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Secondary 4 Pure Biology Preliminary Examination Paper 4
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Questions
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]
(c) Explain why this cell contains a large number of mitochondria. [2]
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]
(c) Suggest why plant cells do not burst when placed in pure water. [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]
(c) State one other factor, not shown in the graph, that could limit the rate of photosynthesis. [1]
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]
(c) Explain why glucose is not found in the urine of a healthy person. [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
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].