Cells & Subcellular Organelles – Detailed Notes for Students

 Understanding Cells: Class 11 Biology Notes for Exam Success

3.1 Cells – The Basic Unit of Life

• Cell: The smallest unit of life capable of performing all life processes.
• Unicellular organisms: Organisms composed of a single cell (e.g., Amoeba, Bacteria) – the single cell carries out all life functions.
• Multicellular organisms: Organisms made of many specialized cells (e.g., plants, animals) – cells work together to sustain life.

All living organisms exhibit 7 basic properties of life, which are carried out at the cellular level:

1. Movement:

   • Cells can move.

   • Examples:

   1. Sperm cells move using flagella (tail-like structure).

   2. White blood cells move through blood to fight infection.
   3. Organelles inside cells move to perform essential tasks.

2. Nutrition:

   • Cells obtain nutrients from their environment to produce energy, build cellular structures, and support biochemical reactions.

3. Respiration:

   • Cells generate energy via cellular respiration.

   • Process: Glucose → broken down → release ATP (Adenosine Triphosphate) → energy for cellular activities.

4. Excretion:

   • Cells remove waste products through diffusion and active transport to prevent toxic buildup.

5. Homeostasis:

   • Cells maintain a stable internal environment by regulating movement of substances across membranes.

   • Example: Controlling water, salts, and pH levels.

6. Growth:

   • Cells grow by taking in nutrients and converting them into cellular components (e.g., proteins, lipids, carbohydrates).

7. Reproduction:

   • Cells reproduce to sustain life and species:

     1. Mitosis: Produces identical daughter cells → for growth and repair.

     2. Meiosis: Produces gametes (sperm and egg) → for sexual reproduction.

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Key Points to Remember

• Cells are the functional and structural units of life.
• Every life process occurs at the cellular level.
• Specialized cells in multicellular organisms perform specific functions, e.g., nerve cells transmit signals, muscle cells help in movement.

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Extra Concept – Why Study Cells?

• Understanding cells helps us explore diseases, stem cell therapy, and biotechnology applications.
• Knowledge of cell structure and function is the foundation of biology, medicine, and research.

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