Sexual and Asexual Reproduction in Living Organisms
Reproduction in Living Organisms
Reproduction is the process by which living things produce new generations of individuals of the same species. The new living things can arise from individual cells, groups of cells, or portions of the parent organisms.
Unicellular Organisms
In unicellular living things, the cell is the full body and divides to give rise to new organisms.
Multicellular Organisms
In multicellular living beings, their constituent cells originate apart from others by successive division. Certain cells are specialized to carry out the process of reproduction.
Sexual Reproduction
Sexual reproduction is a form of reproduction in which both parents produce specialized cells called gametes. Most species are unisexual. It may be formed by a single individual, called hermaphroditism. In both cases, it shall give rise to new individuals.
Sexual Reproduction Process
- Gametogenesis is the process by which male and female gametes are formed, respectively, spermatozoa and ovules. In plants, they are called antherozoids or oosphere and spermatic nuclei.
- Fertilization is the union of the male gamete with the female to form the egg cell or zygote.
- Embryonic development is the process by which an adult organism is formed from successive divisions of the zygote.
Hermaphroditism
Hermaphroditism occurs in species in which each individual has male and female reproductive organs. In animals, the term “monoecious” is used. Some pines and plants have separate male and female flowers on one plant foot, and hermaphrodite plants are useful when they have stamens and pistils in the same flower. There are also some varieties of fish that are male for half of their life and female for the other half, changing sex. Usually, hermaphroditism does not imply self-fertilization. Cross-fertilization almost always occurs, thus enhancing the principal purpose of breeding: the variability of genetic material.
Asexual Reproduction
In asexual reproduction, a single parent produces new generations of their species without the intervention of sexual cells.
Types of Asexual Reproduction
- Bipartition: This happens in single-celled organisms such as algae and protozoa. A stem cell divides, first the nucleus and then the cytoplasm, giving rise to two daughters of equal cell size.
- Budding: This occurs in unicellular and multicellular organisms. On the surface, it creates a bulge of the progenitor called a yolk, from which a new individual develops. It could be attached to the parent, forming colonies, or separated from it.
- Pluripartition: This consists of the repeated division of the cell nucleus. It is typical of protozoa. The multiple cores share the cytoplasm and are surrounded by a plasma membrane, forming small daughter cells that are free when the mother cell membrane breaks.
- Sporulation: The daughter cells are called spores, which are unicellular, and the multicellular nucleus divides several times. Each core is surrounded by a portion of the cytoplasm and forms a protective envelope.
- Excision: This is the process by which a multicellular organism splits into two or more fragments, each of which can form a complete organism.
Basic Principles of Cell Theory
- All living things are made of cells.
- All cells come from other existing cells.
- Vital functions of organisms occur in the cells.
- The cells contain the genetic information necessary for the regulation of cell functions and for the transmission of information to all their descendants.