Question

explain with examples types of asexual reproduction in uniselluar organisms

Answer 1

Spores

Some protozoans and many bacteria, plants and fungi reproduce via spores. Spores are structures naturally grown as part of an organism's life cycle and designed for separation from the organism and dispersal via a medium such as air or water. When conditions are correct, the organism will release its spores, which are each then considered entirely separate and autonomous organisms. Given an environment suitable for life, the spores will then develop into fully grown organisms and eventually grow their own spores, repeating the cycle.

Fission

Prokaryotes and some protozoa reproduce via binary fission. Fission occurs at the cellular level when a cell's contents are replicated internally and then subjected to division. The cell then forms into two distinct entities and separates itself. Each partial cell then reconstitutes the missing parts of its internal structure. At the end of the process, the single cell has become two new fully developed cells, each with identical genetic properties.

Vegetative Reproduction

Many plants have evolved specialized genetic features that allow them to reproduce without the aid of seeds or spores. Examples include the prostrate aerial stems of strawberries, the bulbs of tulips, the tubers of potatoes, the shoots of dandelions, and the keikis of orchids. This form of specialization is most common in environments with seasonally harsh conditions; it allows plants to survive and thrive in situations where the traditional seeding process is subject to frequent interruption.

Budding

Organisms like proteins, yeast, and some viruses reproduce via budding, a process by which an entirely new organism grows on an existing one. Unlike fission, this is not brought about by the separation of an existing organism into two partial entities. The developing organism begins its life as an entirely separate life form from its "parent", separating into an autonomous entity only when it has fully matured. As the "child" organism proceeds through life, it will produce its own buds.

Fragmentation

Segmented worms and many echinoderms such as starfish reproduce asexually via fragmentation. In this process, an organism physically splits and develops new, genetically identical organisms out of each segment. The segments rapidly grow new cells to constitute their muscle fiber and internal structure through mitosis. This split can be either intentional or unintentional on the part of the organism.

Answer 2

Fission

Fission occurs in lower plants and animals such as the bacteria, blue-green algae and protozoa. In this process, the cell divides after the genetic material has divided. If the cell divides into two it is called binary fission. The DNA or the nucleus of a mature cell divides first and then the cell divides into two daughter cells of almost the same size. It is seen in bacteria and protozoans like amoeba and paramoecium.

Binary Fission in a Bacterium

Binary Fission in Amoeba

If the parent cell divides into many daughter cells, it is called multiple fission. It is seen in the life cycle of the protozoa, plasmodium (the malarial parasite). The nucleus divides many times and then the cytoplasm divides and surrounds the nuclei.

Cyst Formation and Release of Cells in a Parasite

The parent cell may get covered by a protective coat called the cyst which bursts to release the daughter cells during favourable condition. Multiple fission is also seen in Chlamydomonas, an alga.

Budding

It is seen in certain fungi and multicellular animals. In budding, the parent cell or body gives out a lateral outgrowth called the bud. The nucleus divides and one of the daughter nuclei passes into the daughter cell. The bud grows in size while being attached to the parent body. It then gets separated from the parent by the formation of a wall. It then falls off and germinates into a new individual. Thus budding results in the formation of daughter cells of unequal sizes that later grow to adult size. For example, yeast, a fungus and Hydra, a multicellular animal. In case of Hydra, the daughter hydra even develops hypostome and tentacles develop around the hypostome before being detached from the parent body.

Budding Cells

Yeast Cells

Budding in Hydra

Spore Formation

It is generally seen in bacteria and most fungi. One of the cells enlarges and forms the sporangium (literally meaning spore sac). The nucleus divides many times and then the daughter nuclei are surrounded with protoplasm bits to form daughter cells called spores. The spores are covered with a thick wall called the cyst. On maturation, the sporangium bursts and releases the spores. The spores germinate on getting favourable conditions. For example, fungi such as Mucor and Rhizopus

Mycelium of Mucor as seen with Low Power of a Light Microscope

Spore formation also occurs in bacteria such as Clostridium and Bacillus. The bacterial spores are also called endospores. They are thick-walled and lightweight.

Endospore Formation

Fragmentation

It takes place in some lower plants and animals such as some worms. The mature organism breaks up into two or more pieces or fragments. The fragments then grow into complete organisms.

For example: Spirogyra, an alga.

Fragmentation in Spirogyra

Worms such as ribbon-worms (Nemertinea) and flatworms (Turbellaria).

Fragmentation in a Turbellaria

Fragmentation takes places in hydra, planaria and sponges. The fragments regenerate to form an entire individual.

Regeneration in Planaria