Support Systems in Animals

Why do animals need support?

Unlike plants, most animals move around actively — and life on land in particular requires a way to resist gravity. Support systems provide support, protection, movement, and in vertebrates, mineral storage and even a role in hearing (the tiny bones of the middle ear).

Three types of skeleton

Different animal groups have evolved different solutions. Compare all three in the Explore tab.

Type	Description	Example
Hydrostatic skeleton	Fluid held under pressure inside a body cavity, pushed against by muscles	Earthworm
Exoskeleton	A hard outer casing surrounding the soft body	Crab, insect
Endoskeleton	An internal framework of bone or cartilage that the body is built around	Human, fish

The human skeleton

The human endoskeleton is divided into two main parts:

Axial skeleton — the skull (cranium and facial bones), including the foramen magnum (where the spinal cord exits) and the palate and jaws.
Appendicular skeleton — the bones of the limbs (arms and legs) and the girdles that attach them to the axial skeleton.

Functions of the human skeleton: support, protection (of organs like the brain and heart), movement (bones act as levers for muscles), storage of minerals (like calcium), and even hearing (three tiny bones in the middle ear transmit sound vibrations).

Bones and joints

A typical long bone has a hard outer layer and, depending on the bone, a store of marrow inside. Where bones meet at a joint, several tissues work together:

Cartilage — a smooth, slightly flexible tissue that cushions the ends of bones where they meet.
Ligaments — tough tissue connecting bone to bone, holding the joint together.
Tendons — tough tissue connecting muscle to bone, allowing muscle contraction to move the bone.

Answer in your exercise book.

Question 1 · (3 marks)

Name the THREE types of animal skeleton and give ONE example animal for each.

Question 2 · (4 marks)

Give TWO advantages and TWO disadvantages of an exoskeleton.

Question 3 · (2 marks)

Name the two main divisions of the human skeleton.

Question 4 · (5 marks)

List FIVE functions of the human skeleton.

Question 5 · (3 marks)

Distinguish between a ligament and a tendon.

Question 6 · (6 marks)

The skeleton acts as a mineral store, particularly for calcium. A laboratory tests three bone samples from different animals and records their mass and calcium content:

Sample	Bone mass (g)	Calcium content (% of bone mass)
Human femur sample	200	25%
Bird wing bone sample	15	18%
Fish rib sample	5	12%

(a) Calculate the mass of calcium, in grams, stored in each of the three bone samples. Show your working. (3)
(b) Using the concept of mineral storage, explain why bones are described as a calcium "reserve" for the body. (2)
(c) Bird bones are typically lighter and less dense than mammal bones. Suggest one reason why this might be an advantage for a bird. (1)

Support Systems in Animals

Why do animals need support?

Three types of skeleton

The human skeleton

Bones and joints

Skeleton Type Comparison