Cell Biology: Structure, Function, and Metabolism Explained

Cellular Organization and Biological Systems

Living beings are formed by microscopic subunits called cells. These cells associate to form tissues that perform specific functions, unite to create organs, and finally form systems that constitute a living being.

The Cell Theory

The fundamental principles of this theory are:

• Every living being is composed of one or more cells.
• The cell is the anatomical and functional unit of life.
• Every cell originates from another pre-existing cell.

Types of Cells

• Prokaryotic Cells: Lack a membrane surrounding the nuclear material and do not contain membrane-bound organelles.
• Eukaryotic Cells: Possess a defined nucleus and membrane-bound organelles. These cells constitute multicellular and unicellular organisms, categorized into animal and plant cells.

Cellular Functions

1. Interaction and Movement

Cells communicate with their environment through response and movement:

• Contraction: Shortening of the cell in one direction without displacement.
• Amoeboid Movement: Use of temporary cytoplasmic extensions called pseudopods to move across surfaces.
• Vibratile Movement: Performed by permanent filaments like cilia or flagella.
• Tactisms: Positive or negative locomotor responses to stimuli.

2. Nutrition and Metabolism

Through nutrition, the cell takes materials from the exterior to manufacture new cellular components and generate energy. This process is known as metabolism:

• Anabolism: Synthesis reactions that create complex substances from simpler ones using energy.
• Catabolism: The breakdown of complex substances into simpler ones, releasing energy.

Cells store energy within the bonds of ATP molecules. Waste products from catabolism are removed via excretion, while useful substances synthesized by the cell are released via secretion.

Autotrophic Nutrition and Photosynthesis

Autotrophic organisms feed on inorganic matter (water, O2, CO2) and transform it into organic matter using environmental energy.

The Photosynthesis Process

An anabolic process that converts light energy into chemical energy:

• Light-Dependent Phase: Absorption of light energy, photolysis of water, release of O2, and production of ATP.
• Dark Phase (Light-Independent): Reduction of CO2 and mineral salts into organic substances using ATP and reducing power.