Introduction to the Human Transport System
For simple unicellular organisms only the cell membrane separates the cell from its surroundings. This means that only diffusion is needed to access the materials they require to support life.
When living organisms get more complex, simple diffusion is no longer sufficient and more elaborate ways of transporting oxygen and material is needed. It is because of this why plants and animals have developed transport systems. In plants, the transport systems are known as the phloem and xylem (vascular system). In humans and other animals, the transport system is made up of blood, blood vessels and a muscular pump (the heart).
Types of materials transported in humans
-Hormones are transported to their target from the glands they are produced
-Oxygen and other nutrients
-Carbon dioxide- waste from respiration
-Nitrogenous waste (urea and uric acids) from the breakdown of protein
The waste products (carbon dioxide and nitrogenous waste) are transported to organs which will remove them from the body. If they are allowed to build up, they are potentially toxic. Materials taken in excess are also expelled from the body.