Mark Scheme

Section A — Structured Questions

Question 1 — Nutrition and Enzymes (9 marks)

(a) Substrate: starch ✓ Product: maltose / sugar / reducing sugar ✓ (2 marks) [Accept: glucose, simple sugar. Do not accept "carbohydrate" alone]

(b) At 60°C the enzyme/amylase is denatured ✓ The high temperature causes the active site to change shape / bonds in enzyme break ✓ The substrate can no longer fit into the active site / enzyme-substrate complex cannot form ✓ (3 marks) [Award 2 marks maximum if "denatured" is not mentioned. Accept "denature" or "denaturation"]

(c) 40°C ✓ (1 mark)

(d) Repeat the experiment (at each temperature) / take multiple readings and calculate a mean ✓ (1 mark) [Accept: use more test tubes at each temperature; increase sample size. Do not accept vague answers like "be more careful"]

(e) Type of food: carbohydrate / starch / polysaccharide ✓ Organ: salivary glands / pancreas / mouth ✓ (2 marks) [Accept either organ. Do not accept "stomach" or "small intestine" alone without salivary glands or pancreas]

Question 2 — Cells and Cell Division (9 marks)

(a) Mitosis ✓ (1 mark)

(b) Chromosomes / chromatids are being pulled / moved / separated ✓ (Moved) to opposite poles / ends of the cell / by spindle fibres ✓ (2 marks) [Award 1 mark only if movement is described but no mention of direction or mechanism]

(c) (i) 46 / 23 pairs ✓ (1 mark)

(ii) 46 / 23 pairs ✓ (1 mark)

(d) Each daughter cell is genetically identical to the parent cell / has the same number of chromosomes ✓ This ensures that new cells can perform the same functions / maintain the characteristics of the tissue ✓ (2 marks) [Accept: produces diploid cells; maintains chromosome number. Must show understanding that identical cells are needed for tissue maintenance]

(e) Type of cell: gamete / sex cell / sperm / egg / ova ✓ Location: testes / ovary / reproductive organs / gonads ✓ (2 marks) [Both parts needed for both marks. Do not accept "reproductive system" without specific organ]

Question 3 — Ecology and Human Impact (9 marks)

(a) Biodiversity refers to the variety of (different) living organisms / species ✓ In a particular habitat / ecosystem / area ✓ (2 marks) [Must mention both variety/number of species AND location/habitat. Accept "diversity of life"]

(b) Natural rainforest has higher/greater biodiversity ✓ Evidence: More tree species (42 vs 18) / more bird species (28 vs 11) ✓ (2 marks) [Must include numerical data from table for second mark. Accept either tree or bird data]

(c) Any TWO from: - Soil erosion has occurred / topsoil has been washed/blown away ✓ - Less leaf litter to decompose and form soil / humus ✓ - Tree roots no longer hold soil in place ✓ - Increased surface runoff removed soil ✓ (2 marks, 1 mark each) [Do not accept vague answers like "forest was cut down" without mechanism of soil loss]

(d) Trees/vegetation/roots intercept rainfall / slow down water flow ✓ Without trees, more water runs off the surface / less infiltration ✓ Less leaf litter/organic matter to absorb water / soil becomes compacted ✓ (Maximum 3 marks) [Award marks for clear causal links. Accept answers that explain the role of tree canopy or root systems]

Question 4 — Transport in Plants (9 marks)

(a) Xylem ✓ (1 mark)

(b) Water is taken up / absorbed by the plant / shoot ✓ (Due to transpiration / water loss from leaves) creating a pressure difference / pulling water along ✓ (2 marks) [Second mark requires explanation of mechanism. Accept "water evaporates from leaves"]

(c) Rate = distance ÷ time ✓ = 58 ÷ 5 = 11.6 mm per minute ✓ (2 marks) [Award 1 mark for correct working even if arithmetic error. Accept 11.6, 11.5-11.7. Must show working for full marks]

(d) Petroleum jelly blocks the stomata / pores ✓ Prevents water vapour escaping / stops transpiration / reduces evaporation ✓ (2 marks) [Both mechanism and effect needed. Do not accept "stops breathing" without reference to water loss]

(e) Any ONE from: - (Higher) temperature / heat ✓ - (Lower) humidity / drier air ✓ - (Increased) light intensity ✓ (1 mark) [Do not accept "water availability" as this affects uptake not transpiration rate directly]

(f) Repeat (the experiment) and calculate a mean / average ✓ OR Use more shoots / plants ✓ OR Leave apparatus to equilibrate before starting / allow shoot to adjust ✓ (1 mark) [Accept any valid reliability improvement. Do not accept "be more accurate" without detail]

Section B — Extended Response

Question 5 (24 marks)

(a)(i) Three ways improper waste disposal affects health and environment (6 marks)

Mark allocation: 2 marks per way described (description must show mechanism/consequence)

Indicative content:

• Water pollution: waste leaches chemicals/toxins into groundwater/rivers/sea → affects drinking water → causes diseases (cholera, typhoid, dysentery)
• Air pollution: burning waste releases toxic fumes/greenhouse gases → respiratory diseases/asthma / contributes to climate change
• Soil contamination: chemicals from waste contaminate soil → affects food crops/food chain → bioaccumulation of toxins
• Breeding grounds for vectors: standing water in containers/tyres → mosquitoes breed → spread dengue/malaria/Zika
• Marine pollution: plastic waste in ocean → animals ingest/entangle → death of marine life/disruption of food chains
• Blocking of drains: solid waste blocks drainage → flooding → water-borne diseases/destruction of property

Marking guidance:

• 2 marks: Clear description of pathway from waste to health/environmental impact with mechanism
• 1 mark: Basic description with limited explanation
• 0 marks: Vague statement without consequence

[Maximum 6 marks — three ways × 2 marks each]

(a)(ii) Evaluate TWO waste management strategies (8 marks)

Mark allocation: 4 marks per strategy (description + advantages + limitations)

Indicative content:

Recycling programmes:

• Advantages: reduces landfill waste, conserves natural resources, creates employment, reduces pollution from manufacturing
• Limitations: requires public education/participation, needs infrastructure/collection systems, initial setup costs high, limited market for recycled goods in some Caribbean countries

Composting organic waste:

• Advantages: reduces landfill volume, produces useful fertilizer, reduces methane emissions, low technology required
• Limitations: requires space, needs proper management to avoid odours/pests, limited to organic waste only, may not be practical in urban areas

Waste-to-energy incineration:

• Advantages: significantly reduces waste volume, generates electricity, reduces landfill needs
• Limitations: high capital costs, air pollution concerns, requires technical expertise, may not be economically viable for small Caribbean islands

Integrated waste management/separation at source:

• Advantages: improves recycling rates, reduces contamination, public awareness increases
• Limitations: requires behaviour change, enforcement needed, ongoing education required

Proper landfill management:

• Advantages: controlled disposal, can capture methane for energy, prevents uncontrolled dumping
• Limitations: land requirements, potential for leachate, long-term monitoring needed

Marking bands per strategy:

• 4 marks: Strategy clearly described; advantages evaluated with specific examples/context; limitations discussed realistically; makes judgement about effectiveness
• 3 marks: Strategy described; some advantages and limitations given; limited evaluation
• 2 marks: Strategy identified; basic advantages or limitations stated; minimal evaluation
• 1 mark: Strategy named; very limited detail
• 0 marks: Irrelevant or no response

[Maximum 8 marks — two strategies × 4 marks each]

(b)(i) Balanced equation for aerobic respiration (2 marks)

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (+ energy/ATP) ✓✓

Mark allocation:

• 2 marks: Completely correct equation with correct formulae and balancing
• 1 mark: Correct substances but incorrect balancing OR word equation with all correct components
• 0 marks: Incorrect equation

[Accept: glucose in place of C₆H₁₂O₆; accept if energy/ATP is shown or omitted]

(b)(ii) Explain how products of photosynthesis are used in respiration and discuss importance (8 marks)

Level 3 (7-8 marks): Comprehensive explanation showing clear understanding of the relationship. Clearly explains that glucose (from photosynthesis) is the substrate for respiration and oxygen is required for aerobic respiration. Discusses importance with multiple well-developed points: interdependence of organisms, cycling of materials, energy flow, maintenance of atmospheric composition. Uses accurate biological terminology throughout. Provides coherent discussion of significance for ecosystems.

Level 2 (4-6 marks): Sound explanation of the basic relationship between photosynthesis and respiration. Identifies glucose and oxygen as products used in respiration. Discusses importance but with less development: may mention oxygen supply, food source, or carbon cycle but lacks detail. Some accurate biological terminology. Discussion may be partially developed or lack coherence.

Level 1 (1-3 marks): Basic or incomplete explanation. May identify that plants make food/oxygen but limited connection to respiration. Importance discussed superficially or with misconceptions (e.g., "plants give us oxygen to breathe" without further development). Limited use of biological terminology. May be largely descriptive without explanation.

0 marks: No creditworthy material.

Indicative content:

• Glucose produced in photosynthesis is used as substrate/respiratory fuel in respiration
• Oxygen produced in photosynthesis is used as final electron acceptor in aerobic respiration
• Carbon dioxide from respiration is used in photosynthesis (cyclical relationship)
• Water from respiration can be used in photosynthesis
• Importance: provides oxygen for aerobic organisms; basis of food chains/webs; photosynthesis captures light energy into chemical energy; respiration releases energy for life processes; maintains balance of atmospheric gases; carbon cycle; interdependence of producers and consumers; without photosynthesis no life would be sustainable on Earth

Question 6 (24 marks)

(a)(i) Explain how meiosis contributes to genetic variation (6 marks)

Level 3 (5-6 marks): Comprehensive explanation of two mechanisms: crossing over (chromatids exchange genetic material during prophase I, creating new combinations of alleles) AND independent assortment (chromosomes line up randomly at equator during metaphase I, producing different combinations in gametes). Both mechanisms clearly explained with accurate terminology. May mention that fertilisation adds further variation.

Level 2 (3-4 marks): Sound explanation of at least one mechanism in detail OR both mechanisms described but with less precision. Some accurate terminology. May confuse stages or lack detail about when processes occur. Understanding evident but explanation incomplete.

Level 1 (1-2 marks): Basic statements such as "chromosomes mix" or "creates different combinations" without explanation of mechanism. Limited terminology. May show misconceptions (e.g., confusing mitosis and meiosis).

0 marks: No creditworthy material.

Indicative content:

• Crossing over / recombination occurs between homologous chromosomes / chromatids
• Occurs during prophase I
• Segments of DNA are exchanged between chromatids
• Creates new combinations of alleles on chromosomes
• Independent assortment / random arrangement of chromosomes
• Occurs during metaphase I
• Maternal and paternal chromosomes line up randomly
• Many different combinations of chromosomes possible in gametes
• Each gamete receives different combination of alleles
• Random fertilisation adds further variation

(a)(ii) Distinguish between continuous and discontinuous variation with examples (6 marks)

Continuous variation (3 marks):

• Shows a range of phenotypes between two extremes ✓
• Controlled by many genes / polygenic ✓
• (Often) affected/influenced by environment ✓
• Example: height / weight / skin colour / hand span / foot size ✓ (1 mark for valid example)

Discontinuous variation (3 marks):

• Shows distinct categories / no intermediates ✓
• Controlled by one gene / single gene ✓
• Not affected / not usually affected by environment ✓
• Example: ABO blood groups / ability to roll tongue / attached/unattached ear lobes / presence/absence of widow's peak ✓ (1 mark for valid example)

Mark allocation: Award up to 2 marks for description of each type + 1 mark for valid example of each [Accept equivalent wording. Reject examples that are incorrect for the category, e.g., eye colour as discontinuous]

(b)(i) Genetic diagram (4 marks)

Parental phenotypes: Carrier / sickle cell trait (both parents) ✓ Parental genotypes: H^A H^S × H^A H^S ✓ Gametes: H^A, H^S from each parent ✓ Punnett square or appropriate diagram showing offspring genotypes:

OR equivalent branching diagram

Offspring genotypes: H^A H^A, H^A H^S, H^A H^S, H^S H^S ✓

Mark allocation:

• 1 mark: Correct parental genotypes shown
• 1 mark: Correct gametes shown
• 1 mark: Punnett square / genetic diagram correctly constructed
• 1 mark: Offspring genotypes correctly shown

[Deduct marks for errors in notation or incomplete diagrams. Must use the notation given in question]

(b)(ii) Calculate probability (1 mark)

¼ or 0.25 or 25% or 1 in 4 ✓ (1 mark)

[Accept any equivalent fraction, decimal, or percentage]

(b)(iii) Explain survival advantage of heterozygous individuals in malaria regions (7 marks)

Level 3 (6-7 marks): Comprehensive explanation showing clear understanding. Explains that H^A H^S individuals have sickle cell trait (not disease). Explains mechanism: malaria parasite (Plasmodium) cannot complete life cycle in sickled red blood cells OR sickled cells are destroyed before parasite can reproduce. Makes clear that H^A H^S individuals have advantage over both H^A H^A (susceptible to malaria) and H^S H^S (have sickle cell disease). Explains this is an example of balanced polymorphism/heterozygous advantage where deleterious allele maintained in population. Uses accurate biological terminology throughout.

Level 2 (3-5 marks): Sound explanation with key points. Explains that H^A H^S individuals are more resistant to malaria than H^A H^A individuals AND do not have severe symptoms of sickle cell disease like H^S H^S individuals. Some explanation of mechanism but may lack detail. May not use term "heterozygous advantage" or explain why allele persists. Some biological terminology used appropriately.

Level 1 (1-2 marks): Basic statements such as "carriers are immune to malaria" (misconception) or "have both advantages" without clear explanation. May correctly state that heterozygotes are more resistant but with no mechanism. Limited terminology. May confuse carrier state with disease state.

0 marks: No creditworthy material.

Indicative content:

• H^A H^S individuals have sickle cell trait (carriers) not sickle cell disease
• Have both normal and abnormal haemoglobin
• When infected with malaria, some red blood cells sickle
• Malaria parasite (Plasmodium) cannot survive/reproduce in sickled cells
• Sickled infected cells are destroyed / removed from circulation
• H^A H^A individuals fully susceptible to malaria (severe/fatal disease)
• H^S H^S individuals have sickle cell disease (often fatal)
• H^A H^S have advantage in malaria regions: partial protection from malaria without severe sickle cell disease
• This is heterozygous advantage / balanced polymorphism
• Explains why sickle cell allele remains relatively common in populations from malaria regions
• Natural selection favours heterozygotes in these environments

Sample Answers with Examiner Commentary

Question 5(a)(ii) — Sample Answers

Evaluate the effectiveness of TWO waste management strategies that could be implemented in a Caribbean country to reduce environmental pollution. (8 marks)

Grade I (Distinction) answer

Two effective waste management strategies for Caribbean countries are recycling programmes and composting of organic waste.

Recycling programmes involve the collection and separation of materials such as plastics, glass, metals, and paper for reprocessing. This strategy is effective because it significantly reduces the amount of waste going to landfills, which is particularly important in Caribbean islands where land space is limited. For example, in Barbados, the recycling initiative has diverted approximately 30% of waste from landfills. Recycling also reduces pollution from manufacturing new products, as making items from recycled materials uses less energy and produces fewer emissions. Additionally, it can create employment opportunities in collection, sorting, and processing. However, the effectiveness is limited by several factors. It requires significant public education to ensure proper separation of waste, and participation rates can be low without enforcement. The infrastructure needed for collection and processing requires substantial initial investment, which may be challenging for smaller Caribbean nations. There is also limited demand for recycled materials in some territories, meaning materials may need to be exported, adding to costs and reducing economic benefits.

Composting organic waste is another effective strategy. In the Caribbean, approximately 40-50% of household waste is organic material such as food scraps and garden waste. Composting this material reduces landfill volume substantially and prevents the production of methane, a potent greenhouse gas produced when organic matter decomposes anaerobically in landfills. The compost produced is a valuable fertilizer that can be used in agriculture and gardening, supporting local food production. This strategy is relatively low-technology and can be implemented at household, community, or municipal levels. Countries like Trinidad and Tobago have successfully implemented community composting projects. However, composting requires space and proper management to prevent odours and pest problems. In densely populated urban areas, finding suitable locations can be difficult. It also requires public education about what can be composted and how to maintain compost bins properly. The strategy only addresses organic waste, so it must be combined with other approaches for comprehensive waste management.

Overall, both strategies are effective in reducing environmental pollution, but their success depends heavily on public participation, adequate funding, and integration into a broader waste management system.

Mark: 8/8

Examiner commentary: This is an exemplary response demonstrating comprehensive evaluation. The candidate describes each strategy clearly, provides specific advantages with contextual Caribbean examples (Barbados, Trinidad and Tobago), critically evaluates limitations with realistic considerations (land constraints, infrastructure costs, public participation), and makes a balanced judgement about effectiveness. The answer uses appropriate technical terminology (anaerobic decomposition, methane, infrastructure) and maintains analytical focus throughout rather than simply listing points. This represents Level 4 performance across both strategies.

Grade III (Pass) answer

Two waste management strategies are recycling and proper landfills.

Recycling is when we reuse materials like plastic bottles, glass, and paper instead of throwing them away. This is good because it reduces the amount of garbage that goes to dumps and helps the environment. Recycling also saves natural resources because we don't have to make as many new products. In Caribbean countries this can help because we have small islands and not much space for garbage. But recycling can be difficult because it costs money to set up recycling centers and people need to learn how to separate their garbage properly. Sometimes people don't bother to recycle because it's easier to just throw everything away together.

Proper landfills are places where garbage is disposed of in an organized way. They are better than open dumps because the waste is covered with soil regularly and the area is managed properly. This prevents bad smells and stops rats and other pests from breeding. Proper landfills also prevent pollution from getting into the groundwater by having special liners at the bottom. This is effective for Caribbean countries because it's better than having illegal dumps everywhere. However, landfills still need a lot of space which is a problem on small islands. They also need to be monitored for a long time even after they're closed, which costs money.

Both strategies can help reduce pollution in the Caribbean but they need proper planning and money to work effectively.

Mark: 5/8

Examiner commentary: This response demonstrates sound understanding with some evaluation, placing it in mid-Level 2. The candidate correctly identifies and describes two strategies with some advantages and limitations discussed. However, the evaluation lacks depth and specific examples. Terms like "helps the environment" are too vague, and there's limited discussion of mechanisms (e.g., how recycling reduces manufacturing pollution). The Caribbean context is mentioned but not developed with specific examples. To reach Grade I, this answer needed more precise terminology, specific examples, and deeper analysis of effectiveness rather than general statements about difficulties and benefits.

Grade V (Near miss) answer

Two waste management strategies are recycling and burning waste.

Recycling is good because we can use things again and not waste them. If we recycle bottles and cans, we won't have so much garbage. This helps the environment because there will be less pollution. Caribbean countries should recycle more to keep the beaches clean for tourists. But some people are lazy and don't want to recycle.

Burning waste is effective because it gets rid of garbage quickly and makes the amount smaller. When you burn garbage, there is less waste to worry about. This is good for small islands that don't have space. But burning waste can cause air pollution and smoke that is bad for people's health. It can also cause global warming.

These two strategies are both effective because they reduce waste in the Caribbean.

Mark: 3/8

Examiner commentary: This response shows basic knowledge but significant weaknesses prevent it from achieving a pass grade. While two strategies are identified, the descriptions lack depth and contain imprecise language ("use things again," "makes the amount smaller"). The burning waste strategy shows a common misconception—conflating uncontrolled burning (often practiced illegally) with waste-to-energy incineration, which requires sophisticated technology. The advantages and limitations are superficial without explanation of mechanisms. The response lacks specific Caribbean examples and doesn't genuinely evaluate effectiveness. To improve, the candidate needs to develop explanations (how does recycling reduce pollution specifically?), use accurate terminology (incineration vs. burning), provide specific examples, and avoid very general statements. The structure shows some attempt at organization, which is credited, but content development is insufficient for higher marks.

Question 6(b)(iii) — Sample Answers

Explain why individuals who are heterozygous (H^A H^S) for the sickle cell allele may have a survival advantage in areas where malaria is common. (7 marks)

Grade I (Distinction) answer

Individuals who are heterozygous (H^A H^S) for the sickle cell allele have both normal haemoglobin (H^A) and sickle cell haemoglobin (H^S). These individuals have sickle cell trait rather than sickle cell disease, meaning they produce both types of haemoglobin and usually show no symptoms or only mild symptoms under extreme conditions.

In areas where malaria is endemic, such as parts of West Africa and historically in the Caribbean, H^A H^S individuals have a significant survival advantage through resistance to malaria. Malaria is caused by the Plasmodium parasite, which is transmitted by Anopheles mosquitoes and infects red blood cells. When the parasite invades the red blood cells of a heterozygous individual, the presence of abnormal haemoglobin causes those infected cells to sickle or change shape. These sickled cells are recognized as abnormal by the immune system and are rapidly removed from the circulation by the spleen before the Plasmodium parasite can complete its life cycle and reproduce. Therefore, H^A H^S individuals have partial protection against severe malaria infection.

This creates a situation where the heterozygote has an advantage over both homozygotes. Individuals who are H^A H^A (homozygous for normal haemoglobin) have no protection against malaria and can suffer severe, potentially fatal infections, particularly in childhood. On the other hand, individuals who are H^S H^S (homozygous for sickle cell) have sickle cell disease, suffering from chronic anaemia, painful crises, organ damage, and often early death due to the continuous sickling of red blood cells.

The H^A H^S genotype therefore provides the best survival outcome in malaria-endemic regions: protection from severe malaria without the debilitating effects of sickle cell disease. This is an example of heterozygous advantage or balanced polymorphism, where natural selection maintains a potentially harmful allele in the population because heterozygotes have higher fitness than either homozygote in that particular environment. This explains why the H^S allele remains at relatively high frequencies in populations from regions where malaria has been historically prevalent, even though the allele is deleterious in the homozygous state.

Mark: 7/7

Examiner commentary: This is an outstanding response that demonstrates comprehensive understanding of heterozygous advantage in the context of malaria resistance. The candidate clearly explains the genotype and phenotype of H^A H^S individuals, describes the mechanism of malaria resistance (parasite life cycle disruption in sickled cells), explicitly compares survival outcomes for all three genotypes (critical for demonstrating "advantage"), and correctly identifies this as balanced polymorphism with an evolutionary explanation. The answer is logically structured, uses precise biological terminology throughout (endemic, Plasmodium, homozygous, heterozygous, phenotype, fitness), and provides sufficient detail to access all available marks in the top band.

Grade III (Pass) answer

Heterozygous individuals (H^A H^S) have sickle cell trait, which means they have one normal allele and one sickle cell allele. They produce some normal haemoglobin and some abnormal haemoglobin.

In areas where malaria is common, heterozygous individuals have an advantage because they are more resistant to malaria than people with normal haemoglobin (H^A H^A). When the malaria parasite infects their red blood cells, the cells can sickle, and the parasite cannot survive as well in the sickled cells. This means that people with sickle cell trait are less likely to get severe malaria than normal people.

At the same time, heterozygous individuals don't suffer from sickle cell disease like people who are H^S H^S. People with sickle cell disease (H^S H^S) have serious health problems because their red blood cells are always sickled, causing pain and organ damage. People with sickle cell trait (H^A H^S) are mostly healthy and only have minor problems.

Therefore, in places with malaria, it is better to be H^A H^S than to be H^A H^A (who can die from malaria) or H^S H^S (who have sickle cell disease). This is why the sickle cell allele is common in Africa and some other places where malaria occurs.

Mark: 4/7

Examiner commentary: This response demonstrates sound understanding and correctly identifies the key comparative advantage (better than both homozygotes), placing it in Level 2. The candidate accurately describes the heterozygous genotype and phenotype, explains basic malaria resistance, and compares outcomes for the three genotypes. However, the explanation of the mechanism is imprecise ("parasite cannot survive as well" rather than explaining interrupted life cycle or removal of infected cells). The answer lacks the depth and precision of terminology expected for top marks—terms like "heterozygous advantage," "balanced polymorphism," or "natural selection" are absent. The phrase "normal people" is imprecise (should specify "homozygous for normal haemoglobin"). To achieve Grade I, the candidate needed more mechanistic detail, precise terminology, and explicit reference to evolutionary concepts.

Grade V (Near miss) answer

Heterozygous people (H^A H^S) have an advantage in malaria areas because they are immune to malaria. They have the sickle cell gene which protects them from getting malaria. This is because their blood cells are sickled so the mosquito cannot give them the disease.

People with sickle cell disease (H^S H^S) are not immune to malaria but they have problems with their blood. People with normal blood (H^A H^A) can get malaria easily.

So heterozygous is the best because you get protection from malaria but you don't have sickle cell disease. This is why many people in Africa have the sickle cell gene.

Mark: 2/7

Examiner commentary: This response shows basic awareness that heterozygotes have some advantage but contains significant misconceptions and insufficient development for a passing grade. The statement that H^A H^S individuals are "immune" to malaria is incorrect—they have partial resistance, not immunity. The mechanism is fundamentally misunderstood: the candidate suggests the mosquito cannot transmit the disease to people with sickled cells, when the actual mechanism involves what happens after infection. The explanation lacks detail about the malaria parasite, how resistance works at the cellular level, or why H^S H^S individuals have health problems. The comparison is present but superficial. To improve, the candidate must correct the misconception about immunity vs. resistance, explain the actual mechanism (parasite in red blood cells, destruction of infected cells), provide more detail about each genotype's outcome, and use appropriate biological terminology. The basic structure showing comparison is the main creditworthy element, earning minimal marks.