IGCSE Biology 2nd edition

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 38. Biotechnology


Page 332
1. Yeast; alcohol and carbon dioxide. Penicillium; penicillin. Lactobacillus; yoghurt, cheese. Aspergillus; enzymes.
2. Aerobic bacteria and protozoa play an important part in purifying human waste.
3. Sterile conditions are essential in order to exclude all micro-organism but the ones needed for the process. ‘Alien’ microbes could produce undesired and unpredictable products.
The other controlled conditions involve temperature, aeration (if any), pH and a controlled supply of nutrients.
4. Curds and whey are intermediate products of cheese-making. The curds are the semi-solid precipitate of milk protein produced when the enzyme chymosin is used to coagulate the milk. They whey is the liquid residue which is drained off.
5. If air is allowed in, aerobic bacteria will metabolise the wanted substances (e.g. methane) completely to carbon dioxide and water.
6. The starch is digested to maltose by the amylase enzymes already present in the barley grains or the flour.
7. If the wine is left exposed to air for long enough, aerobic bacteria will oxidise the alcohol in the wine to ethanoic (acetic) acid.
8. Different mutant forms of Penicillium produce different types of penicillin. The penicillin can also be altered by chemical processes to make it more effective.
9. The bacteria clump the finer particles, which are ingested by the protozoa along with the bacteria. Soluble substances are rendered harmless by being absorbed and metabolised by bacteria.

Downloads
Download the answers in PDF format below
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


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