Question 1

Confusing the biological purpose of adding an oil layer in different laboratory experiments.

Accepted Answer

Remember that in yeast respiration experiments, oil is added to prevent oxygen entry (ensuring anaerobic conditions). In transpiration/potometer experiments, oil is added to the top of the cylinder to prevent water evaporating directly from the container.

Question 2

Failing to convert units (e.g., millimeters to micrometers) before dividing in magnification calculations.

Accepted Answer

Always measure the line or image in millimeters, multiply by 1000 to convert to micrometers ($ \mu\text{m} $), and only then divide by the actual size or magnification.

Question 3

Writing that skin capillaries 'dilate' or 'constrict' during warm or cold temperature regulation.

Accepted Answer

Capillaries do not have muscular walls and cannot constrict or dilate. Always specify that arterioles widen (vasodilation) or narrow (vasoconstriction), which alters blood flow to the capillaries near the skin surface.

Question 4

Suggesting that repeating an experiment makes it more 'accurate'.

Accepted Answer

Repeating experiments and calculating a mean increases 'reliability' and helps identify anomalies. To improve 'accuracy', suggest using more precise, objective measuring instruments (such as a colorimeter, standard color charts, or a digital syringe).

Question 5

Believing that plants only begin to respire in the dark when photosynthesis stops.

Accepted Answer

Respiration is a continuous process that occurs in all living plant cells 24/7. Plants photosynthesize only in the light, but they respire constantly.

Question 6

Stating that algae 'use up' oxygen directly during the process of eutrophication.

Accepted Answer

Explain that algae block light, causing submerged plants and algae to die. Decomposers (bacteria and fungi) then multiply rapidly, and it is their aerobic respiration that uses up the dissolved oxygen in the water.

Question 7

Calculating genetic probabilities of a trait without factoring in the probability of offspring sex.

Accepted Answer

If a question asks for the probability of a couple having a 'male child with the trait,' find the Punnett square trait probability (e.g., 0.75) and multiply it by the sex probability (always 0.5) to get the final uncompounded probability (0.375 or 3/8).

Question 8

Writing 'nutrients' or general element names instead of specific mineral ions in plant nutrition answers.

Accepted Answer

Always name the specific mineral ion: use 'nitrates' (for amino acids/proteins) and 'magnesium' (for chlorophyll) instead of generic terms like 'nutrients', 'nitrogen', or 'magnesium metal'.

Question 9

Failing to state the direction of diffusion when explaining substance exchange across the placenta.

Accepted Answer

Be explicit about movement direction: state that oxygen and glucose diffuse from maternal blood to fetal blood, whereas carbon dioxide and urea diffuse from fetal blood to maternal blood.

Question 10

Describing animal cells as 'plasmolysed' when placed in hypertonic/concentrated salt solutions.

Accepted Answer

The term 'plasmolysed' applies strictly to plant cells because they have cell walls. Animal cells shrivel, crenate, or shrink when they lose water by osmosis.

ฉบับ	เวลา	คะแนน	จำนวนข้อ	น้ำหนักคะแนน	ประเภทคำถาม
Paper 1B / 1BR (Core Biology)	2ชม.	110	11	61.1%	Multiple Choice, Structured and Short Answer, Practical / Experimental Design, Mathematical / Calculation
Paper 2B / 2BR (Advanced Biology)	1ชม. 15นาที	70	6	38.9%	Comprehension Passage, Structured and Short Answer, Practical / Experimental Design, Mathematical / Calculation

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