Cell Theory and Biology

Overview

Cell Theory and Biology is a foundational topic in the Science section of MAHA TET Paper II. Understanding cells is essential because the cell is the basic structural and functional unit of all living organisms. This topic forms the basis for understanding more complex biological concepts like plant and animal systems, reproduction, and genetics.

For MAHA TET, you must know the three postulates of cell theory, the scientists who contributed to it, and the structure and functions of major cell organelles. Questions typically test your ability to distinguish between plant and animal cells, identify organelles by their functions, and apply cell theory principles. This topic carries moderate weightage but is conceptually linked to other biology topics, making it crucial for building a strong science foundation.

Mastery here requires memorising organelle functions, understanding the historical development of cell theory, and being able to compare prokaryotic versus eukaryotic cells and plant versus animal cells.

Key Concepts

• **Cell as the basic unit of life**: All living organisms are made up of one or more cells. The cell carries out all life processes including nutrition, respiration, excretion, and reproduction.

• **Cell Theory (three postulates)**: (1) All living organisms are composed of cells, (2) The cell is the basic unit of structure and function in organisms, (3) All cells arise from pre-existing cells.

• **Discovery of cells**: Robert Hooke (1665) first observed cells in cork and coined the term "cell." Anton van Leeuwenhoek observed living cells. Schleiden and Schwann proposed the cell theory. Rudolf Virchow added that all cells come from pre-existing cells.

• **Prokaryotic vs Eukaryotic cells**: Prokaryotes lack a membrane-bound nucleus and organelles (examples: bacteria, blue-green algae). Eukaryotes have a true nucleus and membrane-bound organelles (examples: plants, animals, fungi).

• **Plant cell vs Animal cell**: Plant cells have a cell wall, large central vacuole, and plastids (including chloroplasts). Animal cells lack these but have centrioles, which plant cells typically lack.

• **Cell membrane (Plasma membrane)**: A selectively permeable membrane that controls the movement of substances in and out of the cell. Made of a lipid bilayer with proteins.

• **Protoplasm**: The living substance of the cell, divided into cytoplasm (outside nucleus) and nucleoplasm (inside nucleus).

Formulas / Key Facts

| Fact | Detail | |------|--------| | Term "cell" coined by | Robert Hooke (1665) | | Cell theory proposed by | Schleiden (botanist) and Schwann (zoologist) in 1838-39 | | "Omnis cellula e cellula" given by | Rudolf Virchow (1855) — meaning all cells arise from cells | | Powerhouse of the cell | Mitochondria (site of cellular respiration and ATP production) | | Kitchen of the cell | Chloroplast (site of photosynthesis in plant cells) | | Suicide bags of the cell | Lysosomes (contain digestive enzymes) | | Control centre of the cell | Nucleus (contains DNA and controls cell activities) | | Protein factories | Ribosomes (site of protein synthesis) | | Smallest cell | Mycoplasma (0.1 micrometres) | | Largest cell | Ostrich egg | | Only animal cell with cell wall | None — animal cells lack cell walls |