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CHAPTER 2 CELL AS A UNIT OF LIFE
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CHAPTER 2

CELL AS A UNIT OF LIFE

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• Cells are basic units of all living things.

• All living things including animals, plants, and humans are made up of cells.

• Like bricks that make up a house, cells are the building block of life.

• Robert Hooke (1635-1703) was the first person to name the cell.

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• A ‘cell’ means a small room. he came across cells when he was examining pieces of cork under the microscope he had invented.

• A cell is the smallest unit of living things. It can be function and survive on its own.

• Cell are responsible to carrying out life processes.

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MICROSCOPE

• A microscope makes an object look bigger than it actually is. It magnifies the object.

• It is used to observe very tiny objects which are not visible to the naked eye.

• Cells of living things can be observed with a microscope.

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• Organism can be divided into 2 groups namely unicellular organisms and multicellular organisms.

UNICELLULAR ORGANISMS• Unicellular organisms are organisms that consist

of only 1 cell only.(‘uni’ means one).

• Also known as unicellular microorganisms because their tiny size.

• These organisms usually live in the sea, rivers, and lakes.

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• Unicellular organisms carry out all the life processes such as movement, response, respiration, digestion, excretion, reproduction, and growth.

• Examples of unicellular organisms are euglena, amoeba, paramecium, yeast, and chlamydomonas.

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MULTICELLULAR ORGANISMS

• Multicellular organisms are organisms that consist of many cell (‘multi’ means many).

• Like unicellular organisms, multicellular organisms carry out all the processes of life.

• Multicellular organisms are made up of many types of cells.

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• Each type of cell has a different structure and carries out only specific function.

• Man is the most complex multicellular organisms.

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Cell organisation in the human body

• Human being are the most complex multicellular organisms(has billions of cells).

• In multicellular organisms, different function are carried out by different types of cells.

• This is known as cell specialisation.

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From cell to tissue

• In multicellular organisms, the same type of cells form groups.

• These group are called tissue.

• Each cell in a tissue carries out the same function.

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From tissue to organ

• A few different types of tissues group together to form an organ.

• An organ carries out a specific function.

• Eg. Heart(organ) is made up of muscular tissue, nervous tissue and connecting tissue. The heart pump blood to all parts of the body.

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BRAIN

EAR

SKIN

HEART

STOMACH

EYE

NOSE

LUNG

LIVER

INTESTINEAPPENDIX

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From organ to system• A few group of organ which work together to

perform a specific function forms a system.

• A system carries out a function.

• System ensure that our bodies function normally.

• The kidneys, the lungs, the liver, the skin are excretory organ. Together they make up the excretory system.

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From system to organism.

• There are many systems in our bodies.

• All systems in the body work together to produce an independent organisms.

• These systems do not work independently. They all cooperate with one another so that the human body function as a whole.

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• Cells are organised in the following way.

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• The end

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