Introduction to Cells: Structure, Types, and Organelles

Introduction to Cells

The Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life. It consists of three main principles:

• All living organisms are composed of cells.

• The cell is the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

Exception: Viruses are considered acellular because they lack cellular structure and cannot carry out life processes independently.

Basic Parts of a Cell

All cells, regardless of type, share certain basic structures:

• Plasma Membrane (Membrana plasmática): A selective barrier that surrounds the cell, controlling the movement of substances in and out.

• Cytoplasm (Citoplasma): The jelly-like substance within the cell where organelles are suspended.

• Genetic Material (Material genético): DNA or RNA that contains the instructions for cellular activities.

Classification of Cells

Cells are classified based on the presence or absence of a nucleus:

• Prokaryotic Cells (Procarionte): Cells without a true nucleus; genetic material is not enclosed within a membrane. Example: Bacteria.

• Eukaryotic Cells (Eucarionte): Cells with a true nucleus, where genetic material is enclosed by a nuclear membrane. Examples: Plant and animal cells.

Cell Organelles

Organelles are specialized structures within cells that perform distinct processes. Major organelles include:

• Mitochondria: Site of cellular respiration and energy (ATP) production.

• Ribosomes: Responsible for protein synthesis.

• Endoplasmic Reticulum (Retículo endoplasmático): Involved in protein and lipid synthesis; can be rough (with ribosomes) or smooth (without ribosomes).

• Golgi Apparatus (Complexo golgiense): Modifies, sorts, and packages proteins and lipids for storage or transport.

• Lysosomes: Contain digestive enzymes to break down waste.

• Centrioles: Involved in cell division (mainly in animal cells).

• Vacuoles: Storage organelles; large central vacuole in plant cells stores water and nutrients.

Types of Eukaryotic Cells

• Plant Cells (Célula Vegetal): Have a cell wall, chloroplasts for photosynthesis, and a large central vacuole.

• Animal Cells (Célula Animal): Lack a cell wall and chloroplasts, but contain centrioles and smaller vacuoles.

Summary Table: Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Organelles	Few (no membrane-bound organelles)	Many (membrane-bound organelles)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Additional info: The cell theory and classification of cells are foundational for understanding all biological processes, from genetics to physiology and ecology.