First, we have to think about the different body systems, or organ systems, found in the human body.

Since the first and basic level of organization is the cellular level, this means that each organ system is made up of the basic unit of life: a cell.

Groups of cells performing similar functions form tissues, and groups of tissues performing similar functions form organs.

Organs performing the same functions form an organ system, which is also known as a body system.

When we say humans have different organ systems, it means each organ system is made up of different organs found in that particular system.

For example, one of the organ systems, or body systems, is the digestive system. So, consider the different organs in the digestive system. From the word "digestive" we can guess that this particular system is related to digestion, the absorption of nutrients from the food we eat. Once you are able to identify the different organs present in the digestive system, then try to place them in order.

For example, one of the organs found in the digestive system is the mouth. Think about where we should place the mouth in this system. Will it be the first organ, the second, the third? A digestive system diagram can help you to identify different organs present in a system.

You will need to think of other organ systems found in the human body in the same way and arrange the organs from beginning to end.

A few of the organ systems, or body systems, found in the human body are the circulatory system, the respiratory system, and the nervous system.

Consider an image of the respiratory system. If we try to identify what the different organs found in this system are, from the word respiratory we can guess that the function of this system is related to respiration, or breathing. So, what should be the first organ of the respiratory system? Will it be the nose, or perhaps the pharynx? Try to follow the diagram and then place the organs found in the respiratory system in order.