IGCSE Science Exam Questions by Topic

A student examines a flower and records: petals are small and green, there is no scent, the anthers hang outside the flower on long filaments, and the stigma is large and feathery and hangs outside the flower. Identify, with reasons, whether this flower is insect-pollinated or wind-pollinated, and describe what happens after a pollen grain from this species lands on a compatible stigma.

1. List the features given: small green (not brightly coloured) petals, no scent, anthers outside the flower on long filaments, a large feathery stigma outside the flower.
2. Compare each feature to the two pollination syndromes: small dull petals and no scent rule out attracting insects; anthers hanging outside the flower on long filaments releases pollen freely into the air; a large feathery stigma outside the flower is adapted to catch airborne pollen grains as they drift past.
3. State the conclusion with the reason: the flower is wind-pollinated, because every listed feature increases the chance of pollen being released into, and caught from, the air rather than attracting an animal pollinator.
4. Describe fertilisation as a sequence: the pollen grain germinates on the stigma and grows a pollen tube down the style towards an ovule in the ovary.
5. Continue the sequence: the pollen tube nucleus and the male gamete nucleus move down the tube to the ovule, and the male gamete nucleus fuses with the egg cell nucleus to form a zygote.
6. Final answer: this is a wind-pollinated flower (dull petals, no scent, exposed anthers and feathery stigma); after pollination, a pollen tube grows to the ovule and the male gamete nucleus fuses with the egg cell nucleus, forming a zygote that develops into a seed.