What Is Metamerism In Biology Class 11?

Metamerism is a type of segmentation in which the body’s outside and inside are separated. The outer body segments correlate to the interior body segments.

Metamerism is the occurrence of producing a linear succession of structurally identical body parts. A metameric segment may alternatively be referred to as a somite.

Metamerism is the recurrence of identical body segments. The Annelids, including earthworms, leech, tubeworms, and their cousins, exhibit this development. In Arthropods, including such crustaceans, insects, and their cousins, it exists in a more evolved form.

Metarism is a biological phenomenon characterized by creating linear and identical structures during growth. Nonetheless, not all structures (also known as segments) are identical.

The architectural differences result from their functions, such as digesting and respiration. In plants and animals, metameric segments are termed metamers. Each segment of an animal with a segmented body is called a somite, but they are called phytomers in plants.

What Is Metamerism In Biology Class 11

Metamerism In Animals

Zoologists define Metamery as a mesodermal occurrence that results in the serial replication of unit subdivisions of ectoderm and mesoderm products in animals. Endoderm does not participate in metamemory.

Segmentation differs from metamerism in that segmentation is limited to ectodermal generated tissue, such as in Cestoda tapeworms. Metamerism is considerably more significant biologically, as it produces metameres, also known as somites, which play a crucial part in advanced locomotion.

Metamerism may be divided into two major categories:

Homonomic Metamorphosis:

Homonomous metamemory is characterized by a close, serial succession of metameres.

It may be further divided into the categories of pseudometamerism and genuine metamerism. The class Cestoda is an illustration of pseudometamerism.

The tapeworm comprises several segments that repeat mostly for reproduction and nutrition exchange. Because each section functions independently of the others, this is not a real example of metamerism.

The earthworm in the phylum Annelida is another example of real metamerism. There is a repeat of organs and muscular tissue in each worm segment. What distinguishes Annelids from Cestoda is that the earthworm’s segments contribute to the organism.

It is believed that segmentation arose for several causes, including increased mobility. Taking the earthworm as an example, the segmentation of its muscle tissue enables it to move in a wriggling manner.

The circular muscles are responsible for segmental elongation, whereas the longitudinal muscles are responsible for segmental contraction.

This pattern extends down the worm’s body, allowing it to creep down a surface. Each segment is permitted to function independently yet contributes to the overall movement of the worm.

Heteronomic Metamemory:

A heteronomous metamemory is a circumstance in which metameres have teamed together to execute similar activities. This is most evident in the insect’s head (5 metameres), thorax (3 metameres), and abdomen (11 metameres, not all discernible in all insects).

Tagmatization is the process that results in the grouping of metameres, and each grouping is known as a tagma (plural: tagmata). It may be difficult to identify considerable metamorphism within a tagma in creatures with highly developed tagmata, such as insects.

It may need to be located in structures that do not necessarily correspond to the aggregated metameric function.

Metamerism In Plants

A metamer is one of several segments that contribute to constructing a shoot or into which a shoot may be resolved (at least conceptually).

According to the metamerism model, a plant is composed of a series of ‘phytons’ or phytomers, each consisting of an internode, its upper node, and a leaf. As stated by Asa Gray in 1850:

The branch, or simple stem itself, is a collection of similar parts arranged atop the other in a continuous series, each of which evolved from the previous generation.

Each of these stem joints, which bears a leaf at its apex, is a plant element; or, as we call it, a phyton, a potential plant with all the organs of vegetation, including stem, leaf, and in its downward development, a root or its equivalent.

This view of the plant’s composition, which is by no means novel, has not been adequately appreciated. I consider it indispensable to a proper philosophical understanding of the plant.

Some plants, particularly grasses, exhibit a metameric structure, but the presence of discrete modules in most others is debatable.

The Phyton theory has been criticized for being an academic theory with little to do with reality. Eames (1961) concluded that “Due to the dominance of the stem- and leaf-theory, concepts of the shoot as a collection of structural units have become obscured. Such anatomical units do not exist; the shoot’s basic unit.”

Nonetheless, some consider comparative study along the length of the metameric organism to be an essential aspect of plant morphology. 

Metameric conceptions often divide the vegetative axis into units that repeat throughout its length, although alternative divisions are feasible.

According to the pipe model idea, plants (particularly trees) are composed of unit pipes (‘metamers’) that sustain a unit quantity of photosynthetic tissue.

Some desert plants with modified stems consisting of isolated bands of xylem with root-to-shoot continuity are also believed to have vertical metamers. It may allow the plant to abscise a substantial portion of its shoot system in response to dryness without harming the remainder.

The shoot system of vascular plants has a metameric structure (repetitive organ units; stem, leaf, and inflorescence), but the root system does not. In spermatophytes and seed plants, the embryo symbolizes the first shoot metamer.

A module is an axis along which the whole sequence of aerial differentiation occurs, from the commencement of the meristem to the onset of sexuality (e.g., flower or cone formation), which completes its growth in plants (particularly trees).

These modules are considered developmental rather than structural components.

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