Welcome this video. In this video, we are going to talk about the importance of flowers in nature. We're going to see what are angiosperms, the parts of a flower, the types of flowers. We will focus on pollination and the importance of flowers in nature. Angiosperms are plants that produce seeds inside a protective chamber that it's called flower. The term comes from the Greek words angeion, that it's capsule or vessel, and sperma, that means seed. Gymnosperms plants, in the other side, produce seeds but these seeds are naked and not enclosed in a flower. Taken altogether, angiosperms are also called plants with real flowers. The Ukrainian botanist Katherine Esau, is internationally recognized for her work in plant anatomy. A field in which she was a pioneer. In 1989, she received the National Medal of Science which is the highest honor that United States give to scientists. Her books, Plant Anatomy and Anatomy of Seed Plants, have been basic texts for biology students in the last four decades. Flowers are the reproductive part of most plants. They share similar sexual structures and a non-reproductive structures called perianth. The productive or sexual structures can be a main structure that it's called stamen or androecium, and it's made of an anther and a filament. In the anther, we can find the pollen grains. In the other side, we have the female structure also called pistil or gynoecium made up by stigma, the style, and the carpel, also called ovary where a female cell is found. The non-sexual structure, the perianth is formed by sepals and the petals. Petals are a bright color. The set of petals form what is called corolla. The function of petals is to attract insects for pollination. The function of sepals which are normally of a green color is the protection of the bud before the flowers opened. But the perianth together with the nectary is very important to covering and protect the flowers in the early stages. In some occasions, flowers lack petals and are called apetalas. There are different types of flowers. Because on the previous page, we have seen that the male and female structures or parts of the flower are together in the same flower, and these are called bisexual flowers with both sexual structures together. But there are a lot of plants that have only sexual flowers: that means that they only have one sexual structure. Between or among these unisexual flowers, we can divide plants as dioecious or monoecious plants. Dioecious plants have male and female flowers on different individuals, so on different plants. Monoecious plants have female and male flowers on the same plant. On top, you have an example of dioecious plant which is papaya flowers, male and female, from different trees. Below, you have an example of monoecious plant like maize which have flowers on the same plant in the same individual. Within that pattern, we can found flowers occurring in many different forms with varying organ number, size, color, and shape as you can see in the different images presented in this slide. Pollination which is very important in the nature because it is the transfer of pollen grains from the anther of the male structure or flower to the stigma which is the female structure of a flower. In this transfer, we need to have a pollinating agent. This pollinating agent can be pollinators or animals or can be the wind. Then, we're talking about anemophilia. Anemophilous plants are those that the pollen is scattered by air. Almost all gymnosperms are anemophilous plants and also many poales including grasses, rushes, and sedges as you can see in the images. The feature of this anemophilous plants are that they lack a showy floral part, so the set of petals, the corolla is not very relevant. They are inconspicuous flowers. They also lack of a scent production. They have a reduced production of nectar as well and a huge production of pollen. There are different types of pollination because flowers have different sexual structures. We can talk about self-pollination and cross-pollination. In self-pollination, the pollen from the stamen of a flower is transferred to the stigma of another flower of the same plant. With that kind of pollination, there is no genetic variation and seeds usually are not viable or of quality. An example of plants that have self-pollination is Arabidopsis thaliana which is a model plant in Brassicales or common crops like wheat. The other type of pollination, cross-pollination, is based on the transfer of pollen from the stamen of one flower to the stigma of another flower in another plant, not in the same plant. With this kind of pollination, we have a greater genetic variation and seeds usually are of high quality. An example is maize. But how does a plant ensure that there are more chances of cross-pollination than self-pollination because we have been saying that with cross-pollination the plants have more genetic variation? When plants have unisexual flowers, the presence of dioecious plants avoids these self-pollination. But for bisexual flowers, we have self-incompatibility which is the recognition of pollen grains from the same plant and abortion of the pollination process. We can also have another type of ensuring that there are more chances of cross-pollination with time or size incompatibility. That is that male and female parts of a flower mature at different times or have a different size, and then self-pollination is avoided. Angiosperms are distinguished from the other seed plants because their flowers have remarkable features. They have stamens with two pair of pollen sacs, as you can see in the image, smaller size of the pollen, closed carpel enclosing the ovules preventing self-fertilization, and a fast dispersal of seeds because they are into fruit. They have evolved faster into different species so they largely dominate terrestrial ecosystems. Angiosperms are the most diverse group of land plants with more than 400 families. They have an importance in nature because plants are the only organisms that can convert light energy from the sun into food. So they are a source of food supply giving us fruits, vegetables, crops, and grain, and so on. Secondly, because they provide habitat for animals. Plants are the primary habitat to thousands of organisms and they live in, on, or under plants. Thirdly, plants provide useful products to people. We have different flowers, Taraxacum flowers for example, that they are a source of antioxidants. We have to Chicoria tea, for example, with the stimulant substances. Or flowers that give us medicines like digitalis related with cardiac affections, and also, cosmetics like aloe vera. Finally, plants and flowers because of their beauty are important as ornamental. So they have ornamental use which is very important economically for humans. With these, we arrive to the end of this video.
