Many animals derived from one ancestor
I believe it is because most animals are the relatively the same if we are assuming that all animals evolved from the same previous life form. Most animals need the same nutrients and are composed of CHNOPS (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur). The molecules of life are carbohydrates, lipids, proteins, and nucleic acids which perform the functions needed for living things to survive. This answer is kind of confusing, but... a shortened version is: Animals are composed of mostly the same substances, and the substances all need the same thing. To get the same nutrients, they have created organs to perform the functions needed to get these nutrients. *Don't quote me on this though. This is my opinion and I have nothing to back me up currently*
The group of organ systems organized from most complex to least complex typically starts with the nervous system, then the circulatory system, followed by the respiratory, digestive, excretory, endocrine, and finally the integumentary system.
The structures of the human body in order from least to most complex are cell, tissue, organ, and organ system.
The body's level of organization from least complex to most complex is as follows: cells, tissues, organs, organ systems, and the whole organism. Cells are the basic structural and functional units, which combine to form tissues, then organs, and ultimately organ systems that work together to support the entire organism.
The hierarchy of complexity from most complex to least complex is: systems (e.g., digestive system), organs (e.g., heart), tissues (e.g., muscle tissue), and cells (e.g., muscle cells). Systems are made up of multiple organs, organs are comprised of tissues, and tissues are composed of cells.
The levels of organization in the body from least complex to most complex are cells, tissues, organs, organ systems, and the whole organism. Cells are the most basic units of life, which combine to form tissues, then organs that work together in organ systems to support the body's overall function.
Organ systems are most complex and fragile starting with the atoms. The most complex organ systems is the organism. In between are the molecules, cell, tissue, organ, and organ system.
Your question doesn't even make sense. Most multicellular organisms are going to have several organ systems. Which one are you talking about?
The Kidneys
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
The skin is considered the largest organ in most animals, including humans.
In most animals it is in the head.
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
One of the most significant differences is that animals have many more organs than plants do. Animals are more complex organisms, and are capable of many more things than are plants. Their internal organ system makes this increased capability and difference possible.
The group of organ systems organized from most complex to least complex typically starts with the nervous system, then the circulatory system, followed by the respiratory, digestive, excretory, endocrine, and finally the integumentary system.