LEVELING OUT THE LEVELS OF ORGANIZATION
Every minute of the day, even when asleep, an organism’s body is busy at work. In complex animals such as vertebrates, blood is being pumped through blood vessels by the heart. Air is being pushed into and out of the body by the lungs. In the organism’s intestines food is being absorbed. Nerves are sending signals from the brain to all of the other parts of the animal’s body. All of these activities are necessary to regulate the processes of an organism’s body.
In order to perform all of the life activities, the work of keeping the organism alive is divided among the different parts of its body. Each part has a specific job to do. As each separate structure performs its specific function, it works in harmony with all the other parts to keep the living thing healthy and alive.
The groupings of these specific structures within the organism are called levels of organization. The levels of organization in a multicellular living organism may include cells, tissues, organs, and organ systems.
In order to perform all of the life activities, the work of keeping the organism alive is divided among the different parts of its body. Each part has a specific job to do. As each separate structure performs its specific function, it works in harmony with all the other parts to keep the living thing healthy and alive.
The groupings of these specific structures within the organism are called levels of organization. The levels of organization in a multicellular living organism may include cells, tissues, organs, and organ systems.
Cells
Living things are made of different cells, which are the building blocks of life. Just as a house is made of many bricks, a multicellular organism is made up of many cells. Each of the trillions of cells in a multicellular organism carries out a specific task. Cells come in all shapes and sizes. There are box-shaped cells, round cells, and thin, elongated cells. Regardless of their particular size and shape, cells work together to keep the multicellular organism alive. Some cells that might be found within living things include skin cells, blood cells, muscle cells, and nerve cells. |
Tissues
An organism’s body is a masterpiece of timing and organization. Its many cells work together to keep a complex organism alive. To help accomplish this task, the cells that make up an organism are organized into tissues. A tissue is a group of similar cells that perform the same function. For example, muscle tissue can contract to move different parts of the organism’s body. When you focus your eyes on this page, you are using muscle tissue. There are 4 types of tissues (shown in the pictures). We will go into these more tomorrow! |
Organs
Just as cells join together to form tissues, different types of tissues combine to form organs. An organ is a group of different tissues with a specific job. The heart, stomach, and brain are familiar examples of organs that can be found in many different organisms. Did you know that the eye, skin, and tongue are also organs? The heart is an example of an organ made up of four different types of tissues. All four tissues types work together to enable the heart to pump blood throughout the organism. |
Organ Systems
Many times a complicated organ like the heart is not adequate enough to perform a series of specialized jobs within the organism. In these cases, an organ system is needed. An organ system is a group of organs that work together to perform a specific job. For example, your body can work as it does because it is made up of many organ systems such as the skeletal, muscular, circulatory, and digestive systems. Although each system performs a special function for the organism’s body, no one system acts alone. |
Organism
Each organ system contributes to the constant teamwork that keeps the organism alive. The different organ systems work together and depend on one another to maintain homeostasis. A complex organism is composed of cells, tissues, organs, and organ systems. The interactions among these levels of organization enable the organism to carry out its life processes. |
So, whether it is an ant, a dog, an elephant, or a human, it should be clear that each organism has different levels of organization, which perform specialized jobs. However, each level is also dependent on the activities of other levels to keep the organism alive.
Adapted from: Prentice Hall Science: Human Biology and Health |