Hi guys! Here are the answers to this year's Cambridge O Level Biology Paper 1 MCQ Answers:
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Question	Answer	Explanations
1	D	Plant cells have large permanent vacuole, mitochondria & ribosomes
2	A	​ER does not store carbohydrates. Smooth ER synthesizes lipids and detoxify substances whereas rER makes proteins. The rest of the answer options (B, C & D) are accurate.
3	D	​Active transport is a process where substances move from low to high concentration region against the concentration gradient with the use of energy. The movement requires a membrane. Only option 3 fits this criteria.
4	D	​The cell wall supports the cell membrane, thus preventing it from bursting when the plant cell is turgid. Hence maintaining turgidity.
5	A	Iodine test result – Brown – means no starch Biuret test result – Purple – means presence of proteins Emulsion test result – Clear – means no fats Benedict’s test result – Green – means have some reducing sugars. ​ Answer option A fits the above observations.
6	B	Fats have the same constituents as carbohydrates – having carbon, hydrogen and oxygen.
7	B	The vessels that bring fluid away from liver is the hepatic vein. Vessel A: Is the hepatic vein (this is the answer) Vessel B: is the hepatic artery. This carries oxygenated blood TO the liver. Vessel C: is the hepatic portal vein. This carries nutrients absorbed by the small intestines TO the liver.
8	B	​When one consume alcohol, one will experience reduction in self-control, slowing down of reaction time and too much alcohol will also damage the liver. Only answer option B fits the above.
9	C	Points X-Y shows that factors other than light intensity are the limiting factors. Only Answer C fits the above.
10	D	​Looking at the leaf structure shown in the figure: Layer 1 – do NOT have chloroplasts Layer 2 and 3 – Have chloroplasts Layer 4 – Only guard cells have chloroplasts. The epithelial cells do not have chloroplasts Only answer option D fits this observation.
11	A	Transpiration is a consequence of photosynthesis. It is because during the day when the plant needs to photosynthesize, the stomata opens for the carbon dioxide to enter. As the stomata is opened, water vapour which is in high concentration inside the intercellular air space will necessary leave via the stomata to the outside down the water vapour gradient. Hence resulting in transpiration.
12	B	Rate of transpiration will be the greatest when the temperature is high, humidity is low and wind speed is high. Option A: Poorly ventilated (means not much wind) during a cool damp evening (temperature is low,  humidity is high) Option B: warm sunny (temperature is high), gentle breeze (little wind) During a sunny day, guard cells are fully opened, hence more water vapour can transpire. Option C: well ventilated room (there’s more wind) during a very warm night (high temperature) Option D: cool rainy day (low temperature, high humidity), gentle breeze (little wind).
13	C	Phloem transports sugar such as sucrose. The location of phloem is C.
14	C	Substances such as glucose and oxygen will enter into the cells from tissue fluid. RBC, platelets and proteins are too big to leave the blood capillary and enter into tissue fluid. Hence only C is the correct answer.
15	C	​Pulmonary vein carries oxygenated blood from the lungs and is at a low pressure since it’s a vein. The arteries will carry blood at a high pressure.
16	B	​P: Hepatic artery which brings oxygenated blood to the liver. Q: Hepatic vein which brings deoxygenated blood away from the liver to the heart. R: Hepatic portal vein which brings nutrients from the small intestines to the liver for assimilation.
17	B	​Cell X which is a cell found on the lining of the human trachea is used to move the mucus (where dust & foreign particles stick to) upwards. The 3rd cell shown in the diagram (called a goblet cell) is then used to secrete mucus.
18	C	Stage X shows a gradual decrease in air pressure inside the lungs. For the air pressure to drop, the air has to be forced out of the lungs (expiration). C is the best answer.
19	B	There are several chemicals in cigarette smoke such as nicotine, tar, carbon monoxide and irritants. Tar is known to cause cancer (uncontrolled division of cell division). Option B and C has (6). B is a better answer than C because tar is not known to cause alertness & increase heart rate (that’s the effect of nicotine). Tar is an irritant and can cause increase in mucus production & bronchitis.
20	C	​Urine of a healthy human should not have glucose as glucose will be completely selectively reabsorbed at the proximal convoluted tubule. Answer should either be A or C but C is a better answer than A as it has urea whereas answer A doesn’t. Urine should have waste substances such as urea.
21	D	​Concentration of urea will be the highest at W when the blood from the patient is first drawn into the kidney machine and at Z where the dialysis fluid flows out of the machine. There should be no urea at Y where the dialysis fluid enter into the machine (so as to create a very steep urea concentration gradient between the dialysate and the blood inside the tubings) and there should be very low urea concentration in the blood returning to the patient (blood X).
22	D	When the body is too cold, the blood arteriole (structure 3) will contract so that less blood will flow towards the skin surface and less heat is lost by conduction, convection and radiation (structure 3). Structure 4 which is the hair erector muscles will contract too, so that hair can stand to trap heat.
23	C	Response of negative feedback will restore conditions back to normal levels.
24	D	Spinal cord will coordinate leg movement and brain will perceive the pain.
25	C	​To change from diagram 1 to 2 (bright to dim, near to far), Option C will occur where iris radial muscles will contract and circular muscles will relax to dilate the pupils and ciliary muscles will relax (suspensory ligaments will become taut to make the lens thinner to see far).
26	D	At 1: a meal is eaten hence glucose level in the blood will increase. At 2: Insulin is secreted to convert excess glucose to glycogen to restore blood glucose back to normal. At 3: Glucose level went below normal level possibly due to the person using up glucose and glucagon is released to convert glycogen to glucose to restore blood glucose back to normal level. At 4: There is a sudden increase in glucose possibly due to fear, anxiety, stress and adrenaline is released to convert glycogen to glucose to increase the glucose concentrations for fight or flight.
27	B	​Answer B fits the description of asexual reproduction.
28	D	​Insect pollinated flower have sticky stigmas inside flowers (the rest of the answer options A, B, C show features of wind pollinated flower).
29	C	Pollen tube is to bring the male gamete to reach the ovule.
30	B	Oestrogen is to grow & repair the uterine lining. Progesterone is to maintain the lining. On Day 12 of the 28-day menstrual cycle, oestrogen level will peak and this signals the brain to produce luteinising hormone for ovulation. Answer B fits the description.
31	C	​Prophase I of meiosis is where crossing over will occur. Independent assortment of chromosomes will occur during metaphase I of meiosis. These 2 stages of meiosis together with fertilization will increase genetic variation.​
32	C	​Body cells of mother and zygote are both diploid. Gametes (ovum) are haploid.
33	D	Anaphase of meiosis II show separation of sister chromatids.
34	A	Complementary base pairing of Thymine with Adenine, Cytosine with Guanine. The circle shown should be the phosphate group and the pentagon shown should be the 5 carbon ribose sugar. Hence Answer A is the best answer.
35	A	Transgenic plant is a plant with a foreign gene inserted into it.
36	C	Option A: Homologous chromosomes are found in all diploid somatic cells but not in gametes which are haploid. Option B: Homologous chromosomes do not carry identical alleles. One of the homologous chromosomes pair come from the father, and the other from the mother. Since the homologous chromosomes come from different parents, they contain different alleles along their length most of the time. Option C: This is right. Homologous chromosomes have identical genes. They must have the same gene order along their length. Option D: They form pairs during meiosis (not mitosis).
37	A	For the child to have blood AB, the child must inherit one A allele and one B allele from each parent. Only A fits this description.
38	A	​The force driving natural selection is competition. If there are enough resources in the environment, there will be no natural selection. Hence if there is competition with other bacteria (such as for space, for food), those bacteria who are better adapted to the environment will more likely to survive and reproduce and pass down their genes to their offsprings.
39	C	Amount of energy available to consumers and decomposers will be 14units (growth & repair) + 46 units (urine & faeces) = 60 units. 60/100 X100 = 60%.
40	B	​As sewage enters river, the concentration of oxygen will decease as the bacteria who decomposes the sewage will increase and they use up the oxygen for aerobic respiration. The number of fishes will decrease as the oxygen level in the river will decrease, causing them to die.