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Chapter 2 Cell as a Unit of Life

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2.1 What is Cell?All living things are made up of cells.

Cells have different shapes & sizes and only be seen byusing microscope.

A cell is the basic unit of life.

Every cell is made up of

Nucleus

Cytoplasm

Cell membrane

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What is microscope?

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What is microscope?

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Steps to use a microscope

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a) Use both hands when carrying a microscope.b) Always keep the stage and other parts of the microscope

dry and clean.c) Always clean the lenses with tissue paper only to avoid

scratching them.d) Always viewing a specimen with the low objective lens

first. Then change to the medium or high power lens ifnecessary.

e) Use the fine adjustment knob for focusing when viewingwith the medium or high power objective lens.

f) Always cover the specimen on the slide with a cover slip.g) Use both eyes to view specimens.

Cell

Every cell is made up of

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a) Nucleus Is a spherical structure in the cellControlsall the activities of the cellContains genes which decide on inheritedcharacteristics

b) Cytoplasm Is a jelly-like fluid in a cellAbout 70% is water and other 30% are protein,starch, mineral salts, vitamins and othersMany chemical reactions take place in thecytoplasm

c) Cell membrane Is a thin semi-permeable layer around a cellProtects the cell and separates a cell from othercellsControls substances (water, gases and others)entering and leaving the cell

protoplasm

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Cell

Structures only found in plant cell

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a) Cell wall Protects the cellMaintains the shape of the cellIs made up of celluloseIs non-living

b) Chloroplasts Are tiny green bodiesMake and contain chlorophyll green pigment

Chlorophyll absorbs sunlight which is requiredby green plants to make food duringphotosynthesis

c) Vacuoles Contain cell sapCell sap contains dissolved sugar and mineralsaltsFound in mature cells

Similarities between an animal cell

and a plant cell

1. Basic units of life in animals and plants

2. Made of protoplasm

3. Has a nucleus4. Has cytoplasm

5. Has a cell membrane

6. Carries out chemical processes such as respiration

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Differences between an animal celland a plant cell

Animal Cell Cell Plant Cell

Smaller Size Bigger

Not fixed Shape Fixed

Does not have a cell wall Cell wall Has a cellulose cell wall

Does not have chloroplast Chloroplast Has chloroplast whichmake chlorophyll

Does not have vacuoles.

But only found in thelower animals (unicellular

organisms)

Vacuole Has large vacuoles usually

in mature cell

Contains granules(glycogen)

Food storage Contains starch granules

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2.2 Unicellular and Multicellular

Organisms

Unicellular Organisms

An organism which is made up of only one cell

Have a body size that is very small, cannot be seen with

the unaided eye and only be seen through themicroscope

Live in water (ponds, lakes, rivers and sea) and wet ormoist places (tree trunks and in the soil)

Carry out all the life processes that large organisms dosuch as respiration, feeding, excretion, movement,growth, reproduction and response to stimuli.

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Unicellular Organisms

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Unicellular Animals Unicellular Plants

Paramecium

Chlamydomonas Euglena

Yeast

2.2 Unicellular and Multicellular

Organisms

Multicellular Organisms

An organism which is made up of many cells

Have different type of cells. Each type of cells serve a

different function. Some multicellular organisms are very complex

(human being, birds, fish, f lowering plants, etc)

Some multicellular organisms are simple(hydra,spirogya, etc)

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Multicellular Organisms

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Multicellular Animals Multicellular Plants

Spirogyragreen colourbecause it haschlorophyll

Mucor

Hydra

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Cells

Tissues

Organs

Systems

Organism

2.3 Cell Organisation in the

Human Body

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CellsHuman body is made up of various type of cells withdifferent shapes, size and structures.Each type of cells carried out a particular function.Sample type of cells found in human body:-

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Type of Cells Functions

a) Muscle cells Contract and relax to provide movements of different parts of body

b) Bone cells Support and protect certain organs in body

c) Nerve cells Receive stimuli and send nerve impulses to allparts of the body

d) Epithelial cells Form a layer to protect the cells below & control

the exchange of substances among parts of thebody and betweens the body & surroundings

e) Red blood cells Transportoxygen to all parts of body(no nucleus)

f) White blood cells Destroy microorganisms & protect body frombeing attacked by microorganisms

g) Sperms Male reproductive cells

h) Ovum Female reproductive cells

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TissuesA group of similar cells performing the same work or functionSample type of tissues found in human body:-

Nervetissues

Muscletissues

Epithelial tissues Connective tissues

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OrgansA group of different tissues which carry out a specific functionEach type of tissue in an organs helps the organ to perform itsfunction. An organ is a specialized structure.Sample type of organs found in human body:-

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SystemsConsists of group of different organs working together to perform

a particular function.Main functions of the different systems found in human body:-

a) Skeletal system support body & protect internal organsb) Muscular system bring about movement of bodyc) Digestive system breakdown food into simple substances so

can be absorbed and used by bodyd) Blood circulatory system transport food, oxygen, waste

products, hormones and others in bodye) Nervous system to receive stimuli, transmit impulses &

coordinate all activities in body

f) Respiratory system absorb and transport oxygen to body &remove CO2 from body

g) Excretory system get rid of excess water and otherunwanted dissolved such as urine from body

h) Reproductive system produce reproductive cells and formnew individuals

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Skeletal system Muscular system

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Digestive system Blood circulatory system

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Nervous system Respiratory system

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Excretory system Reproductive system