Flowering plants are able to survive in a greater variety of habitats than gymnosperms. Flowering plants mature more quickly than gymnosperms, and produce greater numbers of seeds. The woody tissues of angiosperms are also more complex and specialized. Their seeds are enclosed in a fruit for easy dispersal by wind, water, or animals. The leaves of angiosperms are mostly thin, extended blades, with an amazing diversity of shapes, sizes, and types. The surface of the pollen grain has a complex three-dimensional structure.
This structure is unique for each species, like a floral thumbprint. It also means that pollen grains, which are abundant in the fossil record, allow us to reconstruct ancient plant communities, and these communities in turn tells us about ancient climates. All angiosperms produce flowers , reproductive structures that are formed from four whorls of modified leaves. Most flowers have showy petals to attract pollinators, bribing insects and other animals with nectar, to get them to carry the male gametophyte through the air to another flower.
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.
The seed coat is one major advantage seeds have over spores. A spore is a single-celled organism that develops into a plant or fungus when the conditions are right. The spore has no outer protection. A seed is a multicelled organism with an outer shell that protects the inside from damage, dessication and other adverse conditions. Each seed contains nourishment for the embryo inside the seed. The endosperm is the tissue that surrounds the embryo inside the seed. The embryo uses nourishment provided by the endosperm as a jump start to begin growing.
The spore, being a single-celled organism, does not have any built-in system to help a new plant or fungus begin the growth process. Inside each seed is a fully developed embryo that is ready to begin growing. Gymnosperms and Angiosperms. What does Gymnosperm mean? Naked seed. Are gymnosperms vascular or nonvascular?
What is the difference between vascular plants and non vascular plants? Vascular tissue is a conducting system for water minerals, and sugars.
Obviously pine trees are the largest clade of Gymnosperms, what is the name for evergreen aka pine? What does monoecious mean? It means that a plant has both male and female reproductive parts on the same plant. What is a Cyad. The trees Beth and Mark have, so they are palmtree like, and they have strobili coming out of the top, so pollen and seeds. Are Cyads Monoecious? They are dioecious, aka they have male and female structures on different plants.
What is weird about the Cyad and Ginko Biloba sperm? It has vestigial flagellate. Sphenopsida includes more fossil plants than living one. Today there is only one surviving genus Equisetum. A rhizome produces aerial stem. The stems are slender, green, hollow structure, and appear jointed as slender green side branches are present at the nodes.
The small and scale like leaves also form whorls at the nodes, the nodes are separated by internodes. Many horsetails have strobili at the tips of the stem. Why Equisetum is called Horse tail? Ferns a wide-spread group of plants, are much more abundant in warm and moist tropical regions. Ferns range in size from reduced aquatic forms less than a centimetre, to a tree fern that may have trunks more than 24 metres tall, with leaves up to 5 metres or more long.
All but a few ferns are homosporous. Sporophyte generation is much larger, more conspicuous, and more complex than the. Sporophyte is completely independent. Sporangia is foliar i. When the frond is young and immature, it is coiled. This pattern of development is called circinate vernation. It is an important feature of ferns. The moss Sphagnum grows in bogy places that is low lowing, wet, spongy places forming dense and deep masses called peat bog.
One of the distinctive features of this moss is a presence of large empty cells in the leaves, which apparently function to hold water. This feature makes peat moss particularly beneficial as a soil conditioner. When added to sandy soils, for example, peat moss helps to hold and retain moisture. Science, Technology and Society Connections Describe the formation and importance of peat bogs. They have evolved from the primitive vascular plants. There are two main types of leaves in vascular plants: a One veined leaves.
One veined leaves are small and scale like. They have single vascular bundle and vein. Therefore they are called single or one veined leaves or microphyllous leaves e. Many veined leaves are large leaves having prominent blade. As many veins and vascular bundles are present, so they are called many veined leaves or megaphyllous leaves e.
Ginkgo etc. Evolution of Single Veined Leaves There is no fossil record showing the evolution of microphyllous leaves. However two hypotheses singular; hypothesis have been proposed to explain their origin: a outgrowth hypothesis b reduction hypothesis. Out-growth hypothesis: According to this hypothesis single veined leaf originated as simple outgrowth from the naked branches of the primitive plant.
The outgrowths had no vascular tissues. With the increase in size, vascular tissues were needed for the transportation of food, water etc. Thus vascular supply was extended from main vascular bundle of stem giving rise to a single veined leaf.
Reduction Hypothesis: The early vascular plants had leafless branches. These branches were gradually reduced in size. Thus by simplification and reduction in size and flattening of the leafless branches the microphyllous leaves were evolved.
Evolution of Many Veined Leaf It is evident from fossil record that these leaves have evolved through. According to this view the following three steps have taken place. Plannation: The forked branches were changed to a single plane. Webbing: The spaces between the bundles and branches of vascular tissues became filled with photosynthetic tissues. The structure resembles superficially to the webbed foot of the duck and thus a many veined leaf evolved.
Life Cycle of Fern The life cycle of Adiantum Maidenhair fern shows heteromorphic alternation of generation. The gametophyte is small reduced, haploid and independent. It bears antheridia and archegonia which produce antherozoids sperms and eggs ova respectively. Fertilization leads to zygote formation which develops into an embryo within the archegonium. Embryo develops into an independent sporophyte.
The sporophyte is dominant, diploid plant body and produces on the underside of the leaflets of compound leaves frond , number of sori. Each sorus contains a cluster of sporangia, producing haploid spores. The spores are dispersed by wind. When a spore falls on a moist soil it germinates under favourable conditions forming haploid gametophyte.
Adaptations of Ferns: a Have true roots, stems and leaves. Adaptations of Gymnosperms: Gymnosperms have well developed roots and stem. Many are tall trees that can withstand heat, dryness and cold.
Pollen grains are transferred by wind, and the growth of the pollen tube delivers a sperm to an egg. Enclosure of the dependent megagametophyte in an ovule protects it during its development and shelters the developing zygote as well. Finally the embryo is protected within the seed. All these factors increase the chance for reproductive success on land.
Adaptations of Angiosperms: The evolutionary adaptations of flowering plants account for their success in terms of ecological dominance and large number of species. Angiosperms have true roots, stems and leaves. Roots are often modified for storage e. The vascular tissue is well developed. Xylem tissue in angiosperms is different from that of virtually all other vascular plant groups because it contains xylem vessels as well as tracheids. Leaves are generally broad, expanded blades and are very efficient in absorbing light for photosynthesis.
Shedding of leaves during cold or dry spells is also an advantage for survival in harsh environment. Angiosperms are found in all sorts of habitats and some have even returned to water. The reproductive organs are in the flowers, which attract animal pollinators.
Flowers are modified in wind pollinated plants. Seeds are reproductively superior to spores for three main reasons. First a seed contains a multicellular, well-developed young plant with embryonic root, stem and leaves already formed, whereas a spore is a single cell. Second, a seed contains a food supply. After germination, the plant embryo is nourished by food stored in the seed until it becomes selfsufficient.
Because a spore is a single cell, few food reserves exist for the plant that develops from a spore. Third a seed is protected by a well resistant seed coat, as compared to the thick wall of the spore. Along with primary growth secondary growth has also helped the survival of angiosperm also gymnosperms on land.
Importance of Seedless Vascular Plants The seedless vascular plants are of economic importance. Lycopodium and Selaginella are chiefly grown as ornamental plants and are utilized in the preparation of christmas wreathes. Spores and stems of Lycopodium have got some medicinal importance.
Ducks and other aquatic animals feed upon the corm of Isoetes. The ferns are mostly ornamental plants of gardens and greenhouses.
Some of them are used in the preparation of bouquets and are also placed in the buttonholes. In some tropical countries stems and leaves of tree ferns are used for building purposes, because the wood of the ferns resists decay particularly by termites.
Some genera, like Pteris, Ceratopteris and Marsilea, are edible. The rhizome of the male fern yields a drug, which is utilized for removing the intestinal parasites. The maidenhair fern are the source of expectorant. Practically all the members of the seedless vascular plants have contributed extensively to coal formation. The seed of gymnosperm are produced exposed on the surface of the sporophylls that make up cones.
The seeds of angiosperms are usually enclosed by a fruit produced from a flower. From ecological and evolutionary perspective seed represents an important evolutionary advancement. A seed may be considered as a fertilized megasporanguim. It has integument around the embryo. The seed is found in higher vascular plants i. During evolution the seed has passed through the following stages. Development of Heterospory All seed plants are heterosporous produce microspore and megaspore. Microspores are formed in microsporangia and megaspores are formed in megasporangia.
The megaspore grows into a female gametophyte and microspore grows into a male gametophyte. The megaspores of the seed plants are retained inside the sporangium, where the megaspore develops into a tiny female gametophyte.
Evolution of Pollen Tube The evolution of pollen tube parallels the evolution of seeds. The egg produced inside an ovule is very well protected in the sporangium. It is so well protected that flagellated sperm would not have the slightest chance of ever reaching an egg.
This obstacle has been overcome by the development of pollen tubes. Once the pollen grain reaches the cone or flower, it germinates.
The germinated pollen grain is a tiny male gametophyte. It produces a long pollen tube, which grows to the ovule and then digests its way through the protecting layers to the enclosed egg. Evolution of Integument Around the Megasporangium and Seed In carboniferous period geological period millions years ago , fern like plants were present. The sporophyte of these plants had little protective branch like outgrowths, surrounding the megasporangium. During evolution the outgrowths fused together forming integument, enclosing the megasporangium.
Megaspore is retained in the megasporangium.
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