Biology Lecture: Fundamental Unit of Life

Overview

• All living organisms have bodies made of cells.
• Functions in the body are performed because of cells.
• Robert Hooke discovered cells.
• Human body organs: brain, heart, kidneys, lungs, pancreas.
• Substances move within cells via diffusion.

Introduction

• Lecture by Samriddhi, Biology mentor and educator on Physics Wallah platform.
• Welcome to the sprint series for Class IX.
• Sprint analogy: Short, fast efforts needed due to limited time.
• Aim: Cover all chapters in one shot.

Cells: The Fundamental Unit of Life

• Cells are the structural and functional units of life.
• Life refers to living organisms: humans, plants, animals, bacteria, fungi, algae, amoeba.
• Body structure and functions in organisms are due to cells.
• Size of organisms doesn't matter; their bodies are made of cells.
• Organs are made of tissues, which are made of cells.
• Processes like breathing, respiration, nutrition are due to cells.

Structural Organization

• Cells form tissues, tissues form organs, organs form organ systems, and organ systems form organisms.
• Examples: Brain, heart, kidneys, lungs, pancreas.
• Organ systems: Respiratory, digestive, circulatory, excretory, reproductive, nervous, muscular, skeletal.

Discovery of Cells

• Robert Hooke discovered cells in 1665 using self-designed microscope and observed cork cells.
• Hooke’s cells were dead cells.
• Antonie van Leeuwenhoek observed first living cells in 1674.
• Robert Brown discovered the nucleus in 1831.
• Purkinje coined 'protoplasm' in 1839.
• Schleiden (1838) and Schwann (1839) proposed cell theory.
• Rudolf Virchow (1855) extended cell theory: “Omnis cellula e cellula” (Every cell comes from a pre-existing cell).

Cell Variety

• Cells vary in shape, size, and number.
• Unicellular organisms: Single cell (e.g., bacteria, amoeba, paramecium).
• Multicellular organisms: Many cells (e.g., humans, plants, animals).
• Cell shapes: Oval, rod-shaped, branched, spindle-shaped.
• Example cells: Nerve cells (neurons), egg cells, muscle cells.
• Mycoplasma: Smallest cells; Ostrich egg: Largest cell.
• Bacterial cells are smaller than animal cells.

Cell Components

• Plasma Membrane (Cell Membrane): Outer boundary, selectively permeable, made of lipids (phospholipids) and proteins.
• Cell Wall: Present in plants, bacteria, fungi; outside plasma membrane; cellulose (plants), peptidoglycan (bacteria), chitin (fungi).
• Nucleus: Control center, contains DNA, has double membrane (nuclear envelope) with pores, nucleoplasm inside.
• Cytoplasm: Jelly-like substance inside plasma membrane, contains cell organelles.
• Cell Organelles: Specialized structures within cells performing specific functions.

Types of Transport Across Cell Membrane

• Passive Transport: No energy required, substances move from high to low concentration (e.g., diffusion, osmosis).
• Active Transport: Energy required, substances move from low to high concentration.
• Diffusion: Movement of solids, liquids, gases from high to low concentration.
• Osmosis: Movement of water molecules from high to low concentration across a selectively permeable membrane.
• Endocytosis: Cell engulfs materials.
• Exocytosis: Cell expels materials.
• Plasmolysis: Shrinking of cell membrane in plant cells in hypertonic solutions.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: No nucleus, simple, smaller, found in bacteria, nucleoid region, few organelles.
• Eukaryotic Cells: True nucleus, complex, larger, found in plants, animals, fungi, protists, many organelles.

Cell Organelles

• Endoplasmic Reticulum (ER): Network of tubules, two types:
  • Rough ER (RER): With ribosomes, protein synthesis.
  • Smooth ER (SER): No ribosomes, lipid synthesis, detoxification.
• Golgi Apparatus: Stacks of cisternae, modifies, sorts, packages proteins and lipids.
• Lysosomes: Contain digestive enzymes, break down waste material, known as 'suicide bags'.
• Vacuoles: Storage sacs, larger in plants.
• Mitochondria: Powerhouse of the cell, site of ATP production, double membrane, own DNA and ribosomes.
• Plastids: Only in plant cells, three types:
  • Chromoplasts: Color pigments.
  • Chloroplasts: Green pigment (chlorophyll), site of photosynthesis.
  • Leucoplasts: Colorless, storage.
• Ribosomes: Protein synthesis, found in prokaryotic and eukaryotic cells.
• Centrosomes/Centrioles: Involved in cell division, not in plant cells.

Cell Division

• Two types: Mitosis (equational division) and Meiosis (reductional division).
• Mitosis: Two identical daughter cells, same chromosome number.
• Meiosis: Four non-identical daughter cells, half chromosome number.
• Mitosis: Growth, repair.
• Meiosis: Gamete formation.

Homework Questions

1. Why does a person vomit after drinking a salt solution?
2. Match the following plastids with their functions.
3. Why do plant cells have large vacuoles?
4. Explain what happens to dry apricots in pure water and sugar solution.
5. What happens to RBCs in saline solution?
6. Predict effects of breaking plasma membrane.

• Review and understand details for better grasp of concepts.