2.3 CELL ORGANIZATION

The human body is organised in the following way:

The organisation of cells in this way enable multicellular organisms to carry out various

processes of life such as moving, breathing and reproduction.

CELLS• Cells performing a particular type of

work are similar in many respects.

• Different cells carry out different types of work and are modified accordingly.

• The human body is made up of various cells that carry out specific functions in the body.

Nerve cell: receive and transmit sensations and nerve impulses

Red blood cell: transport oxygen in the body

Epithelial/ skin cells: prevent the loss of water from the body

Reproductive cells: take part in fertilisation process

Skeletal muscle cell: Controls movements of bones and organs of body

Bone cells: support and protect organs

White blood cell: protect the body from being attacked by microorganisms

TISSUE• Tissue is a group of similar cells that

performs the same work.

• Example: muscle tissue is made of muscle cells.

• There are many types of tissues which include covering tissue or protective tissue, supporting tissue, connecting tissue, muscle tissue, nerve tissue, etcetera.

• Our bodies possess four specific types of tissues which include:

1. Epithelial tissue2. Connective tissue

3. Muscle tissue4. Nerve tissue

ORGANS • An organ is a group of different tissues

performing a particular kind of work.

• An organ consists of two or more type of tissues that perform a certain functions.

• Each type of tissue in an organ helps that organ to perform its function.

• Example: each type of tissue in the heart organ helps it to pump blood to all parts of the body.

SYSTEM • A system is a few organs that work

together to perform a certain function in a life process.

• The systems such as the digestive system, the reproductive system, the excretory system and others work together in harmony in an organism.

Muscular system

Function: contracts and relaxes muscles to move the body

Skeletal system

Function: supports and protects the inner organs of the body

Digestive systemFunction: breaks up food into simpler form so that it is easily absorbed by the body

Respiratory systemFunction: absorbs oxygen and get rids of carbon dioxide and vapour from the body

Blood circulatory systemFunction: transports food substances, oxygen, carbon dioxide and excretory products in the body

Function: responds to sensation from the surroundings and sends impulses from one part of the body to another

Excretory system

Function: removes excretory waste such as urea

Reproductive system

Testis

Penis

Male reproductive system

Function: produces young for the next generation

Organs in systemSystem Organs in systemMuscular All types of muscles and tendonsSkeletal Bones, cartilage, joints, ligamentsDigestive Mouth, oesophagus, stomach, pancreas,

intestines, liverRespiratory Nose, trachea, lungs, bronchus, bronchiole,

alveolusBlood circulatory

Heart, veins, arteries

Nervous Brain, spinal cord, nervesExcretory Kidney, skin, liver, urinary bladder, lungsreproductive Testis, ovary