The Cell: Basic Unit of Life

The Cell - The Basic Unit of Life

• Living organisms are composed of cells, which are the basic structural units.
• Cells were first observed by Robert Hooke using improved microscopes.
• Today, advanced microscopes with high magnification allow us to study cell structure and functions in detail.

Similarities and Differences Between Cells and Bricks

• Cells in living organisms are analogous to bricks in a building, serving as fundamental building blocks.
• Despite being made of similar components, buildings can have distinct designs, shapes, and sizes.
• Similarly, living organisms vary significantly in appearance and structure but are all composed of cells.
• Unlike non-living bricks, cells are complex living structures carrying out essential life processes.

The Cell: A Complex and Dynamic Structure

• A hen's egg is a single cell, large enough to be visible without a microscope.

Diversity in Living Organisms - Cell Number, Shape, and Size

• Scientists use microscopes and stains to study living cells.
• Living organisms exhibit a wide range of shapes, sizes, and numbers of cells.
• Multicellular organisms are composed of multiple cells, while unicellular organisms consist of a single cell.
• Human bodies contain trillions of cells.
• The number of cells in an organism does not determine its complexity or functioning.
• A single-celled organism begins its life as a fertilized egg cell, which multiplies and differentiates during development.
• Unicellular organisms exhibit all essential life processes, such as capturing food, respiration, excretion, growth, and reproduction, within their single cell.
• Multicellular organisms perform these functions through specialized groups of cells forming tissues and organs.

Amoeba - A Single-celled Organism with Shape-shifting Abilities

• Amoeba is a single-celled organism that lacks a definite shape.
• Its shape is constantly changing due to the formation of pseudopodia (false feet), which aid in movement and capturing food.
• White blood cells (WBCs) in human blood are also single-celled structures that can change their shape.
• Amoeba is a complete organism capable of independent existence, while WBCs are part of a larger organism.

Shape of Cells: Relationship to Function

• Cell shape is related to its function.
• Spherical or elongated cells are common.
• Cells with a spindle shape are long and pointed at both ends.
• Branched cells, like nerve cells (neurons), receive and transmit messages throughout the body.

Size of Cells

• Cell size varies depending on its function.
• Nerve cells, for example, are elongated and branched, regardless of the organism's overall size.