Class 12 common misconceptions

Does pollination produce a seed immediately? — Tempting mistake: “Once pollen lands on the stigma, fertilisation is complete.”

1 worked visual example · 8 “If your child says…” checks

Where does fertilisation usually happen? — Tempting mistake: “Fertilisation usually occurs in the uterus because that is where the baby develops.”

1 worked visual example · 8 “If your child says…” checks

Do all contraceptive methods reduce STI transmission? — Tempting mistake: “Any method that prevents pregnancy also reduces the chance of a sexually transmitted infection.”

1 worked visual example · 8 “If your child says…” checks

Can dominance tell you the frequency of an allele? — Tempting mistake: “A dominant allele must be carried by most members of the population.”

1 worked visual example · 8 “If your child says…” checks

Does a cell transcribe all its DNA at once? — Tempting mistake: “A cell must copy its whole genome into RNA whenever it needs a protein.”

1 worked visual example · 8 “If your child says…” checks

Does a bacterium evolve because it needs to survive? — Tempting mistake: “An antibiotic makes each bacterium develop the resistance it needs.”

1 worked visual example · 8 “If your child says…” checks

Does receiving antibodies build long-term immune memory? — Tempting mistake: “Ready-made antibodies give lasting immunity because the body now has the antibodies it needs.”

1 worked visual example · 8 “If your child says…” checks

Does fermentation always make the same product? — Tempting mistake: “Every microbe that ferments sugar produces alcohol.”

1 worked visual example · 7 “If your child says…” checks

Does antibiotic survival prove the target gene is present? — Tempting mistake: “Every colony that grows on the antibiotic must contain the desired DNA insert.”

1 worked visual example · 8 “If your child says…” checks

Does Bt maize protect against every insect? — Tempting mistake: “A crop carrying a Bt gene resists all insect pests.”

1 worked visual example · 8 “If your child says…” checks

Does a population grow exponentially forever? — Tempting mistake: “A population that doubles once should keep doubling indefinitely.”

1 worked visual example · 8 “If your child says…” checks

Does all the energy fixed by plants become new biomass? — Tempting mistake: “All of the energy that plants fix by photosynthesis stays in their new biomass.”

1 worked visual example · 8 “If your child says…” checks

Can species count alone describe biodiversity? — Tempting mistake: “Two habitats with the same number of species have equal biodiversity in every respect.”

1 worked visual example · 8 “If your child says…” checks

Does molarity stay constant when a solution is warmed? — Tempting mistake: “The molarity remains unchanged because the amount of solute stays the same.”

1 worked visual example · 8 “If your child says…” checks

Does the anode always have a negative sign? — Tempting mistake: “Every anode is negative because the anode is negative in a galvanic cell.”

1 worked visual example · 8 “If your child says…” checks

Why are the rates for two reactants different? — Tempting mistake: “In 2A + B → products, A and B disappear at the same rate.”

2 worked visual examples · 5 “If your child says…” checks

Is every d-block element a transition element? — Tempting mistake: “Zinc is a transition element because it sits in the d block.”

1 worked visual example · 6 “If your child says…” checks

Is coordination number the number of ligands? — Tempting mistake: “In [Co(en)₃]³⁺, the coordination number is 3 because there are three ligands.”

1 worked visual example · 6 “If your child says…” checks

Should chlorobenzene react like chloroethane? — Tempting mistake: “Chlorobenzene readily substitutes chloride under the same conditions as chloroethane.”

1 worked visual example · 6 “If your child says…” checks

Is phenol as weak an acid as ethanol? — Tempting mistake: “Phenol and ethanol are equally acidic because both contain an –OH group.”

1 worked visual example · 6 “If your child says…” checks

Will every carbonyl compound give a silver mirror? — Tempting mistake: “Both ethanal and propanone give a positive Tollens test because both have C=O.”

1 worked visual example · 6 “If your child says…” checks

Do carbon atoms determine the amine class? — Tempting mistake: “Ethylamine is secondary because its ethyl group has two carbons.”

1 worked visual example · 5 “If your child says…” checks

Is every disaccharide made with glucose reducing? — Tempting mistake: “Sucrose must be reducing because one of its units is glucose.”

1 worked visual example · 6 “If your child says…” checks

Does every function have an inverse function? — Tempting mistake: “Squaring can be undone by square root for every real input.”

1 worked visual example · 8 “If your child says…” checks

Does inverse sine always recover the original angle? — Tempting mistake: “sin⁻¹(sin 150°) is 150°.”

1 worked visual example · 8 “If your child says…” checks

Can you reverse a matrix product? — Tempting mistake: “If A and B are square, AB must equal BA.”

1 worked visual example · 8 “If your child says…” checks

What happens to the determinant when every entry doubles? — Tempting mistake: “Doubling every entry doubles the determinant.”

1 worked visual example · 8 “If your child says…” checks

Does a continuous curve always have a tangent slope? — Tempting mistake: “Every continuous function is differentiable.”

1 worked visual example · 8 “If your child says…” checks

Does a zero derivative guarantee a maximum or minimum? — Tempting mistake: “Every point where f′(x) = 0 is a turning point.”

1 worked visual example · 8 “If your child says…” checks

Does the power integration rule work for 1/x? — Tempting mistake: “Integrating x⁻¹ gives x⁰/0 by the usual power rule.”

1 worked visual example · 8 “If your child says…” checks

Can areas above and below the x-axis cancel? — Tempting mistake: “The area between y = x and the x-axis from −1 to 1 is zero.”

1 worked visual example · 8 “If your child says…” checks

Does an initial value only check a solution? — Tempting mistake: “All curves y = Ceˣ solve y′ = y, so any one works when y(0) = 2.”

1 worked visual example · 8 “If your child says…” checks

Does a zero dot product mean a vector is zero? — Tempting mistake: “If two vectors have dot product 0, at least one has length 0.”

1 worked visual example · 8 “If your child says…” checks

Must nonparallel lines meet in space? — Tempting mistake: “Two nonparallel lines always intersect.”

1 worked visual example · 8 “If your child says…” checks

Can you optimise using just one constraint at a time? — Tempting mistake: “A point is feasible if it satisfies at least one constraint.”

1 worked visual example · 5 “If your child says…” checks

Can you swap the event and the condition? — Tempting mistake: “The probability of a heart given red equals the probability of red given a heart.”

1 worked visual example · 8 “If your child says…” checks

Does zero enclosed charge mean zero field everywhere on a surface? — Tempting mistake: “If the net electric flux is zero, the electric field must vanish at every point of the surface.”

1 worked visual example · 8 “If your child says…” checks

Can the electric potential be zero while the field is nonzero? — Tempting mistake: “If electric potential is zero at a point, the electric field there must also be zero.”

1 worked visual example · 8 “If your child says…” checks

Is the same current through two resistors proof of the same voltage drop? — Tempting mistake: “Two resistors in series have identical voltage drops because they carry the same current.”

1 worked visual example · 8 “If your child says…” checks

Does a magnetic field push a moving charge along the field? — Tempting mistake: “A positive charge is pushed in the direction the magnetic field points.”

1 worked visual example · 8 “If your child says…” checks

Can you separate the north pole by cutting a magnet? — Tempting mistake: “Cutting a bar magnet in half gives one north pole and one south pole.”

1 worked visual example · 8 “If your child says…” checks

Will a stationary magnet keep inducing current? — Tempting mistake: “A strong magnet held inside a coil keeps inducing a current.”

1 worked visual example · 8 “If your child says…” checks

Can AC with zero average current still heat a resistor? — Tempting mistake: “A resistor on AC cannot heat because the current averages to zero.”

1 worked visual example · 8 “If your child says…” checks

Do higher-frequency electromagnetic waves travel faster in a vacuum? — Tempting mistake: “X-rays cross a vacuum faster than radio waves because their frequency is higher.”

1 worked visual example · 8 “If your child says…” checks

Do mirrors always form images you can catch on a screen? — Tempting mistake: “A screen behind a plane mirror can catch the image I see there.”

1 worked visual example · 8 “If your child says…” checks

Does a dark fringe mean the light's energy disappeared? — Tempting mistake: “Two waves destroy their energy when they make a dark fringe.”

1 worked visual example · 8 “If your child says…” checks

Can brighter light always release photoelectrons? — Tempting mistake: “Light below the threshold frequency ejects electrons if it is bright enough.”

1 worked visual example · 8 “If your child says…” checks

Is an emitted photon set by the upper energy level alone? — Tempting mistake: “The photon energy equals the atom's energy at the upper level.”

1 worked visual example · 8 “If your child says…” checks

Does half-life remove the same number of nuclei each time? — Tempting mistake: “If the first half-life removes an expected 800,000 of 1,600,000 nuclei, the next removes another 800,000.”

1 worked visual example · 8 “If your child says…” checks

Does a diode conduct as soon as any positive voltage appears? — Tempting mistake: “A silicon diode behaves like a short circuit at any forward voltage.”

1 worked visual example · 8 “If your child says…” checks