Biological Organization, Cell Biology, and Human Tissues

Biological Organization: From Subatomic to Biosphere

Universal Levels of Organization

• Subatomic Level: Protons, neutrons, and electrons.
• Atomic Level: Formed by atoms.
• Molecular Level: Formed by molecules.
• Cellular Organelles: Structures performing complex biological functions within cells.
• Cellular Level: Formed by cells.
• Multicellular Level: Includes tissues, organs, and systems.
• Population Level: Includes groups of living things of the same species.
• Community Level: Interacting populations within a shared environment.
• Ecosystem Level: A community of living organisms interacting with their non-living environment.
• Biosphere Level: Formed by all living things and their environments on Earth.

Human Body Organization

• Cells: The simplest living structures capable of performing the three vital functions of living organisms.
• Tissues: A group of cells of the same type and origin, specialized in performing a particular function.
• Organ: Formed by several different tissues joined together to perform a specific function.
• System: A group of organs working together.
• Organism: Formed by the ensemble of systems that function in a coordinated way.

The Cell: Structure, Nutrition, and Reproduction

Cell Structure: Key Components

• Cell Membrane: Controls the movement of substances into and out of the cell.
• Cytoplasm: The jelly-like substance filling the cell, containing organelles. The cytoskeleton, found in the cytosol, provides structural support and aids in organelle movement.
• Nucleus: Contains the cell’s genetic material (DNA).
• Endoplasmic Reticulum (ER): A membrane system forming a complex network of tubules and sacs throughout the cytoplasm.
  • Rough ER: Has ribosomes attached, involved in protein synthesis and modification.
  • Smooth ER: Lacks ribosomes, involved in lipid synthesis and detoxification.
• Mitochondria: Elongated organelles with a double membrane. Function: To obtain energy for the cell through cellular respiration.
• Lysosomes: Membranous vesicles containing digestive enzymes. They perform the digestion of large molecules and cellular waste.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
• Ribosomes: Small organelles responsible for protein synthesis.
• Centrosome: An organelle consisting of two centrioles, involved in cell division.
• Cilia and Flagella: Hair-like structures involved in cell movement or moving substances across the cell surface. Cilia are short and abundant; flagella are long and typically fewer in number.

Cellular Nutrition & Waste Elimination

Cells receive nutrients and eliminate waste products through the plasma membrane.

• Diffusion: The free passage of small molecules, such as oxygen and carbon dioxide, across the membrane from an area of higher concentration to lower concentration.
• Osmosis: The passage of water across a semi-permeable membrane from a more diluted solution to a more concentrated solution.
• Active Transport: When substances cannot pass through the membrane by diffusion, or need to move against a concentration gradient, the cell can incorporate them by using energy.

Cells can also carry out bulk transport processes:

• Endocytosis: To transport molecules into the cell by engulfing them.
• Exocytosis: To transport molecules out of the cell by fusing vesicles with the plasma membrane.

Cellular Reproduction: Mitosis & Meiosis

• Mitosis: A type of cell division where the daughter cells are genetically identical to the parent cell.
• Meiosis: A type of cell division that produces new cells (gametes) containing half of the original genetic information, essential for sexual reproduction.

Tissues: Building Blocks of the Body

Epithelial Tissues: Covering & Protection

Epithelial tissues cover the surface of the body and line internal organs and cavities. Their cells are arranged very closely together. According to their function, epithelial tissues are classified into various types:

• Epithelium Tissue: Covers and protects external surfaces and internal cavities of the human body, such as the skin and mucous membranes.
• Glandular Epithelium: Specialized cells that produce and release substances for different purposes, forming glands.

Connective Tissues: Support & Connection

The main function of connective tissues is to support, unify, and connect systems throughout the organism. They are diverse in structure and function.

• Loose & Dense Connective Tissue: Provides support and connects other tissues, found in the deepest layer of the skin (loose) and forming structures like ligaments and tendons (dense).
• Adipose Tissue: Primarily functions as an energy reserve, also providing insulation and cushioning.
• Cartilaginous Tissue: Provides flexible support and protects joints from bone-on-bone friction.
• Bone Tissue: A rigid tissue providing structural support, protection, and mineral storage.
• Blood: A fluid connective tissue composed of cells suspended in plasma, transporting substances throughout the body.

Muscle Tissue: Movement & Contraction

Muscle tissue is composed of muscle fibers, specialized for contraction and generating force for movement.

Nervous Tissue: Communication & Control

Nervous tissue is responsible for transmitting electrical signals and coordinating body functions.

• Neurons: Specialized cells that transmit electrical impulses.
• Glial Cells: Support cells found alongside neurons, providing nourishment, insulation, and protection.