Fundamental Unit of Life: The Cell

Introduction

• All living organisms' bodies are made up of cells.
• All functions in the body are performed by cells.
• Discovery of Cell: By Robert Hooke in 1665.
• Human body has different organs: brain, heart, kidneys, lungs, pancreas, etc.

Biology and Sprint Series

• Instructor: समृद्धि, Biology Mentor and Educator at Physics Wallah.
• Addressing Class 9 Students for Sprint Series in Biology.

Cells: The Structural and Functional Unit of Life

• Definition: Structural, fundamental unit of life performing all functions.
• Life here means living organisms (including bacteria, fungi, algae, amoeba, plants, animals, human beings).
• Body structure and functions are due to cells, irrespective of organism’s size or complexity.

Diffusion Concept

• Movement of substances/material within parts of a cell causes diffusion.
• Diffusion example: substances moving from higher concentration to lower concentration.

Cell Organization

• Structures Involved:
  • Cell: Smallest unit.
  • Tissues: Group of similar cells.
  • Organs: Different tissues organized together (e.g., brain, heart, kidneys).
  • Organ Systems: Different organs working together (e.g., respiratory, digestive, circulatory systems).

Importance of Cells

• Cells form the basis for all life processes (e.g., breathing, respiration, nutrition).
• Discovery of cells and their function critical to understanding biology.

Discovery of Cells

• Robert Hooke: Discovered cells in 1665 using a self-designed microscope.
  • Observed dead cork cells, hence discovered dead cells.
• Antonie van Leeuwenhoek: Discovered living cells in 1674.
• Robert Brown: Discovered the nucleus in 1831.
• Purkinje: Coined the term 'protoplasm' in 1839.
• Matthias Schleiden and Theodor Schwann: Formulated Cell Theory.
  • Schleiden: Plants made up of cells.
  • Schwann: Animals made up of cells.
• Rudolf Virchow: Extended Cell Theory, stating ‘Omnis cellula e cellula’ (every cell originates from a pre-existing cell).

Types of Cells

• Unicellular: Organisms made up of one cell (e.g., bacteria, amoeba, paramecium).
• Multicellular: Organisms made up of multiple cells (e.g., humans, plants).

Varieties in Cell Shape, Size, and Number

• Shapes: Can be circular, oval, rod-shaped, branched, spindle-shaped, etc.
• Size: Varies widely; smallest cells like Mycoplasma, largest cell example Ostrich egg.

Basic Components of Cell

• Cell/Plasma Membrane: Protective outer boundary; regulates entry/exit; made of lipids and proteins.
• Cell Wall: Additional protective layer in plant cells and bacteria, made of cellulose (plants) or peptidoglycan (bacteria).
• Nucleus: Control center of the cell; contains DNA.
• Cytoplasm: Jelly-like substance within the cell containing the cell components.
• Organelles: Specialized structures within cells performing specific functions (e.g., mitochondria, Golgi apparatus).

Transport Across Membrane

• Passive Transport (Diffusion, Osmosis)
  • Movement from higher to lower concentration without energy (e.g., exchange of gases, water movement).
• Active Transport
  • Movement against concentration gradient requiring energy (e.g., nutrient uptake).
• Endocytosis and Exocytosis: Movement of large particles into (endocytosis) and out of cells (exocytosis).

Cellular Structures

• Nucleus: Contains genetic material (DNA); surrounded by nuclear envelope; contains nucleoplasm.
• Endoplasmic Reticulum (ER): Synthesis of proteins (Rough ER) and lipids (Smooth ER); detoxification (Smooth ER).
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
• Lysosomes: Contains digestive enzymes; breaks down waste (known as suicide bags).
• Vacuoles: Storage sacs; larger in plant cells.
• Mitochondria: Powerhouse of the cell; site of aerobic respiration; produces ATP.
• Plastids (Plant Cells): Chloroplasts (photosynthesis and green color), Chromoplasts (color other than green), Leucoplasts (storage).

Cellular Division

• Mitosis: Produces two identical daughter cells maintaining chromosome number.
• Meiosis: Produces four daughter cells with half the chromosome number (in gametes).

Recap and Concluding Notes

• Revisiting key points on cell theory, types, organization, and functions.
• Understanding cell membrane transport mechanisms and their importance.
• Highlighting distinctions between prokaryotic and eukaryotic cells, plant and animal cells.

Important Terms

• Plasma Membrane, Cell Wall, Nucleus, Cytoplasm, Organelles, Diffusion, Osmosis, Endocytosis, Exocytosis, Mitosis, Meiosis, etc.

Homework Questions

• Q1: Why do plant cells have larger vacuoles?
  • Store water and nutrients as plants can’t move to search for food.
• Match the following types of plastids to their functions.
• Explain CO2 and water transport in/out of cells.
• Mention differences b/w bacterial cells and plant cells, plant cells and animal cells.
• Practical scenarios: changes in cell when placed in various solutions (hypertonic, hypotonic, isotonic).

Note: Revise these notes and ensure you understand fundamental concepts of cells and their roles in biology.

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