2.9 SPECIALIZED CELLS Many complex organisms, such as a human being or a maple tree, begin life as a single fertilized egg or a single cell. The cells in a complex organism are not all identical. Specialized cells have structures that allow them to perform specific functions instead of doing everything an organism needs to stay alive. One cell is specialized for digesting food while another might be responsible for coordinating the body’s movements. Specialized cells have physical and chemical differences that allow each type to perform one job very well. For example, the specialized cells in the photo help keep dirt out of the lungs. The orange goblet cells secrete mucus, while the hair-like extensions of the cells (called cilia) move the mucus along the trachea to remove inhaled dust and dirt.

2.9 SPECIALIZED CELLS Some of the specialized cells found in animals are: red blood cells, white blood cells, muscle cells, fat cells, skin cells, nerve cells, bone cells and sperm cells. Cells such as muscle cells that use a lot of energy have a lot of mitochondria. Cells that produce mucus in the intestine have many Golgi bodies. These cells are specialized to perform particular functions

2.9 SPECIALIZED CELLS Plants also have specialized cells Cells in the leaf of a tree have a different structure and function from the cells in the trunk. Review the photos and captions below to learn about the functions of various plant cells.

The Hierarchy of Structure in Animals Animals are multicellular organisms that are made up of many different types of specialized cells. Each cell has been specialized to perform a specific function. Specialized animal cells cannot survive on their own. They live and work as part of a larger group of cells that make up the body of an animal. Single cells die quickly when separated from surrounding cells. Large animals may contain trillions of individual cells. This entire collection of cells working together as a whole organism makes up an animal.

The Hierarchy of Structure in Animals The bodies of animals are organized in a structural hierarchy, with the “most complex” at the top and the “least complex” at the bottom. The functioning of the whole organism depends on the hierarchy of the organization within the animal. The levels of organization are organ systems, organs, tissues, and cells.

The Animal Body – Levels of Organization Consider the hierarchy of organization within a specific animal (e.g., a white-tailed deer). Cellular Level (heart muscle cell) → Tissue Level (heart muscle tissue) → Organ Level (heart) → Organ System Level (circulatory system) → Organism Level (deer)

Organ Systems All animals, regardless of their size and appearance, need to accomplish the same basic functions: obtain oxygen and nutrients, eliminate wastes, sense and respond to their environment, grow and repair damage, and reproduce. The organ systems are responsible for performing these basic functions. All organ systems contain one or more organs and other structures working together to perform a vital life function. Examples of organ systems include the digestive, reproduction, and respiratory systems.

Organs Each organ system is made up of highly specialized organs and other structures that work together to perform the overall function of the system. An organ is made up of two or more types of tissue that work together to perform a complex life function. Examples of organs include the heart, lungs, and stomach. The digestive system, for example, is made up of many organs: stomach, small and large intestines, liver, and pancreas

Anatomy vs. Physiology Anatomy as the structural components of the body e.g. the structure of the heart Physiology as the functional components of body structure e.g. the function of the heart is to pump blood (carrying nutrients and dissolved gasses) throughout the body

The Circulatory System The Digestive System

The Respiratory System The Musculoskeletal System The Respiratory System

The Reproductive System The Excretory System The Reproductive System

The Central Nervous & Endocrine (hormonal) Systems

Tissues Tissues are groups of similar cell types that perform a common function. There are four main tissue types: epithelial, connective, muscle, and nerve. Each of these types of tissue contains many types of specialized cells, and each is found in most organ systems

Epithelial Tissue Epithelial tissues are a thin covering that protects organs, lines body cavities, and covers the surface of the body. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.

Connective Tissue Connective tissue provides support and holds various parts of the body together. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone, and fat tissue. In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.

Muscle Tissue Muscle tissues contain sheets or bundles of muscle cells that contract to produce movement, both involuntary like the cardiac muscles (which circulates the blood throughout your body) and voluntary muscles (like your leg and calf muscles which allow you to walk). Smooth muscle is found in the walls of the digestive tract, uterus, bladder, blood vessels, and other internal organs.

Smooth Muscle Tissue Smooth muscle features long, narrow "spindle" shaped cells with a single central, somewhat elongated, nucleus. These cells are arranged parallel to one another. This type of muscle is called "involuntary" because it acts to contract and relax without conscious thought (i.e., you can't will your intestines to contract, they just do - this is what causes that embarrassing grumbling half way through class when you're hungry!)

Nervous Tissue Nervous tissue provides communication between all body structures. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body.

Animal Tissue Types