**1. Flower Structure and Morphology:**
– Etymology of the term ‘flower’ and its historical origins
– Flower morphology comprising vegetative and reproductive parts
– Detailed structures of a typical flower including calyx, corolla, androecium, and gynoecium
– Formation of perianth through calyx and corolla
– Variations in floral structure among plant species
**2. Development and Transition of Flowers:**
– Flowers develop from modified shoots or axes
– Transition to flowering influenced by cues like hormones and environmental changes
– Vernalization and florigen as key signals for inducing flowering
– Irreversible nature of flower development once initiated
– Floral primordia differentiation due to biochemical changes
**3. Reproductive Functions of Flowers:**
– Roles of androecium and gynoecium in pollen production and ovule development
– Heterosporous nature of flowering plants producing microspores and megaspores
– Endosporic development of gametophytes inside spores
– Importance of flowers in facilitating reproduction at individual and species levels
– Significance of perfect flowers with pistils and stamens in most species
**4. Pollination Mechanisms in Flowers:**
– Biotic and abiotic pollination methods involving insects, animals, wind, and water
– Cross-pollination for genetic variation and species survival
– Self-pollination for reproductive success but limited genetic diversity
– Coevolution between flowers and pollinators over time
– Strategies used by flowers to attract specific pollinators for effective pollen transfer
**5. Flower Pollination and Fertilization:**
– Promotion of cross-pollination by flowers for genetic complementation
– Outcrossing benefits like hybrid vigor and masking of deleterious mutations
– Consequences of inbreeding depression from self-pollination
– Fertilization process involving plasmogamy, karyogamy, and double fertilization in angiosperms
– Seed development from zygote formation to the nourishment of the developing embryo
A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.
Most flowering plants depend on animals, such as bees, moths, and butterflies, to transfer their pollen between different flowers, and have evolved to attract these pollinators by various strategies, including brightly colored, conspicuous petals, attractive scents, and the production of nectar, a food source for pollinators. In this way, many flowering plants have co-evolved with pollinators to be mutually dependent on services they provide to one another—in the plant's case, a means of reproduction; in the pollinator's case, a source of food.
When pollen from the anther of a flower is deposited on the stigma, this is called pollination. Some flowers may self-pollinate, producing seed using pollen from a different flower of the same plant, but others have mechanisms to prevent self-pollination and rely on cross-pollination, when pollen is transferred from the anther of one flower to the stigma of another flower on a different individual of the same species. Self-pollination happens in flowers where the stamen and carpel mature at the same time, and are positioned so that the pollen can land on the flower's stigma. This pollination does not require an investment from the plant to provide nectar and pollen as food for pollinators. Some flowers produce diaspores without fertilization (parthenocarpy). After fertilization, the ovary of the flower develops into fruit containing seeds.
Flowers have long been appreciated by humans for their beauty and pleasant scents, and also hold cultural significance as religious, ritual, or symbolic objects, or sources of medicine and food.