Cell: The Unit of Life
CELL: THE UNIT OF LIFE
UNIT-1: Basic Biology
Syllabus Overview:
The cell as the unit of life
Protoplasm and the structure of prokaryotic vs. eukaryotic cells
Differences between animal and plant cells
Overview of cell theory and cell organelles:
Protoplasm, Cytoplasm, Cell Wall, Cell Membrane, Nucleus, Nucleolus, Mitochondria, Endoplasmic Reticulum, Ribosome, Golgi Bodies, Plastids, Lysosomes, Centrosome, and Vacuole.
2.1 What is a Cell?
Definition:
Fundamental structural and functional unit of all living beings.
Smallest unit capable of independent existence and essential life functions.
Composition of Organisms:
Composed of numerous cells (e.g., skin, brain, plants).
Cell Lifespan:
Lifecycles involve continuous cell death and regeneration, starting from a single cell (egg).
Visibility:
Cells are microscopic and require magnification to be viewed.
2.2 The Invention of the Microscope
Antony van Leeuwenhoek:
Developed first simple microscope with single lens, magnifying up to 200 times.
Robert Hooke:
Created a compound microscope and coined the term "cells" after observing cork cells.
Advancements:
Electron microscope developed for magnifications over 200,000 times.
Uses beams of electrons compared to light in traditional microscopes.
2.3 Cell Theory
Founders: Matthias Schleiden (1838) and Theodor Schwann (1839)
Key Points:
The cell is the smallest unit of structure in all living things.
The cell is the unit of function in all living things.
All cells arise from pre-existing cells (Rudolf Virchow, 1858).
Examples:
Cellular structure seen in tissues of frogs and mango plants.
Functions performed by cells are crucial to the organism's activities.
2.4 Cells - How Numerous?
Single-celled Organisms: Bacteria, yeast, amoeba.
Few-celled Organisms: Spirogyra, Volvox.
Multi-celled Organisms: Humans, Mango, etc.
Human Cell Count:
Approximately 1,000 million million cells in an adult human.
2.5 Cells - How Small?
Smallest Cells: Bacteria (0.3-5 micrometers), red blood cells (7 micrometers).
Largest Cells: Ostrich egg, a single cell before development.
Efficiency of Small Cells:
Rapid communication between regions, large surface area-to-volume ratio enhances diffusion.
2.6 Cell Shapes to Suit Functional Requirements
Shape Variations:
Epithelial cells, muscle cells, nerve cells, etc.
Function-Shape Relationship:
Example: Red blood cells are biconcave for efficient oxygen transport.
2.7 Structure of a Cell
Generalized Cell Structure:
Composed of three main parts: Cell membrane, Nucleus, Cytoplasm.
Cell Organelles:
Miniature organs performing specific functions (e.g., mitochondria for energy production).
2.7.1 Cell Membrane and Cell Wall
Cell Membrane:
Semi-permeable, regulates substance entry and exit.
Cell Wall: (Plant cells only)
Rigid structure providing shape and support, made of cellulose.
2.7.2 Cytoplasm
Definition: Semi-liquid substance where chemical reactions occur.
Components Include:
Endoplasmic Reticulum, Mitochondria, Golgi Apparatus, Ribosomes, etc.
2.7.3 Nucleus
Importance:
Controls cell functions, regulates cell division, carries genetic information.
Components:
Nuclear membrane, nucleoplasm, chromatin fibers (which condense to chromosomes during cell division).
2.8 The Plant and Animal Cells
Similarities: Both have cell membranes, cytoplasm, and organelles.
Differences:
Plant cells have cell walls, plastids, and larger vacuoles; animal cells have centrosomes and smaller vacuoles.
2.9 Protoplasm
Definition: Living substance in cells, includes nucleus and cytoplasm.
Chemical Composition: Carbon, hydrogen, oxygen, nitrogen, etc.
2.10 Prokaryotic and Eukaryotic Cells
Prokaryotic: No defined nucleus (e.g., bacteria).
Eukaryotic: Defined nucleus present (e.g., plants, animals).
2.11 Cellular Activities
Core Functions: Growth, repair, movement, nutrient absorption, waste excretion, and reproduction depend on cellular activities.