Now, angiosperms are more widely distributed and populous, and can be considered the dominant plant life on the planet. Angiosperms comprise a far more diverse range of plants, with a range of , to , species. They inhabit every kind of land and aquatic environment except the most extreme habitats. Angiosperms may be dicots or monocots. Examples of angiosperms are monocots like lilies, orchids, agaves known for agave nectar and grasses; and dicots like roses, peas, sunflowers, oaks and maples.
Gymnosperm species number only in the thousands, with a little more than 1, extant species. They are found in desert to semi-desert habitats. Since gymnosperms and angiosperms are both vascular plants, they have a sporophyte -dominant life-cycle. Tissue formation in angiosperms exceeds the amount and complexity found in gymnosperms. Angiosperms have a triploid vascular tissue, flat leaves in numerous shapes and hardwood stems. Gymnosperms are haploid, have spiky, needle-like leaves and are softwood.
Gymnosperms are "simpler" anatomically because they do not bear flowers or fruit, and although of different species, are usually only tall evergreens with brown cones. More details about the anatomical differences between angiosperms and gymnosperms are explained in the following video:.
Animal pollination is common in angiosperms, in contrast to the mostly wind-pollinated gymnosperms. The ovules in angiosperms are encased in an ovary, not exposed on the sporophylls of a strobilus, as they are in gymnosperms. Angiosperm means "covered seed". The ovules develop into seeds , and the wall of the ovary forms a fruit to contain those seeds.
Fruits attract animals to disperse the seeds. Flowers consist of four whorls of modified leaves on a shortened stem: sepals , petals , stamens an anther atop a slender filament , and one or more carpels. Imagine a broad leaf with sporangia fastened along the edges of the leaf. Some ferns actually look like this. Now fold that leave over along the midrib, and you've enclosed the sporangia in a protected chamber.
You've just made a carpel. The carpels are fused together to form a pistil , which consists of a stigma upper surface , a style long, slender neck , and an ovary round inner chamber at the bottom containing one or more ovules. The flower is analogous to the strobilus of pines and more primitive plants, except that only the inner two whorls stamens and carpels actually bear sporangia. The base of the flower is called the receptacle , and the tiny stalk that holds it is the pedicel.
The life cycle of flowering plants is described in more detail below. Microspores develop in microsporangia in the anthers , at the tip of the stamen.
Each anther has four microsporangia. Microspores develops by meiosis from the microspore mother cell. These microspores develop into pollen grains. Pollen grains are the male gametophytes in flowering plants. Inside the pollen grain, the microspore divides to form two cells, a tube cell and a cell that will act as the sperm.
Cross walls break down between each pair of microsporangia, forming two large pollen sacs. These gradually dry out and split open to release the pollen. Meanwhile, inside the ovary, at the base of the carpel, the ovules, are developing, attached to the wall of the ovary by a short stalk. The megasporangia is covered by an integument , protective tissues that are actually part of the parent sporophyte. The megaspore mother cell divides by meiosis to produce four haploid megaspores.
Three of these megaspores degenerate, and the surviving fourth megaspore divides by mitosis. Each of the daughter nuclei divides again, making four nuclei, and these divide a third time, making a grand total of eight haploid nuclei. This large cell with eight nuclei is the embryo sac. This embryo sac is the female gametophyte in flowering plants. One nucleus from each group of four migrates to the center.
These are called the polar nuclei. The remaining three nuclei of each group migrates to opposite ends of the cell. Cell walls form around each group of three nuclei. The mature female gametophyte thus consists of only seven cells, three at the top, three at the bottom, and a large cell in the middle with two nuclei. One cell of the bottom three cells will act as the egg. When the pollen grain reaches the stigma of the carpel, it germinates to form a pollen tube. This pollen tube will grow through the neck or style, all the way down to the bottom of the carpel, to a small opening called the micropyle.
The male gametophyte has two cells. One is the tube cell, the other will act as a sperm. As the pollen tube grows closer to the embryo sac, the sperm nucleus divides in two, so the mature male gametophyte has three haploid nuclei.
While the pollen tube is entering the ovule, the two polar nuclei in the female gametophyte fuse together, making one diploid nucleus. The two sperm nuclei enter the embryo sac. One sperm nucleus fuses with the egg nucleus to form a diploid zygote.
The other sperm nucleus fuses with the fused polar nuclei to make a triploid cell. This 3N cell will divide repeatedly to form the endosperm, the stored nutritive material inside the seed. The integuments develop into the tough outer seed coat, which will protect the developing embryo from mechanical harm or dessication. Thus the ovule, the integuments and the megasporangium they enclose, develops into the seed.
The walls of the ovary then develop into the fruit. There is an incredible diversity of flower structure, not only in the number of sepals, petals, stamens, and carpels, but also in the way these modified leaves are attached with respect to the ovary. Linnaeus used these very characteristics to sort out the different related groups of flowering plants in his invention of binomial nomenclature, genus and species.
All of these differences can affect the final physical appearance of the fruit. The ovary wall has three layers, each of which can develop into a different part of the fruit. Simple fruits are fruits that develop from a single ovary. They can be either dry , like grains, nuts and legumes, or fleshy , like apples, tomatoes and cucumbers.
Compound fruits develop from a group of ovaries. They can be either multiple fruits or aggregate fruits. In multiple fruits , like the pineapple, the group of ovaries come from separate flowers. Each flower makes a fruit, and these fruit fuse together. In aggregate fruits , like strawberries and blackberries, the fruit develops from a flower with many carpels. Each of these carpels develops as a separate fruitlet, that fuse together to form the compound fruit.
Seeds all bear the plant version of the belly button. They have a crescent-shaped scar called a hilum , where the ovule was attached to the wall of the ovary. Right above the hilum, if you look very carefully, you can also see a little pinprick scar that is a vestige of the micropyle.
Inside the seed, the tiny sporophyte embryo develops. When it is nearly ready to germinate, the seed contains one or two thick embryonic leaves. These seed leaves, or cotyledons , will support the tender baby plant while it establishes its roots and starts to grow its regular leaves.
Most angiosperms, like roses, marigolds, and maple trees, are members of the Class Dicotyledones, the dicots , sp. These flowers have seeds with two seed leaves di - cotyledon.
Some angiosperms, like lilies, onions, and corn , are in the Class Monocotyledones, the monocots 65, sp. The seeds of monocots have only one seed leaf mono - cot.. There are several other differences between these two groups, which we summarized in the last lab plant structure.
There are seed leaves everywhere in Spring, and its impossible to tell what they will become just by looking at them. A new diploid sporophyte is formed when a male gamete from a pollen grain enters the ovule sac and fertilizes this egg. Improve this page Learn More. Skip to main content. Module 9: Plant Reproduction.
Search for:. Angiosperms versus Gymnosperms Figure 1. Watch this video to see an animation of the double fertilization process of angiosperms. In Summary: Angiosperms versus Gymnosperms The flower contains the reproductive structures of a plant.
Gymnosperms and angiosperms are more highly evolved than nonvascular plants. Both are vascular plants with vascular tissue that live on land and reproduce by making seeds. They are also classified as eukaryotes , meaning they have a membrane-bound nucleus.
Only angiosperms are known as flowering plants. Many have beautiful petals, fragrant blossoms and fruit that contains dozens of seeds. Angiosperms typically drop their leaves when the seasons change and chlorophyll production ceases.
By contrast, gymnosperms such as pine trees produce bare, uncovered seeds, usually in pine cones. The flowers of angiosperms have male and female reproductive parts. Stamens are male sex structures that make pollen on their anthers. A pollen tube in a structure called the style helps the generative cell in pollen reach the ovarian embryo sac.
The generative cell in pollen splits into two sperm cells. One fertilizes the egg, and the other one helps make endosperm through a process known as double fertilization.
Fertilized eggs mature into seeds protected inside fruit. Sporophytes in gymnosperms make male and female gametophytes.
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