Biology Chapter on Cell and Tissue Organization

Human Organization

• The human body begins as a single-celled zygote, formed by the fusion of sperm and egg.
• This zygote divides, resulting in trillions of cells.
• Humans are multicellular organisms with cells having specific structures and functions.

Levels of Biological Organization

• Biologists study biology and classify organisms from atoms to biomolecules to cells, organisms, populations, ecosystems, and biospheres.
• This classification helps understand the different components of an ecosystem.
• The organization progresses from simple to complex as follows: atoms, molecules, macromolecules, organelles, cells, tissues, organs, organ systems, organism, population, community, ecosystem, biosphere.

Structural Levels of Organization in the Human Body

• Chemical level: Formed by atoms, molecules, macromolecules
• Cellular level: Formed by various types of cells such as blood cells and epithelial cells.
• Tissue level: Groups of cells perform a specific function. An example is connective tissue.
• Organ level: Different types of tissues combine to form organs such as the heart, lungs, and kidneys.
• Organ system level: Different organs combine to form systems that have a particular set of functions. Examples are circulatory systems, nervous systems, and digestive systems.
• Organism level: The complete and fully functioning being is the organism level.

Biological Levels of Organization

• Cells: The fundamental structural and functional units of life, varying in structure & function; smallest basic units
• Tissues: Grouped cells of similar structure and embryonic origin. They work together to carry out a shared purpose.
• Organs: Composed of different tissue types, performing a specific function. Example: the stomach, the heart, etc.
• Systems: Groups of organs collectively performing a specialized function. An example is the digestive system.
• Organisms: A complete and fully functioning being made of the organ systems that interact to maintain life.

Human Body Tissues

• Four main types: Connective, Muscle, Nervous, and Epithelial tissue.
• These are categorized based on similarities in structure and function.

Epithelial Tissue

• Forms coverings and linings.
• Tightly packed cells arranged in sheets.
• Covers body surfaces, lines internal cavities and organs.
• Also forms glands.
• Protects and conducts secretion, filtration, and absorption.

Connective Tissue

• Most abundant tissue type, connects different parts of the body.
• Supports and protects other tissues and organs.
• Contains cells embedded in an extracellular matrix.
• The matrix consists of ground substance and fibers, such as collagen (thick, strong fibers).
• Types of connective tissues: loose, dense, special connective tissues (bone, blood, cartilage).
• The matrix type determines the tissue's specific functions; for example, cartilage matrix is rubbery, while bone matrix is hard.

Types of Connective Tissues

• Loose Connective Tissue: Found in areas where support is needed but flexibility is required. Example: adipose tissue stores fat. Provides support & protection and fills space.
• Dense Connective Tissue: Densely packed collagen fibers arranged in parallel, producing strength. Example: tendons & ligaments. Provide resistance and protection.
• Specialized Connective Tissues: Bone, Cartilage, and Blood.
  • Bone: Hard matrix, supportive framework for the body.
  • Cartilage: Firm rubbery matrix offering support & protection.
  • Blood: Liquid matrix. Aids in transport and various other functions.

Muscle Tissue

• Responsible for movement in the body.
• Three types: skeletal (voluntary), smooth (involuntary), cardiac (involuntary & rhythmic).

Nervous Tissue

• Specialized tissue forming the brain, spinal cord, and nerves.
• Conducts electrical and chemical messages throughout the body.
• Consists of neurons (conducting cells) and neuroglia (supporting cells).

Organ Systems & Homeostasis

• Different organs and organ systems work together to maintain a stable internal environment (homeostasis).
• Human body systems: Reproductive, Urinary, Respiratory, Digestive, Lymphatic, Endocrine, Cardiovascular, Skeletal, Integumentary, Nervous, and Muscular.