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Secondary 4 Pure Biology Preliminary Examination Paper 4

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TuitionGoWhere Practice Paper - Pure Biology Secondary 4

TuitionGoWhere Secondary School (AI)
PRELIMINARY EXAMINATION 2024
Version 4 of 5

Subject: Pure Biology
Level: Secondary 4
Paper: 2 (Theory)
Duration: 1 hour 30 minutes
Total Marks: 60

Name: ________________________
Class: ________________________
Date: ________________________

Instructions to Candidates

Write your name, class, and date in the spaces provided.
Answer all questions.
Write your answers in the spaces provided on the question paper.
The number of marks is given in brackets [ ] at the end of each question or part question.

Section A: Cell Structure and Organisation

Answer all questions in this section.

1. Fig. 1.1 shows an electron micrograph of a specialised animal cell involved in secretion.

(Note: In a real exam, Fig 1.1 would show a cell with extensive Rough Endoplasmic Reticulum and Golgi Apparatus)

(a) Identify the organelle labelled X which appears as a stack of flattened sacs. [1]

(b) State the function of organelle X in this cell. [1]

2. A student observed two cells, Cell A and Cell B, under a light microscope.

Cell A has a cell wall, a large central vacuole, and chloroplasts.
Cell B has no cell wall, small temporary vacuoles, and no chloroplasts.

(a) Identify whether Cell A is a plant cell or an animal cell. [1]

(b) State one function of the cell wall found in Cell A. [1]

(c) The student placed Cell B in a concentrated salt solution. After 10 minutes, the cell appeared shrivelled. (i) Name the process that caused water to leave the cell. [1]
_________________________________________________________________________

(ii) Explain, in terms of water potential, why water left the cell. [2]  
_________________________________________________________________________  
_________________________________________________________________________

3. Root hair cells are specialised for absorption.

(a) Describe one structural adaptation of a root hair cell that increases its efficiency in absorbing water. [1]

(b) Water enters root hair cells by osmosis. Define osmosis. [2]

(c) Mineral ions are often absorbed by root hair cells against a concentration gradient. (i) Name the process used to absorb these mineral ions. [1]
_________________________________________________________________________

(ii) State why energy is required for this process. [1]  
_________________________________________________________________________

Section B: Biological Molecules and Enzymes

Answer all questions in this section.

4. A student performed food tests on three unknown solutions: A, B, and C. The results are shown in Table 4.1.

Table 4.1

Solution	Iodine Test	Benedict's Test (heated)	Biuret Test	Ethanol Emulsion Test
A	Blue-black	Blue	Purple	Clear
B	Brown	Brick-red precipitate	Blue	Clear
C	Brown	Blue	Blue	White emulsion

(a) Identify the biological molecule present in each solution. (i) Solution A: _________________________ [1] (ii) Solution B: _________________________ [1] (iii) Solution C: _________________________ [1]

(b) Describe how the ethanol emulsion test is carried out for Solution C. [2]

5. Enzymes are biological catalysts. Fig. 5.1 shows the effect of temperature on the rate of reaction of enzyme Z.

(Note: Graph shows rate increasing from 10°C to 40°C, peaking at 40°C, then dropping sharply to zero at 60°C)

(a) State the optimum temperature for enzyme Z. [1]

(b) Explain why the rate of reaction decreases rapidly after 40°C. [3]

(c) Enzyme Z is found in the human stomach, which has a pH of 2. Another enzyme, Y, is found in the small intestine (pH 8). (i) Suggest which enzyme (Z or Y) is likely to be pepsin. [1]
_________________________________________________________________________

(ii) Explain why enzyme **Z** would not function effectively in the small intestine. [2]  
_________________________________________________________________________  
_________________________________________________________________________

6. The "lock and key" hypothesis explains enzyme specificity.

(a) Define the term active site. [1]

(b) Explain why an enzyme that digests starch cannot digest protein. [2]

Section C: Movement of Substances and Applications

Answer all questions in this section.

7. Fig. 7.1 shows an experiment set up to investigate diffusion.

Visking tubing (a partially permeable membrane) containing starch and glucose solution is placed in a beaker of distilled water.
After 30 minutes, the water in the beaker is tested.

(a) Predict the results of testing the beaker water for: (i) Starch: _________________________ [1] (ii) Glucose: _________________________ [1]

(b) Explain your prediction for glucose. [2]

8. Active transport is essential for nutrient absorption in the human ileum.

(a) State two features of the villi that increase the rate of absorption of digested food. [2]

(b) Glucose is absorbed into the blood capillaries of the villi. (i) Name the blood vessel that carries blood away from the villi to the liver. [1]
_________________________________________________________________________

(ii) Explain the role of the liver in regulating blood glucose levels immediately after a meal. [2]  
_________________________________________________________________________  
_________________________________________________________________________

9. In an investigation, potato cylinders were placed in sucrose solutions of different concentrations. The change in mass was recorded after 1 hour.

Table 9.1

Sucrose Concentration (mol/dm³)	Change in Mass (g)
0.0	+0.5
0.2	+0.2
0.4	-0.1
0.6	-0.4
0.8	-0.7

(a) Estimate the concentration of the cell sap of the potato cells. [1]

(b) Explain why the potato cylinder gained mass in the 0.0 mol/dm³ solution. [2]

10. Red blood cells are specialised for oxygen transport.

(a) State two adaptations of red blood cells for their function. [2]

(b) If red blood cells are placed in pure water, they burst. Explain why this happens. [2]

Section D: Data Interpretation and Synthesis

Answer all questions in this section.

11. A patient suffers from a genetic disorder where their cells lack a specific enzyme required to break down a certain lipid. This leads to the accumulation of the lipid in lysosomes, causing cell damage.

(a) Identify the organelle responsible for breaking down waste materials and lipids in a normal cell. [1]

(b) Explain how the absence of this enzyme affects the cell using the concept of enzyme specificity. [2]

(c) Suggest why this condition might affect the nervous system severely, given that nerve cell membranes are rich in lipids. [2]

12. Fig. 12.1 shows the rate of photosynthesis in a plant at different light intensities and carbon dioxide concentrations.

(Note: Graph shows two curves. Curve A (0.04% CO2) plateaus at lower light intensity. Curve B (0.1% CO2) plateaus at higher light intensity and higher rate.)

(a) Identify the limiting factor for photosynthesis at point X on Curve A (low light intensity). [1]

(b) Explain why increasing the carbon dioxide concentration from 0.04% to 0.1% increases the rate of photosynthesis at high light intensities. [2]

13. Antibiotics are drugs used to treat bacterial infections.

(a) Explain why antibiotics are ineffective against viral infections such as influenza. [2]

(b) Overuse of antibiotics has led to the emergence of "superbugs". Explain how natural selection leads to antibiotic resistance in bacteria. [3]

14. DNA carries the genetic code for protein synthesis.

(a) Name the four nitrogenous bases found in DNA. [2]

(b) Describe the structure of a DNA molecule. [3]

15. Genetic engineering involves transferring genes from one organism to another. Human insulin is now produced by genetically engineered bacteria.

(a) Outline the steps involved in producing human insulin using bacteria. [4]

(b) State one advantage of producing insulin using genetically engineered bacteria compared to extracting it from pigs. [1]

16. Fig. 16.1 shows a pedigree chart for a genetic condition.

(Note: Standard pedigree with affected and unaffected individuals)

(a) Determine if the allele for the condition is dominant or recessive. Give a reason for your answer. [2]

(b) If individual 3 (unaffected carrier) and individual 4 (affected) have another child, calculate the probability that the child will be affected. Show your working. [2]

17. Homeostasis maintains a constant internal environment.

(a) Define homeostasis. [1]

(b) Describe how the body regulates blood glucose levels when they drop below normal. [3]

18. The kidney plays a key role in excretion and osmoregulation.

(a) Name the functional unit of the kidney. [1]

(b) Describe the process of ultrafiltration in the kidney. [2]

19. Global warming is linked to increased carbon dioxide levels.

(a) Describe the role of photosynthesis in the carbon cycle. [2]

(b) Suggest two ways in which human activities have increased atmospheric carbon dioxide levels. [2]

20. Conservation of biodiversity is important for ecosystems.

(a) Define biodiversity. [1]

(b) Explain why the loss of a single species can have a significant impact on an ecosystem. [2]

END OF PAPER

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Answers

TuitionGoWhere Practice Paper - Pure Biology Secondary 4

ANSWER KEY & MARKING SCHEME
Version 4 of 5

Section A: Cell Structure and Organisation

1.
(a) Golgi apparatus / Golgi body [1]
(b) To modify, sort, and package proteins (for secretion) [1]
(c) Mitochondria produce ATP / energy [1]; Energy is required for the synthesis and transport/secretion of proteins [1].

2.
(a) Plant cell [1]
(b) Provides structural support / maintains cell shape / prevents bursting under turgor pressure [1]
(c) (i) Osmosis [1]
(ii) The salt solution has a lower water potential than the cell cytoplasm [1]; Water moves out of the cell down the water potential gradient [1].

3.
(a) Long hair-like projection increases surface area for absorption [1]
(b) The net movement of water molecules [1] from a region of higher water potential to a region of lower water potential [1] through a partially permeable membrane.
(c) (i) Active transport [1]
(ii) To move ions against the concentration gradient [1].

Section B: Biological Molecules and Enzymes

4.
(a) (i) Starch [1]
(ii) Reducing sugar / Glucose [1]
(iii) Fat / Lipid [1]
(b) Mix the solution with ethanol [1]; Shake and pour into water; a white emulsion indicates fat [1].

5.
(a) 40°C [1]
(b) High temperature causes the enzyme to denature [1]; The shape of the active site changes [1]; The substrate can no longer fit into the active site [1].
(c) (i) Enzyme Z [1]
(ii) Enzyme Z is adapted to pH 2 (acidic) [1]; At pH 8, the enzyme will denature / change shape and lose activity [1].

6.
(a) The specific region on the enzyme where the substrate binds [1]
(b) The active site of the starch-digesting enzyme has a specific shape complementary to starch [1]; It is not complementary to the shape of protein molecules [1].

Section C: Movement of Substances and Applications

7.
(a) (i) Negative / No colour change (remains brown/yellow) [1]
(ii) Positive / Brick-red precipitate [1]
(b) Glucose molecules are small enough to diffuse through the pores of the Visking tubing [1]; Starch molecules are too large to pass through [1].

8.
(a) Any two:
1. Thin walls (one cell thick) for short diffusion distance [1]
2. Large surface area (due to villi/microvilli) [1]
3. Rich blood supply to maintain concentration gradient [1]
(b) (i) Hepatic portal vein [1]
(ii) Insulin is secreted by the pancreas [1]; Glucose is converted to glycogen for storage in the liver [1].

9.
(a) 0.3 mol/dm³ (Accept range 0.25 - 0.35 where change in mass is zero) [1]
(b) The water potential of the pure water is higher than that of the potato cells [1]; Water enters the cells by osmosis, causing them to gain mass [1].

10.
(a) Any two:
1. Biconcave shape increases surface area for gas exchange [1]
2. No nucleus / contains haemoglobin to carry oxygen [1]
(b) Water enters the RBCs by osmosis because the cytoplasm has a lower water potential than pure water [1]; The cell membrane is weak and bursts (haemolysis) as it cannot withstand the pressure [1].
(c) Plant cells have a rigid cell wall [1]; The cell wall withstands the turgor pressure and prevents bursting [1].

Section D: Data Interpretation and Synthesis

11.
(a) Lysosome [1]
(b) Enzymes are specific to their substrate [1]; Without the specific enzyme, the lipid substrate cannot be broken down / accumulated [1].
(c) Nerve cells rely on intact membranes for impulse transmission [1]; Lipid accumulation damages the membrane structure, disrupting nerve function [1].

12.
(a) Light intensity [1]
(b) Carbon dioxide is a raw material for photosynthesis [1]; Increasing CO2 allows the Calvin cycle / light-independent reaction to proceed faster, increasing the overall rate [1].
(c) Temperature [1]

13.
(a) Viruses reproduce inside host cells / do not have their own metabolism [1]; Antibiotics target bacterial structures/metabolism (e.g., cell wall synthesis) which viruses lack [1].
(b) Mutation creates variation in bacteria, some are resistant [1]; Antibiotics kill non-resistant bacteria, leaving resistant ones to survive [1]; Resistant bacteria reproduce and pass on the resistance gene [1].

14.
(a) Adenine, Thymine, Guanine, Cytosine [2] (1 mark for 2-3 correct, 2 marks for all 4)
(b) Double helix structure [1]; Made of two strands of nucleotides [1]; Bases pair specifically (A with T, C with G) held by hydrogen bonds [1].

15.
(a) Any four:
1. Isolate the human insulin gene [1]
2. Cut the gene and bacterial plasmid with the same restriction enzyme [1]
3. Join the gene to the plasmid using DNA ligase [1]
4. Insert the recombinant plasmid into bacteria [1]
5. Bacteria reproduce and produce human insulin [1]
(b) Human insulin is identical to natural human insulin / less likely to cause allergic reaction / ethical concerns avoided [1].

16.
(a) Recessive [1]; Two unaffected parents (e.g., 1 and 2) have an affected child (3) [1].
(b) Let A = normal, a = affected. Individual 3 is Aa (carrier), Individual 4 is aa (affected).
Cross: Aa x aa
Offspring: Aa, Aa, aa, aa
Probability of affected (aa) = 2/4 = 50% or 0.5 [2] (1 mark for correct cross/ratio, 1 mark for final answer).

17.
(a) The maintenance of a constant internal environment despite external changes [1]
(b) Pancreas detects low blood glucose [1]; Secretes glucagon [1]; Glucagon stimulates the liver to convert glycogen to glucose [1].

18.
(a) Nephron [1]
(b) High blood pressure in the glomerulus [1] forces small molecules (water, glucose, urea, salts) out of the blood into the Bowman’s capsule [1].
(c) Glucose is reabsorbed by active transport [1] from the renal tubule back into the blood capillaries [1].

19.
(a) Plants take in carbon dioxide from the atmosphere [1] to produce glucose/organic compounds during photosynthesis [1].
(b) Any two:
1. Burning of fossil fuels [1]
2. Deforestation / burning of forests [1]

20.
(a) The variety of living organisms in an area / ecosystem [1]
(b) Species are interconnected in food webs [1]; Loss of one species may remove a food source or predator, causing population imbalances in other species [1].