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17A Cells: the body’s building blocks
7A.1 What living things are made from (HSW)
OutcomesYou should already know Keywords
Question 1
Question 3
2
4
skulleye
brain
Cystis
(bladder)
Aidoion
(penis)Orchis
(testis)
cartilage
bone
bone marrow
Aristotle lived in Greece over 2000 years ago. He was very
interested in plants and animals and in how the human body works.
Look at the drawing by Aristotle of some parts of the human body.
We call these parts . Old drawings and texts from China and
the Middle East also show human organs. Some even show plant
organs.
Aristotle’s drawing.
A scan through part of the head.
Part of a thigh bone.
A closer look at human organs
In the late 18th century, a French doctor called Xavier Bichat did
hundreds of post-mortems. Post-mortems are operations carried
Bichat found that each human organ contains more than one kind
of material. He listed 21 different kinds. We call these materials
. Bichat couldn’t see the detailed structure of these tissues
because he didn’t have a microscope.
• operations
• cutting up dead bodies.
Now we can look at X-rays and body scans, too.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
2 7A Cells: the body’s building blocks
7A.2 How microscopes helped to change our ideas (HSW)
KeywordsYou should already know Outcomes
Question 1 2 3
Hooke’s drawing of cork cells.
Leeuwenhoek’s microscope.
Onion cells as seen using Robert
Brown’s microscope.
1665 Hooke published his drawings of microscopic structures.
One of the drawings was of a slice of cork. It showed
that cork is made up of what look like tiny boxes.
He called these boxes .
1683 Leeuwenhoek published his drawings of microscopic
creatures. Because his lens was so much better, the
images were clearer than Hooke’s. He could see
more details.
1831 A Scot, Robert Brown, saw and named the .
1840 German scientists, Matthias Schleiden and Theodor
Schwann, published the cell theory – that all plants and
animals are made of cells.
were invented in the 16th century but their lenses
were not very good.
Type of
microscope
Invented by About the images
simple
(1 lens)
not very clear
compound
(2 lenses)
Hans and Zacharias
Janssen (Dutch)
in 1590 and later
by Robert Hooke
(English)
better images
simple
(1 lens – but
a better one)
Antonie van
Leeuwenhoek
(Dutch) in 1673
even better – things looked
200 times larger than they
really were
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
37A Cells: the body’s building blocks
Question 4 5 6 7 8
This ladybird is 4 mm long.
Scale drawings
When we draw what we see under a microscope, we draw
things much bigger than they really are. We draw them to .
We often use scale drawings in our lives, not just in science.
Maps and plans are scale diagrams. They show places smaller
than they really are. We call this scaling down.
When we show things bigger than they really are, we are
scaling up.
You can show a scale in one of these ways:
than it really is. This means you
can see more detail.
7A.2 How microscopes helped to change our ideas
20 1 mm
Under a magnifying lens, the
ladybird looks three times as
big, so the scale factor is ×3.
This is Leon’s drawing of the same ladybird.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
4 7A Cells: the body’s building blocks
7A.3 What cells are like
KeywordsYou should already know Outcomes
Question 1
Question 2
A
C
B
D
Four microscope views of living and non-living things.
Cells are very small
Remember that
• all living things are made of cells
• cells are so small that you need a microscope to see them.
If you magnify cells a hundred times or more, you can see smaller
parts inside them.
Non-living things show different types of structure.
Sometimes there is no detail to see under a light microscope.
Cells are not all alike
All cells are very small. But they are not all the same size.
In this square,
• 2500 rhubarb skin cells, or
• 10 000 human skin cells.
Cells also vary in shape.
Plant and animal cells look quite different under the microscope.
Plant and
animal cells.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
57A Cells: the body’s building blocks
Question 3 4
Question 5 6
cytoplasm
vacuole
nucleus
cell membrane
chloroplast
cell wall
cytoplasm
nucleus
cell membrane
A closer look at animal cells
Cells are made of lots of different parts.
Each part has a different job to do to keep the cell
• alive
• working properly.
Plant cells aren’t quite the same
Chris also made a slide of a moss leaf.
She looked at the cells under a microscope.
Chris scraped some cells
from the skin inside her
cheek.
Cells in a moss leaf.
7A.3 What cells are like
Under the microscope the cells look
coloured. The colour is a stain that
makes them show up more clearly.
A moss plant.
Cheek cells.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
6 7A Cells: the body’s building blocks
7A.4 Different cells for different jobs
Question 1
Question 2 3 4
KeywordsYou should already know Outcomes
this cell
secretes
mucus
dust carried out
of breathing tubes
tiny hairs (cilia)
mucus and dust
senses in
your fingers
very long nerve fibre connections to nerve
cells in your brain and
spinal cord
soil and
water
root hair cell
inside the
root
B
A
Two kinds of cells in breathing
tube linings.
There are over a million different types of animal. They all have
different shapes and sizes.
But in all these animals there are only about 200 different kinds
of cell. These cells are different because they do different jobs.
The cells on the inside of the breathing tubes of humans and other
animals are similar because they do the same jobs.
Goblet cells
Called this
because...
of their shape cilia = beating hairs
epithelium = skin or lining
Job to make sticky mucus
to trap dust and
micro-organisms
to carry the mucus out of
the lungs
More specialised cells
are very long. Your brain and spinal cord send and
receive messages in the form of nerve impulses from all over
your body.
Your are full of a chemical
called haemoglobin. This can join with oxygen.
So your blood can carry oxygen to every cell in
the body.
Plants have special cells too.
are one example. The hairs give the roots a
bigger surface for absorbing water.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
77A Cells: the body’s building blocks
7A.4 Different cells for different jobs
Question 5
Question 6 7 Check your progress
How building materials build up into a house. How cells build up into a plant.
cellsbuilding
materials
parts of
room
room
house
tissues
plant
organs
How cells work together
A house doesn’t look like a living thing! However, the way the
building materials of a house are grouped is similar to the way
that cells in a living thing are organised.
There are many different rooms in a house.
Each room has a different purpose.
In a house, different groups of building
materials are joined together to make
the rooms.
In a living thing, several tissues are joined
together to make an .
In a living thing, there are many different
organs. Each organ has a different job.
The bricks in a house are like the cells in a
living thing. A group of bricks is called a wall.
A group of similar cells is called a .
All the cells in a tissue are the same.
They work together to do the same job.
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
8 7A Cells: the body’s building blocks
7A.5 How new cells are made
Question 1
Question 2
KeywordsOutcomesYou should already know
nucleus
specialised cell
cell
cell
Cell cycle.
People used to think that living things sometimes appeared out
of nowhere.
• They saw maggots appear in rotting meat.
• Leeuwenhoek described tiny living animals in rotting things.
So the idea seemed to be sensible.
In the 19th century, Louis Pasteur proved that this idea was wrong.
He showed that living things come only from other living things.
Cells don’t just appear from nowhere either.
In 1858, a German scientist called Rudolph Virchow suggested that
new cells could only grow from cells that were already there.
Now we know that new cells form only when cells divide.
How a cell divides
in more materials, they grow. When they are big enough, the cells
divide again. We call this the .
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
97A Cells: the body’s building blocks
Question 3
Question 4
Summary
Review your work
new cell
wall forms
nucleus divides to
form two nuclei How a plant cell divides.
Unspecialised cells divide
over and over again.
Muscle cells are specialised.
They don’t divide.
Plant cell division
When a plant cell divides, it’s not just the nucleus and cytoplasm
that divide. A new cell wall forms between the new nuclei.
The nucleus of a cell holds
all the information that tells
a cell how to develop and
to work.
Before it divides, the
nucleus makes a copy of
this information.
One copy goes into each
new nucleus. So the new
cells are identical to the
old one.
The nucleus controls how a cell develops
Specialised cells
Some cells divide over and over again, but other cells become
specialised to do particular jobs. Specialised cells don’t
divide again.
7A.5 How new cells are made
© Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information
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