecture | One massive central vacuole | Multiple microscopic vacuoles | Turgidity, osmotic tonicity storage |
| Centrosome / Centriole | Mostly absent | Present | Organizes spindle during cell division |
2. Prokaryote vs. Eukaryote Diagnostics
- Prokaryotes (अकेंद्रकी): Primitive genetic architecture. Nuclear material (DNA) is not enclosed by a nuclear envelope. Lacks mitochondria and chloroplasts (e.g., E. coli, Blue-green algae/Cyanobacteria).
- Eukaryotes (सुकेन्द्रकी): Advanced cell architecture. Nucleus surrounded by double-layered porous nuclear membrane; specialized membrane-bound organelles (e.g., Onion epidermal cells, Human buccal mucosa cells).
Test Your Mastery: Cell — Structure and Functions
Authentic CBSE exam questions tested directly from this NCERT chapter.
Which of the following sets of cellular organelles is found EXCLUSIVELY in plant cells and is ABSENT in animal cells?
कोशिकांगों का कौन-सा समूह विशेष रूप से पादप कोशिकाओं में पाया जाता है और जंतु कोशिकाओं में अनुपस्थित होता है?
Organisms whose cells lack a distinct nuclear membrane surrounding their genetic material are termed:
वे जीव जिनकी कोशिकाओं में उनकी आनुवंशिक सामग्री के चारों ओर एक स्पष्ट केंद्रक झिल्ली का अभाव होता है, क्या कहलाते हैं?
Why do plant cells require a rigid cell wall in addition to a plasma membrane?
Plants cannot move to shelter themselves from harsh climatic fluctuations, violent winds, and osmotic pressure. The rigid cellulose cell wall provides structural endurance.
What structures would a student observe under a microscope when examining an onion peel cell compared to a human cheek cell?
The student will observe a prominent outer cell wall and large central vacuole in the onion peel cell, both of which are absent in human cheek cells.