Question

how a flower with single carpel produce many seed

Answer 1

Fertilization of an egg within a carpel by a pollen grain from another flower results in seed development within the carpel.

Answer 2

Answer:

Flowers with one carpel only require fertilization of one of the two ovules to produce fruit. In contrast, species with multiple fused carpels require fertilization of a smaller proportion of the total ovules within a flower for fruit development.