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  1. Introduction to Biology | Week 1
    6 Topics
    1 Quiz
  2. Recognizing Living Things | Week 2
    3 Topics
    1 Quiz
  3. Organisation of Life | Week 3
    3 Topics
  4. Classification of Living Organisms | Week 4
    7 Topics
    1 Quiz
  5. Kingdom Prokaryotae / Monera & Kingdom Protista | Week 5
    3 Topics
    3 Quizzes
  6. Kingdom Fungi & Kingdom Plantae | Week 6
    9 Topics
    2 Quizzes
  7. Kingdom Animalia I | Week 7
    6 Topics
    1 Quiz
  8. Kingdom Animalia II | Week 8
    5 Topics
    1 Quiz
  9. The Cell | Week 9
    3 Topics
    1 Quiz
  10. The Cell Structure and Functions | Week 10
    4 Topics
    1 Quiz
  11. The Cell and its Environment | Week 11
    4 Topics
    1 Quiz
  12. Nutrition in Plants | Week 12
    4 Topics
    1 Quiz

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

living things 2

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

Set of unicellular organisms (protozoa): Paramecium caudatum, Amoeba proteus, Chlamydomonas and Euglena viridis.

Examples of multicellular organisms are;

a. Blood cells
b. Phloem 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. Xylem
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 tissueIt forms the skin cells
around the body.
b.Blood tissueThey convey food and oxygen
around the body.
c.Skeletal tissueSupports the body and its
d.Connective tissueBinds together tissue.
e.Nerve tissueCoordinates and conducts
f.Muscle tissueFor the Movement of parts of
the body.
g.Bone tissueFor 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;


i. Anchorage
ii. Absorption of water 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 photosynthesis

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.LungsFor respiration.
b.LiverProduces bile, Homeostasis.
c.KidneyFor excretion and regulation of
body internal environment.
d.BrainNervous coordination.
e.EyesFor sight.
f.EarFor hearing.
g.HeartFor blood circulation.
Lungs are examples of Organs.

4. Organ System:

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

Examples of systems in plants are;

 Name of systemMain Organs Main Function
a.Root systemRoot and root hairsAnchorage and absorption
b.Shoot systemStem and leavesSupport photosynthesis

Examples of systems in animals are;

 Name of System in MammalMain organs in
the System
a.Respiratory systemNose and lungsIntake of air and
exchange of gas.
b.Nervous systemBrain and spinal cordNervous co-ordination.
c.Reproductive systemTestes, ovaries, uterusFor reproduction.
d.Digestive systemOesophagus, stomach,
pancreas, intestine
Digestion of food.
e.Circulatory systemHeart and lungsBlood circulation.
f.Skeletal systemBones and cartilageProvide places for the
attachment of muscles
and it also gives support
to the body.
g.Excretory systemLungs and kidneys, SkinRemoval of metabolic
waste products from
the body.
organ system
The Digestive System.

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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