2022 HKDSE Biology Practice Paper | DSE Mock

A plant tissue is treated with a respiratory inhibitor. Which of the following processes in the plant will be significantly reduced?

(1) Mineral uptake by root hair cells
(2) Translocation of sucrose in phloem
(3) Transpiration pull in xylem

Which of the following comparisons between the hepatic portal vein and the hepatic vein is correct shortly after a meal rich in proteins?

In humans, the alleles for ABO blood groups show co-dominance and complete dominance. A man with blood type A and a woman with blood type B have a child with blood type O. What is the probability that their next child will be a boy with blood type AB?

Green algae were illuminated with light in a closed chamber. The light source was then turned off. Which of the following describes the immediate change in the concentrations of the 5-carbon compound (carbon dioxide acceptor) and the 3-carbon compound inside the algal cells?

A scientist analyzed a double-stranded DNA molecule and found that \(22\%\) of the bases were cytosine (C). What is the percentage of adenine (A) in this DNA molecule?

A healthy volunteer drinks 1 litre of hypertonic saline solution. Which of the following correctly describes the physiological response of the body to restore water balance?

During vigorous exercise, which of the following changes in the blood is the primary chemical stimulus that triggers an increase in the breathing rate?

Two populations of a land snail species were separated by the formation of a wide river. After thousands of years, the river dried up, but the two populations could no longer interbreed to produce fertile offspring. Which of the following is the primary cause of this speciation?

In a normal 28-day menstrual cycle, which of the following events is directly triggered by a surge in the level of luteinizing hormone (LH) around Day 14?

The discharge of untreated domestic sewage containing organic matter into a river often leads to a rapid decrease in the dissolved oxygen level. Which of the following is the direct cause of this oxygen depletion?

A stem of a herbaceous dicotyledonous plant was placed in a beaker containing red dye. After 3 hours, cross-sections of the stem and the leaf midrib were examined under a light microscope. Which of the following correctly identifies the region(s) that would be stained red?

A dialysis tubing (representing the small intestine wall) is filled with a mixture of olive oil, pancreatic juice, and bile salts, and suspended in a beaker of distilled water at \(37^\circ\text{C}\). After 2 hours, which of the following molecules can be detected in both the dialysis tubing and the beaker?

A population of beetles lives on an island with light-green sandy soil. Most of the beetles are light-green, while a few are brown. A volcanic eruption covers half of the island with dark basaltic ash. Over several generations, the proportion of brown beetles in the ash-covered area increases significantly. Which of the following is the most appropriate evolutionary explanation?

A healthy person has been deprived of water in a hot environment for 24 hours. Compared to their normal state, which of the following combinations correctly describes the physiological changes in this person?

An enzyme-catalyzed reaction shows a very low rate at both \(10^\circ\text{C}\) and \(70^\circ\text{C}\). To investigate whether the low rates are due to low kinetic energy of molecules or denaturation of the enzyme, which of the following experimental procedures is most appropriate?

A couple with normal phenotypes has a daughter who suffers from an autosomal recessive genetic disorder. They also have a son who is phenotypically normal. What is the probability that the son is a carrier of the disorder?

A template strand of DNA has the following nucleotide sequence: 3'- T A C G G C T T A A C T -5'. Which of the following correctly shows the mRNA sequence transcribed from this template and the number of amino acids in the translated polypeptide?

A healthy person was injected with Antigen X on Day 0. On Day 28, the person was injected with a mixture of Antigen X and Antigen Y. Which of the following statements about the antibody levels in this person is correct?

Active chloroplasts were isolated and incubated in a reaction medium containing water labeled with oxygen-18 isotope (\(H_2^{18}O\)) and normal carbon dioxide (\(C^{16}O_2\)). The chloroplasts were then illuminated. In which of the following products will the oxygen-18 isotope be detected?

The following events may occur in a freshwater pond after a discharge of untreated domestic sewage containing high levels of inorganic nutrients: (1) Decomposers rapidly multiply and consume oxygen. (2) Algae on the water surface grow excessively, blocking sunlight. (3) Submerged plants die due to insufficient light. (4) Fish and other aquatic organisms die from suffocation. Which of the following shows the correct chronological order of these events?

A respiratory inhibitor is added to the root cells of a plant. Which of the following processes in the plant will be least affected in the short term?

Which of the following correctly describes the absorption of lipid digestion products in the human small intestine?

The table below shows the results of biochemical tests on a sample of food:
- Iodine test: yellow-brown
- Benedict's test: blue
- Biuret test: violet
- Grease spot test: no translucent spot

The food sample is incubated with enzyme X at 37°C for 1 hour. After incubation, the Benedict's test is performed again and shows an orange-red precipitate. Which of the following is most likely enzyme X?

Which of the following statements about the development of antibiotic resistance in a bacterial population is correct?

A healthy person drinks 1 litre of pure water within 10 minutes. Which of the following physiological changes will occur in this person's body over the next hour?

A person breathes into and out of a sealed paper bag for several minutes. Which of the following correctly describes the physiological changes in this person's body?

In a pedigree of a family with a single-gene genetic disease, a couple where both parents are affected has an unaffected daughter. Which of the following deductions about the disease-causing allele must be correct?

The sequence of a mRNA strand transcribed from a normal gene is shown below:
`5'- A U G C C G U U U U A G -3'`
A mutation occurs in the DNA template strand, resulting in the third codon of the mRNA changing from `UUU` to `UUA`.
(Codon table: `UUU` = Phenylalanine; `UUA` = Leucine; `UAG` = Stop codon)
Which of the following statements about this mutation is correct?

A patient bitten by a stray dog immediately receives an injection of rabies immunoglobulins (antibodies). Two weeks later, the patient receives a series of rabies vaccine injections. Which of the following correctly describes the type of immunity provided by these two treatments?

In some marine ecosystems, a pyramid of biomass can be inverted (i.e., the standing crop biomass of phytoplankton is less than that of the zooplankton consuming them at a given moment). Which of the following best explains this phenomenon?

Which of the following statements about the absorption and transport of nutrients in the human small intestine are correct?

I. Glucose is absorbed into the epithelial cells of the villi by active transport.
II. Fatty acids and glycerol are reassembled into lipids inside the epithelial cells before entering the lacteals.
III. Amino acids absorbed into the blood vessels are transported directly to the heart via the hepatic portal vein.

An experiment was set up to study the rate of water uptake of a leafy shoot under different wind speeds using a potometer. The results are as follows:

- At wind speed \(0\text{ m/s}\): rate of water uptake = \(1.2\text{ arbitrary units/h}\)
- At wind speed \(2\text{ m/s}\): rate of water uptake = \(3.5\text{ arbitrary units/h}\)
- At wind speed \(5\text{ m/s}\): rate of water uptake = \(5.2\text{ arbitrary units/h}\)
- At wind speed \(10\text{ m/s}\): rate of water uptake = \(3.8\text{ arbitrary units/h}\)

Which of the following is the most likely reason for the decrease in water uptake when the wind speed increased from \(5\text{ m/s}\) to \(10\text{ m/s}\)?

The following DNA template sequence encodes a short peptide:

3'- T A C G C A T T A A T T -5'

Below is a list of codons and the amino acids they encode:
- 5'-AUG-3': Methionine (Start)
- 5'-CGU-3': Arginine
- 5'-AAU-3': Asparagine
- 5'-UAU-3': Tyrosine
- 5'-UAA-3': Stop

If the 7th nucleotide (T, underlined: 3'- T A C G C A [T] T A A T T -5') of the DNA template strand is substituted by A, how will the polypeptide product change?

Drug X is a diuretic that blocks the active transport of sodium ions out of the thick ascending limb of the loop of Henle. Which of the following are the expected effects of Drug X on renal function?

I. The solute concentration in the medullary interstitial fluid decreases.
II. Less water is reabsorbed from the collecting duct into the medullary interstitial fluid.
III. The volume of urine produced increases.

The diagram below represents a phylogenetic tree of four modern species (P, Q, R, and S) and their common ancestors (X, Y, and Z):

```
Ancestor X
/ \
Species P Ancestor Y
/ \
Species Q Ancestor Z
/ \
Species R Species S
```

Which of the following statements can be correctly deduced from this tree?

On Day 0, Individual X was injected with a vaccine containing inactivated pathogens, while Individual Y was injected with monoclonal antibodies against the same pathogen. On Day 40, both individuals were exposed to the live pathogen. Which of the following statements are correct?

I. Individual X develops active immunity, whereas Individual Y develops passive immunity.
II. Upon exposure to the live pathogen on Day 40, Individual X will produce antibodies faster and in larger amounts than Individual Y.
III. The treatment received by Individual Y on Day 0 provides longer-lasting protection than that received by Individual X.

An experiment was conducted to study the effect of light quality on the transpiration rate of a herbaceous plant using a potometer. (a) Describe how a potometer is used to measure the rate of transpiration. (3.2 marks) (b) Explain why blue light typically results in a higher transpiration rate than red light in many plants. (2 marks) (c) State one precaution when setting up the potometer and explain its physiological importance. (2 marks)

The small intestine is highly adapted for the absorption of nutrients. (a) Explain how the villi and microvilli of the small intestine increase the efficiency of nutrient absorption. (3.2 marks) (b) Compare the absorption and transport of glucose and fatty acids from the lumen of the small intestine into the bloodstream. (4 marks)

A population of green beetles lives in a forest where the tree trunks became blackened by wildfire soot. A new predatory bird species that hunts visually is introduced. (a) Describe how natural selection leads to an increase in dark-colored beetles over generations. (4.2 marks) (b) Explain how geographical isolation of a subpopulation on a nearby island could eventually lead to speciation. (3 marks)

During a marathon, a runner loses a significant amount of water through sweating, leading to dehydration. (a) Describe how the human body detects this decrease in blood volume/water potential and coordinates the hormonal response. (3.2 marks) (b) Explain how antidiuretic hormone (ADH) acts on the kidney tubules to regulate urine volume and concentration. (4 marks)

A student inhales air containing a higher-than-normal level of carbon dioxide (\(3\%\)) for a brief period. (a) Describe the physiological pathway by which this elevated carbon dioxide level stimulates an increase in the breathing rate and depth. (4.2 marks) (b) Explain how this response helps restore blood pH and gas homeostasis. (3 marks)

The regulation of blood glucose levels is critical for homeostatic balance. (a) Describe the negative feedback mechanism that lowers blood glucose levels in a healthy individual after a carbohydrate-rich meal. (4.2 marks) (b) In a person with Type 1 diabetes, explain why the lack of insulin leads to high blood glucose levels and the presence of glucose in the urine. (3 marks)

An experiment was set up to study the activity of salivary amylase at different pH values (pH 2, pH 7, and pH 11). (a) Explain why the rate of starch hydrolysis is highest at pH 7 but drops to zero at pH 2 and pH 11. (3.2 marks) (b) Design a control for this experiment to show that the hydrolysis of starch is due to the catalytic action of salivary amylase rather than a non-biological chemical reaction. (2 marks) (c) State two variables that must be kept constant to ensure a fair test in this experiment. (2 marks)

A pedigree chart of a family shows that two healthy parents, John and Mary, have a son who suffers from a rare genetic disorder, cystic fibrosis. (a) Deduce, with reasons, whether the allele causing cystic fibrosis is dominant or recessive. (4.2 marks) (b) If John and Mary decide to have another child, calculate the probability that their next child will be a healthy carrier of the disease. Show your working. (3 marks)

Seed germination requires specific environmental conditions to activate metabolic processes. (a) Describe how water absorption (imbibition) triggers the mobilization of food reserves in a germinating barley seed. (4.2 marks) (b) Explain why oxygen and a suitable temperature are essential for the growth of the embryo during germination. (3 marks)

Sickle-cell anemia is caused by a single-base substitution mutation in the gene encoding the beta-globin chain of hemoglobin. (a) Explain how a single-base substitution in DNA can result in an altered protein structure and reduced oxygen-carrying capacity. (4.2 marks) (b) Describe the distinct roles played by mRNA and tRNA during the translation process in the ribosome. (3 marks)

Describe how the structures of the glomerulus and the proximal convoluted tubule are adapted to their respective functions in urine formation. Explain how the hormonal control mechanism regulates water reabsorption in the kidneys when a person is dehydrated.

Describe how the structures of the glomerulus and the proximal convoluted tubule are adapted to their respective functions in urine formation. Explain how the hormonal control mechanism regulates water reabsorption in the kidneys when a person is dehydrated.

An athlete participated in a study investigating the physiological responses to exercise under different environmental conditions. The athlete ran on a treadmill at a constant speed of \(10\text{ km/h}\) in a climate chamber under two different conditions:

Condition I: \(35^\circ\text{C}\), \(20\%\) relative humidity (hot and dry)
Condition II: \(35^\circ\text{C}\), \(80\%\) relative humidity (hot and humid)

(a) Explain why the core body temperature of the athlete increased more rapidly in Condition II than in Condition I, even though the ambient temperature was the same. (4 marks)

(b) As core body temperature rises, physiological mechanisms are activated to facilitate heat loss and regulate water balance.
(i) Describe the role of the hypothalamus in detecting the rise in core body temperature and initiating sweating. (3 marks)
(ii) State how sweat secretion affects the osmolarity of blood plasma, and explain how the pituitary gland responds to this change to conserve body water. (5 marks)

(c) Prolonged running in Condition II leads to a significant reduction in plasma volume due to heavy sweating.
(i) Explain how this reduction in plasma volume affects cardiac output and blood pressure. (4 marks)
(ii) Describe the cardiovascular compensatory mechanisms involving the nervous system that are activated to restore normal blood pressure. (4 marks)

A biotechnology company is developing a transgenic lettuce plant that expresses a viral surface antigen as an edible vaccine against a gastroenteritis virus.

(a) Describe how the target gene encoding the viral antigen can be isolated from the virus and amplified using Polymerase Chain Reaction (PCR). Explain the roles of primers and Taq polymerase in this process. (5 marks)

(b) The amplified target gene is to be inserted into a plasmid vector.
(i) Explain how restriction enzymes and DNA ligase are used to construct the recombinant plasmid. (4 marks)
(ii) The plasmid vector contains a kanamycin-resistance gene as a selectable marker. Explain how this marker is used to screen for and select successfully transformed transgenic plant cells. (3 marks)

(c) To verify whether the target gene has been successfully integrated into the plant genome, PCR was performed using DNA extracted from three different transgenic plant lines (A, B, and C) and primers specific to the target gene. The PCR products were analyzed using agarose gel electrophoresis.
- Line A showed no band on the gel.
- Line B showed a single band of the expected size (\(1.2\text{ kb}\)).
- Line C showed two bands: one at \(1.2\text{ kb}\) and another unexpected band at \(0.5\text{ kb}\).

(i) Suggest one possible reason why Line A did not show any band on the gel. (2 marks)
(ii) Suggest an explanation for the occurrence of two bands in Line C. (2 marks)

(d) Discuss one potential ecological risk and one bioethical concern associated with the widespread commercial cultivation of these transgenic vaccine-producing plants in open fields. (4 marks)