Common errors in S5 bio Mock Exam.

Common error /

Note

1(a)(ii) /
  1. Sexual intercross not involved in this method
  2. Embryo is implanted artificially in this method.
  3. Genes of the baby is different from the mother giving birth to it / The method allows the selection of sex.
/ 1.  Sexual intercourse
  1. Embryo is also implanted naturally in this method but artificially put into the uterus. Implantation refers to the process that the embryo buries itself into the wall of the uterus, not how the embryo gets into the uterus.
  2. Not about the process but its results or significance.

1(b)(i) / A hole reduces the pressure generated by the contraction of the ventricles and thus less blood could be supplied to the cells. / This answer is acceptable but not as good as the mixing of oxygenated and deoxygenated blood.
1(c)(i)(2) / Enzyme is involved as the reaction rate is low at very low and very high T. / All chemical reactions, whether controlled by enzymes or not, would have low rate at low T, and the rate increases as T increases. This property does not reflect whether a reaction involves enzymes or not.
2(a)(i) / Phagocytes / Though phagocytes form the first line defense but it is not the one broken by the mosquitoes.
2(a)(iii) / The phagocytes take 3 to 14 days to engulf all viruses. / If the phagocytes could kill all viruses, the patient would have no symptoms at all. Besides, the action of phagocytes does not need so many days.
If symptoms do appear but the patient recovers later, it must involve the production of antibodies.
2(a)(iv)(1) / Most answers described in details the first immune response but it is not needed.
2(b)(iii) /
  1. State cell division instead of meiosis.
  2. Only state that errors occur in meiosis without clearly pointing out what the errors are.
The error is that the chromatids did not separate.
2(c)(i) / 1.  Wastes from the farm without pointing out that they are organic wastes.
2.  Organic wastes promote growth of algae.
  1. Bacteria broke down the organic wastes with oxygen, without mentioning aerobic respiration.
/ 2. Organic wastes promote growth of bacteria only, while inorganic minerals promote growth of algae
2(c)(ii) / Ammonia comes from the sewage of the farm. / Ammonia from the farm will be diluted at site C.
3(a)(iii) / Calculate the conc. by comparing the area of the clear zones of the fresh lemon juice and the 0.1% ascorbic acid. / It is not an accurate method as compared with the titration method.
3(c)(i) / The soil provides nutrients to the plants. / Nutrient is a general term including the seven food substances except water. Avoid using it as it is not specific enough.
3(c)(ii) /
  1. The glucose is very concentrated.
  2. The root cells lost water by osmosis and the plant wilted.
/
  1. You must state that the glucose solution has a lower water potential than that of the plant root cells.
  2. The root cells lost water so that the plant cannot absorb water from soil. However, the wilting of plant was a result of the water loss of the cells in stems. It is caused by the water loss by transpiration at leaves.

4(a)(i) /
  1. Most students did not calculate the rate of respiration with the data in tube A (the control).
  2. The graph did not show correct unit of rate of respiration – cm per minute. The plots are not joined up with straight lines.

4(b)(iv) / 1.  The person would still have withdraw reflex as reflex does not involve the brain.
2.  Withdrawal reflex involved cerebellum. / 1.  Reflex may involve the brain but not the cerebrum.
2.  Withdrawal reflex of the hand involves the spinal cord only.
4(c)(i) / 1.  Most answers described the thermoregulatory responses of the body, but not focus on explaining why the body T rose.
Most answers did not attend fully to the hints provided by the questions : all the water has been drunk, a hot and humid day, walking uphill.
4(c)(ii) / Let the patient drink water. / How can a unconscious patient drink water ?

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Item / Explanation
4 / In cell 1, the chromatids of chromosomes have separated, leading to doubling of chromosome number.
5 / l  D is wrong as some enzymes may have an optimum pH at low pH.
l  A is wrong as some enzymes are secreted into blood though some are released outside the body, e.g. in the gut, in the mouth.
l  C is wrong as enzymes in human body have optimum T around 40oC, and enzymes of other organisms would have optimum T related to their respective environment they live.
7 / l  All viruses are parasitic.
l  Some bacteria are parasitic(pathogens/disease causing) while some are saprophytic(decomposer in ecosystem)
l  Most fungi are saprophytic but the fungi causing athlete’s foot are parasitic.
8 / l  Protein also has energy value the same as carbohydrate.
9 / l  In (1), the correct spot test is “leaving a permanent translucent spot” or “ leaving a translucent spot after drying” or “ the translucent spot disappear after immersed in alcohol”
l  (2) and (3) describe Emulsion test in which water and alcohol have to be added and then shake.
13 / l  All answers (1) (2) and (3) are wrong. Amino acids are deaminated into a carboxylic acid and an amino group. The carboxylic acid will be converted into glycogen stored in liver, while the amino group will be converted into urea after combining with CO2.
15 / l  A is wrong as it is just a repetition of the result and no deduction is made.
l  B is a wrong deduction as no oxygen is supplied and the yeast cannot carry out aerobic respiration.
l  D is wrong as the glucose solution is boiled but not boiling. ‘Boiled’ means it has been boiling but it is cooled down now.
l  Deduction is similar to explanations on the results. Conclusion is not explanation. The conclusion of this experiment would be “ Yeast cannot carry out anaerobic respiration in concentrated glucose solution”.
17 / l  B is wrong as more oxygen is supplied to muscles even though the muscles are undergoing anaerobic respiration, because of the increased heart rate, breathing rate and vasodilation of arterioles to skeletal muscles during exercise. However, the oxygen demand also increase sharply as muscles need vast amount of ATP for their contraction, and ATP is supplied from aerobic respiration. If the oxygen demand exceeds its supply, some muscle cells will undergo anaerobic respiration.
l  D is wrong as the significance of anaerobic respiration is to supply additional ATP when oxygen is in shortage.
18 / l  The most correct and detailed process of inhalation is :
Diaphragm contracts and lowered. Or/and Intercostals muscles contract which makes the rib cage/thorax/thoracic cavity expand/move outward and upward. --> The lung expands(as lung is attached to the thoracic wall and diaphragm) --> the air sacs of the lung expand --> air pressure inside the air sacs decreases to lower than that of the atmospheric pressure --> air is inhaled in.
l  C and D are wrong as the lung cannot expand by itself as it is not made up of muscles.
l  A is wrong as it reverses the cause and effect : the ‘lung expand’ is the cause for the ‘air rushes into the lungs
23 / l  A is wrong, the elastic wall of artery cannot increase the pressure but maintain a high pressure during relaxation of ventricles.
l  B is wrong as the size of lumen is not related to the blood pressure but the flow rate of blood.
29 / l  (1) is wrong as the thickened wall is used to prevent the vessels from collapse by the low water pressure/tension.
31 / l  Water flow along Q (xylem vessels) is by mass flow under pressure gradient built up by transpiration pull.
l  Water flows across the root cells to xylem vessel at root, and from xylem vessels to the air across the mesophyll cells at leaves are mainly by : pressure gradient along cell wall and intercellular space. As most water does not pass through the cell membrane into the cells, osmosis is not the main process for the water to move from one cell to another.
34 / l  (1) is wrong as only the hepatic vein would have higher urea content as it receives blood from liver.
l  (2) is right as the blood in hepatic portal vein has passed through the gut in which some glucose is used by the respiration of the gut cells. However, this situation will be reversed after meal.
35 / l  Tissue fluid is formed at arterial end and reabsorbed at venous end. However, the diffusion of materials is unrelated to the flow of tissue fluid. Diffusion occurs along the whole length of capillary as long as the diffusion gradient exists.
36 / B is right as :
l  1(cereburm) is involved in seeing the film and then send impulses to the medulla to control the heartrate.
l  2(cerebellum) is involved in almost all voluntary actions to coordinate the muscles contractions so as to ensure a coordinated motion.
37 / B is the potato of the last year. It supplied food for the growth of the potato plant. After the plant has grown up, it makes its own potatoes(A and C) with the food supplied from the photosynthesis of its leaves.
38 / l  Placenta(1) is a mixture of tissues of the mother and the foetus
l  The amnion(3) and umbilical cord(2) are derived from the foetus only.
40 / l  We have to determine the length of menstrual cycle of the woman first : 28 days
l  Then we have to calculate the date of ovulation of next menstrual cycle : 14 days from the 1st day of the last cycle(26th March)
l  The three days before and after the date of ovulation is considered as safe period.
41 / l  A is wrong as the X(plumule) would increase its dry mass by absorbing food from Y(cotyledon)
l  B is wrong as X does not have true leaves to carry out photosynthesis right now. It would be true in the later days of germination where green leaves are present.
l  D is wrong as the dry mass of Y decreases as a result of the respiration of the food to produce carbon dioxide which evolves into the air. Digestion of food would not lead to change in mass.
43 / l  (2) is wrong as the seed dispersal is a random process which may or may not enable the seed to find a better place, it may be worser.
47 / l  Both A and D are incorrect so they are both the answers of that question.
l  A is incorrect as insulin is not an enzyme and cannot catalyze a reaction. Instead, insulin causes/results in/leads to the change of glycogen into glucose.
l  D is incorrect as insulin, and most hormones, are released constantly from endocrine glands, but are released more or less in response to some stimuli.
51 / l  After drinking water, less proportion of water is reabsorbed by the kidney. However, the actual amount of water reabsorbed is even greater (189 or 210l). 210 l is impossible as the kidney even reabsorb more water than the amount taken in.