Cytoplasm Class 11 Notes Biology

 

Cytoplasm and Cell Organelles – Structure, Composition & Functions

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🔹 Definition

The cytoplasm is a semi-viscous, semi-transparent substance filling the cell interior.

• In eukaryotic cells: Located between the plasma membrane and the nuclear envelope.
• In prokaryotic cells: Occupies the entire space beneath the plasma membrane.

It acts as a medium for organelles, molecules, and biochemical reactions.

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🔹 Origin & Discovery

• Term “Cytoplasm” coined by: Eduard Strasburger (1882).
• Robert Hooke (1665): First observed cell compartments.
• E. B. Wilson (1896): Explained cytoplasm as the region where cell metabolism occurs.

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🔹 Literal Meaning

• “Cyto” = cell (Greek kytos = hollow vessel)
• “Plasma” = formed/molded (Greek plásma)

• 👉 Thus, cytoplasm = “that which forms the cell.”

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🔹 Chemical Composition of Cytoplasm

Approximate percentage composition:

• Water: 70–80% (solvent & medium for reactions)
• Proteins: 10–15% (structural + enzymatic functions)
• Lipids: 2–3% (membrane formation, energy storage)
• Carbohydrates: 1–2% (glycogen, starch granules for energy)
• Nucleic Acids: ~1% (RNA, DNA fragments)
• Inorganic Salts/Ions: ~1% (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, phosphate, bicarbonate)

This composition makes the cytoplasm dynamic, semi-fluid, and reactive.

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🔹 Sol–Gel Nature of Cytoplasm

The cytoplasm shows a property of sol–gel transformation:

• Sol (fluid state): Cytoplasm behaves like a solution, allowing rapid movement of molecules (cytoplasmic streaming).
• Gel (semi-solid state): Cytoplasm becomes more viscous near the cell membrane, providing support.

👉 This reversible transition is essential for movement, endocytosis, exocytosis, and amoeboid locomotion.

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🔹 Functions of Cytoplasm

• Provides medium for organelles to remain suspended.
• Site of many biochemical reactions (glycolysis, protein & fatty acid metabolism).
• Cytoplasmic streaming enables transport of molecules within the cell.
• Maintains cell shape and turgidity.
• Stores nutrients like glycogen, lipids, pigments.
• Acts as a buffer, protecting organelles.

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🔹 Cell Organelles

Organelles are specialized structures within cytoplasm that perform specific functions.

🔸 Non-Membranous Organelles

1. Ribosomes

   1. Discovered by: George Emil Palade (1955).

   2. Literal Meaning: Ribo (RNA) + soma (body).

   3. Types: 70S (prokaryotes), 80S (eukaryotes).

   4. Function: Protein synthesis.

2. Cytoskeleton

3. Network of microtubules, microfilaments, and intermediate filaments.

4. Provides mechanical support, intracellular transport, and motility.

5. Centrosome & Centrioles

   • Absent in higher plants.

   • Function: Organize spindle fibers during cell division.

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🔸 Membranous Organelles

1. Endoplasmic Reticulum (ER)

   • Rough ER: With ribosomes → protein synthesis.

   • Smooth ER: Lipid synthesis, detoxification.

2. Golgi Apparatus

   • Discovered by: Camillo Golgi (1898).

   • Function: Packaging, secretion, and modification of proteins & lipids.

3. Lysosomes

   • Discovered by: Christian De Duve (1955).

   • Literal Meaning: “Lysis body.”

   • Function: Intracellular digestion (“suicidal bags”).

4. Mitochondria

   • Discovered by: Richard Altmann (1890, called them “bioblasts”).

   • Function: ATP production → “powerhouse of the cell.”

   • Special Feature: Own DNA and ribosomes (semi-autonomous).

5. Plastids (plants only)

   • Chloroplasts: Photosynthesis (contain chlorophyll).

   • Chromoplasts: Pigments for color in flowers/fruits.

   • Leucoplasts: Storage (starch, fats, proteins).

6. Vacuoles

   • Large central vacuole in plants.

   • Stores water, ions, wastes, pigments.

7. Peroxisomes & Glyoxysomes

   • Functions: Fat metabolism, detoxification, photorespiration.

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🔹 Quick Exam-Oriented Points

• Cytoplasm = cytosol + organelles + inclusions.
• Shows sol–gel transformation (for movement & endocytosis).
• Site of glycolysis & metabolic pathways.
• Ribosomes discovered by: Palade.
• Golgi discovered by: Camillo Golgi.
• Lysosome discovered by: De Duve.
• Mitochondria discovered by: Altmann.
• Term Cytoplasm coined by: Strasburger (1882).

🔹 Internal Linking 

Boss, as you asked earlier, here are 3 real links from your site to interlink in the footer or middle of the article (helps SEO):

1. Structure of Cell Wall – Composition, Types & Functions

2. Microscopy – Principles, Types and Stains in Biology

3. Plasma Membrane – Models, Structure and Functions

🔹 FAQs Section for Blog Post

❓ What is the cytoplasm made of?

The cytoplasm is made of 70–90% water, proteins, lipids, carbohydrates, nucleic acids, and inorganic salts. It also contains organelles and inclusions.

❓ What is the sol-gel nature of cytoplasm?

The cytoplasm shows sol-gel nature because it can shift between a sol state (liquid, less viscous) and a gel state (semi-solid, more viscous), helping in streaming and transport.

❓ Who discovered the cytoplasm?

The term “cytoplasm” was coined by Strasburger in 1882. Robert Hooke (1665) first observed cell compartments, and E. B. Wilson (1896) described it as the site of metabolism.

❓ What are the main functions of cytoplasm?

• Provides a medium for organelles

• Site of biochemical reactions (e.g., glycolysis)

• Maintains cell shape and turgidity

• Stores important molecules

• Helps in transport by cytoplasmic streaming

❓ What are cell organelles?

Cell organelles are specialized structures within the cytoplasm that perform distinct functions like protein synthesis (ribosomes), energy production (mitochondria), packaging (Golgi), and digestion (lysosomes).

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