Levels of Cellular Organisms

3A-2

Learning Goals:

-differentiate between unicellular and

multicellular organisms

-distinguish between tissues, organs, and

organ systems

-differentiate between colonial organisms

and organisms containing organ systems

-discuss the three types of cell junctions

Whether the organisms is a one-celled amoeba or a gigantic sequoia tree, it is composed of cells.

Those organisms that are composed of just one cell are called unicellular organisms

Bacteria, as well as many protozoans, algae, and fungi, are unicellular.

A paramecium is a unicellular organism belonging to the kingdom Protista, so it isn't exactly a plant or an animal. The organism can digest food, move through water by propelling itself with cilia, and reproduce. As one of the oldest organisms on earth, it has evolved and developed very simple methods of defense, genetic exchange, and mobility.

Example:

Multicellular organisms are made of many cells.

Some algae and fungi are multicellular, as are animals, humans, and plants.

A colonial organism is a collection of similar cells living together, and except for certain specialized reproductive cells, any of the cells could carry on the processes of the organism if they were separated from colony.

Colonial organisms can vary in complexity from what appears to be a clump of cells to a highly organized mushroom.

Use of these terms should alert the reader that the writer may be writing from an evolutionary perspective, implying that the more complex organisms developed later as the “early” organisms evolved.

However, these terms are not correct since all life was created during the week of Creation.

Sometimes unicellular or colonial organisms are referred to as “first” or “early” organisms.

Most unicellular organisms are made of cells that are organized

into tissues.

A tissue is a group of similar cells that work together to carry out a specific function.

The muscle cells of the body compose tissues whose primary function is movement.

The skin that covers and protects the body is another example of a tissue.

Many multicellular organisms have organs

Organs are composed of several types of tissues working together to perform a specific function.

The stomach is an example of an organ.

It is made of muscle tissue that churns the food, a special tissue that lines the inside of the stomach to protect it from the acid, nerve cells that direct the movement of the stomach, connective tissue cells that hold the stomach together, and cells embedded in the stomach lining that produce acid and other enzymes.

All these tissues work together to help digest the food that is eaten.

Organ SystemAn organ system is made up of a group of organs that work together to accomplish life functions.

For example the digestive system:

The digestive system includes the mouth, stomach, intestines, and other organs that work together to digest food and eliminate waste so that the body can function properly.

However, none of the specialized systems or tissues can survive alone.

They depend on other tissues and organ systems to supply their needs.

So they are very interdependent

Muscles provide movement, but they depend on the digestive system to provide the energy needed for movement, the circulatory system to bring them food and oxygen, and the nervous system to tell them when and how to move.