Mark Scheme

Section A — Multiple Choice Answer Key

Detailed Marking Notes

Question 1 (Answer: B)

• Rhizobium bacteria form symbiotic relationships with leguminous plants and convert atmospheric nitrogen (N₂) into ammonia (NH₃), making nitrogen available to plants.
• Accept: Nitrogen fixation only
• Reject: "Helps plants grow" (too vague); "Makes nitrogen" (imprecise)

Question 2 (Answer: C)

• Interveinal chlorosis (yellowing between veins with veins remaining green) is the characteristic symptom of iron deficiency.
• Reject: Nitrogen deficiency causes uniform yellowing; Phosphorus causes purpling; Potassium causes marginal necrosis

Question 3 (Answer: B)

• Memorization standard: Sow = 114 days (3 months, 3 weeks, 3 days); Ewe = 150 days; Cow = 283 days; Bitch = 63 days

Question 4 (Answer: C)

• Ratoon cropping involves allowing the plant to regenerate from the base after harvest, producing suckers naturally. This is standard commercial practice for bananas in the Caribbean.
• Reject: Grafting and budding are used for tree crops; Layering is not commercial-scale

Question 5 (Answer: B)

• Biological control uses living organisms (predators, parasites, pathogens) to control pests.
• Accept: Any example of introducing natural enemies
• Reject: A = chemical control; C = cultural control; D = cultural control

Question 6 (Answer: A)

• Standard definition; transpiration is the evaporation of water from aerial parts of plants, mainly through stomata.

Question 7 (Answer: C)

• Hereford is a beef breed; Holstein, Jersey and Guernsey are dairy breeds (dairy cattle are named for Channel Islands or Dutch origins in typical exam questions).

Question 8 (Answer: B)

• pH 4.5 is acidic; lime (calcium carbonate or calcium hydroxide) raises pH by neutralizing soil acidity.
• Reject: Ammonium sulphate and urea lower pH; Potassium chloride does not significantly affect pH

Question 9 (Answer: C)

• Standard terminology: Apiculture = bees; Aquaculture = aquatic organisms; Sericulture = silkworms; Silviculture = forest trees

Question 10 (Answer: B)

• Kudzu (Pueraria lobata) is a leguminous cover crop used in the Caribbean for soil improvement and erosion control.
• Reject: All other options are grasses (non-leguminous)

Question 11 (Answer: C)

• The anther produces pollen grains which contain male gametes; ovary contains female gametes

Question 12 (Answer: B)

• Calcium is the primary component of eggshells; deficiency results in thin, weak shells.

Question 13 (Answer: B)

• Sheet erosion = uniform removal of thin soil layers over broad areas
• Gully = deep channels; Rill = small channels

Question 14 (Answer: C)

• Ethylene is the ripening hormone (also used commercially to ripen bananas)
• Reject: Auxin = cell elongation; Gibberellin = stem elongation; Cytokinin = cell division

Question 15 (Answer: A)

• Mulching with bagasse (sugar cane waste) suppresses weeds by blocking light and adds organic matter.
• Accept: Any correctly explained mulching benefit
• Reject: C would increase competition among crop plants, not reduce weeds

Question 16 (Answer: A)

• Grading = sorting by quality attributes
• Standardization = establishing uniform specifications (but not the sorting process itself)

Question 17 (Answer: B)

• Newcastle disease (Asiatic fowl pest) is a viral disease with respiratory and nervous symptoms, causing high mortality.
• Reject: Fowl pox = skin lesions; Coccidiosis = protozoan (bloody diarrhea); Fowl typhoid = bacterial

Question 18 (Answer: C)

• Inbreeding = mating related animals; increases homozygosity
• Cross-breeding = mating different breeds; Out-breeding = mating unrelated animals; Upgrading = successive use of superior male

Question 19 (Answer: C)

• Macronutrients: N, P, K, Ca, Mg, S (required in large quantities)
• Micronutrients: Fe, Mn, B, Zn, Cu, Mo, Cl (required in small quantities)

Question 20 (Answer: A)

• Financial credit/loans are classified as capital input in agricultural production.
• Factors of production: Land, Labour, Capital, Management (Entrepreneurship)

Sample Answers with Examiner Commentary

Question 2 — Sample Answers

Note: While Paper 1 consists entirely of multiple choice questions, for demonstration purposes of the examiner commentary requirement, the following illustrates how different levels of student understanding might be revealed if students were asked to EXPLAIN their answer choice.

If the question were extended to: "Explain why iron deficiency causes this symptom pattern in tomato plants."

Grade I (Distinction) answer

Iron deficiency causes interveinal chlorosis because iron is essential for chlorophyll synthesis. Although iron is not a component of the chlorophyll molecule itself, it is required as a cofactor for several enzymes involved in chlorophyll production. When iron is deficient, young leaves particularly are affected because iron is relatively immobile in the phloem and cannot be easily translocated from older to younger tissue. The veins remain green because they contain vascular tissue where small amounts of iron accumulate, while the interveinal areas cannot produce sufficient chlorophyll and turn yellow. This symptom differs from nitrogen deficiency which causes uniform yellowing because nitrogen is mobile and deficiency appears first in older leaves.

Mark: 6/6 marks

Examiner commentary: This response demonstrates comprehensive understanding of both the biochemical role of iron and the physiological reasons for the symptom pattern. The candidate correctly identifies that iron is required for chlorophyll synthesis (not as a component but as a cofactor), explains why young leaves are most affected (immobility in phloem), and contrasts this with nitrogen deficiency to show depth of understanding. The technical terminology is precise and accurately used throughout.

Grade III (Pass) answer

Iron deficiency causes yellow leaves with green veins because the plant needs iron to make chlorophyll. When there is not enough iron, the plant cannot make enough chlorophyll so the leaves turn yellow. The veins stay green because they still have some iron. This happens mostly in the young leaves at the top of the plant because iron does not move easily in plants.

Mark: 3/6 marks

Examiner commentary: This answer earns credit for identifying that iron is needed for chlorophyll production and that young leaves are primarily affected. The candidate correctly notes that iron does not move easily in plants. However, the response lacks precision—it does not explain iron's specific role (cofactor vs. component), does not use the term "interveinal chlorosis," and does not explain WHY veins remain green beyond saying "they still have some iron." The answer demonstrates basic understanding but lacks the detail and accuracy required for higher marks.

Grade V (Near miss) answer

The yellow leaves with green veins are caused by iron deficiency. Iron is an important nutrient that plants need to stay healthy and grow properly. When the plant does not get enough iron from the soil, the leaves cannot stay green and they turn yellow. The plant is sick because it is not getting the minerals it needs. To fix this problem, the farmer should add iron fertilizer to the soil or spray the leaves with iron solution.

Mark: 1/6 marks

Examiner commentary: This response demonstrates a common misconception at CSEC level—treating the question as a general description rather than a specific explanation of the mechanism. While the candidate correctly identifies iron deficiency and suggests appropriate remedial action (though this was not asked for), they fail to explain WHY this particular symptom pattern occurs. The statement that "iron is important" is too vague, and there is no mention of chlorophyll, interveinal chlorosis, or why veins remain green. To improve, the student needs to focus on the specific biological processes involved (chlorophyll synthesis) and address all parts of the symptom description (why yellow AND why veins stay green).

Question 5 — Sample Answers

Note: Extended to "Explain how biological control differs from chemical control and give ONE advantage and ONE disadvantage of using biological control."

Grade I (Distinction) answer

Biological control involves using living organisms such as predators, parasites or pathogens to control pest populations, while chemical control uses synthetic or natural pesticides to kill pests directly. In the example given, parasitic wasps are natural enemies that attack aphids, either by laying eggs inside them or feeding on them, which reduces the aphid population naturally.

One major advantage of biological control is that it is environmentally sustainable and does not leave harmful chemical residues on crops or in the soil. Beneficial insects can establish themselves in the ecosystem and provide long-term pest control without repeated applications. One disadvantage is that biological control is slower to act than chemical pesticides—it may take several weeks for the natural enemy population to build up sufficiently to control the pest, while a chemical spray provides immediate knockdown of the pest population. This makes biological control less suitable when immediate action is required to prevent crop damage.

Mark: 6/6 marks

Examiner commentary: This is an exemplary response that clearly distinguishes between the two control methods using precise terminology. The candidate correctly identifies biological control as using living organisms and provides appropriate examples (predators, parasites, pathogens). The advantage cited (environmental sustainability with no residues) and disadvantage (slower action) are both valid, well-explained and directly compared to chemical control. The answer demonstrates sophisticated understanding of integrated pest management principles appropriate for CSEC level.

Grade III (Pass) answer

Biological control is when you use natural enemies like the parasitic wasps to kill the aphids. Chemical control is when you spray pesticides on the crops to kill the pests. They are different because one uses living things and one uses chemicals.

An advantage of biological control is that it does not harm the environment like chemicals do. Chemicals can pollute the water and kill useful insects but biological control only kills the pest. A disadvantage is that biological control costs more money and is harder to find the right natural enemy to use.

Mark: 3/6 marks

Examiner commentary: This answer correctly identifies the basic distinction between biological and chemical control and provides a valid advantage (environmental safety). However, the explanation lacks depth—the candidate does not explain HOW parasitic wasps control aphids. The disadvantage cited (cost and difficulty sourcing natural enemies) is less commonly emphasized than the time lag issue, though it can be valid in some contexts. The response would benefit from more specific examples and clearer explanation of mechanisms. The phrase "only kills the pest" is imprecise—biological control reduces populations rather than eliminating them.

Grade V (Near miss) answer

Biological control is better for the environment than using chemicals because chemicals are dangerous. When you use parasitic wasps instead of malathion, you are protecting nature. The wasps will eat all the aphids and the plants will be healthy again.

The advantage is that it is organic and natural, so people prefer to buy organic food. The disadvantage is that the wasps might fly away to another farm and then you will not have any pest control.

Mark: 1/6 marks

Examiner commentary: This response reveals several common misconceptions. The candidate treats biological control as simply "better" without explaining what it actually IS or how it differs mechanically from chemical control. The statement that "wasps will eat all the aphids" is inaccurate—parasitic wasps typically parasitize aphids rather than eating them, and biological control rarely eliminates pests entirely. The advantage conflates biological control with organic farming marketing rather than explaining an actual biological or environmental benefit. The disadvantage about wasps flying away, while creative, is not a standard limitation recognized in agricultural science. To improve, the student must define terms precisely, explain actual mechanisms, and distinguish between marketing considerations and scientific principles.