Plant breeders have genetically altered characteristics of a few hundred wild angiosperm species through artificial selection for over 10,000 years, converting them into the crops we grow today.

The diversity and speed with which we may change plants have expanded tremendously as a result of genetic engineering. In Chapters 29 and 30, we looked at plant reproduction from an evolutionary standpoint, tracing the origins of land plants back to algal predecessors.

Because angiosperms are the most important group of plants in agricultural and most other terrestrial ecosystems, we will look in-depth at their reproductive biology in this chapter.

The attached image shows an idealized flower.

Flowers, double fertilization, and fruits are all essential components of the angiosperm life cycle.

All plants have an alternation of generations in which multicellular haploid (n) and multicellular diploid (2n) generations alternately generate each other (see Figure 13.6b). By meiosis, the diploid plant, the sporophyte, generates haploid spores. Mitosis divides these spores, resulting in multicellular gametophytes, the male and female haploid plants that generate gametes (sperm and eggs). Fertilization, or the union of gametes, produces a diploid zygote, which divides by mitosis and gives rise to a new sporophyte. The sporophyte is the main generation in angiosperms: It

The flowers, the sporophytic structure of angiosperms adapted for sexual reproduction, are generally made up of four different types of floral organs: carpels, stamens, petals, and sepals (as shown in the image attached). These organs resemble concentric whorls when viewed from above. Carpels make up the first (innermost) whorl, stamens make up the second, petals make up the third, and sepals make up the fourth (outermost) whorl.

All are connected to a section of the stem known as the receptacle. Flowers are fixed stems that stop growing after the bloom and fruit have developed.

Carpels and stamens are sporophylls—reproduction-specialized modified leaves; sepals and petals are sterile modified leaves.

The stigma is a sticky feature at the apex of the style that catches pollen. The ovary contains one or more ovules, which develop into seeds when fertilized; the number of ovules varies depending on the species. Although they bloom in the image attached above only have one carpel, many species have several carpels. The carpels are united in most species, resulting in a complex ovary with two or more chambers, each holding one or more ovules.

• The term pistil can refer to a single carpel or two or more joined carpels (as shown in the image attached above).

The angiosperm life cycle is characterized by flowers, double fertilization, and fruits.

Angiosperm reproduction is characterized by a generational switch between a multicellular diploid sporophyte generation and a multicellular haploid gametophyte generation. Flowers, which are generated by the sporophyte, are used for sexual reproduction.

Sepals, petals, stamens, and carpels are the four floral organs.

The flower bud is shielded by sepals. Pollinators are attracted by the petals.

Stamens produce anthers, which contain haploid microspores that mature into pollen grains bearing a male gametophyte. In their swelling bases, carpels contain ovules (immature seeds). Megas grow into embryo sacs (female gametophytes) within the ovules.

Megaspores grow into embryo sacs (female gametophytes) within the ovules.

Pollination is the placement of pollen on the stigma of a carpel, which occurs before fertilization.

Following pollination, the pollen tube releases two sperm into the female gametophyte. Double fertilization requires two sperm, which is a procedure in which one sperm fertilizes the egg, creating a zygote and, eventually, an embryo, while the other sperm does not.

• The term stamen (microsporophyll) is made up of a stalk called the filament and a terminal component called the anther, which contains chambers called microsporangia (polysporangia).

Megaspores grow into embryo sacs (female gametophytes) within the ovules.

Pollination is the placement of pollen on the stigma of a carpel, which occurs before fertilization.

Following pollination, the pollen tube releases two sperm into the female gametophyte. Double fertilization requires two sperm, which is a procedure in which one sperm fertilizes the egg, creating a zygote and, eventually, an embryo, while the other sperm does not.

A seed is made up of a latent embryo and a food supply stored in the endosperm or the cotyledons. Seed dormancy guarantees that seeds germinate only under ideal conditions for seedling survival. Environmental signals, such as temperature or illumination changes, are frequently required to break dormancy.

The contained seeds are protected by the fruit, which assists in wind dispersal or the attraction of seed-dispersing animals.

Flowering plants reproduce sexually, asexually, or both sexually and asexually. Asexual reproduction, often known as vegetative reproduction, allows successful plants to multiply rapidly. The majority of the genetic diversity that allows for evolutionary adaptation is generated through sexual reproduction.

Plants have evolved a variety of mechanisms to avoid self-fertilization, including male and female flowers on separate individuals, nonsynchronous production of male and female parts within a single flower, and self-incompatibility reactions in which pollen grains bearing an allele identical to one in the female are rejected.

Plants may be cloned from single cells, which can then be genetically modified before being released into the wild.

Crops are modified through breeding and genetic engineering.

Hybridization of various plant types and even species is frequent in nature and has been exploited by ancient and modern breeders to introduce new genes into crops. Plant breeders choose offspring with the desired characteristics after successfully hybridizing two plants.

Genes from unrelated species are inserted into plants using genetic engineering. Genetically modified (GM) plants have the potential to improve the quality and quantity of food available throughout the world, as well as play a growing role in biofuel production.

Concerns have been raised regarding the unknown hazards of releasing genetically modified organisms into the environment.