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A Level H2 Biology Practice Paper 1

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TuitionGoWhere Practice Paper - Biology H2 A-Level

TuitionGoWhere Secondary School (AI)

Subject: Biology H2
Level: A-Level
Paper: PRACTICE Paper 2
Duration: 2 hours
Total Marks: 75

Name: _________________ Class: _________________ Date: _________________

Instructions

  • Answer ALL questions
  • Write your answers in the spaces provided
  • Show all working for calculations
  • Use appropriate scientific terminology throughout
  • Where figures are provided, refer to them in your answers

Section A [25 marks]

Question 1

Fig. 1.1 shows a transmission electron micrograph of part of a cell.

[THIS IS FIGURE: TEM image showing cellular organelles with structures labeled A, B, C, and D. Structure A appears to be the nucleus, B shows mitochondria, C indicates rough endoplasmic reticulum, and D points to ribosomes]

(a) (i) Identify the structures labelled A, B, C and D. [4]

A: _________________________________________________________________

B: _________________________________________________________________

C: _________________________________________________________________

D: _________________________________________________________________

(ii) State the magnification used if the actual diameter of structure A is 8 μm and its diameter in the micrograph is 32 mm. [2]

Working:

Magnification = _________________________________________________________________

(b) With reference to Fig. 1.1, explain how structure B is adapted for its role in aerobic respiration. [4]

Question 2

Fig. 2.1 shows the results of gel electrophoresis analysis of haemoglobin from four individuals.

[THIS IS FIGURE: Gel electrophoresis diagram showing 4 lanes with different banding patterns. Lane 1 shows one band, Lane 2 shows two bands, Lane 3 shows one band at different position, Lane 4 shows two bands]

Individual 2 is heterozygous for the sickle cell allele.

(a) Describe and explain how gel electrophoresis is used to diagnose sickle cell anaemia. [4]

(b) With reference to Fig. 2.1, explain the different numbers of fragments seen in different individuals. [3]

(c) Identify which individual(s) would be expected to show symptoms of sickle cell anaemia. Explain your answer. [2]

Individual(s): _________________________________________________________________

Explanation: _________________________________________________________________

Question 3

An experiment was carried out to investigate the effect of substrate concentration on enzyme activity. The enzyme used was amylase and the substrate was starch.

(a) Describe how you would test for the presence of starch. [2]

(b) Fig. 3.1 shows the results of the experiment.

[THIS IS FIGURE: Graph showing enzyme activity (arbitrary units) on y-axis vs substrate concentration (mol dm⁻³) on x-axis. Curve starts at origin, rises steeply then levels off to plateau]

(i) Explain the shape of the curve between points X and Y. [3]

(ii) Explain why the curve levels off after point Y. [2]

Section B [25 marks]

Question 4

Fig. 4.1 shows part of the lac operon in E. coli.

[THIS IS FIGURE: Diagram of lac operon showing promoter region, operator, and three genes (lacZ, lacY, lacA) with regulatory protein binding sites]

(a) The lac operon codes for inducible enzymes. Explain why it is advantageous for E. coli to have an inducible operon for lactose metabolism. [3]

(b) With reference to Fig. 4.1, describe and explain what happens when:

(i) lactose is absent from the growth medium [4]

(ii) lactose is present in the growth medium [4]

Question 5

A suspension of isolated mitochondria was prepared in a buffer containing ADP and inorganic phosphate (Pi). The oxygen concentration in the buffer was monitored and recorded as shown in Fig. 5.1.

[THIS IS FIGURE: Graph showing oxygen concentration vs time, with arrows indicating addition of glucose at point A and sodium azide at point B. Oxygen concentration decreases after glucose addition, then increases after sodium azide addition]

(a) Explain why oxygen concentration decreases after the addition of glucose at point A. [3]

(b) Sodium azide is an inhibitor of cytochrome oxidase in the electron transport chain. With reference to Fig. 5.1, explain the effect of adding sodium azide at point B. [4]

(c) Calculate the rate of oxygen consumption between 2 and 4 minutes. Show your working. [2]

Working:

Rate = _________________ arbitrary units per minute

Question 6

Describe the structure of proteins, explaining how the different levels of structure contribute to protein function. [10]

Section C [25 marks]

Question 7

Fig. 7.1 shows the results of a genetic cross involving feather colour in chickens. The gene for feather colour has two alleles: C^B (black feathers) and C^W (white feathers).

[THIS IS FIGURE: Genetic cross diagram showing: Parents: Black male × Splashed white female F1: All blue feathers F1 × F1 cross F2: 89 black : 183 blue : 94 splashed white]

(a) (i) Using appropriate symbols, write the genotypes of the parent generation. [2]

Male: _________________________________________________________________

Female: _________________________________________________________________

(ii) Explain the phenotype of the F1 generation. [2]

(b) A chi-squared (χ²) test was carried out to determine whether the F2 results fit the expected ratio for this type of cross.

(i) State the null hypothesis for this test. [1]

(ii) Calculate the expected numbers for each phenotype class in the F2 generation. [3]

Total F2 offspring = _________________________________________________________________

Expected black: _________________________________________________________________

Expected blue: _________________________________________________________________

Expected splashed white: _________________________________________________________________

(iii) The calculated χ² value was 0.89. The critical value at p = 0.05 with 2 degrees of freedom is 5.99.

State the conclusion of this test and explain what this means. [2]

Conclusion: _________________________________________________________________

Explanation: _________________________________________________________________

Question 8

Fig. 8.1 shows a simplified diagram of photosystem II in the thylakoid membrane.

[THIS IS FIGURE: Diagram showing photosystem II with electron transport chain, showing light energy input, water splitting, and electron movement to photosystem I]

(a) With reference to Fig. 8.1, explain the role of electrons as they move from photosystem II to photosystem I. [4]

(b) Explain how the light-dependent reactions of photosynthesis produce ATP. [6]

(c) Describe and explain the effects of an increase in oxygen concentration on the rate of photosynthesis in C3 plants. [5]

[END OF PAPER]

Answers

TuitionGoWhere Practice Paper - Biology H2 A-Level - Mark Scheme

Total Marks: 75

Section A [25 marks]

Question 1

(a) (i) Identify the structures labelled A, B, C and D. [4]

  • A: Nucleus [1]
  • B: Mitochondrion [1]
  • C: Rough endoplasmic reticulum / RER [1]
  • D: Ribosomes [1]

(ii) State the magnification used if the actual diameter of structure A is 8 μm and its diameter in the micrograph is 32 mm. [2]

  • Convert units: 32 mm = 32,000 μm [1]
  • Magnification = 32,000 ÷ 8 = ×4000 [1]

(b) With reference to Fig. 1.1, explain how structure B is adapted for its role in aerobic respiration. [4]

  • Inner membrane folded into cristae [1]
  • Increases surface area for electron transport chain / ATP synthesis [1]
  • Matrix contains enzymes for Krebs cycle [1]
  • Double membrane allows compartmentalization / proton gradient formation [1]

Question 2

(a) Describe and explain how gel electrophoresis is used to diagnose sickle cell anaemia. [4]

  • Electric field / potential difference applied across gel [1]
  • Proteins move according to charge and molecular mass [1]
  • Normal haemoglobin (HbA) and sickle haemoglobin (HbS) migrate differently [1]
  • Different migration patterns allow identification of genotype [1]

(b) With reference to Fig. 2.1, explain the different numbers of fragments seen in different individuals. [3]

  • Different alleles produce proteins of different sizes/charges [1]
  • Heterozygotes carry two different alleles, so show two bands [1]
  • Homozygotes carry identical alleles, so show one band [1]

(c) Identify which individual(s) would be expected to show symptoms of sickle cell anaemia. Explain your answer. [2]

  • Individual(s): Individual 3 [1]
  • Explanation: Shows only one band in position of HbS / is homozygous for sickle cell allele [1]

Question 3

(a) Describe how you would test for the presence of starch. [2]

  • Add iodine solution [1]
  • Blue-black colour indicates presence of starch [1]

(b) (i) Explain the shape of the curve between points X and Y. [3]

  • Increasing substrate concentration increases rate of reaction [1]
  • More substrate molecules available for enzyme active sites [1]
  • More enzyme-substrate complexes formed per unit time [1]

(ii) Explain why the curve levels off after point Y. [2]

  • All enzyme active sites are occupied / enzyme is saturated [1]
  • Further increase in substrate concentration has no effect on rate [1]

Section B [25 marks]

Question 4

(a) The lac operon codes for inducible enzymes. Explain why it is advantageous for E. coli to have an inducible operon for lactose metabolism. [3]

  • Enzymes only produced when lactose is present [1]
  • Saves energy/resources when lactose is absent [1]
  • Allows rapid response to lactose availability [1]

(b) (i) lactose is absent from the growth medium [4]

  • Repressor protein binds to operator [1]
  • RNA polymerase cannot bind to promoter / transcription blocked [1]
  • No mRNA produced [1]
  • No enzymes for lactose metabolism produced [1]

(ii) lactose is present in the growth medium [4]

  • Lactose acts as inducer / binds to repressor protein [1]
  • Repressor protein changes shape / cannot bind to operator [1]
  • RNA polymerase can bind to promoter [1]
  • Transcription occurs / enzymes for lactose metabolism produced [1]

Question 5

(a) Explain why oxygen concentration decreases after the addition of glucose at point A. [3]

  • Glucose provides substrate for respiration [1]
  • Oxygen is used as final electron acceptor in electron transport chain [1]
  • Rate of oxygen consumption increases [1]

(b) Sodium azide is an inhibitor of cytochrome oxidase in the electron transport chain. With reference to Fig. 5.1, explain the effect of adding sodium azide at point B. [4]

  • Electron transport chain is blocked [1]
  • Oxygen cannot accept electrons / is not reduced [1]
  • Oxygen consumption stops [1]
  • Oxygen concentration increases as it is no longer being used [1]

(c) Calculate the rate of oxygen consumption between 2 and 4 minutes. [2]

  • Change in oxygen concentration = (reading at 4 min) - (reading at 2 min) [1]
  • Rate = change ÷ time = change ÷ 2 minutes [1] Note: Specific values depend on graph scale provided

Question 6

Describe the structure of proteins, explaining how the different levels of structure contribute to protein function. [10]

Mark scheme:

  • Primary structure: sequence of amino acids joined by peptide bonds [1]
  • Determines all higher levels of structure [1]
  • Secondary structure: α-helices and β-pleated sheets [1]
  • Held by hydrogen bonds between backbone atoms [1]
  • Provides structural stability [1]
  • Tertiary structure: 3D folding of polypeptide chain [1]
  • Held by various bonds (hydrogen, ionic, disulfide, hydrophobic interactions) [1]
  • Determines active site shape in enzymes / binding sites [1]
  • Quaternary structure: association of multiple polypeptide chains [1]
  • Examples: haemoglobin (4 subunits), enzymes with multiple subunits [1]

Section C [25 marks]

Question 7

(a) (i) Using appropriate symbols, write the genotypes of the parent generation. [2]

  • Male: C^B C^B [1]
  • Female: C^W C^W [1]

(ii) Explain the phenotype of the F1 generation. [2]

  • All F1 are C^B C^W (heterozygous) [1]
  • Codominance results in blue feathers (intermediate phenotype) [1]

(b) (i) State the null hypothesis for this test. [1]

  • The observed results fit the expected 1:2:1 ratio [1]

(ii) Calculate the expected numbers for each phenotype class in the F2 generation. [3]

  • Total F2 offspring = 89 + 183 + 94 = 366 [1]
  • Expected black: 366 ÷ 4 = 91.5 [1]
  • Expected blue: 366 ÷ 2 = 183 [1]
  • Expected splashed white: 366 ÷ 4 = 91.5 [1]

(iii) State the conclusion of this test and explain what this means. [2]

  • Conclusion: Accept null hypothesis / no significant difference [1]
  • Explanation: Observed results fit expected 1:2:1 ratio / genes assort independently [1]

Question 8

(a) With reference to Fig. 8.1, explain the role of electrons as they move from photosystem II to photosystem I. [4]

  • Electrons are excited by light energy at PSII [1]
  • Move through electron transport chain [1]
  • Energy released is used to pump H+ into thylakoid lumen [1]
  • Creates proton gradient for ATP synthesis [1]

(b) Explain how the light-dependent reactions of photosynthesis produce ATP. [6]

  • Light energy excites electrons in photosystems [1]
  • Electrons move through electron transport chain [1]
  • Energy released pumps H+ from stroma into thylakoid lumen [1]
  • Creates proton gradient across thylakoid membrane [1]
  • H+ flow back through ATP synthase [1]
  • ADP + Pi → ATP (chemiosmosis) [1]

(c) Describe and explain the effects of an increase in oxygen concentration on the rate of photosynthesis in C3 plants. [5]

  • Rate of photosynthesis decreases [1]
  • RuBisCO catalyses both carboxylation (with CO2) and oxygenation (with O2) [1]
  • High oxygen concentration favours oxygenation of RuBP [1]
  • This leads to photorespiration [1]
  • Photorespiration produces no ATP or NADPH, reducing net photosynthesis [1]