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Homeostasis and ResponsePhototropismPlant responsesAuxin

AQA GCSE · Question 03.2.1 · Homeostasis and Response

Figure 5Experiment 1ShootSeedDampcotton woolLightExperiment 2Light-proofcardboardbox

A student investigated the effect of one-sided light on the growth of plant seedlings as shown in Figure 5. Which diagram shows what the seedling in Experiment 1 would look like after 12 hours?

Answer options:

A.

<svg width='100' height='120' viewBox='0 0 100 120'><ellipse cx='50' cy='110' rx='40' ry='10' fill='#f0e6d2'/><path d='M 50,100 C 60,80 70,60 75,40' stroke='green' stroke-width='3' fill='none'/><circle cx='50' cy='105' r='4' fill='brown'/></svg>

B.

<svg width='100' height='120' viewBox='0 0 100 120'><ellipse cx='50' cy='110' rx='40' ry='10' fill='#f0e6d2'/><path d='M 50,100 C 50,80 50,60 50,40' stroke='green' stroke-width='3' fill='none'/><circle cx='50' cy='105' r='4' fill='brown'/></svg>

C.

<svg width='100' height='120' viewBox='0 0 100 120'><ellipse cx='50' cy='110' rx='40' ry='10' fill='#f0e6d2'/><path d='M 50,100 C 40,80 30,60 25,40' stroke='green' stroke-width='3' fill='none'/><circle cx='50' cy='105' r='4' fill='brown'/></svg>

D.

<svg width='100' height='120' viewBox='0 0 100 120'><ellipse cx='50' cy='110' rx='40' ry='10' fill='#f0e6d2'/><path d='M 50,100 C 50,120 50,140 50,160' stroke='green' stroke-width='3' fill='none'/><circle cx='50' cy='105' r='4' fill='brown'/></svg>

How to approach this question

Experiment 1 has light coming from one side. Plant shoots exhibit positive phototropism, meaning they grow towards a light source. This is caused by the hormone auxin accumulating on the shaded side, causing cells there to elongate more. Select the diagram that shows the shoot bending towards where the light would be.

Full Answer

A.<svg width='100' height='120' viewBox='0 0 100 120'><ellipse cx='50' cy='110' rx='40' ry='10' fill='#f0e6d2'/><path d='M 50,100 C 60,80 70,60 75,40' stroke='green' stroke-width='3' fill='none'/><circle cx='50' cy='105' r='4' fill='brown'/></svg>✓ Correct
In Experiment 1, the seedling is exposed to light from one side. Plant shoots are positively phototropic, which means they grow towards light. The hormone auxin, which controls growth, moves to the shaded side of the shoot. This causes the cells on the shaded side to grow longer and faster than the cells on the lighted side, making the shoot bend towards the light source.

Common mistakes

✗ Choosing the diagram for Experiment 2 (growing straight up). ✗ Choosing the diagram showing negative phototropism (growing away from light).
03.1All questions03.2.2

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