This free quiz has 10 real AQA A-level Biology exam questions on stimuli, receptors and heart rate (28 marks, about 35 minutes). It marks itself: the tick-box and table questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.6.1)
light sensitivity and how photoreceptors connect to neurones in the retina
why a fovea packed with cones lets an eagle see its prey in detail
the structure of a Pacinian corpuscle and how it produces a generator potential
naming the behaviour shown in a choice chamber and suggesting its advantage
how IAA affects cell wall plasticity and the growth of stem segments
describing IAA results for shoots and predicting the effect on roots
how chemoreceptors and the cardiac centre raise heart rate, and how a drug that blocks acetylcholine does too
myogenic stimulation and how contraction of the atria and ventricles is coordinated (5 marks)
How to use it
Write each written answer in full before you open the mark scheme, then tick only the points you really made. Use the exact terms examiners look for: impulses (never signals or messages), sodium ions rather than sodium, and cell elongation rather than growth. For heart rate, follow the whole chain from receptor to cardiac centre to sympathetic or parasympathetic neurones to the SAN.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Taxis, not kinesis. The most common wrong names for directional movement towards or away from light were “kinesis”, “tropism” and “phototropism”. Vague advantages such as “to survive” or “to get more favourable conditions” scored nothing, and some said animals moved towards light “for photosynthesis”.
✔ Gains credit: directional movement in response to light is a (positive or negative photo)taxis, with a specific advantage such as being less likely to be seen or eaten by predators.
Tips produce IAA. A significant number of students said the shoot tip “contains” IAA, which was not credited, and few mentioned IAA diffusing. Some wrote that IAA “accumulates” on the shaded side without the idea of movement.
✔ Gains credit: the tip produces IAA, which diffuses down into the shoot; in directional light, IAA moves to the shaded side.
Cell elongation, not growth. Only the better answers said “cell elongation”; “more growth” or “more elongation” was not credited. Many said IAA causes cell elongation without linking it to cell wall plasticity, and some said roots would get shorter.
✔ Gains credit: IAA increases cell wall plasticity, allowing more cell elongation in shoots, while high IAA concentrations inhibit growth in roots.
Generator potentials. Some students wrote “stretch-mediated membrane” or “stretch-mediated response”. Many were held to 2 marks for writing “sodium” rather than “sodium ions”, and few said the ions diffuse in, writing “influx” instead.
✔ Gains credit: pressure deforms stretch-mediated sodium ion channels so they open, sodium ions diffuse in, and the membrane depolarises to give a generator potential.
Red-sensitive, not red, cones. Writing “red”, “green” or “blue” cones or pigments, without “sensitive”, was rejected. Some said rods are involved in colour vision or that cones absorb different colours rather than different wavelengths. Only 2.6% of students gained full marks on one such question.
✔ Gains credit: colour vision uses three types of cone, each with a different pigment absorbing a different range of wavelengths; other colours are seen when more than one type of cone is stimulated, e.g. more absorption by red-sensitive than green-sensitive cones.
Impulses to the SAN. Some students said chemoreceptors detect a rise in pH or respond only to oxygen. “An impulse”, “signals” and “messages” lost marks, and relatively few mentioned the SAN.
✔ Gains credit: chemoreceptors detect a rise in CO₂ (or H⁺, a fall in pH) and send more impulses to the cardiac centre in the medulla, which sends more impulses along sympathetic neurones (or fewer along the parasympathetic) to the SAN.
SAN, then AVN delay. A significant minority left out that impulses from the SAN make the atria contract, and the delay at the AVN was not always included. Weaker answers confused the SAN with the AVN or got the pathway through the bundle of His wrong.
✔ Gains credit: the SAN releases a wave of electrical activity so the atria contract; the AVN passes it on after a short delay, through the bundle of His and Purkyne tissue, so the ventricles contract from the bottom upwards.
Keep practising
The AQA 3.5 self-marking quizzes: Photosynthesis · Respiration · Energy and ecosystems · Nutrient cycles
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.