All organisms, from plants to animals, reproduce using any of the two forms of reproductive methods; Asexual or sexual reproduction.
Reproduction is the creation of offspring and is a circle of life for all living organisms, including microorganisms, to keep surviving. Asexual reproduction involves genetically copying the parent itself into its offspring. Hence, the parent and the offspring share the same genetic identity. Due to this cloning between the parent and offspring, any diseases that are non-resistant to the parent, the offspring is also susceptible to the same diseases. Whereas sexual reproduction creates a unique offspring as one genetic material is obtained from each parent. The two genetic materials from both parents will combine to form an individualistic offspring. Therefore, the offspring will have good resistance to most common diseases, due to the higher probability of mutations. Additionally, there are some rare species like sea anemones, slime molds, etc., that are capable of reproducing sexually and asexually.
There are different types of asexual reproduction: binary fission, sporogenesis, parthenogenesis, fragmentation, apomixis, and vegetative propagation. Syngamy of male and female gametes does not occur in asexual reproduction. Here the organism reproduces by itself without requiring another parent. Therefore, the offspring produced by this reproductive method is an exact clone of the parent. Some examples that reproduce via asexual means are plants, bacteria, fungi, etc.
This type of asexual reproduction involves duplicating genetic material into two and finally separating the
body into two (cytokinesis). The two daughter bodies contain one copy of the genetic material. Some examples of organisms reproducing by binary fission are paramecium, Escherichia coli, amoeba, etc.
Plants, algae, and fungi produce spores as a part of their reproductive cycle. Sporogenesis is the formation of spores. In flowering plants, both male sporophytes (microsporophytes) and female sporophytes (megasporophytes) undergo meiosis to produce microspores and megaspores in males and females, respectively. In plants, microsporogenesis is the formation of pollen grains (containing male gamete) in the anther of the stamen (male reproductive part). While, megasporogenesis is the formation of the egg cells (female gamete) inside the ovule of an ovary, which is a part of the plant’s female reproductive structure.
The development of an offspring without undergoing fertilisation is called parthenogenesis. In this case, the males are not involved; instead, the female’s gamete (egg cell) develops itself into a new offspring. Examples of some organisms include; bees, ants, wasps, etc.
Fragmentation is the process of breaking an organism into small parts, each that could grow individually and independently but identical to the parent organism. This process mainly occurs in multicellular organisms. Examples of organisms that undergo the fragmentation process include; fungi, molds, etc.
In this process, the organisms can avoid the most rudimentary steps, meiosis, and fertilisation of sexual reproduction, leading to the embryo’s development. For instance, a plant seed does not require a male gamete to produce offspring. Instead, the seed germinates, developing into a fully matured plant.
Vegetative propagation occurs naturally or can be manufactured (artificial vegetative propagation). In this process, regenerative parts of a parent plant are planted to grow into a new mature plant. The different vegetative propagation techniques include grafting, cutting, layering, tissue culture, and suckering.
Sexual reproduction involves the syngamy of two sex cells (gametes) from both parents to create offspring. The species that sexually reproduce can either be anisogamous (the size of male and female gametes are different) or isogamous (the morphology of male and female gametes are similar). A male
gamete (sperm cell) is produced inside the male reproductive structure that fuses and later fertilises with the female gamete (egg cell) within the female’s body (conception). After fertilisation of sperm and egg cells, it forms into a zygote. The zygote (cells) continue dividing to adhere itself to the female uterus (in animals) or ovary (in plants), where the zygote is developed into an embryo, finally into a fetus.
The period during which the fetus receives its nourishment from the female body is called the gestation period, which is varied for different animals. Once the fetus is fully developed, the female parent is ready to deliver the offspring, finally able to flourish on its own. Some aquatic animals can reproduce externally, where the male and female sex cells are fertilised in the water. Additionally, humans can also fertilise eggs externally by in-vitro fertilisation. Whereas reptiles and birds fertilise their eggs internally, they lay eggs that hatch and produce offspring. Moreover, plants reproduce sexually through pollination, either by self-pollination or cross-pollination.
Distinguish between Asexual and Sexual Reproduction
- Asexual reproduction involves only a single parent, while two parents (male and female) are engaged in sexual reproduction.
- Syngamy (fusion of gametes) is absent in asexual reproduction, whereas in sexual reproduction presence of syngamy induces fertilisation of a sperm cell and an egg cell.
- Meiotic cell division is not required for asexual reproduction; therefore, the offsprings are genetically identical to the parent (or a clone of the parent). However, meiosis is a necessary step to generate male and female gametes in sexual reproduction. Hence the offsprings produced are different from their parents and genetically unique.
- Types of asexual reproduction include; binary fission, sporogenesis, parthenogenesis, fragmentation, apomixis, and vegetative propagation. In contrast, types of sexual reproduction include; syngamy and conjugation.