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 structural and functional unit of life.

• All cells arise from pre-existing cells.

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

Basic Parts of a Cell

All cells share certain basic components that are essential for their structure and 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 cell function and reproduction.

Classification of Cells

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

• Prokaryotic Cells: Do not have a true nucleus; genetic material is found in the nucleoid region. Example: Bacteria.

• Eukaryotic Cells: Have a true nucleus 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: Synthesize proteins from amino acids.

• 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 in animal cells.

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

Types of Eukaryotic Cells

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

• Animal Cells: Lack a cell wall and chloroplasts but have centrioles and smaller vacuoles.

Summary Table: Prokaryotic vs. Eukaryotic Cells

Additional info: The image provides a visual summary of cell theory, basic cell parts, organelles, and the distinction between plant and animal cells, which are foundational topics in General Biology.