新综合科学 牛津原版 3PDF电子书下载

Unit 13 Food and TransportSubstances in food 2

Food tests 3

Functions of food 8

Balanced diet 13

Storing food 19

More about food chains and food webs 25

Teeth 27

Tooth decay 32

Digestion 36

Absorption of food　 41

Digestive juices 43

A closer look at the digestive system 44

More about enzymes 45

Transport system in mammals 48

Pulse and pulse rate 56

Blood pressure 58

Water balance 58

The kidneys and their functions 61

Nutrients for plant growth 64

Absorption and transport of water in plants 68

Xylem and phloem 72

The main uses of water in plants 72

Summary 73

Difficult words 79

Unit 14　Materials from the EarthThe Earth 82

The soil 91

Building materials 96

Metals from the Earth's crust 101

The pollution problem 107

Coal 111

Crude oil or petroleum 117

Materials from the sea 124

Water pollution 129

More materials from the sea 131

Chalk,limestone and marble 135

Summary 137

Difficult words 142

Unit 15　Electricity and ElectronicsElectrostatics 144

The Van de Graaff generator 146

Looking at atoms-a revision 150

Pushing charges 152

Voltage and the voltmeter 154

Safety with the mains voltage 158

Dynamo effect 159

Alternating current and direct current 166

Transmitting electrical energy 166

Transformers 171

Power transmission 173

Using electricity 174

Power and energy 176

Current in gas 179

Lightning 180

Fluorescent lamps 185

Current in a vacuum 185

Diode 187

C.R.O.and TV 197

Some useful electronic components 197

Switches 205

Electronic logic 212

Applications of the AND gate　 219

Summary　 222

Difficult words　 227

Index　 228