Question

Mention two strategies evolved in flowers to prevent self-pollination in flowers.

Answer 1

For self-pollination, a flower should be bisexual. Examples of several types of bisexual flowers are orchids, sunflowers, dandelions. When pollen grain from the same plant arrives at the stigma of a flower of the same flower or to another flower of the same plant is called self-pollination.

Complete answer:
Mechanical systems
-In mechanical systems of delayed selfing, physical changes within the positioning of floral structures during anthesis end in delayed autonomous self-pollination.
-Changes within the positions of reproductive organs occur during a sort of way to market delayed selfing. As an example, in numerous species within the Malvaceae, the sorts of unpollinated flowers curve backward because the flower ages, creating contact between stigmas and monadelphous stamens that surround the styles.
-Dichogamy which suggests temporal separation of stigma receptivity and pollen presentation is present in many angiosperms during which it's going to function to stop self-fertilization or pollen–pistil interference.
-A developmental mechanism of delayed selfing can occur when male and feminine phases partially overlap.
-In incomplete protogyny, stigmas become receptive first, allowing cross-fertilization. This results, another dehisce while stigmas are still receptive, causing delayed selfing to occur.
Physiological mechanisms
-Physiological mechanisms include changes in self-incompatibility (SI) that cause delayed selfing.
-SI systems generally prevent self-fertilization; however, a temporal breakdown in expression during anthesis, or transient SI, is often a mechanism for delayed self-fertilization, as reported in Leptosiphon jepsonii.
-Transient SI is amid reduced herkogamy in Leptosiphon and progressive stigma curvature in Campanula, both of which promote late deposition of self-pollen as flowers result in self-compatibility.

Note: -When the pollination occurs before the flower bloom such types of pollination are pure self-pollination is called cleistogamy. Example - chasmogamous flower. Pollination can take place by air, water, wind, rain, bees, birds, bats.
The disadvantage of self-pollination
-This lack of variation.
-This can lead to inbreeding depression caused by a deleterious recessive mutation.
-The genetic defects in self-pollination plants cannot be eliminated by genetic recombination.