FY12CE Biology common mistakes
FY12CE Biology · Understand the traps and how to avoid them.
When explaining enzyme activity, the candidate states that raising temperature always increases reaction rate, without noting that beyond the optimum the enzyme denatures and the rate falls sharply.
The candidate generalises from everyday experience that heat speeds up reactions and forgets that enzymes are proteins whose tertiary structure is disrupted by high temperature; graphs showing a temperature optimum are often misread as continuing upward.
What to do instead
For every enzyme graph, identify the optimum and describe both sides: rising rate due to more kinetic energy and successful collisions, then falling rate due to denaturation of the active site. Practise sketching and annotating the curve with these two phases.
In genetics problems, the candidate writes gamete genotypes without halving the chromosome number, for example giving AB and ab from a parent of genotype AaBb but also listing AaBb as a gamete.
The candidate confuses the diploid parental genotype with haploid gametes and does not consistently apply the principle that gametes carry one allele per gene; this leads to incorrect Punnett squares and ratio answers.
What to do instead
Before drawing a Punnett square, explicitly write the parent genotype, then list gametes by taking one allele from each gene pair. Check that each gamete has half the number of letters of the parent genotype. Use a systematic grid (FOIL for two genes) to avoid missing combinations.
The candidate describes natural selection as an organism deliberately changing to suit its environment, or says that individuals adapt during their lifetime and pass the change on.
Everyday language uses 'adapt' for individual adjustment, and Lamarckian inheritance is intuitive; the candidate does not separate random variation, differential survival, and heritable change in allele frequencies across generations.
What to do instead
Use a strict four-step template for every natural selection answer: (1) variation already exists in the population, (2) a selection pressure favours some variants, (3) those individuals survive and reproduce more, (4) allele frequencies in the population change over generations. Explicitly state that mutation is random and not directed by need.
When asked about transport in plants, the candidate says water and minerals travel in the phloem and sugars in the xylem, or states that transpiration is an active process requiring ATP.
The two vascular tissues are taught together and their functions are easily swapped; transpiration is driven by evaporation and cohesion-tension, but the candidate associates all movement with energy-consuming pumps.
What to do instead
Build a two-column comparison table: xylem (dead, lignified, water and mineral ions upward, passive, driven by transpiration pull) versus phloem (living, sieve tubes and companion cells, sugars and amino acids, translocation, energy from companion cells). Recite the table before answering any transport question.
In ecology questions on energy flow, the candidate calculates the energy passed to the next trophic level as 100% or as 50%, or draws a pyramid of energy with the apex wider than the base.
The candidate does not apply the typical 10% transfer efficiency and confuses biomass or numbers with energy; heat loss through respiration is overlooked.
What to do instead
Memorise that only about 10% of energy at one trophic level is incorporated into the next, with the rest lost as heat in respiration, in uneaten parts, and in excretory products. Always draw energy pyramids with the widest bar at the producer level and label the loss at each step.
When describing DNA replication or protein synthesis, the candidate mixes up transcription and translation, placing transcription in the cytoplasm of eukaryotes or pairing DNA bases with amino acids directly.
The two stages are taught as a sequence but the candidate memorises phrases without the location and template for each; the role of mRNA as an intermediate is not secure.
What to do instead
Write a one-line summary for each: transcription makes mRNA from a DNA template in the nucleus; translation makes a polypeptide from mRNA at the ribosome, using tRNA to bring amino acids. Draw the flow DNA → mRNA → polypeptide with locations labelled, and practise identifying which stage a given description belongs to.
In monohybrid and dihybrid crosses, the candidate gives a genotypic ratio when the question asks for a phenotypic ratio, or reports 9:3:3:1 without stating the phenotypes.
The candidate performs the Punnett square correctly but does not read the final instruction carefully, and does not translate genotypes into observable traits, especially when dominance is not complete.
What to do instead
Before writing the answer, underline the words 'phenotypic' or 'genotypic'. After completing the square, group offspring by observable trait and assign a phenotype to each class. For dihybrid crosses, list the four phenotype classes explicitly with the 9:3:3:1 ratio.
When explaining speciation, the candidate says that two populations become different species simply because they live in different places, without mentioning reproductive isolation or the accumulation of genetic differences.
The candidate equates geographical separation with speciation and omits the requirement that gene flow must stop and that isolating mechanisms must arise, so the answer is incomplete for full marks.
What to do instead
Use the sequence: geographical isolation → no gene flow → independent mutation and selection → genetic divergence → reproductive isolation (for example, incompatible mating times or infertile hybrids) → new species. State that isolation alone is not sufficient; reproductive isolation is the criterion.
In questions on the mammalian heart or gas exchange, the candidate states that arteries always carry oxygenated blood and veins always carry deoxygenated blood, or that blood in the left side of the heart is deoxygenated.
The candidate learns a simplified rule without the pulmonary exception and does not trace the double circulation from the body to the right side, to the lungs, and back to the left side.
What to do instead
Define arteries and veins by direction of flow relative to the heart, not by oxygen content, and give the pulmonary artery and pulmonary vein as the counterexamples. Trace the path of a red blood cell on a diagram, labelling oxygenated and deoxygenated segments at each step.
In ecology questions on the carbon cycle, the candidate omits respiration and decomposition as carbon dioxide sources and lists only combustion and photosynthesis.
Combustion and photosynthesis are the most frequently mentioned processes in media and introductory lessons, so the candidate recalls those first and forgets that all living organisms respire and that decomposers release carbon dioxide.
What to do instead
List all carbon dioxide sources and sinks explicitly: sources are respiration by plants, animals and microorganisms, decomposition, and combustion of fossil fuels; sinks are photosynthesis and ocean dissolution. Practise drawing the carbon cycle with at least six labelled arrows before answering.