Cambridge Essentials Science Core 7 With CD Rom
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Transcript of Cambridge Essentials Science Core 7 With CD Rom
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7Core
Jean Martin Sam Ellis
Science
Cambridge Essentials
Cambridge University Press www.cambridge.org
Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisFrontmatterMore information
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CAMBRIDGE UNIVERSITY PRESS
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Cambridge University Press 2008
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First published 2008
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Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisFrontmatterMore information
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iiiThe contents of this book and CD-ROM are copyright Cambridge University Press 2008
ContentsAdvice
Introduction iv
Biology
7A Cells: the bodys building blocks
7A.1 What living things are made from 1
7A.2 How microscopes helped to change our ideas 2
7A.3 What cells are like 4
7A.4 Different cells for different jobs 6
7A.5 How new cells are made 8
7A.HSW How ideas change 10
Questions 13
7B Reproduction
7B.1 Patterns of reproduction 16
7B.2 Reproduction and development of humans 19
7B.3 The menstrual cycle 22
7B.4 The uterus as home to the developing baby 23
7B.5 Birth and care of the baby 24
7B.6 How humans change as they grow 26
7B.HSW Help with reproduction ethical issues 28
Questions 30
7C Environment and feeding relationships
7C.HSW Choosing a method for investigating animals 34
7C.1 Habitats 36
7C.2 Changing environmental conditions 38
7C.3 Feeding relationships 42
Questions 44
' 9DULDWLRQDQGFODVVLFDWLRQ7D.1 The same but different 48
7D.2 The causes of variation 50
7D.3 Describing living things 52
7D.4 Sorting things into groups 54
7D.5 How scientists classify living things 56
7D.HSW Developing systems for classifying
and naming 60
Questions 62
Chemistry
7E Acids and alkalis
7E.1 What acids and alkalis are like 66
7E.2 Telling acids and alkalis apart 68
7E.3 Universal indicator and the pH scale 70
7E.4 Neutralisation 72
7E.5 Where neutralisation is important 74
7E.HSW Investigations and safety 76
Questions 78
7F Simple chemical reactions
7F.1 Chemical reactions 80
7F.2 Reactions between acids and metals 82
7F.3 Reactions between acids and carbonates 84
7F.4 Burning and fossil fuels 86
7F.HSW You dont always get what you want 88
Questions 90
7G Particle model: solids, liquids and gases
7G.1 Looking at substances 92
7G.2 The particle theory 94
7G.3 Using the particle model 96
7G.4 More uses of the particle model 98
7G.HSW Brownian motion 100
Questions 102
7H Solutions
7H.1 Mixing solids and liquids 104
7H.2 Common salt 106
7H.3 Separating solvents and solutes 108
7H.4 Solubility 110
7H.HSW Investigations with salt 112
Questions 114
Physics
7I Energy resources
7I.1 Energy and fuels 116
7I.2 Fossil fuels 118
7I.3 Renewable energy resources 120
7I.4 Living things and energy 122
7I.HSW Ethical problems 124
Questions 126
7J Electrical circuits
7J.1 Switches, circuits and symbols 128
7J.2 Inside a circuit 130
7J.3 Energy for the circuit 132
7J.4 Parallel circuits 134
7J.5 Using electricity safely 136
7J.HSW Electricity: the pluses and the minuses 138
Questions 140
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Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisFrontmatterMore information
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iv Introductioniv
IntroductionTake advantage of the CD
Cambridge Essentials Science comes with a CD in the
back. This contains the entire book as an interactive
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17A Cells: the bodys building blocks
7A.1 What living things are made from (HSW)
OutcomesYou should already know Keywords
Question 1
Question 3
2
4
6FLHQWLFHQTXLU\
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 RUJDQV. Old drawings and texts from China and the Middle East also show human organs. Some even show plant
organs.
Aristotles 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
RXWRQGHDGERGLHVWRQGRXWZKDWNLOOHGWKHPBichat found that each human organ contains more than one kind
of material. He listed 21 different kinds. We call these materials
WLVVXHV. Bichat couldnt see the detailed structure of these tissues because he didnt have a microscope.
$WUVWLQIRUPDWLRQDERXWKXPDQRUJDQVFDPHIURP
operations cutting up dead bodies.Now we can look at X-rays and body scans, too.
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2 7A Cells: the bodys building blocks
7A.2 How microscopes helped to change our ideas (HSW)
KeywordsYou should already know Outcomes
Question 1 2 3
Hookes drawing of cork cells.
Leeuwenhoeks microscope.
Onion cells as seen using Robert
Browns 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 FHOOV.
1683 Leeuwenhoek published his drawings of microscopic
creatures. Because his lens was so much better, the
images were clearer than Hookes. He could see
more details.
1831 A Scot, Robert Brown, saw and named the QXFOHXV.
1840 German scientists, Matthias Schleiden and Theodor
Schwann, published the cell theory that all plants and
animals are made of cells.
0LFURVFRSHV 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
6RPHRIWKHUVWPLFURVFRSHV
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37A Cells: the bodys building blocks
Question 4 5 6 7 8
7KLVLVWKHUHDOVL]HRIDHD
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 VFDOH.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:
5REHUW+RRNHGUHZDHDELJJHUthan 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 Leons drawing of the same ladybird.
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4 7A Cells: the bodys 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, \RXFRXOGW
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.
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57A Cells: the bodys 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 arent 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.
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6 7A Cells: the bodys building blocks
7A.4 Different cells for different jobs
Question 1
Question 2 3 4
KeywordsYou should already know Outcomes
this cellsecretesmucus
dust carried out
of breathing tubes
tiny hairs (cilia)
mucus and dust
senses inyour fingers
very long nerve fibre connections to nervecells in your brain andspinal cord
soil andwater
root hair cell
inside theroot
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 &LOLDWHGHSLWKHOLDOFHOOVCalled 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
1HUYHFHOOV are very long. Your brain and spinal cord send and receive messages in the form of nerve impulses from all over
your body.
Your UHGEORRGFHOOV 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. 5RRWKDLUFHOOVare one example. The hairs give the roots a
bigger surface for absorbing water.
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77A Cells: the bodys 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.
cellsbuildingmaterials
parts ofroom
room
house
tissues
plant
organs
How cells work together
A house doesnt 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 RUJDQ.
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 WLVVXH.All the cells in a tissue are the same.
They work together to do the same job.
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8 7A Cells: the bodys 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 dont 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
7KHQXFOHXVGLYLGHVUVWDQGWKHQWKHFHOO$VWKHQHZFHOOVWDNHin more materials, they grow. When they are big enough, the cells
divide again. We call this the FHOOF\FOH.
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97A Cells: the bodys building blocks
Question 3
Question 4
Summary
Review your work
new cellwall forms
nucleus divides toform two nuclei How a plant cell divides.
Unspecialised cells divide over and over again.
Muscle cells are specialised. They dont divide.
Plant cell division
When a plant cell divides, its 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 dont
divide again.
7A.5 How new cells are made
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