Introduction to Cells: Structure, Types, and Organelles

Teoria Celular (Cell Theory)

Principles of Cell Theory

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

• All living beings are formed by cells.

• Cells are the basic morphological and functional units of living organisms.

• All cells arise from pre-existing cells.

Exception: Viruses are considered acellular because they do not possess a cellular structure and cannot carry out life processes independently.

Basic Parts of the Cell

Major Cellular Components

All cells share certain basic structures that are essential for their function:

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

• Cytoplasm: The jelly-like substance within the cell where organelles are suspended and metabolic reactions occur.

• Genetic Material: DNA or RNA that contains the instructions for cellular function and reproduction.

Classification of Cells

Prokaryotic vs. Eukaryotic Cells

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

• Prokaryotic Cells: Do not have a membrane-bound nucleus. Genetic material is found in the cytoplasm. Example: Bacteria.

• Eukaryotic Cells: Have a true nucleus enclosed by a membrane. Found in plants, animals, fungi, and protists.

Cell Organelles

Main Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct processes:

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

• Ribosomes: Responsible for protein synthesis.

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

• Golgi Complex: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.

• Centrioles: Involved in cell division in animal cells.

• Vacuoles: Storage organelles, larger in plant cells for water and nutrient storage.

Types of Eukaryotic Cells

Plant vs. Animal Cells

• Plant Cells: Have a cell wall, chloroplasts for photosynthesis, and large central vacuoles.

• Animal Cells: Lack cell walls and chloroplasts but contain centrioles and smaller vacuoles.

Additional info: The image provides a visual summary of cell theory, basic cell structures, organelles, and the distinction between prokaryotic and eukaryotic cells, as well as plant and animal cells. It also highlights viruses as an exception to the cell theory.