Aqa GCSE (9-1) Combined Science Trilogybook 2

Book Preface

There are certain conditions that your body needs to keep stable in order to survive. You need to have enough glucose in your blood for your cells to respire. Not enough would leave you without sufficient energy, and too much would send you into a coma. You need to be warm. Too hot or too cold and your enzymes wouldn’t be able to control your cellular reactions. You need to have sufficient water. Too little or too much water in your body would kill you. So your body maintains at particular levels or concentrations your:

blood glucose concentration
body temperature
water balance.

The maintenance of these three key conditions (and many others) is called homeostasis. This is the detection of changes to these conditions and responses to return the body to normal. The definition of homeostasis is the regulation of the internal environment of a cell or organism to maintain optimal conditions for function in response to internal and external changes. These changes are automatic. You do not know that they are occurring. They are described as involuntary.

Many of your body’s systems are involved in maintaining internal conditions. Your nervous system coordinates your voluntary and involuntary actions. It does this by transmitting electrical impulses along your nerve cells. These electrical impulses move very quickly along your neurones. As a consequence, homeostatic responses that involve your nervous system happen very quickly.

Other parts of your body produce chemicals called hormones. These are proteins, and they are released by glands into your bloodstream. Hormones travel around the blood until they reach their target organ, where they act. Because hormones travel in the blood, their effects are much slower than those of nerve impulses.

The electrical impulses that travel along your nerve cells from receptors reach parts of your body called coordination control centres. These include your brain, spinal cord and pancreas, and they process the information and respond accordingly. These centres can respond by releasing a hormone in the case of the glands in your brain or your pancreas. Coordination centres can also send electrical impulses back along your nerve cells. These usually end in glands or muscles, which are called effectors because they can bring about a response. For example, the sweat glands in your skin might produce more sweat in response to a high temperature.

Contents
Get the most from this book iv
Biology 2
19 Homeostasis and the human nervous system 1
20 Hormonal coordination in humans 11
21 Reproduction 27
22 Variation 45
23 The development of understanding of genetics and evolution 57
24 Classifi cation of living organisms 67
25 Adaptations, interdependence and competition 74
26 Organisation of an ecosystem 88
27 Biodiversity and the effect of human interaction on ecosystems 102
Chemistry 2
28 The rate and extent of chemical change 117
29 Organic chemistry 141
30 Chemical analysis 153
31 Chemistry of the atmosphere 166
32 Using the Earth’s resources 189
Physics 2
33A Forces 206
33B Observing and recording motion 224
34 Waves 254
35 Magnetism and electromagnetism 274
Appendix: the periodic table 287
Glossary 288
Index 292
Acknowledgements 296