Systems - The Unit of Life

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2009 Marshall Cavendish International (Singapore) Private Limited


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Questions to think about

What forms the

basic unit of

life?

What are the different

parts of a plant cell and

an animal cell and what

are their functions?

How is an animal

cell different from a

plant cell?

What are the different

types of cells?

How do cells

produce new cells?



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Cells

All living things are made of

cells.

A cell is the smallest unit of lifein the body.

Most living things like people,

cows and trees are made up of

millions of cells.



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Cells

We can look at cells

and study them with

the help of a powerfulmicroscope.

an optical microscope



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Cells

Some living things are made of fewer cells,

like certain algae, mosses and anemones.

algae

moss

anemone



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Cells

Some other living things are made up of only one

cell.

These are single-cell organisms, such as

bacteria, yeast and paramecium.

The cells can only be seen under a microscope.

paramecium

yeast

bacteria



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Different types of cellsDifferent types of cells

Plants are made up of

cells too.

There are cells in all partsof a plant the leaves,

the stem, the roots.



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Some cells in a leaf make foodfor the plant.

These cells contain chlorophyll.

Chlorophyll traps light energy

from the Sun to allow plants tocarry out photosynthesis.

There are also cells that controlthe size of the stoma.

stoma

cells in a leaf




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Some cells in the stem

transport food and water

within the plant.

The xylem and phloem

tubes are made up of such

cells.

xylem

cells in a stem

phloem




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Non-living things

Unlike living things, non-living things do

not have cells.



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Different types of cells

What is inside a typical animal cell?

Cytoplasm All cells is made up of a

jelly-like substance called

the cytoplasm.

The cytoplasm allows

substances such as foodand oxygen to move

around within the cells.

Many activities of the cells

take place in the cytoplasm

Cell membrane Surrounding the cytoplasm

is a soft and thin cell

membrane.

The cell membrane holds

the cytoplasm inside it. It also controls substances

that go in or out of a cell.

Nucleus In both plant and animal

cells, there is a nucleus

found in the cytoplasm.

The nucleus is a very

important part of a cell. It controls everything that

happens inside the cell.



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What is inside a typical plant cell?

o A plant cell has cytoplasm, a cell membrane, and

nucleus, just like the animal cell.

o However, a plant cell has other parts that are notfound in an animal cell.

cytoplasm

cell membrane

nucleus



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What is inside a typical plant cell?

Cell wall

A plant cell has a cellwall outside the cell

membrane.

The cell wall is made up

of a stiff material that

gives a plant cell itsshape.

Cell walls are not found

in animal cells.

Chloroplast

Achloroplast is a tinygreen structure that is

found in the cytoplasm of a

plant cell.

Chloroplasts contain

chlorophyll, a pigment thattraps sunlight for

photosynthesis.

Chloroplasts are not

present in animal cells.

Sap

A liquid which fills the cavityin the centre of most plant

cells.

The sap keeps the cell firm.

Firm cells help the plant to

stand upright as plants do

not have a skeletal system to

provide support.

Animal cells do not have

such cavities in them.



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Cells come in different

shapes and sizes.


have different functions.

In the human body, cells

work in groups, like those

in the heart and the brain.

They form the organs in

the body.

a brain cell

heart muscle cells



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Other cells such as

red and white blood

cells travel within the

body to do their jobs.

red blood cells



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Producing new cells

Our bodies increase in size as wegrow.

This is due to an increase in thenumber of cells in the body.

Cells increase in number by dividingthemselves.

The nucleus and cytoplasm of one celldivide to produce two cells.

The two new cells later divide into fourcells.

These four cells can divide to formmore cells.

This process is known as cell division.

It takes place all the time to allow cellsto multiply.

cell division



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Producing new cells

Single-cell organisms, such as paramecium, yeast and

bacteria, multiply by cell division.

The new cells produced are identical to the original cell.

Yeast multiplies by a special cell division method calledbudding (see below).

o In budding, a small bud grows from a yeast cell.

o The bud slowly increases in size and then breaks away.

bud growing



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Producing new cells

Cells do not live forever.

Old cells die and new ones are produced toreplace them.

This takes place in our bodies all the time. Our skin cells can live for 3 weeks while the cells

lining out intestines are replaced after 3 days.

Some cells also divide to help repair damaged

parts of our bodies.



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Systems - The Unit of Life

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