Chapter – 5

The Fundamental Unit of Life

In this post we have given the detailed notes of class 9 Science Chapter 5 (The Fundamental Unit of Life) in English. These notes are useful for the students who are going to appear in class 9 board exams.

Chapter 5: The Fundamental Unit of Life

5.1 What are Living Organisms Made Up of? 🌱

• Cells: The basic building blocks of all living organisms. 🧱
• Robert Hooke: The first person to observe cells 👁️ in a cork slice 🍾 using a primitive microscope 🔬 in 1665.
• Microscope: A tool used to magnify small objects, such as cells, to make them visible to the human eye. 🔬

5.2 What is a Cell Made Up of?

• Cell Organelles: Specialized structures within a cell that perform specific functions. ⚙️
• Plasma Membrane: The outer covering of the cell that separates its contents from the external environment. 🎈
  • Selectively Permeable: Allows only certain materials to enter or exit the cell. 🚧
• Cell Wall: An additional rigid outer covering found in plant cells 🌱, located outside the plasma membrane. 🎈
  • Cellulose: A complex substance that provides structural strength to plant cells. 💪
• Nucleus: A membrane-bound organelle that contains the cell’s genetic material (DNA). 🧬
  • Chromosomes: Rod-shaped structures made of DNA 🧬 and protein that carry genetic information.
• Cytoplasm: The fluid content inside the cell that surrounds the organelles. 💧

5.2.5 Cell Organelles

• Endoplasmic Reticulum (ER): A network of membrane-bound tubes and sheets involved in the transport of materials within the cell. 🚚
  • Rough ER (RER): Has ribosomes attached to its surface and is involved in protein synthesis. 🏭
  • Smooth ER (SER): Involved in the synthesis of lipids and detoxification of poisons. 🧪
• Golgi Apparatus: A stack of membrane-bound vesicles that store, modify, and package proteins and lipids. 📦
• Lysosomes: Membrane-bound sacs filled with digestive enzymes that break down waste materials and cellular debris. 🗑️
• Mitochondria: The “powerhouses” of the cell, responsible for producing energy in the form of ATP. ⚡
• Plastids: Organelles found only in plant cells 🌱, involved in photosynthesis and storage.
  • Chloroplasts: Contain chlorophyll and are the sites of photosynthesis. ☀️
  • Leucoplasts: Store starch, oils, and protein granules. 🥔
• Vacuoles: Storage sacs for solid or liquid contents, much larger in plant cells 🌱 than in animal cells. 💧

5.3 Cell Division

• Mitosis: The process of cell division for growth and repair, producing two identical daughter cells. 👯
• Meiosis: The process of cell division for producing gametes (sex cells), resulting in four daughter cells with half the number of chromosomes. 🥚

Remember: Cells are the fundamental units of life 🧬, and their organelles work together 🤝 to perform all the functions necessary for life. 🕺

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