cambridge essentials science core 7 with cd rom

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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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



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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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.


Cambridge University Press978-0-521-72567-5 - Cambridge Essentials Science Core 7Jean Martin and Sam EllisExcerptMore information

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




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.




7A.3 What cells are like


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.




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.




7A.4 Different cells for different jobs

Question 1

Question 2 3 4


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.




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.




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.




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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