Biological Organization and Cellular Structure Explained

Levels of Biological Organization

• Atom: The smallest component of chemical elements that make up living things (bioelements), primarily Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N), Phosphorus (P), Sulfur (S), Calcium (Ca), Magnesium (Mg), and Sodium (Na).
• Molecule: A group of two or more atoms joined together chemically.
• Organelles: A group of biomolecules that work together to form cell structures, such as membranes, ribosomes, and mitochondria.
• Cell: A group of organelles and structures. A cell is the simplest level of life.
• Tissue: A group of specialized cells that work together to perform a specific function.
• Organ: A group of different tissues that work together to carry out a specific function.
• Organ System: A group of similar or different organs that work together to carry out life functions.
• Organism: An independent living thing made up of organ systems that can carry out all life functions.

Types of Organisms

• Unicellular organisms: Microscopic living things made up of one cell.
• Multicellular organisms: Generally macroscopic living things made up of many cells; their organization is complex.

Cellular Metabolism

Cellular nutrition is the process in which cells obtain the matter and energy necessary to perform life functions.

• Catabolism: Complex organic substances → simple substances + energy.
• Anabolism: Simple substances + energy → complex organic substances.

Cell Types

Prokaryotic Cells

These cells lack a nucleus; genetic material is dispersed in the cytoplasm. Ribosomes are the only organelles. The cell membrane is covered by a cell wall, bacteria capsule, and appendices (flagella), containing a bacterial chromosome.

Eukaryotic Cells

Larger than prokaryotic cells, they feature a cell membrane that surrounds the cell and enables the exchange of substances with the outside environment. The cytoplasm fills the space between the cell membrane and the nucleus, containing the hyaloplasm, organelles, cytoskeleton, and the nucleus.

Key Organelles

• Mitochondria: Produces energy.
• Vesicles: Transport and digestion of substances.
• Endoplasmic Reticulum: Rough (synthesis and modification of proteins) and Smooth (no attached ribosomes; synthesis of lipids).
• Golgi Body/Apparatus: Processing and packaging of substances; secretory vesicles.
• Ribosomes: Protein synthesis.
• Centrosomes: Involved in cell division.
• Cilia and Flagella: Involved in cell movements.
• Cytoskeleton: Maintains cell shape.