Welcome to myschoollibrary! Our biology lessons continues, do have a great moment studying with us!

Lesson Note
Subject: Biology
Topic: Tissue and Supporting System.
Lesson Objectives: By the end of the lesson, the learners should be able to:

1. Define the term skeleton;
2. State the forms of Forms of Skeleton
3. Mention the types of Skeleton;
4. Stare the differences between bones and cartilage;
5. State the functions of Skeleton.
Support in Vertebrates
Axial and Appendicular Skeleton
Supporting Tissues in Plants

To carry out life processes, all organisms (plants and animals) need tissues. Tissues are group of similar cells that carry out specific functions. Skeleton is the framework of the body which provides support, shape and protection to the soft tissues and organs in animals. It forms the central core of human body and it is covered by muscles and blood vessels and skin.

                     The Human Skeleton

There are three forms of skeletal materials founds  in animals. These are: Chitin, Cartilage, and Bones.

It is a tough non-living material present in arthropods (invertebrates). It acts as a hard outer covering to the animal and is made up of series of plates covering or surrounding organisms. Chitin is very tough, light and flexible. However, it can be strengthened by impregnation with ‘tanned’ proteins and particularly in the aquatic crustaceans like crabs, by calcium carbonate.

This is a tissue present in skeleton of complex vertebrates. Cartilage consists of a hard matrix penetrated by numerous connective tissue fibres. The matrix is secreted by living cells called chondroblasts. These later become enclosed in spaces (lacunae) scattered throughout the matrix. In this condition the cells are termed chondrocytes. It acts as a shock absorber in between bones during movement because it is tough and flexible with a great tensile strength. It is found predominantly in mammals and cartilaginous fishes e.g. shark.

Cartilages are of three main types in mammals and they are

This contains a dense meshwork is the most common type and can be found on surface of moveable joint, trachea and bronchi (for ease of respiration) and also in protruding parts of the nose.

Tougher than the hyaline cartilage and can be found in the intervertebral disc of vertebral column.

Found in the external ear (pinna) and epiglottis (*cartilaginous flap covering the trachea active during food swallowing).

This is the major component of skeletal system and it consist of living cells (osteocytes), protein fibers (collagen), and minerals such as calcium carbonate and calcium phosphate. These minerals (the non- living constituent) makes up two-third of a mass of bone .Hence, bone is strong and very rigid unlike
cartilage. Bones are highly vascularised.

The skeleton of a young vertebrate embryo is made up of cartilage. As the embryo grows bone cells (osteocyte) replaces cartilage cells. Hence, the cartilage tissue becomes hardened into bone through the addition of minerals in a process called OSSIFICATION.

Differences Between Bones And Cartilage.

1 Bones produce red and white blood cells while  Cartilages do not.

2. Bone is Made up of both living cells and dead cells
Whereas cartilage is made up of mainly living cells.

3. Bones are often rigid meanwhile Cartilage are often flexible.

4. Bones are made up mainly of mineral substance such as calcium but in cartilage, mineral substance are absent.

5 Bones Can never be replaced by cartilage but cartilage Can be replaced by bones.

6. Bones are flexible only in young ones while are flexible in both young ones and adult.

The three main types of skeleton in animals are
1. Hydrostatic skeleton: This is the type present in soft bodied animals e.g. earthworm, sea anemones etc. Such animal use pressure to support itself. They also have a muscular body wall which is filled with fluid. The fluid presses against the muscular wall causing them to contract and exerting force against the fluid.

2. Exoskeleton: This is the outer skeleton present in arthropods. It is secreted by the cells covering the body of the animals and the main component is chitin (non livingsubstance). Exoskeleton also supports animals against gravity and enables them to move about. Animals with these skeleton types periodically shed the old skeleton; grow rapidly in size when the new exoskeleton is still soft and extensible. The shedding process is called MOULTING or ECDYSIS.

3. Endoskeleton: This is an internal skeleton present in all vertebrates. Endoskeleton of vertebrates are composed mainly of bones and the bones grow steadily as the animal grows (hence no need for moulting). Bones of many sizes and shapes make up the endoskeleton of vertebrates. These bones are attached together as moveable joints by tough flexible fibers called ligaments hence the skeleton is flexible. Muscles are also attached to the bones usually by tendons to provide posture and bring about body movement.


  • It supports the body of organisms.
  • Skeleton acts as the framework of the body
  • Protection of delicate organs e.g. heart, brain, etc.
  • Used for locomotion through the limbs in action.
  • Important component of respiration e.g. breathing involve active movement of the ribs.
  • Production of blood via bone marrows.

Done studying? See all previous lessons in biology.
Take a quick test for this lesson.
1. What is skeleton?
2. State two main components of skeleton. 
3. Differentiate between cartilage and chitin.

4. With examples differentiate between hyaline and elastic cartilage.
5. Distinguish between bone and cartilage.
6. State the functions of skeleton.

Questions answered correctly? Bravo!!

Do stay connected to myschoollibrary for more educational contents. Continue Studying hard for success awaits you!