Introduction to Cells: Structure, Types, and Organelles

Introduction to Cells

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.

• Cells are the basic morphological and functional units of life.

• 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

• Plasma Membrane: The outer boundary of the cell that controls the movement of substances in and out.

• Cytoplasm: The jelly-like substance inside the cell where organelles are suspended.

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

Classification of Cells

Presence or Absence of Nucleus

• Prokaryotic Cells: Cells without a defined nucleus. Genetic material is found in the cytoplasm (e.g., bacteria).

• Eukaryotic Cells: Cells with a true nucleus enclosed by a nuclear membrane (e.g., 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 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 storage or transport.

• Lysosomes: Contain digestive enzymes to break down waste.

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

• Vacuoles: Storage organelles, larger in plant cells.

Types of Eukaryotic Cells

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

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

Summary Table: Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Organelles	Few, not membrane-bound	Many, membrane-bound
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Additional info: The image provides a visual summary of cell theory, basic cell parts, organelles, and the distinction between prokaryotic and eukaryotic cells, including diagrams of plant and animal cells for comparison.