Angiosperms - Defination & Characteristics

What are Angiosperms - Definition and Meaning

Angiosperms are the flowering plants. The most diverse group of the plant kingdom on Earth is the group of angiosperms. They can be distinguished by their ability to produce flowers and enclosed seeds within fruits. These species are critical in supporting most biomes on the land by offering animals and plants food, shelter, and homes.

Angiosperms began in the Cretaceous period, approximately 90- 130 million years ago. They have since diversified to the extent of occupying most of the plant niches on earth. Their adaptive features make them dominate in ecosystems. These angiosperms are ecologically important in agriculture, horticulture, and medicine. So angiosperms are crucial in the current biological sciences.

Characteristics of Angiosperms

Angiosperms have special features that make them different from gymnosperms. The general characteristics of angiosperms that make them distinctive are as follows:

• Flowering organs - these are the reproductive parts of the plant. The flowers help the plant to reproduce without many crossings with related species. It creates several varieties, leading to the vast diversity of species dominating the land.

• Endosperm - the nutritive tissue formed just after fertilisation and zygote formation. It provides necessary food for the growing embryo and the cotyledons till they disintegrate.

• Reduced male gametophyte - the pollen is smaller than that in gymnosperms, making fertilisation faster. It gives angiosperms an advantage in evolution.

• Stamen - they are lighter and more adapted to cross-pollination. It helps in reducing the possibilities of self-pollination, thereby increasing species diversity.

• Carpels enclosing ovules - this helps to prevent self-pollination and fertilisation. The enclosing carpels later turn into fruit, attracting pollinating agents, thereby helping in the dispersion of seeds.

Classification of Angiosperms- Monocots and Dicots

Angiosperms belong to the Plant Kingdom. They are divided into two main classes - Monocots and Dicots. This angiosperm classification is based on seed structures, leaf venation, and root system, with the floral patterns. The classification is described below:

Taxonomic Classification of Angiosperms

Examples of Angiosperms with Families

Angiosperms or flowering plants include numerous families with diverse characteristics. These families show a wide variety of Angiosperms in the Plant Kingdom. The examples of angiosperms with families are given below:

Fabaceae (Leguminosae)

Fabaceae is one of the biggest Legume plant families. Some of the plants belonging to this family are beans, Phaseolus, peas, Pisum, and soybean, Glycine Max. Well-known for the property of fixing nitrogen and being economically valuable in farming.

Asteraceae (Compositae)

Some of the plants belonging to Asteraceae are sunflowers. They are scientifically known as Helianthus, daisy known scientifically as Bellis, and aster known scientifically as Aster. In this, the plant has a compound inflorescence that has a large number of small flowers closely grouped.

Orchidaceae

Orchids are very diverse and are found almost all over the world. There are some 25,000 in number. Characterised by their delicate and frequently ostentatious flowers that are evolved for specific pollination techniques.

Rosaceae

Some of the plants that fall under Rosaceae are roses, commonly known as Rosa, apples( Malus), strawberries( Fragaria) and cherries (Prunus). They are famous for their pulse and the flowers that are eaten raw or cooked.

Lamiaceae (Labiateae)

Mint plants can also be sorted based on the botanical family, which includes mint (Mentha), basil (Ocimum), and sage (Salvia). These are the plants with sweet-smelling leaves and medical uses.

Poaceae (Gramineae)

A large number of important cereal crops are plants of this family. Examples include wheat (Triticum), rice (Oryza), and maize (Zea). They are essential in the human diet and for the production of crops.

Morphological Features of Angiosperms

Angiosperms morphological features include structures like roots, stems, leaves and flowers. These features help angiosperms survive, grow, and reproduce in the Plant Kingdom.

Structure of Flowering Plants

The structure of flowering plants includes:

1. Roots

Flowering plants have different kinds of root systems, such as a tap root system and a bristle root system. They hold the plant in the ground, take water and nutrients from the soil and contain some supply in them.

2. Stems

Petioles in flowering plants provide Mechanical support to the plant organs like flowers and fruits, help in the conduction of water and nutrients from roots to the aerial parts and food substances from the leaves to other parts of the flowering plant and sometimes have food storage. It has nodes, which are areas of connection of leaves and buds and internodes, which are the spaces between nodes.

3. Leaves

There are various forms and structures of leaves, such as the type, e.g., simple and compound, and the shape of a leaf, for instance, needle-shaped or broad-shaped. They execute photosynthesis, convert light energy to sugars, and release gases into the surroundings.

4. Flowers

Flowers are the specialised structures for reproduction in plants. Depending on the species, flowers may have different levels of complexity. They may be branched or unbranched with such structures as sepals, petals, stamen (the male organ of reproduction), and pistils (the female organ of reproduction). They ensure pollination to enhance the reproduction process, especially through the development of seeds.

Diagram of an Angiosperm Flower

Reproductive Structures of Angiosperms

Angiosperms are flowering plants. Their reproduction depends on the flower. The flowering plants have both male and female reproductive structures. These structures exhibit complex reproductive strategies in the plant kingdom.

Angiosperms Male Reproductive Structure - Stamen

• Stamens produce pollen grains.

• Each stamen has an anther and a filament.

• Pollen carries male gametes.

Angiosperms Female Reproductive Structure - Carpel/ Pistil

• Carpels enclose ovules.

• Each pistil has a stigma, a style, and an ovary.

• The ovary protects the ovules and later forms fruit.

Diagram of Reproductive Structures of Angiosperms

Pollination and Fertilisation in Angiosperms

The angiosperms' reproduction depends on pollination and fertilisation. These processes ensure seed and fruit formation in the plant kingdom. The mechanism of pollination is described below:

Pollination

Pollination is the process through which pollen grains with male gametophytes are placed on the stigma part of the female reproductive organ, the style, while the anther is the male reproductive organ. It can occur through various mechanisms:

• Types of Pollination: There are two types of pollination- self-pollination, which is pollination by pollen from the same flower or another from the same plant and cross-pollination, which is the transfer of pollen from the flower of one plant to another.

• Agents of Pollination: The pollination techniques include anemophily or wind pollination, entomophily or insect pollination, ornithophily or bird pollination, mammalophily or mammal pollination, and hydrophily or water pollination. The colour, fragrance and nectar presentation of flowers also vary to correspond with the following pollinators.

Fertilisation Process

Once pollen comes in contact with a compatible stigma, the pollen tube germinates and grows down the style or the stalk of the pistil and reaches the ovule, the structure within the ovary that contains the female gametes. The male gametes reach the female gametes through a pollen tube to impregnate the ovule part which is enveloped. This process of fertilisation causes the development of a zygote into an embryo within the seed coat.

Physiological Processes of Angiosperms

Angiosperms survival depends on three main physiological processes - photosynthesis, respiration and transpiration. The physiological process of angiosperms is described below:

Photosynthesis in Angiosperms

The angiosperms directly capture light in chlorophyll found in chloroplasts to synthesise glucose and oxygen from carbon dioxide and water. Besides, this process facilitates the growth and development of plants and also plays an important role in oxygen generation and the Earth’s carbon cycle.

Respiration in Angiosperms

The flowering plants use glucose derived from photosynthesis for the production of ATP through aerobic respiration. This process takes place in mitochondria and is pertinent to the overall cellular process of nutrition, growth and division.

Transpiration in Angiosperms

Transpiration is the process of loss of water vapour from tissues of plants, particularly stomata in the leaves. This process has the effect of developing a pressure deficit at the upper end, which drives the upward movement of water and dissolved nutrients from the roots to the shoots. Transpiration is responsible for cooling the plant's level, preserving the internal pressure of plant cells, and transporting minerals to different parts of the plant.

Economic Importance of Angiosperms

Angiosperms are the backbone of human life. They provide services from food to medicine. Flowering plants touch every part of a human’s daily existence. Without angiosperms, survival would be impossible.

• Food and Crops - Wheat, rice, maize, fruits, and vegetables all come from Angiosperms. They form the foundation of our diet.

• Medicinal Plants - Tulsi, neem, mint, and aloe vera are Angiosperms that heal and protect us.

• Industrial Uses - Cotton for clothes, timber for houses, and paper from trees are all products of Angiosperms.

• Oils and Beverages - Mustard oil, coconut oil, tea, coffee, and cocoa are everyday essentials from Angiosperms.

• Ecological Role - They produce oxygen, keep soil fertile, and provide shelter for animals.

• Commercial Value - Rubber, sugarcane, tobacco, and spices are Angiosperms that drive global trade.

Angiosperms are not just flowering plants. They are the foundation of human survival. Angiosperms provide food security, medicine, industry and ecology. This makes them truly necessary in both biology and everyday life.

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