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Secondary 4 Pure Biology Preliminary Examination Paper 5

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Secondary 4 Pure Biology - Preliminary Examination

Subject: Pure Biology (6093)
Level: Secondary 4
Paper: Preliminary Paper 2 (Version 5 of 5)
Duration: 2 Hours
Total Marks: 80
Name: __________________________ Class: __________ Date: __________

Instructions to Candidates

Answer all questions.
Write your answers in the spaces provided.
Use a black or blue pen.
Diagrams should be drawn clearly with a pencil.
Show all working for calculation questions.

Section A: Cellular and Molecular Basis of Life

Question 1 The diagram below shows an electron micrograph of a typical plant cell. (Imagine a diagram with labels: A - Cell Wall, B - Chloroplast, C - Mitochondrion, D - Nucleus, E - Rough Endoplasmic Reticulum)

(a) Which labelled structure is the site of ATP production through aerobic respiration? [1]

(b) Structure E is often studded with small granules. (i) Name these granules. [1]

(ii) State the function of these granules. [1]

Question 2 A student investigated the effect of different solutions on red blood cells. (a) If red blood cells are placed in a solution with a significantly lower water potential than the cell cytoplasm, describe the movement of water and the resulting state of the cell. [3]

(b) Explain why a plant cell would not burst when placed in distilled water, whereas a red blood cell would. [3]

Question 3 The table below shows the results of food tests on an unknown food sample X.

Test	Observation
Iodine solution	Remains yellow-brown
Benedict's solution (heated)	Brick-red precipitate
Biuret reagent	Purple coloration
Ethanol emulsion test	Cloudy white emulsion

(a) Identify the biomolecules present in sample X. [3]

(b) Sample X contains a protein. Describe how this protein is built from smaller units. [2]

Question 4 Enzymes are biological catalysts that are highly specific. (a) Explain the "lock-and-key" hypothesis of enzyme action. [4]

(b) A graph shows the rate of reaction of an enzyme increasing with temperature up to 40°C, then dropping sharply to zero at 60°C. Explain the sharp decrease in the rate of reaction. [3]

Question 5 (a) Define active transport. [2]

(b) Explain the importance of active transport for a root hair cell absorbing mineral ions from the soil. [3]

Section B: Human Physiology and Plant Biology

Question 6 (a) Describe the structure of the alveolus and explain how it is adapted for efficient gas exchange. [4]

(b) Explain why carbon monoxide poisoning is dangerous to the human body. [3]

Question 7 A patient with kidney failure undergoes haemodialysis. (a) Explain how the dialysis machine removes urea from the blood using the principle of diffusion. [4]

(b) If the initial urea concentration in the blood is 50 mg/dL and after 4 hours of dialysis it is 20 mg/dL, and the total blood volume processed is 2000 mL, calculate the average hourly rate of urea removal. Show your working. [3]

Question 8 (a) State the balanced chemical equation for photosynthesis. [2]

(b) Describe how an increase in light intensity affects the rate of photosynthesis, and identify the point at which light intensity is no longer the limiting factor. [4]

Question 9 (a) Define translocation. [2]

(b) Explain the relationship between the rate of transpiration and the opening of stomata during a hot, sunny day. [3]

Question 10 (a) Explain why most living organisms depend on photosynthesis for survival. [6]

Answers

Answer Key - Pure Biology Preliminary Paper 2 (Version 5)

Section A: Cellular and Molecular Basis of Life

Question 1 (a) C (Mitochondrion) [1] (b) (i) Ribosomes [1] (ii) Site of protein synthesis [1] (c) 1. Plant cell has a cell wall; animal cell does not. [1] 2. Plant cell has chloroplasts; animal cell does not. [1] (Alternatively: Plant cell has a large central vacuole; animal cell has small temporary vacuoles).

Question 2 (a) Water moves out of the red blood cell [1] by osmosis [1] down a water potential gradient. The cell becomes shrunken/crenated [1]. (b) Plant cells have a rigid cell wall made of cellulose [1]. When water enters, the cell becomes turgid but the cell wall prevents the cell from bursting [1]. Red blood cells lack a cell wall [1], so the plasma membrane ruptures under osmotic pressure.

Question 3 (a) Reducing sugars (Brick-red) [1], Proteins (Purple) [1], Fats/Lipids (Cloudy emulsion) [1]. (b) Proteins are polymers [1] built from amino acids joined by peptide bonds [1].

Question 4 (a) The enzyme has a specific 3D shape with an active site [1]. The substrate has a complementary shape to the active site [1]. The substrate fits into the active site to form an enzyme-substrate complex [1], where the reaction is catalyzed to form products [1]. (b) At 60°C, the high thermal energy breaks the bonds holding the enzyme's tertiary structure [1]. The active site changes shape/is lost [1], meaning the substrate can no longer fit (enzyme is denatured) [1].

Question 5 (a) The movement of substances across a cell membrane from a region of lower concentration to a region of higher concentration [1] using energy from respiration (ATP) [1]. (b) Mineral ion concentration in the soil is often lower than inside the root hair cell [1]. Ions must move against the concentration gradient [1], which requires active transport to ensure the plant gets sufficient nutrients [1].

Section B: Human Physiology and Plant Biology

Question 6 (a)

One-cell thick walls / very thin walls $\rightarrow$ short diffusion distance [1]
Large surface area $\rightarrow$ increases rate of gas exchange [1]
Moist lining $\rightarrow$ allows gases to dissolve before diffusing [1]
Rich network of capillaries $\rightarrow$ maintains steep concentration gradient [1] (Any 4 points) (b) Carbon monoxide binds more strongly/irreversibly to haemoglobin than oxygen [1]. This reduces the oxygen-carrying capacity of the blood [1], leading to oxygen deprivation in tissues/organs [1].

Question 7 (a) Blood flows past a dialysis fluid with a lower urea concentration [1]. A concentration gradient is established [1]. Urea moves from the blood into the dialysis fluid [1] across a semi-permeable membrane by diffusion [1]. (b) Total urea removed = $(50\text{ mg/dL} - 20\text{ mg/dL}) \times (2000\text{ mL} / 100\text{ mL}) = 30 \times 20 = 600\text{ mg}$ [1] Average hourly rate = $600\text{ mg} / 4\text{ hours} = 150\text{ mg/hour}$ [2] (1 mark for working, 1 mark for correct value, 1 mark for unit).

Question 8 (a) $6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$ (Light and Chlorophyll) [2] (b) As light intensity increases, the rate of photosynthesis increases [1] because more energy is available to drive the reaction [1]. Eventually, the rate plateaus/levels off [1]. At this point, light is no longer the limiting factor; other factors like $\text{CO}_2$ concentration or temperature are limiting [1].

Question 9 (a) The transport of organic solutes (sucrose and amino acids) through the phloem from source to sink [2]. (b) On a hot sunny day, stomata open to allow $\text{CO}_2$ in for photosynthesis [1]. This increases the rate of water vapor escaping the leaf [1], thereby increasing the rate of transpiration [1].

Question 10

Photosynthesis converts light energy into chemical energy stored in glucose [1].
Plants (producers) use this glucose for growth and respiration [1].
Herbivores and carnivores (consumers) depend on eating plants or other animals for their energy source [1].
Without photosynthesis, there would be no food/energy for the rest of the food chain [1].
Photosynthesis releases oxygen as a byproduct [1].
Oxygen is essential for the aerobic respiration of most living organisms to produce ATP [1]. (Max 6 marks)