Levels of Organisation
There are different levels of organisation of life e.g. cells, tissues, organs and systems.
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;
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
d. Ova or eggs
e. Nerve cells
f. Epidermal 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
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 |
|d.||Connective tissue||Binds together tissue.|
|e.||Nerve tissue||Coordinates and conducts |
|f.||Muscle tissue||For the Movement of parts of |
|g.||Bone tissue||For support.|
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;
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
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
i. Carrying out photosynthesis
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;
|b.||Liver||Produces bile, Homeostasis.|
|c.||Kidney||For excretion and regulation of |
body internal environment.
|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 |
|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, |
|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
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.
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