Humans, just like all living things, perform three vital functions: nutrition, interaction and reproduction.

Our bodies need energy. We receive this energy in the form of food and drink, which is processed by the digestive system. The respiratory system extracts oxygen from the air and uses it to convert the nutrients into energy. The circulatory system then transports this energy to different parts of the body. Finally, the excretory system gets rid of unwanted or toxic substances.

There are different systems involved in the function of interaction: the nervous system, the locomotor system and the senses.

The nervous system controls both voluntary action (like conscious movement) and involuntary actions (like breathing), and sends signals to different parts of the body. The central nervous system includes the brain and spinal cord. The peripheral nervous system consists of nerves that connect every other part of the body to the central nervous system. Nerves are made up of neurons.

Our sense organs allow us to interact with the world around us. They detect information which is transmitted to the brain through the sense nerves. This information is deciphered and the brain then sends a response through the motor nerves.

Our body moves in response to signals from the brain. These signals travel through the nervous system to our muscles. These contract and relax to allow us to move. These muscles are supported by the skeleton and joints. 

Write about how smoking and drinking alcohol can affect your body. Use these videos and your science book page 23 activity 3.