Hierarchy of Structure in Animals

Study Notes

Animals are multicellular, meaning they are made of many specialized cells.
Specialized animal cells cannot survive independently, requiring cooperative groups of cells to form tissues, organs, and organ systems.
Large animals can comprise trillions of individual cells.

Animals are composed of many different specialized cells.
These specialized cells work together as part of a larger group, forming the organism's body.
Complex organisms may include trillions of cells.

Animals display varying degrees of complexity. Visual examples (images) of animal complexity are shown.

Cells form a hierarchy, with increasing levels of complexity.
An arrangement or classification of things by order of increasing complexity in animals.
Functioning in organisms depends on the hierarchy of organization within the animal.

Organ systems consist of one or more organs and structures operating together for essential life functions.
Examples include the digestive, circulatory, and respiratory systems.
Diagrams (illustrations) depict the respiratory and digestive systems.

Organs are made of two or more tissue types working together for complex life processes.
Specific organ examples are shown: heart, lungs, and stomach.

Tissues are collections of similar cells that perform specific, though limited, functions.
Types of tissue include: epithelial, connective, muscle, and nerve tissue
Examples of specific tissues are provided, such as lining of digestive system, tendons, smooth muscle, and nerves in sensory organs.
Additional detail on epithelial tissue: (example provided).
Additional detail on connective tissue: (example provided).
Additional detail on muscle tissue (example provided).
Additional detail on nerve tissue (example provided).

Stem Cells: Undifferentiated cells capable of differentiating into various cell types.
Stem cells give rise to all the specialized cell types in the body.
A diagram illustrates the connection between stem cells and various differentiated cells (muscle, blood, nerve, cardiac).

Differentiation is the process that creates specialized cells to carry out particular functions.
Genetic material (DNA) directs differentiation and is passed on through generations.
A diagram illustrates the process of differentiation, showing the expression of specific genes to generate distinct cell types.

Embryonic Stem Cells: Pluripotent (able to differentiate into many cell types).
Tissue (Adult) Stem Cells: Multipotent (capable of differentiating into limited cell types).

Embryonic stem cells: Derived from embryos. Can differentiate into many cell types.
Tissue (adult) stem cells: Found in adult tissue. Can differentiate into a limited range of cell types.
Examples include stem cells from bone marrow, umbilical cord.

In complex animals, some tissues can regenerate or repair after damage (e.g., muscle, skin, bone).
Other tissues cannot regenerate (e.g., nerve tissue).
A diagram (illustration) shows the regeneration of a starfish arm.

Solutions to assigned textbook questions regarding organ systems and cells are provided.
Detailed explanations of those solutions are included (cell differentiation and regeneration).