IGCSE & GCSE Biology by D. G. Mackean

Here you will find the answers to the 'in-text' questions which occur in IGCSE Biology (2nd edition) and GCSE Biology (3rd edition) by D. G. Mackean, published by Hodder Education, London, UK.

Chapters: | Index | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 |

Chapter 33. Breathing

Page 300

1. It depends on how you cut the shape

If you cut it like a each half will have a surface area of 4(2x1) +2(1x1) = 10cm². The volume will be 2cm³. The ratio of surface area to volume is 10cm²/2cm³.

If you cut it like b each half will have a surface area 2(2x2) + 4(2x0.5) = 12cm². The volume will be 2cm³. The surface area/volume ratio is 12cm²/2cm³.

2. Judging by the scale, the bacterium is about 0.00125mm wide. The maximum diffusion distance will be half this figure, namely 0.0006mm (approximately).
3. A frog is most likely to use its lungs during and after a period of activity.
4. Most large animals, active or not, are unable to exchange gases through their skins. They therefore have need of organs specialised for gaseous exchange. The distances from these organs to all the tissues of the body are too great for diffusion to be effective. A circulatory system allows the gases to be carried from the respiratory surface to all parts of the body and vice versa.
5. In a fish, a fresh supply of water containing dissolved oxygen passes continuously in one direction over the gills so that a fresh supply is in direct contact with the exchange surface.
    In the lungs the air is only intermittently exchanged with the atmosphere and there is always a ‘stagnant’ layer through which the oxygen has to diffuse before coming into contact with the respiratory surface.
6. a In mammals, the muscular activity takes place in the intercostal muscles and the diaphragm.
    b In fish, the muscular activity takes place largely in the floor of the mouth.

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Section 1, Chapters 1-5
Section 2, Chapters 6-9
Section 3, Chapters 10-12
Section 3, Chapters 13-17
Section 3, Chapters 18-20
Section 4, Chapters 21-24
Section 5, Chapters 25-27
Section 5, Chapters 28-29
Section 6, Chapters 30-34
Section 6, Chapters 35-37
Section 7, Chapters 38-39
Section 8, Chapters 40-41