1. AS-level Biology (Edexcel): 99 questions
that students should be able to answer
Unit 1
1. What are the physical characteristics of water that make it useful to living things?
2. What are carbohydrates?
3. What are the main types of monosaccharide, and what roles do they have in living
things?
4. How are disaccharides (sucrose, lactose and maltose) formed from monosaccharides?
5. How is Benedict's test used to detect reducing and non-reducing sugars?
6. What is the difference between the polysaccharides starch (amylose and amylopectin),
glycogen and cellulose?
7. How is iodine used to detect starch?
8. What are triglycerides, and what roles do they have in living things?
9. What is the difference between saturated and unsaturated fats?
10. What are phospholipids, and how are phospholipid molecules arranged in cell
membranes?
11. What makes up the primary, secondary, tertiary and quaternary structure of a protein?
12. What are fibrous and globular proteins, and what roles do they have in living things?
13. How is the Biuret test used to detect protein?
14. What are DNA and RNA molecules made from, and how do they differ?
15. What is complementary base pairing?
16. What is semi-conservative replication of DNA, and how does it work?
17. How and where are DNA molecules transcribed into messenger RNA?
18. How and where are messenger RNA molecules translated into polypeptides?
19. How and where are polypeptides folded and assembled into finished protein
molecules?
20. What is the Human Genome Project, and what issues does it raise?
21. What are enzymes?
22. What factors affect the rate of an enzyme-catalysed reaction?
23. How do competitive and non-competitive inhibitors affect an enzyme?
24. How can enzymes be used commercially?
25. How and why can enzymes be immobilised?
26. What are prokaryotes and eukaryotes?
27. What are the components of a typical prokaryotic cell (bacterium)?
28. What are the components of a typical animal cell?
29. What are the components of a typical plant cell?
30. Why can electron microscopes achieve a higher magnification than light
microscopes?
31. How do substances move in and out of cells?

2. 32. What is osmosis, and how can it affect a cell?
33. What are endocytosis and exocytosis?
34. What is the difference between a tissue and an organ?
35. What are chromosomes made of?
36. What is the difference between mitosis and meiosis?
37. What are the stages of mitosis, and what happens at each stage?
38. What is cloning, when does it occur in nature, and how is it carried out artificially?
Unit 2
39. Why do large animals need specialised organs for gas exchange (lungs or gills) and
circulatory systems, whilst smaller ones do not?
40. How is gas exchange achieved in a single-celled organism?
41. What is the internal structure of a plant leaf?
42. How and why do plants open and close their stomata?
43. How are the human lungs designed to maximise gas exchange, and how do they avoid
collapsing?
44. How does ventilation (moving of gas in and out of the lungs) occur in humans?
45. What controls the rate of breathing?
46. What are tidal volume and vital capacity?
47. What is a respirometer, and how might it work?
48. What are the different sections of the human digestive system, and what are their
roles?
49. What enzymes are secreted in the small intestine, and what do they break down?
50. How do water and minerals move through a plant?
51. What is the structure of a xylem vessel?
52. What affects the rate of transpiration from a plant?
53. What is a potometer, and how might it work?
54. How do organic nutrients move around a plant?
55. What is the structure of a phloem vessel?
56. What is the structure of the human heart?
57. How is the rhythm of the heart generated?
58. How is the rate of heartbeat controlled?
59. What are the differences between arteries, veins and capillaries?
60. What are tissue fluid and lymph, and where do they come from?
61. What types of cell are found in the blood, and what are their roles?
62. What types of protein are found in the blood, and what are their roles?
63. What other substances are dissolved in blood plasma?
64. How are oxygen and carbon dioxide transported in the blood?
65. What does an oxygen dissociation curve show?
66. How do myoglobin and foetal haemoglobin differ from normal haemoglobin?
67. What is the Bohr effect, and why is it useful?
68. How are xerophytes adapted to dry conditions?
69. How are hydrophytes adapted to watery environments?
70. How are some marine animals adapted to low-oxygen conditions?
71. What is the advantage of sexual reproduction?

3. 72. Why is meiosis necessary, and how does it generate gametes with varied
combinations of genes?
73. What is the structure of a flower?
74. What are the differences between a wind-pollinated flower and an insect-pollinated
flower?
75. How do some flowers avoid self-pollination?
76. What are the structures of the male and female reproductive systems in humans?
77. How do hormones lead to the events of the menstrual cycle?
78. How is the placenta formed, and what is its role?
79. What is the role of the hormones prolactin and oxytocin?
Unit 3
80. What are autotrophs and heterotrophs?
81. What does holozoic nutrition involve?
82. How are herbivores (e.g. ruminants) and carnivores adapted to their diets?
83. How do moulds (e.g. Rhizopus) demonstrate saprobiontic nutrition?
84. How do tapeworms (e.g. Taenia) demonstrate parasitism?
85. How do nitrogen-fixing bacteria (e.g. Rhizobium), and the cellulose-digesting
microbes in ruminants, demonstrate mutualism?
86. What are habitats and ecosystems?
87. What are producers, consumers, and decomposers?
88. How is energy transferred through a food chain, and why is some energy lost at each
stage?
89. What are gross primary production and net primary production?
90. What do pyramids of numbers, pyramids of biomass, and pyramids of energy
represent?
91. What are the stages in the water cycle?
92. How is carbon cycled through an ecosystem?
93. How is nitrogen cycled through an ecosystem?
94. What are the roles of nitrifying bacteria (e.g. Nitrosomonas, Nitrobacter), nitrogen-
fixing bacteria (e.g. Rhizobium, Azotobacter), and denitrifying bacteria (e.g.
Pseudomonas, Thiobacillus)?
95. What are the causes and effects of deforestation and desertification?
96. What causes global warming, and what are its possible consequences?
97. How and why are renewable fuel sources (e.g. gasohol and biogas) used as an
alternative to fossil fuels?
98. What causes acid rain, and how does it damage the environment?
99. What is eutrophication, and why does it occur?