HOTS Science Primary 5 Cycles

Siti wants to investigate whether a certain chilli plant can undergo self-pollination. She covers all the flowers on the plant with fine mesh bags before any pollen is released. The mesh bags prevent insects, wind and all other external agents from reaching the flowers. She leaves the bags on for the entire flowering period. At the end of the experiment, she finds that NO seeds have formed in any of the bagged flowers. She concludes: "The chilli plant cannot self-pollinate." Which of the following best identifies the flaw in Siti's experimental design AND explains what correct conclusion can be drawn from her results?

A The experiment is flawed because the mesh bags prevented both self-pollination and cross-pollination by blocking all pollen transfer, so the absence of seeds only shows that pollen transfer of some kind was needed — it does not prove that self-pollination specifically cannot occur.
B The experiment is flawed because mesh bags also block sunlight and carbon dioxide, preventing photosynthesis in the petals, which is necessary for seed development, so the absence of seeds was caused by a lack of nutrients rather than a lack of pollination.
C The experiment is valid because mesh bags only block insects, and since chilli plants rely entirely on insect pollination, the absence of seeds correctly proves that self-pollination did not occur under natural conditions.
D The experiment is flawed because Siti should have used plastic bags instead of mesh bags; plastic bags would allow self-pollination to occur while blocking cross-pollination by insects, giving a fair test of whether self-pollination is possible.
Show Worked Solution

Worked Solution

Step 1: Identify what the experiment was designed to test Siti wanted to determine whether chilli plants can self-pollinate. To test this, she needed to exclude cross-pollination (pollen from other plants/flowers) while leaving open the possibility of self-pollination (pollen from the same flower or the same plant). Step 2: Identify the critical flaw The mesh bags were designed to block external agents (insects, wind). However, the bags also physically prevented the anthers of each flower from releasing pollen onto the stigma of the same flower. Fine mesh bags block all pollen transfer — both cross-pollination AND self-pollination. Siti unintentionally blocked the very process she was trying to test. Step 3: Determine what the result actually shows The absence of seeds shows only that some form of pollen transfer was necessary for seed formation — it does not distinguish between self-pollination and cross-pollination. We cannot conclude that self-pollination is impossible, only that completely blocking all pollen transfer prevented seed formation. Step 4: Match to the correct option Option A correctly identifies the flaw (mesh blocks all pollen, not just cross-pollen) and correctly limits the conclusion to "pollen transfer of some kind was needed", avoiding the unsupported leap to "self-pollination cannot occur". A proper experiment would require an unbagged control group and ideally a setup that allows anthers to shed pollen onto the same flower's stigma while blocking external pollen.

Correct answer: The experiment is flawed because the mesh bags prevented both self-pollination and cross-pollination by blocking all pollen transfer, so the absence of seeds only shows that pollen transfer of some kind was needed — it does not prove that self-pollination specifically cannot occur.

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