1. To support or hold in shape many living organisms have a skeletal system.
Organisms may have
An exoskeleton – skeleton on the outside of the body eg. Insects
Endoskeletons – skeletons on the inside of the body eg. Humans
The human skeleton is made of
bones that meet each other
to form joints,
covered on each end by cartilage and
are moved by the contraction and relaxation of muscles

2. The skeletal system serves five main functions:
Support
Movement
Protection
Making red and white blood cells
Storage of some minerals

3. Bone is made of:
Bone is
Mostly mineral substances such as calcium phosphate and small amounts of magnesium salts
And Collagen fibres (gives it elasticity). Collagen is a protein
Alive
Needs to be supplied with food and oxygen
Have different layers:
Compact bone – on the outside
Spongy bone – layer underneath that has spaces in it to keep the bone from being too heavy
Bone marrow – in the centre, has a good blood supply and is very soft, red and white blood cells and platelets are made here

4. Joints Cartilage Is much softer than bone
Allows bones to move easily over each other
Found at the end of bones
Contains collagen
There are different kinds of joints:
Fibrous joints – joins bones by fibres such as in the skull. These are called Sutures
Synovial Joints – found when two bones need to move freely. The bones are held together by ligaments. Eg. Elbow or shoulder. There are two types of Synovial Joints
Hinge joints – such as the elbow work like a door on a hinge. Allows up and down movement or side to side
Ball and socket joints – such as the shoulder and hip. A ball end fits into a socket in the other. Allows circular movement

5. There are three kinds of muscle:
Cardiac Muscle (C ) – found only in the heart
Smooth muscle (Sm) -also called involuntary muscle since we do not control them consciously. It is found in organs such as bladder and alimentary canal
Striated muscle (St) – attached to bones to make bones move by contraction (the muscle gets shorter) or relaxation (the muscle gets longer). These are also called voluntary muscles because we control them
Tendons are collagen fibres that join muscles to bones
Tendons do not stretch but they are very strong