Reproduction - SS1 Biology Lesson Note

Reproduction refers to the process by which new individuals of the same species are produced, allowing for the continuation and propagation of the species. It is a fundamental biological process that ensures the survival and genetic diversity of organisms.

There are two primary modes of reproduction:

1.     Asexual reproduction: Asexual reproduction involves the production of offspring without the involvement of gametes or the fusion of genetic material fro

m two parents. In asexual reproduction, a single parent organism can give rise to genetically identical or nearly identical offspring, often referred to as clones. Common mechanisms of asexual reproduction include binary fission, budding, fragmentation, and vegetative propagation. Asexual reproduction is commonly observed in many single-celled organisms, plants, and some animals.

There are several types of asexual reproduction observed in different organisms. Here are some common modes of asexual reproduction:

§  Binary fission: Binary fission is a form of asexual reproduction where a single parent organism divides into two nearly equal-sized daughter cells. It is commonly seen in single-celled organisms such as bacteria and protists. The parent cell replicates its genetic material and then divides into two identical daughter cells.

§  Budding: Budding involves the formation of a small outgrowth or bud on the parent organism, which eventually grows and detaches to become a separate individual. The bud may develop into a miniature version of the parent or undergo further growth and differentiation. Budding is observed in organisms such as yeast, Hydra, and some plants.

§  Fragmentation: Fragmentation occurs when a parent organism breaks into fragments, and each fragment develops into a new individual. This can happen through accidental breakage, intentional fragmentation, or regeneration of lost body parts. Fragmentation is commonly seen in organisms like flatworms, starfish, and some plants.

§  Vegetative propagation: Vegetative propagation involves the production of new individuals from specialized vegetative structures, such as runners, rhizomes, tubers, bulbs, or plantlets. These structures can give rise to new offspring that are genetically identical to the parent plant. Vegetative propagation is observed in many plants, including strawberries, potatoes, and some succulents.

 

§  Parthenogenesis: Parthenogenesis is a type of asexual reproduction in which unfertilized eggs develop into offspring. It occurs without the involvement of male gametes. This process can happen through various mechanisms, such as mitotic division of the egg or the activation of an egg by external stimuli. Parthenogenesis is seen in certain invertebrates, reptiles (e.g., some species of lizards and snakes), and even in a few species of fish and birds.

§  Apomixis: Apomixis is a mode of asexual reproduction in plants where seeds are produced without fertilization. The seeds develop directly from the maternal tissues, bypassing meiosis, and the formation of gametes. The offspring produced through apomixis are genetically identical to the parent plant. Apomixis is found in some plants, such as certain grasses and dandelions.

 

1.     Sexual reproduction: Sexual reproduction involves the fusion of specialized cells called gametes from two parent organisms, typically a male and a female. The male gamete (sperm) and the female gamete (egg or ovum) unite during a process called fertilization, forming a zygote with a unique combination of genetic material from both parents. Sexual reproduction contributes to genetic diversity as it allows for the reshuffling and recombination of genetic material through meiosis, a specialized cell division process. Sexual reproduction is predominant in most animals, including humans, as well as in many plants and some fungi.

Figure 62 image from researchgate.net