By Jake Schwartz

external image floweringplant

These flowers are beautiful

Diagnostic Characteristics:
Angiosperms, phylum Anthophyta, are easily recognizable because they are flowering plants that use fruit for seed dispersal. Angiosperms also foster their seeds in protected chambers called ovaries. The ovaries enclose the ovules. The ovules are housed within a carpel, which also contains the stigma, where pollen germination takes place. They are also characterised as being vascular seed plants. Double fertilization is another key characteristic of angiosperms. Like any other plant, angiosperms are heterosporous. Heterosporous means that the angiosperm produces two types of spores differing in size, function, and sex. These two forms are explained in the 'double fertilization' section below. Only angiosperms and a few types of ferns are heterosporous.
Angiosperms are a very diverse plant group on Earth, with around 260,000 species that have the ability to live in many different types of habitats, and have many external forms. They make up more than eighty percent of known living green plants species. They are vascular seed plants with flowers that contain the plant's reproductive structures. Some exist as epiphytes, which means that they live on other plants, others inhabit marine ans freshwater ecosystems, ans still others are land-dwelling plants. Angiosperms differ in size and external type: some are vines, small herb, huge tress, and even parasites.

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Double Fertilization:
Two sperm cells unite with two cells in the embryo sac to form a zygote and endosperm. After this cotyledons, the seed leaves of a sporophyte embryo with a rudimentary root, are formed. The cotyledons of monocots contain one seed leaf. Dicot cotyledons contain two seed leaves. Then the triploid nucleus in the center of the embryo sac divides repeatedly creating a triploid tissue called endosperms. Endosperms are the reserves for starch and other food. Monocot seeds store most of their food in the endosperm while dicot seeds transfer most of their food from the endosperms to the nucleus. Double fertilization is useful because it synchronizes development of food storage in seeds with the development of the embryo. The embryo sporophyte consists of the following: nutrient-storage areas called cotyledons, the epicotyl (epi upon, over), which is the region above the cotyledon(s), and which will become the stem and leaves. The hypocotyl (hypo under, beneath), which is the region under the cotyledon(s). The lower end of the hypocotyl, which becomes the root system, is called the radicle (radix = root) and will become the roots.

A seed is comprised of an embryo, endosperm, sporangium, and a seed coat created by the outer layer of the ovule. The ovary becomes fruit as the ovules become seeds. Angiosperms package their seeds in fruit to attract fruit-eating organisms to consume them. By doing this, the seeds can be dispersed by means of the organism defecating and moving the seeds to a new location. The seeds get dispersed and germinate. The seed coat ruptures giving rise to a seedling. The seedling uses the food that was stored in either the endosperm or cotyledons. Seeds do not germinate though until the climate is able to support the pant. The seeds lay inactive until these conditions have been met.

Dicot Seed (BY)
Dicot Seed (BY)

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Fruit (Transport of Materials):
As an ovary matures and develops, it becomes a fruit in order to to protect the seeds inside. Some plants have fruits that are burrs or propellers, others produce edible fruits. Edible fruits are designed to be eaten by animals so that the seeds can travel through the digestive system unharmed and be dispersed miles away from the parent plant. There are three types of fruit; simple fruit, aggregate fruit, and multiple fruit. A simple fruit is just one ovary from one flower. The cherry is a good example of a simple fruit. An aggregate fruit consists of multiple ovaries from one flower, such as the raspberry. A multiple fruit multiple ovaries from many flowers clumped together, like the pineapple. This occurs when the ovaries fuse together and become one fruit.

Major Types:
1.Monocots-Leaves with veins running parallel to eachother. (Monophyletic group) The embryo has one cotyledon. A cotyledon is the leaf of the embryo for a seed plant. Monocots also have floral parts usually in 3s (as opposed to in 4s or 5s as in dicots), and fibrous roots, which consist of a mat of thin roots that spread out below the soil surface.
EX. Lillies, orchids, yuccas, palms, grasses, sugar cane, corn, wheat, rice
2.Dicots-Netlike venation in leaves. The vascular bundles (water-bearing tubes) inside a dicot's stem are arranged in concentric rings (as opposed to the scattered vascular bundles in a monocot). When the seed sprouts, it raises two cotyledons above the ground and the future stem of the plant rises between them.
3.Eudicots-A clade, evolutionary branch, that contains most Dicots. Eudicots appeared on earth around 125 million years ago and arose soon after angiosperms did, according to fossil evidence.
Ex. Roses, peas, buttercups, sunflowers, oaks, maples
4. Ambexternal image 97223-004-D7C26DDC.jpgorella Trichopoda-Oldest branch, represented by a single species. It is a rare, vesselless, understory shrub or small tree with two-ranked leaves without stipules. This branch has survived for over 130 million years and it is native to New Caledonia in the South Pacific. If this branch had not existed and evolved, we would not have flowers and many plants that we have today.

Amborella Trichopoda

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Stucture of Flower:
The flower of an angiosperm is made of four parts; Sepals, Stamen, Petals, Carpels. Located at the bottom of the flower, sepals are modified leaves that enclose the flower before opening. The petals, located above the sepals, are modified leaves that are usually colorful in order to attract pollinators. Sepals and petals are sterile parts of the flower. The non sterile parts of the plant are the stamens and carpels. Stamens are the male reproductive organs and carpels are the female reproductive organs. These are both called sporophylls, which produse spores and gametophytes. A stamen is comprised of filament, or stalk, and the pollen producing terminal sac called an anther. The stigma at the top of the carpel receives pollen.
At the bottom is the ovary is is connected by the style.
The ovules are inside the ovary and become seeds.

Other Structures:
Angiosperms contain three types of xylem cells: traechids, fiber cells, and the vessel element. The traechids are long, tapered cells that are used for mechanical support and for the transportation of water. Fiber cells act as extra support for the xylem. The vessel element also transfers water, and is more effective at it than the traechids.external image Xylem%20Vessels.gif

The root system of an angiosperm take in water and nutrients to disperse these needed materials throughout the plant. Angiosperms may have either primary or adventitious root systems. In primary root systems, there is a taproot (primary root) that grows vertically down from the stem of the plant, and smaller horizontal or diagonal roots branch off from the taproot. The primary root system is the most common type of root system. In the adventitous root system, the taproot is replaced by many smaller roots from the stem of the plant.
The leaves can come in several types of structure. Each leaf can be in one piece, a simple leaf, or in multiple pieces, a compound leaf composed of several leaflets. Leaves can also be alternating, with one leaf coming off the stem at any given point; opposite, with two leaves coming off the stem at the same point; or whorled, with three or more leaves branching from the same point.

Evolution/Environmental Adaptions:
Angiosperms provide food for animals in the form of fruit and nectar, and in return animals act as pollinators for the angiosperms and disperse their seeds around. Angiosperms have modified their characteristics such as their color, fragrance, and structure in order to become more attractive to their pollinators. Flowers that get pollinated by hummingbirds are often pink or red because birds are extra sensitive to these colors. Hummingbirds have long, thin beaks and tounges in order to suck out the nectar from the floral tubes in these flowers. Another adaption that angiosperms have made is developing fruit that is capable of being dispersed. This can come in the form of anything from edible fruit to propellar like fruit.
A Hummingbird feeds with ease in this well adapted flower

It is very hard to tell which group of nonflowering plants angiosperms are most closely related due to their extremely fast evolution and the extinction of many closely related lineages of seed plants. Angiosperms are most likely more closely related to an extinct lineage of seed plants than any other remaining seed plant lineage.

Angiosperms, like gymnosperms, are the organisms of the plantae kingdom which have evolved to survive on land. It is believed that plantae started with marine plants such as green algae and progressively adapted to be able to live on land. Angiosperms have used the seed approach to reproduction to live on land.

There are around 250,000 species of angiosperms scattered throughout the globe. Many angiosperms are designed to disperse their seeds and get them far away from where they began. Because of this the habitat of angiosperms is basically anywhere that it can grow.

Review Questions:
1) Please label each part of the flower and describe each parts function.
2) Discuss the adaptations of angiosperms in regards to pollination and dispersion for reproduction.
3) What are some major types of angiosperms and some of their characteristics?
4) If the angiosperm has evolved from a marine plant name 3 characteristics that it has devolved that differ from its ancestor?
5) Why can angiosperms of the same species inhabit a large geographic area?

Barron's AP Biology Book
"SparkNotes: Plant Structures: The Seed." SparkNotes: Today's Most Popular Study Guides. Web. 26 Oct. 2009. <http://www.sparknotes.com/biology/plants/plantstructures/section1.html>.
http://www.jseaman.com/images/Ruby_throated_Hummingbird_JC_Raulston_Arboretum_Raleigh,_NC___2005_07_10_9141-resized.jpg (Jesse Landy)