Levels of Organisation

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There are different levels of organisation of life e.g. cells, tissues, organs and systems.

1. Cells:

The cell is the basic unit of a living thing capable of doing all life activities.

A cell can exist independently as a single-celled or unicellular organism or as a part of a multicellular organism.

Examples of unicellular organisms are;

a. Amoeba
b. Paramecium
c. Euglena
d. Plasmodium
e. Trypanosome
f. Chlamydomonas

Examples of multicellular organisms are;

a. Blood cells
b. PhloemPhloem is a plant vascular tissue that conducts foods made in the leaves during photosynthesis, downwards to all other parts of the plant. More cells
c. Spermatozoa
d. Ova or eggs
e. Nerve cells
f. Epidermal cells

Human cells e1658683634943 — *_{Human cells.}*

2. Tissues:

cell microscope071117 — *_{Tissue is a collection of cells.}*

A tissue is a collection of cells which are similar in structure and perform the same function. Hydra and obelia are organisms at the tissue level.

Examples of tissues in higher plant organisms are;

a. XylemXylem is a plant vascular tissue that transports water and dissolved minerals from the roots to the stems and leaves and also provides physical support. Xylem is one of the two... More
b. Phloem
c. Epidermal
d. Sclerenchyma tissues

Examples of tissues in higher animals and their functions are listed in the table below;

	Tissue on man	Function
a.	Epithelial tissue	It forms the skin cells around the body.
b.	Blood tissue	They convey food and oxygen around the body.
c.	Skeletal tissue	Supports the body and its movement.
d.	Connective tissue	Binds together tissue.
e.	Nerve tissue	Coordinates and conducts impulses.
f.	Muscle tissue	For the Movement of parts of the body.
g.	Bone tissue	For support.

3. Organ:

An organ is a structure made up of two or more tissues working together to perform a specific function.

Below are examples of organs in plants and the functions they perform;

Root:

i. Anchorage
ii. Absorption of waterIn higher plants, water and minerals are absorbed through root hairs which are in contact with soil water, and form a root hair zone a little behind the root tips. Diagrammatic... More and mineral salts from the soil
iii. Storage function

The Stem:

i. Conduction of water, mineral salts and manufactured food through the plant
ii. Holding the leaves in the best position to absorb light for photosynthesisPhotosynthesis is the process by which green plants, and some algae and bacteria, convert the energy of sunlight into chemical energy. This energy is then used to synthesize carbohydrates such as... More

The Leaves:

i. Carrying out photosynthesis
ii. Transpiration
iii. Acts as a storage organ in bitter leaf

In plants, other organs are flowers, fruits and bulbs e.g. onions.

Below are examples of organs in higher animals and the functions they perform;

	Organs:	Functions:
a.	Lungs	For respiration.
b.	Liver	Produces bile, Homeostasis.
c.	Kidney	For excretion and regulation of body internal environment.
d.	Brain	Nervous coordination.
e.	Eyes	For sight.
f.	Ear	For hearing.
g.	Heart	For blood circulation.

4. Organ System:

This refers to several organs working together to perform a common function.

Examples of systems in plants are;

	Name of system	Main Organs	Main Function
a.	Root system	Root and root hairs	Anchorage and absorptionAbsorption is the movement of digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol). The small intestine absorbs most of... More
b.	Shoot system	Stem and leaves	Support photosynthesis

Examples of systems in animals are;

	Name of System in Mammal	Main organs in the System	Main Function
a.	Respiratory system	Nose and lungs	Intake of air and exchange of gas.
b.	Nervous system	Brain and spinal cord	Nervous co-ordination.
c.	Reproductive system	Testes, ovaries, uterus	For reproduction.
d.	Digestive system	Oesophagus, stomach, pancreas, intestine	Digestion of food.
e.	Circulatory system	Heart and lungs	Blood circulation.
f.	Skeletal system	Bones and cartilage	Provide places for the attachment of muscles and it also gives support to the body.
g.	Excretory system	Lungs and kidneys, Skin	Removal of metabolic waste products from the body.

5. Multicellular Organisms:

This is made up of several organ systems. They form an organism (or living thing) when they work together. For an organism to perform well, all the cells tissues, organs and systems must also function perfectly.