¨       All living things are composed of cells, use the same basic chemistry, follow the same genetic code, and contain the same kinds of organelles.

¨       The differences arise from the ways in which cells are specialized to perform certain tasks and the ways in which cells associate with each other to form multicellular organisms.

Unicellular Organisms

¨       Sometimes, a cell is an organism.

¨       A single-celled organism is called a unicellular organism.

¨       Unicellular organisms do everything that you would expect a living thing to do – grow, respond, transform energy and reproduce.

¨       Unicellular organisms dominate life on Earth.

Multicellular Organisms

¨       Organisms that are made up of many cells are celled multicellular.

¨       All multicellular organisms depend on communication and cooperation among specialized cells.

¨       Cell specialization is cells developing in different ways to perform different tasks.

Specialized Animal Cells

¨       Animal cells are specialized in many ways.

Ø       Red blood cells transport oxygen.

Ø       Cells specialized to produce proteins are found in the pancreas, a gland that produces enzymes to digest food.

Ø       Muscle cells help in movement.  They contain a large amount of cytoskeleton proteins, actin and myosin.

Specialized Plant Cells

¨       Plants seem passive but are interacting with the environment at every moment.

Ø       Exchanging carbon dioxide, oxygen, water vapor and other gases through openings called stomata.

Ø       Guard cells regulate this exchange and monitor the plant’s internal environment changing shape according to conditions.

Levels of Organization

¨       The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems.

Tissues

¨       Cells are the first level of organization in multicellular organisms.

¨       Tissue is a group of similar cells that perform a particular function.

¨       Most animals have four main types of tissue: muscle, epithelial, nervous, and connective.

Organs

¨       An organ is many types of tissues working together.

¨       Each muscle in your body is an individual organ. 

¨       Within a muscle, there is much more than muscle tissue – nerve tissues and connective tissues with each type performing an essential task to help the organ function.

Organ Systems

¨       An organ completes a series of specialized tasks.

¨       An organ system is a group of organs that work together to perform a specific function.

¨       Due to the organization of the body’s cells into tissues, organs, and organ systems, a division of labor is created to make multicellular life possible.

¨       Specialized cells such as nerve and muscle cells are able to function because other cells are specialized to obtain food and oxygen needed by those cells.