Biogenesis is a proven idea that living things can only come from other living things. This concept is very important in biology and molecular genetics because it explains how new living things are made from ones that already exist. The word “biogenesis” comes from two parts: “bio,” which means “life,” and “genesis,” which means “beginning.” According to the theory of biogenesis, living things can only come from other living things. This was a big deal because, for a long time, people thought that maybe living things could appear from anywhere, even dead matter. It wasn’t until the 1850s and 1860s, about 200 years after microorganisms were first discovered, that scientists finally figured out that all living things come from other living things. To simplify, take the example of chickens. Chickens lay eggs, and those eggs hatch into chicks. But where do those eggs come from? Being one of the most debatable topics, with no agreeable answer, let’s just say that chickens come from other chickens, which come from other chickens, and so on. This idea of life coming from already existing life is called biogenesis. It changed our understanding of biology and disproved the old belief in spontaneous generation, which suggested that living things could come from non-living matter. It sounds ridiculous now, but back then, spontaneous generation theory was widely supported, and it took more than 100 years for the truth to be proved. Biogenesis examples include biogenesis experiments and modes of reproduction in living beings. Here are some of the biogenesis examples that surround us.
1. Biogenesis experiments
The theory of biogenesis, which states that living organisms arise from pre-existing living organisms, rather than spontaneously generating from non-living matter, has been supported by several experiments conducted over the centuries. Here are a few notable experiments that provided evidence in favour of biogenesis:
- Francesco Redi’s Experiment (1668)
Francesco Redi, an Italian physician, conducted an experiment involving jars of decaying meat to challenge the idea of spontaneous generation. He placed the meat in three different jars: one open to the air, one covered with gauze to allow air in but keep insects out, and one completely sealed. The meat in the open jar quickly putrefied, and maggots appeared, while the meat in the gauze-covered jar and sealed container remained free of maggots. This demonstrated that maggots (living organisms) did not spontaneously appear and were offsprings of flies after they laid eggs on the open meat. Redi’s experiment supported the theory that living organisms only come from other living organisms.
- Louis Pasteur’s Swan-Neck Flask Experiment (1861)
Louis Pasteur’s famous experiment involved a flask with a long S-shaped neck that allowed air to enter but prevented dust and microorganisms from reaching the sterile broth inside. He heated the broth to kill any existing microorganisms and left it exposed to the air. No microorganisms grew in the broth, demonstrating that the broth remained free of life as long as it was protected from contamination (unless the glass neck was intact). This experiment conclusively disproved the idea of spontaneous generation and provided strong evidence for the theory of biogenesis.
- John Tyndall’s Dust Experiment (1877)
John Tyndall, an Irish physicist, conducted experiments that showed how dust particles in the air carry microorganisms. He passed air through a heated glass tube to kill any microorganisms and then exposed it to dust. He found that the dust carried microorganisms and that when the dust was removed, the air remained sterile. This experiment further confirmed the role of pre-existing microorganisms in contamination and supported biogenesis.
- Lazzaro Spallanzani’s Sealed Flask Experiment (1768)
Lazzaro Spallanzani, an Italian biologist, conducted experiments during which he boiled nutrient-rich broth in sealed flasks to kill any existing microorganisms. The sealed flasks remained free of microorganisms as long as they remained sealed, supporting the idea that living organisms could not spontaneously arise in a sterile environment.
2. Sexual reproduction in animals
Sexual reproduction exemplifies the theory of biogenesis because the offspring are not generated spontaneously from non-living matter but rather result from the union of gametes from two living parent organisms. The genetic material carried by these gametes comes from pre-existing living organisms. Animals, including humans, reproduce through sexual reproduction, and offspring inherit genetic material from two parent organisms. In mammals, fertilization occurs when a sperm cell from a male combines with an egg cell from a female. This fusion of genetic material leads to the development of a new individual with a unique combination of traits inherited from both parents. The embryo develops within the mother’s womb and is eventually born as a new living organism, continuing the cycle of life. The steps involved in sexual reproduction are as follows:
- Gamete Formation
In sexual reproduction, specialized reproductive cells called gametes are produced by each parent. In most animals, there are two types of gametes: sperm (produced by males) and eggs (produced by females). Gametes are haploid, meaning they contain half the number of chromosomes as the parent’s somatic (body) cells.
- Fusion of Gametes
The male and female gametes, sperm and egg, respectively, come together during fertilization. This union is often facilitated by various mechanisms, such as copulation in mammals or external fertilization in aquatic organisms. When the sperm cell penetrates the egg, their genetic material combines.
- Zygote Formation
The fusion of gametes results in the formation of a zygote. The zygote is the first cell of the new organism and contains a complete set of chromosomes, with half coming from each parent. This is a crucial step in biogenesis because it represents the beginning of a new, unique individual.
- Embryonic Development
The zygote undergoes a series of cell divisions and differentiations through a process called embryonic development. These divisions give rise to a multicellular embryo, which eventually develops into an organism with specialized tissues, organs, and systems.
- Birth or Hatching
After the embryo reaches a certain stage of development, it is typically born (in mammals) or hatched (in oviparous animals like birds and reptiles). This marks the completion of the biogenetic process, as the new organism is now capable of independent life.
3. Asexual reproduction in animals
Asexual reproduction involves the formation of new individuals without the fusion of gametes. Instead, offspring are typically genetically identical or nearly identical to the parent organism. Asexual reproduction in animals demonstrates that new individuals arise from pre-existing living organisms, even though they may be genetically identical or very similar to the parent. Hence, it exemplifies biogenesis. Animals that reproduce asexually include sharks, komodo dragons, boa constrictors, crayfish, sponges, hydra, aphids, starfish, etc. In animals like hydra and some sea creatures, new individuals develop as outgrowths or buds on the parent organism’s body and then detach to live independently. In some insects, reptiles, and amphibians, females can produce offspring without mating. These offspring are genetically similar to the mother as they develop from unfertilized eggs. The process is called parthenogenesis. Some animals, such as starfish and planarians, can regrow lost body parts, and these parts can develop into new individuals. This process is called regeneration and is a form of asexual reproduction.
4. Sexual reproduction in plants
Sexual reproduction in plants is an excellent example of biogenesis in which plants produce offspring through the fusion of specialized reproductive cells, called gametes. The male gametes, found in pollen grains, typically contain sperm cells, while the female gametes are typically housed in the ovule within the flower’s pistil. During pollination, these gametes meet, leading to fertilization, which ultimately results in the formation of a new plant embryo. This method of propagation ensures genetic diversity and adaptation in plant populations. Sexual reproduction takes place via seed and spore formation in plants. In most flowering plants (angiosperms), sexual reproduction involves the formation of seeds. It typically includes pollination, fertilization, and seed development. Pollination is the transfer of pollen from the male reproductive part (anther) to the female reproductive part (stigma) of the same or another flower. This can be done by wind, insects, birds, or other animals. After pollination, the pollen tube grows down to the ovule in the ovary, where fertilization occurs. The sperm cell from the pollen combines with the egg cell in the ovule, forming a zygote. This zygote develops into an embryo within the seed. The fertilized ovule develops into a seed, containing the embryo, a food source (endosperm), and a protective seed coat. When the seed is mature, it can be dispersed and germinate to grow into a new plant when conditions are favourable. Some plants, such as ferns and mosses (Non-Angiosperms), reproduce sexually through the formation and dispersal of spores. Spores are single-celled reproductive structures that can grow into new plants under suitable conditions. This process does not involve the production of seeds.
5. Asexual reproduction in plants
Asexual reproduction in plants often involves the production of new individuals from vegetative structures, such as stems, roots, or leaves. In this process, new plants arise without the involvement of seeds or the fusion of gametes, highlighting the continuity of life through the replication of existing individuals. Methods such as vegetative propagation, apomixis, and grafting, where new plants develop from stems, roots, or leaves of the parent plant, exemplify how living organisms create new life without the need for sexual reproduction. Asexual reproduction reaffirms the fundamental biological concept proved by the theory of biogenesis that life begets life (life creates life). Plants reproduce asexually via various methods to propagate and generate genetically identical offspring. Some common types of asexual reproduction in plants include:
a) Vegetative propagation
This involves the growth of new plants from vegetative structures like stems, roots, or leaves. Examples include Stolons or Runners: Above-ground horizontal stems that produce new plants at nodes (Strawberries), Rhizomes: Underground stems that give rise to new shoots (Ginger), Tubers: Enlarged, fleshy underground stems that store nutrients and can sprout new plants (Potatoes), and Bulbs: Underground storage structures with an embryonic shoot and surrounding leaves (Onions).
Some plants can produce seeds without fertilization, resulting in genetically identical offspring. This process is known as apomixis and is observed in certain grasses and dandelions.
c) Bulb offsets
Many bulb plants, like tulips and daffodils, produce small bulbs or offsets at the base of the parent bulb. These offsets can be separated and planted to grow into new plants.
d) Adventitious plantlets
Certain plants, like spider plants, produce small plantlets along the edges of their leaves. These can be separated and potted to grow into new plants.
e) Artificial asexual reproduction
The artificial methods of asexual reproduction include Cuttings: Plant cuttings taken from stems or leaves, develop into new plants when placed in soil or water. This method is commonly used for propagating houseplants and ornamental shrubs; Layering: This involves encouraging a branch or stem to take root while still attached to the parent plant. Once rooted, it can be separated and grown as a new individual; Grafting: This method involves joining the stem or bud of one plant onto the rootstock of another and is widely used in horticulture to create plants with desired traits or to propagate fruit trees; Micropropagation: It involves the cultivation of small plant tissue samples in a controlled laboratory environment and offers numerous advantages, such as rapid multiplication of desirable plant varieties, disease-free propagation, and the preservation of unique genetic traits.
6. Reproduction in microorganisms
Microorganisms, including bacteria, archaea, protists, and some fungi, exhibit various modes of reproduction, and these processes can be explained as examples of biogenesis. Here are some common types of reproduction in microorganisms:
- Binary Fission (Asexual Reproduction)
Binary fission is a common mode of asexual reproduction in microorganisms, particularly in bacteria (E.coli) and archaea. A single parent cell replicates its genetic material, typically a single circular chromosome. The parent cell undergoes a process of elongation and eventual splitting into two genetically identical daughter cells. This division results in the formation of two separate living microorganisms both of which are of the same species as the parent cell.
- Budding (Asexual Reproduction)
Budding is another form of asexual reproduction seen in microorganisms like Saccharomyces cerevisiae (baker’s yeast) and some protists. The parent cell develops a protrusion or “bud” on its surface. The bud enlarges and eventually detaches from the parent cell. The bud contains a nucleus and other organelles, and it can continue to grow independently. Once detached, the bud becomes an independent microorganism, genetically identical to the parent cell. This process is a clear example of biogenesis as the offspring arise from a living parent organism.
- Spore Formation (Asexual or Sexual Reproduction)
Many microorganisms, including some fungi and bacteria (Bacillus and Clostridium), can form spores. Spores are highly resistant structures that can withstand harsh environmental conditions and serve as a means of reproduction. Under unfavourable conditions, the parent microorganism produces spores within specialized structures called sporangia. When conditions become more favourable, the spores are released into the environment. When a spore encounters suitable conditions, it can germinate and develop into a new microorganism. This is a clear example of biogenesis, as a living organism (the spore) gives rise to another living organism.
- Conjugation (Sexual Reproduction)
Some microorganisms (like E.coli) engage in sexual reproduction processes like conjugation. Although sexual reproduction involves the exchange of genetic material between two individuals, it still exemplifies biogenesis because it leads to the formation of new individuals. During conjugation, two microorganisms of the same species temporarily merge and exchange genetic material, typically in the form of plasmids or fragments of DNA. The exchange of genetic material can result in new combinations of genes, which can provide genetic diversity. After conjugation, each microorganism can go on to reproduce asexually (e.g., through binary fission), producing offspring that have inherited the new genetic material.
Certain bacteria (like E.coli) can naturally take up genetic material from their surroundings. This genetic material can come from other microorganisms that have lysed or released their DNA into the environment. Once incorporated, the foreign DNA can become a functional part of the bacterium’s genome, leading to genetic diversity and adaptation over time. This method of horizontal gene transfer is called transformation, and it exemplifies the theory of biogenesis. By demonstrating how living organisms can acquire genetic material from their living or once-living counterparts, the transformation mode of reproduction fuels genetic variation and evolution within microbial populations.
Transduction is a method by which certain bacteriophages (viruses that infect bacteria) inadvertently transfer bacterial DNA from one host bacterium to another during infection. When a bacteriophage infects a bacterial cell, it may accidentally package a fragment of the host DNA along with its genetic material. Later, when this phage infects another bacterium, it can inject the combined genetic material and incorporate the bacterial DNA into the new host’s genome. This natural gene transfer between bacteria via bacteriophages demonstrates the biogenesis theory that living organisms arise from pre-existing living entities.
7. Viral reproduction
Viruses are unique entities that are not considered living organisms. They rely on infecting host cells to replicate and reproduce since they lack the cellular machinery for independent reproduction. When a virus infects a host cell, it takes over the cell’s machinery to produce new viral particles. These particles can then go on to infect other host cells, repeating the viral life cycle. Viral reproduction demonstrates the fundamental concept of biogenesis that even dead entities such as viruses depend on pre-existing living organisms for their continuation.
8. Parasitic reproduction
Parasitic organisms, such as tapeworms or fleas, rely on host organisms for sustenance and reproduction since they cannot exist independently. They lay eggs or produce offspring within the host’s body. These offspring then develop and continue the life cycle of the parasite within the host, often causing harm or disease to the host organism. Parasites often have complex life cycles, with stages adapted to different host environments. This dependence on other living organisms for their survival and reproduction exemplifies the theory of biogenesis.
9. Cell culture
Cell culture is a valuable tool in biology and medicine for understanding cellular processes and diseases, and developing treatments. In a laboratory setting, cell culture involves the cultivation and propagation of living cells derived from organisms. These cells are typically taken from a living organism, isolated, and nurtured in a controlled environment. With proper nutrients and conditions, these cells divide and replicate to create new cell populations, supporting the theory of biogenesis.
10. Cell division
In multicellular organisms, cell division is essential for growth, development, and tissue repair. Cell division is a fundamental biological process in which a single cell divides to produce two or more daughter cells. It serves as an important example of biogenesis. In cell division, the process begins with an existing, living cell. This cell, often referred to as the “parent” cell or “mother” cell, is already a product of previous cell divisions. It has its own set of organelles, genetic material (DNA), and cellular machinery. Before cell division, the parent cell replicates its genetic material (DNA) through a process called DNA replication. This ensures that each daughter cell will receive a complete and identical set of genetic instructions. Depending on the type of cell division, the parent cell undergoes either Mitosis (Asexual Cell Division) or Meiosis (Sexual Cell Division).
In mitosis, a single parent cell divides into two genetically identical daughter cells. Each daughter cell inherits a complete set of genetic materials and organelles from the parent cell. This process is characteristic of somatic cell division and is responsible for tissue growth, repair, and maintenance in multicellular organisms.
Meiosis consists of two distinct stages: meiosis I, and meiosis II. In meiosis, I, a diploid cell with two sets of chromosomes divides into two haploid daughter cells. This reduction in chromosome number is essential for sexual reproduction as it ensures that when gametes (sperm and egg cells) combine, the resulting zygote will have the correct diploid chromosome number. In meiosis II, these haploid cells further divide, producing a total of four unique haploid gametes. Each of these gametes carries a distinct combination of genetic material, enabling genetic diversity in offspring. Cell division is a fundamental process in biology that clearly demonstrates biogenesis. It establishes that new cells, whether they are genetically identical (as in mitosis) or genetically diverse (as in meiosis), originate from pre-existing living cells and inherit the traits and characteristics of their parent cells. This process is a significant concept in biology and supports the biogenesis principle that all living organisms, no matter how small or simple, arise from other living organisms.
11. Genetic inheritance
Genetic inheritance serves as a prime example of biogenesis. This process begins with parent organisms, each containing their own unique set of genetic material (DNA) within their cells. During reproduction, whether through sexual or asexual means, this genetic material is transmitted from parent to offspring, facilitating the inheritance of traits. In sexual reproduction, the combination of genetic material from both parents results in a unique genetic code for the offspring. Hence, genetic inheritance demonstrates that life and its genetic information are not spontaneously generated from non-living matter but instead arise from the transfer of genetic material from one generation of living organisms to the next, firmly supporting the concept of biogenesis and the continuity of life.
12. Yeast fermentation
Yeast cells (Saccharomyces cerevisiae), commonly called Baker’s or Brewer’s yeast, are used in baking and brewing and reproduce through a process called budding. In budding, a small yeast cell, known as a bud, forms on the surface of a larger parent yeast cell. Over time, the bud grows and eventually separates, becoming a new yeast cell. This method of asexual reproduction allows yeast to multiply rapidly during fermentation processes. During fermentation, yeast cells metabolize sugars and convert them into alcohol and CO2 in the absence of oxygen (Anaerobic). Yeast fermentation is utilized by humans to produce valuable products for consumption. Yeast cells, through their reproduction and metabolic activities, serve as a living source of biogenesis.
The given examples of biogenesis illustrate a fundamental concept in biology that all living beings come from other living beings, thus supporting the theory of biogenesis. Whether we observe the reproduction of plants, the growth of microorganisms, or the division of cells, it is clear that life’s continuation depends on pre-existing life.