Characteristics of Living Things

Characteristics of Living Things

• Energy production and consumption involve metabolism, which is the sum of chemical reactions that drive life functions
• Metabolism includes anabolism (building large molecules from small molecules) and catabolism (breaking large molecules into small molecules)
• Growth and repair involve increasing size and specialization, as well as mechanisms to fix malfunctioning cells
• Adaptation involves responsiveness to stimuli and homeostasis, which is the ability to maintain a constant internal environment
• Reproduction involves replication of cells for growth and repair, as well as creating new organisms

Levels of Organization in the Body

• Chemical Level: atoms and molecules that make up the basic components of the cell
• Cellular Level: basic building blocks of tissues with distinct functions and unique positions in the body
• Tissue Level: made up of similar cells with a common function, including epithelial, muscle, connective, and nervous tissues
• Organ Level: two or more tissue types that perform a specific function for the body
• System Level: multiple organs that work together to accomplish a common purpose
• Organismal Level: represents the sum total of the structural levels working together to promote life

Cell Theory

• All living organisms are comprised of one or more cells
• Cells are the fundamental unit of life, carrying out metabolic activity and biological work
• Cells originate only from preexisting cells, and hereditary information is used to generate biomolecules for reproduction

Cells: The Living Unit of Life

• Cells are the building blocks of tissue and have the machinery to maintain homeostasis
• All cells have three basic shared components: membrane, genetic material, and cytosolic fluid
• Human cells also have membrane-bound organelles, leading to compartmentalization and complexity, and gene expression leading to specialization

Cell Differentiation

• Development of specific and distinctive features and functions in cells
• Typically irreversible, with cells differentiating during early development to perform specialized functions

Tissues

• Group of cells that are similar in structure and perform a common or related function
• Four basic types: epithelial (covering), connective (support), muscle (movement), and nervous (control)
• Most organs combine all four tissue types, and their arrangement determines organ structure and capabilities

Organs

• A structure composed of two or more tissues that work together to form a specific complex function
• Each tissue must work together to accomplish the function

Organ Systems

Integumentary System

• Skin, hair, nails, sweat glands, and oil glands
• Protection, defense, and body temperature regulation

Nervous System

• Brain, spinal cord, and nerves
• Detection of internal and external signals and coordination of physiological responses

Musculoskeletal System

• Bone, skeletal muscle, cartilage, tendons, and ligaments
• Movement, support, protection, and blood cell production

Respiratory System

• Nasal passage, trachea, and lungs
• Route of entry for air and regulation of gas levels in blood

Cardiovascular System

• Heart, blood vessels, and blood
• Movement of blood through the body to carry materials

Immune and Lymphatic Systems

• Lymphoid tissues, spleen, thymus, lymph nodes, and immunocytes
• Defense against pathogens and return of lymphatic fluid to blood

Endocrine System

• Hormone-secreting glands (thyroid, pancreas, pituitary, adrenal, and parathyroid)
• Coordination of growth, metabolism, reproduction, and physiological homeostasis

Urinary System

• Kidneys, ureters, urinary bladder, and urethra
• Conditioning of the blood, regulation of plasma volume, and excretion

Digestive System

• Mouth, salivary glands, esophagus, stomach, intestines, liver, gall bladder, and pancreas
• Coordinated digestion of food matter and nutrient absorption

Reproductive System

• Production of gametes, sex steroids, and subsequent embryonic development