Table of Contents
Angiosperm can be defined as those whose fertilized eggs forms seed within the ovary.
What is Angiosperm?
The word Angiosperm originates from a Greek word where “angeion” means vessel and “sperma” means seed. Flower bearing plants are called as Angiosperms. Belonging to the plants group. Along with the flower, it also bears seeds. It is one of the vast group of plants, with 453 families and 260,000 species within. In the category of Angiosperms are 80% of green plants.
In angiosperms, female and male organs are both found. They are found in almost all location, excluding those with extreme climatic condition such as in the depth of the ocean, poles, mountain ranges and etc. while they are present in various climatic conditions, they may be immersed in soil, water or present on the surface or freely floating. They vary in size from very small in millimeters to 100 meters. Example are huge trees to tiny shrubs and intermediary plants. Orchidaceae is the abundant species of Angiosperms. Examples are grasses, pea and daisies. They have applications in various fields such as medicine, wood products, jewelry, industrial products and pharmaceutical products.
Angiosperm Anatomy and Morphology
They belong to the phylum Anthophyta of flowering plants and consist of stamens, carpels and pollens. In flowering plants, pollen grains are the sperms, producing stamens. Within the pollen grain lies the males game which will interact with the female gamete in the plant’s ovaries. Angiosperms can reproduce sexually as well as asexually. As the pollen grains are smaller than that of gymnosperms, thus, reaching the eggs of female quicker. Without fertilization as well angiosperms can undergo the process through pollens; where stamens has a vital role in the flowering plants life cycle of fertilization. Through cross-pollinations, insects get attracted towards the flowers, due to their colors as well as smell.
Behind the flower, are ovaries encapsulated in the carpels. To produce seeds, fruits and flowers, pollens are obtained by the ovaries which starts the process. Thus, the very first step involves seed development, followed by flowers and its pollination to produce fruit. Angiosperms have characteristics that resemble synapomorphies. Within the carpels are the ovules present which carries the pollination process. For the double fertilization to occur and for the endospore formation, it requires pollen sac and three stamens. Sieve tubes and companion cells are present in phloem tissues.
Angiosperm Flowers and Anatomy
For the reproduction to occur, pollination is quite important. The male sex organ are the stamens that produces pollen, which then get translocated to the pistil, which is the part of the female angiosperm.
Angiosperm Flowers Anatomy
Pollination occurs when the pollen from the male reaches the female part. There are two types of pollination; self-pollination and cross pollination. Pollination agents are insects, invertebrates, mammals and wind.
Structure of Angiosperms
The reproductive organ in Angiosperms are flowers and roots, stems and leaves are the asexually reproductive organs. Root system and shoot system are the angiosperm structures. Shoot system is the one present above the soil, whereas the root system is the one that is present in the soil. Root system comes under the root domain whereas the shoot lies under the shoot domain.
Roots are the most vital part of the plant; without them the plant is nothing. Absorption of minerals, water, nutrient from the soil is the function of the roots and transfer it to the tips. Primary and Tertiary root system are the types of root systems, where taproot is seen which grows towards the ground in length to form roots, which can further grow diagonally and horizontally is the primary root system and from taproots production of more roots is known as secondary roots. Primary roots have a very short life-span, and thus their position is occupied by supplementary system of roots. Depending on the function, primary and tertiary roots gets altered. Examples are beetroot and carrot.
To make the plant stand, and on which the fruits and flowers come is the stem. From the roots the nutrients, water and other essential requirements moves to the stem and then to the leaves, fruits, plants and animals. Hypocotyl allows the continuous transfer of nutrients from roots to stem. From the stem, when the leaves are formed it is known as nodes and the distance between two nodes is known as internodes. The type of branching seen in angiosperms are axillary and dichotomous; in axillary there are two types of branching sympodial and monopodial.
From the stem emerges the leaves. For the formation of leaves, lamina is the main part which consist of petiole, stipule and blade. To the petiole the base of the leaf and the blade is linked and on both the sides is the stipule present. From the blade, photosynthesis occurs and thus is green and flattened in shape. However, some leaves shows the absence of petiole and stipules. The pattern on the stem can be opposite, whorled, alternate and paired.
Angiosperm Life Cycle and Reproduction
Double fertilization occurs in the angiosperms, where from the seeds the male and female gametophyte are produced. Sporophyte is the step in the life cycle, where the adult angiosperm is formed are heterosporous. The pollens will be generated from the microspores and the gametophyte are the pollen grains of the male. The female gametophytes which is the ovule will be formed from megaspores. Within the pollen lies two types of cell, one will form the pollen tube and the other will make up sperms.
The ovule is covered by another wall to keep the megasporangium intact, where meiosis takes place to produce a huge and three tiny megaspores, where only the huge megaspore reaches the embryo sac and gets three time divided after which the eight cell further moves. The four cells move towards the equator and the rest move to the pole resulting in the formation of 2n polar nucleus. There are helping cells present which are the synergids, nucleus, antipodal cell and an egg sac which is inside a mature embryo sac. As soon as the pollens reach the stigma, the sperms reaches the embryo sac and double fertilization starts, where the sperm and egg combines to form the embryo, whereas there is fusion of the polar nuclei and the second sperm going on. They form an endosperm, which stores the food.
On the basis of the leaves, angiosperms can be divided into eudicots and the monocots. On the embryo surface there are seed leaves which contain protein, lipid and sugars. There exist three species of angiosperm and they are where on the flower, stamen and pistil are present is the hermaphroditic. Monecious, where both the stamen and pistil are on the same plant but different flower. When both stamens and pistil are present on different plants and different flower it is called as dioecious.
In 1703, they were first discovered by Ray. In the seed presence of a single cotyledon are called as monocots. These monocots phylogenetic studies have been done in 19th century. They consist of fibrous system of roots. The flowers in monocots consist of three parts and are called as Trimerous. Woody tissues are either absent or only present in few cases. A vital feature seen in monocots is the presence of a single layer of pollens, which is even seen today. Examples of monocots plant are orchid, lilies, grasses and others, whereas monocot crops are sugarcane, pineapple, corns and others.
More than one cotyledon in the seed is the Dicot. The flower in dicot consist of four or either five parts. The network seen in leaf is of reticulate venation type. The vascular tissue present in the ring forms the dicot. They are capable of producing woody tissues. In dicots the pollen consist of three layers. They have taproot system. Dicot examples are sunflowers, beans and oak.
There are numerous examples of angiosperms, however the most common one are the flowering plants. The most studied example of angiosperm are fruit trees. The fruits are formed from various flowering plants. Grains and grasses are also included in angiosperms. Fruits such as apple, cherries and oranges. However, the insects, birds, wind and mammals are the agents of pollination. After the pollination process get completed and the carpel has opened up, flowers get converted to fruits and will also change colors.
As wheat, rice grow in grasses and they cannot attract pollinators thus, the agent for pollination to take place is wind as they carry the seed because its light in weight. Thus, angiosperms are very vitals as various crops are available to humans because of them.
History of Angiosperm
In the Mesozoic era, the fossil records have been first seen in history. They possess both male and female gametophytes and are the flowering plants. Around 100 million years ago, these plants were identified in the middle cretaceous and were viewed 125 million years prior by the paleontologist. Although there aren’t much traces of history of angiosperm but fossil of pollen has been obtained, and were believed to have quite similarity to angiosperms.
It is said that from the gymnosperms, angiosperm has been arrived, but yet studies are going on, as they form a different set of species on the basis of its features. They believed angiosperms to be originated from tropical grasses or woody bushes.
In the south pacific, there is a rain forest in New Caledonia which has a flowering plant which is quite small and is quite ancient it is the Amborellatrichopoda and is confirmed that is a flowering plant. The other angiosperms are the monocots and the eudicots. Basal angiosperms were also part of the angiosperm, but however have been removed from the category of angiosperm.
Angiosperm Fossil Record
The very first record of the angiosperm fossil is of 132 million years ago. There is quite a lot of differences seen in the size, structure, flowers in the ancient old angiosperms and those of the modern era. Although the only similarity found was in the flowers. Thus, classifying them into the category of Angiosperms.
Estimation of Age of the Angiosperms
This information of how old the angiosperms are since how long they have existed can be identified with the fossil. Modern and molecular techniques have been used to determine the origin of flowering plants and has said that they are 5-45 millions years old. Various researchers have worked on the finding of origination of angiosperm using various tools and techniques and have found that the age of angiosperm is 165-199 Ma and for other plants as well have been found.
Angiosperms Ecological Importance
They have a huge role in various fields, on the environment and on humans as well as animals. The flowering plants are quite important as they keep the food chain continuing. Many insects, birds and other mammals eat these plants. These plants are also source of pollination to other insects. They provide us fruits, flowers along with seed, as many animals can continue lifecycle when they consume the fruits and obtain energy.
The seed propagation takes place when birds and other mammals eat them and take the seeds to various locations, thus resulting in more flowering plants. They also produce various products such as alkaloid, oil and glycosides. They also prevent the predators from causing harm to the other plants and stop them from producing toxic compounds. It is said that thousands of birds, animals get their food the angiosperm tree, thus, they maintain the food chain and keep it running.
Economic Importance of Angiosperm
They have application in various industries which starts from the pharmaceutical industry. Majority of the antibiotics, drugs are either made from angiosperms or are the derivative of angiosperms. Narcotic, vitamins, aspirin and quinine are some of the example. These angiosperms have shown promising results in treating cardiac arrest and various forms of cancer.
For heart surgeries and for relaxation of muscle, curare is used. For treating malaria, quinine is used. For cancer, vincristine has been used and for oral contraceptives diosgenin has been used. They also play a role in preserving the environment. Humans and animals are dependent on angiosperms for food and their absence would have a major impact on the environment as well as on every individual.
Angiosperms vs Gymnosperms
Flowering plants are Angiosperms. Example are grains, fruits, vegetables and others. Gymnosperms are non-flowering plants and their examples are juniper, pine, cedar and fir. Accumulation of gymnosperms form, cones whereas the accumulation of angiosperm forms flowers. Angiosperms are mostly unisexual whereas the gymnosperms are bisexual. In angiosperms there are various flowering parts such as style, stigma, petals and sepals. Archegonia is found in gymnosperms and is absent in angiosperms. On the stalk are the angiosperms present. Angiosperms and gymnosperms also vary in the cotyledon number. Angiosperms have application in food, ornament, timber and pharmaceutical, whereas gymnosperms in making of ply, paper and lumber.
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