Anthoceros - Classification, Reproduction, and Life Cycle

Anthoceros: Anthoceros is a type of hornwort, a group of simple plants without vascular systems, found worldwide in damp, shaded areas of subtropical and temperate regions. These plants are small and do not have true roots, stems, or leaves. Instead, they have a flat, leaf-like structure called a thallus that is greenish in colour and lies on the ground. The thallus is often lobed or divided and contains chloroplasts with pyrenoids. The plant is anchored by root-like structures called ventral rhizoids, which also form partnerships with cyanobacteria (Nostoc). Anthoceros NEET Biology Notes are provided in the article below.

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What is Anthoceros?

Anthoceros, a genus of hornworts, belongs to the Anthocerotaceae family. It is widely distributed around the world and is considered the largest genus of hornworts. Typically, it grows best in damp, shaded areas within sub-tropical and temperate climates. Its distinguishing feature is a small to medium-sized green body with lobed edges.

Anthoceros reproduces both asexually and sexually. Asexual reproduction happens through methods like fragmentation, tubers, and persistent growth points. Sexual reproduction involves oogamy, where male structures called antheridia produce sperm and female structures called archegonia contain egg cells. The sporophyte, emerging from the archegonium, is characterized by a horn-shaped structure.

Structural Organisation in Animals

Anthoceros Classification

Anthoceros is a type of hornwort belonging to the Anthocerotaceae family. It is the largest genus among hornworts and is distributed worldwide in damp and shaded areas of subtropical and temperate regions. The following is the classification of Anthoceros:

Cell The Unit of Life

Anthoceros Habitat and Distribution

Anthoceros is a type of bryophyte. Let's explore where it lives and how widespread it is:

Distribution:

• There are around 200 species of Anthoceros.
• These species live on land and are found all over the world.
• They do well in damp, shady places like slopes, rocks, and the edges of ditches.
• Some species even grow on rotting wood.

Habitat:

• Anthoceros prefer damp, shady places.
• Anthoceros can be found in subtropical and tropical regions worldwide.
• They are common in the mountainous areas, humid valleys, along riverbanks, near water sources, and in swampy areas.

Sexual Reproduction in Flowering Plants

Anthoceros Structure

Anthoceros belongs to a group of plants called hornworts, which are non-vascular bryophytes. Unlike mosses and liverworts, hornworts lack the complex structures found in plants with vascular systems. However, they possess a distinct and well-defined structure both externally and internally.

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External Structure of Anthocerous

• Thallus: The main body of Anthoceros is a flat, green structure known as a thallus. It has two distinct surfaces: the upper surface is smooth and lobed, while the lower surface is anchored to the ground by hair-like structures called rhizoids.
• Rhizoids: These structures serve to anchor Anthoceros to the substrate and aid in water absorption.
• Nostoc colonies: On the lower surface of the thallus, there are often small colonies of blue-green bacteria known as Nostoc. These bacteria have a symbiotic relationship with Anthoceros, converting nitrogen from the air into a form usable by the plant.

Internal Structure of Anthocerous

• Epidermis: The outermost layer of the thallus consists of a single layer of cells called the epidermis. It protects the internal tissues from damage and helps regulate water loss.
• Parenchyma: Beneath the epidermis lies a layer of parenchyma cells. These cells are responsible for various functions such as photosynthesis, storage of nutrients, and providing structural support. They contain large chloroplasts with pyrenoids, which are characteristic of hornworts.
• Air chambers: Within the parenchyma tissue, there are air-filled chambers that facilitate gas exchange.
• Embedded reproductive structures: Antheridia and archegonia, which produce sperm and eggs, respectively, are embedded in the upper surface of the thallus.

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Structure of Sporophyte

Although Anthoceros primarily exists in its gametophyte (thallus) form, it also has a sporophyte generation, which is smaller and less prominent. The sporophyte develops from a fertilized egg and remains attached to the gametophyte. It consists of three main parts:

• Foot: This bulbous structure anchors the sporophyte to the gametophyte and absorbs nutrients.
• Intercalary zone: A narrow zone of meristematic cells that allows for sporophyte growth.
• Capsule: The capsule is a long, horn-like structure extending from the thallus. It contains spores that are released when mature.

The internal structure of Anthoceros is relatively simple compared to vascular plants, yet it is well-suited for its habitat, enabling it to thrive in moist and shaded environments where it can reproduce effectively.

Structure of Spores

In Anthoceros, the spore is haploid, containing one nucleus, and is semicircular with a notable triradiate marking. It comprises two layers:

1. The outer layer, called the exospore, is thick and textured.
2. The inner layer, known as the endospore, is thin.

Between these two layers, there are oil droplets, colorless plastids, and stored food materials.

Anthoceros Reproduction

Anthoceros, a type of hornwort genus, reproduces through two primary methods: asexual and sexual reproduction.

Asexual Reproduction of Anthoceros

Anthoceros have developed several adaptations for asexual reproduction, aiding in rapid propagation and survival during tough conditions. Here are the different ways Anthoceros achieve asexual reproduction:

• Fragmentation: This is the most common method where the thallus (the flat, lobed body of the plant) breaks into fragments, each of which can grow into a new thallus.
• Tubers: These are small underground structures that store nutrients and water. They remain dormant in dry conditions and sprout new thalli when conditions improve.
• Persistent apices: In certain species, only the tips of the thallus survive adverse conditions. These tips can grow into new thalli when environmental conditions become favorable.
• Apospory: This involves the development of spores directly from the tissue of the gametophyte without fertilization.

Sexual Reproduction of Anthoceros

Sexual reproduction in Anthoceros follows the oogamous type, involving the fusion of eggs and sperm. Anthoceros plants can be monoecious (having both male and female organs on the same plant) or dioecious (male and female organs on separate plants). The sex organs are:

Antheridium

Antheridia grow on the upper surface of the plant body in a sequence from base to tip within special chambers. They have a club-like shape with a long stalk made of multiple cells arranged in four vertical rows. The antheridium is covered by a sterile outer layer, inside of which are androcytes. These androcytes mature into sperm cells called biflagellated antherozoids.

Archegonium

Archegonia also grow sequentially on the upper surface of the plant body, without specialized chambers. They are flask-shaped structures consisting of a neck and a bulbous base (venter). The neck cells break down as the archegonium matures, turning into a sticky substance.

Unlike the antheridium, the archegonium lacks a sterile outer layer. Instead, it has four cover cells or lid cells at its tip.

Fertilization

In the presence of water, antherozoids fertilize eggs within the archegonia, forming a diploid zygote. This zygote undergoes meiosis to produce haploid spores. These spores are released from the sporophyte—a slender capsule growing from the thallus—to germinate and form new gametophytes.

The sporophyte capsule matures and releases spores when ready.

This reproductive strategy ensures Anthoceros' survival and adaptation in various environments through both efficient asexual propagation and genetic diversity via sexual reproduction.

Anthoceros Life Cycle

The life cycle of Anthoceros, a type of hornwort, represents the alternation of generations. This means it includes a predominant haploid phase (gametophyte) and a shorter-lived diploid phase (sporophyte). Here's an overview of its life stages:

1. Spore Dispersal and Germination: The life cycle begins with haploid spores produced by meiosis within the sporophyte. These spores germinate when they land in a moist environment, giving rise to a flat, green, thallus-like gametophyte.
2. Gametophyte (Dominant Phase): The gametophyte is the predominant phase in the Anthoceros life cycle. This flattened, green structure contains embedded reproductive organs called antheridia (male) and archegonia (female). Antheridia produce sperm (antherozoids), while archegonia produce eggs.
3. Sexual Reproduction and Fertilization: Water is necessary for fertilization. Motile sperm swim through water to reach the archegonia, where one sperm fertilizes the egg.
4. Sporophyte Development: The fertilized egg develops into a diploid sporophyte, which grows embedded within the gametophyte. The sporophyte relies on the gametophyte for water and nutrients through a structure known as a placenta. Within the sporophyte, a sporangium forms and undergoes meiosis to produce haploid spores.
5. Spore Release and Germination: Upon maturity, the sporangium bursts open, releasing haploid spores into the environment. These spores then germinate to initiate a new life cycle.

In summary, the life cycle of an Anthoceros involves:

• Germination of spores to form a dominant gametophyte.
• Sexual reproduction via antheridia and archegonia.
• Fertilization leads to the development of a sporophyte.
• Sporophytes produce spores through meiosis.
• Release and germination of spores to restart the cycle.

This type of life cycle, characterized by alternation of generations with a dominant haploid phase, is termed diplontic.

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