Advanced Science Primary 3 Cycles

Ahmad set up a fair test to compare the development of frog eggs in three containers. He placed 10 frog eggs in each container: • Container 1: pond water at 25°C, in sunlight • Container 2: pond water at 25°C, in darkness • Container 3: clean tap water at 25°C, in sunlight After two weeks, Container 1 had the most tadpoles that survived and grew well. Container 2 had fewer tadpoles, and Container 3 had the fewest. Which conclusion is best supported by these results?

A Both sunlight and the type of water affect the survival and growth of tadpoles, because Container 1 had both sunlight and pond water while Container 3 lacked the nutrients in pond water and Container 2 lacked sunlight.
B Sunlight is the only factor that affects tadpole survival, because Containers 1 and 2 had the same water but different amounts of sunlight, and Container 1 did better.
C The type of water is the only factor that affects tadpole survival, because Containers 1 and 3 had the same sunlight but different water, and Container 1 did better.
D Temperature is the most important factor for tadpole survival, because all three containers were kept at 25°C and all produced some tadpoles.
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Worked Solution

Step 1 – Identify the variables: Independent variables being tested: (1) sunlight vs darkness; (2) pond water vs tap water. Controlled variable: temperature (25°C in all three). Step 2 – Compare Containers 1 and 2: Same pond water, different light → Container 1 (sunlight) did better than Container 2 (darkness). This shows sunlight helps tadpole survival. Step 3 – Compare Containers 1 and 3: Same sunlight, different water → Container 1 (pond water) did better than Container 3 (tap water). This shows pond water (which contains nutrients and microorganisms) helps tadpole survival. Step 4 – Combine both comparisons: Since both comparisons show an effect, BOTH sunlight and water type affect survival. Option A correctly states that both factors matter. Options B and C each commit the error of drawing a conclusion from only one comparison while ignoring the other.

Correct answer: Both sunlight and the type of water affect the survival and growth of tadpoles, because Container 1 had both sunlight and pond water while Container 3 lacked the nutrients in pond water and Container 2 lacked sunlight.

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