GENERAL SCIENCE REVIEWER
The Human and Animal Body
I. LEVELS OF ORGANIZATION
Cell – the basic structural and functional unit of life.
Tissue – a group of similar cells working together.
Organ – a structure made of different tissues that performs a specific function.
Organ system – a group of organs working together to perform major body functions.
Organism – an individual living thing.
II. MAJOR HUMAN BODY SYSTEMS
Integumentary System – Skin, hair, nails, sweat glands; protects the body and helps regulate temperature.
Skeletal System – Bones, cartilage, and joints; supports the body, protects organs, and works with muscles for
movement.
Muscular System – Muscles; produces movement, maintains posture, and generates heat.
Nervous System – Brain, spinal cord, and nerves; controls and coordinates body activities and responds to stimuli.
Endocrine System – Hormone-producing glands; regulates growth, metabolism, reproduction, and other body
processes.
Circulatory/Cardiovascular System – Heart, blood, and blood vessels; transports oxygen, nutrients, hormones, and
wastes.
Respiratory System – Nose, throat, trachea, bronchi, and lungs; brings oxygen into the body and removes carbon
dioxide.
Digestive System – Mouth, esophagus, stomach, intestines, liver, pancreas, and gallbladder; breaks down food and
absorbs nutrients.
Urinary/Excretory System – Kidneys, ureters, bladder, and urethra; removes wastes and helps balance water and
salts.
Immune/Lymphatic System – Lymph vessels, lymph nodes, spleen, thymus, and immune cells; helps defend the body
against pathogens.
Reproductive System – Produces sex cells and supports reproduction.
III. IMPORTANT HUMAN ORGANS
Brain – main control center of the nervous system.
Heart – muscular organ that pumps blood throughout the body.
Lungs – organs where gas exchange occurs.
Stomach – muscular organ that mixes food and begins major chemical digestion.
Small intestine – major site of digestion and nutrient absorption.
Large intestine – absorbs much of the remaining water and forms feces.
Liver – processes nutrients, produces bile, and helps detoxify substances.
Kidneys – filter blood and produce urine.
Skin – largest organ; protects the body and helps control temperature.
The Human and Animal Body
I. LEVELS OF ORGANIZATION
Cell – the basic structural and functional unit of life.
Tissue – a group of similar cells working together.
Organ – a structure made of different tissues that performs a specific function.
Organ system – a group of organs working together to perform major body functions.
Organism – an individual living thing.
II. MAJOR HUMAN BODY SYSTEMS
Integumentary System – Skin, hair, nails, sweat glands; protects the body and helps regulate temperature.
Skeletal System – Bones, cartilage, and joints; supports the body, protects organs, and works with muscles for
movement.
Muscular System – Muscles; produces movement, maintains posture, and generates heat.
Nervous System – Brain, spinal cord, and nerves; controls and coordinates body activities and responds to stimuli.
Endocrine System – Hormone-producing glands; regulates growth, metabolism, reproduction, and other body
processes.
Circulatory/Cardiovascular System – Heart, blood, and blood vessels; transports oxygen, nutrients, hormones, and
wastes.
Respiratory System – Nose, throat, trachea, bronchi, and lungs; brings oxygen into the body and removes carbon
dioxide.
Digestive System – Mouth, esophagus, stomach, intestines, liver, pancreas, and gallbladder; breaks down food and
absorbs nutrients.
Urinary/Excretory System – Kidneys, ureters, bladder, and urethra; removes wastes and helps balance water and
salts.
Immune/Lymphatic System – Lymph vessels, lymph nodes, spleen, thymus, and immune cells; helps defend the body
against pathogens.
Reproductive System – Produces sex cells and supports reproduction.
III. IMPORTANT HUMAN ORGANS
Brain – main control center of the nervous system.
Heart – muscular organ that pumps blood throughout the body.
Lungs – organs where gas exchange occurs.
Stomach – muscular organ that mixes food and begins major chemical digestion.
Small intestine – major site of digestion and nutrient absorption.
Large intestine – absorbs much of the remaining water and forms feces.
Liver – processes nutrients, produces bile, and helps detoxify substances.
Kidneys – filter blood and produce urine.
Skin – largest organ; protects the body and helps control temperature.
