7.2.1. Fission

For unicellular organisms, cell division, or fission, leads to the creation of new individuals. Many different patterns of fission have been observed. Many bacteria and protozoa simply split into two equal halves during cell division.

Fission is a type of asexual reproduction commonly found in unicellular organisms, meaning organisms made up of a single cell. During fission, a single organism divides into two separate, smaller organisms. This process is a straightforward way for these organisms to reproduce effectively without needing a mate. Different organisms have developed various methods of fission. Some, like many bacteria, split equally in two during this process, leading to two identical daughter cells.

Think of fission like a photocopier. When you place an original document in the copier and hit 'print,' it creates an identical copy of that document. In the same way, when a unicellular organism undergoes fission, it essentially 'copies' itself, resulting in two new, identical cells.

In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

Amoeba, a common protozoan found in fresh water, allows for flexibility in its reproduction. When it undergoes binary fission, the division can occur at various angles or planes, rather than always splitting down the middle. This flexibility means that the cells can divide in whichever way is most efficient given the organism's shape or environmental factors at the time.

Imagine cutting a pie. You can slice it in a variety of ways. Sometimes you might cut it in half, other times into quarters or smaller pieces, depending on how you're plating it. Similarly, Amoeba can choose its 'cutting method' based on its body shape and environmental conditions when it divides.

However, some unicellular organisms show somewhat more organisation of their bodies, such as is seen in Leishmania, which have a whip-like structure at one end of the cell. In such organisms, binary fission occurs in a definite orientation in relation to these structures.

Not all unicellular organisms are the same; some, like Leishmania, are more structurally complex. The presence of specific structures, like the whip-like flagellum on Leishmania, influences how they undergo binary fission. Instead of being completely random, the orientation of their fission is determined by these specific cellular components, resulting in a more organized method of reproduction compared to simpler unicellular organisms.

Think of a car that needs to move in a particular direction based on the terrain it’s navigating. Just like the car adjusts its route based on its surroundings, Leishmania must also orient its fission process according to its body structure to ensure efficient reproduction.

Other single-celled organisms, such as the malarial parasite, Plasmodium, divide into many daughter cells simultaneously by multiple fission.

Multiple fission is another aspect of cellular reproduction seen in some unicellular organisms like Plasmodium, which causes malaria. Instead of dividing into just two cells, it undergoes multiple fission, resulting in the production of several daughter cells. This method can be highly effective for survival, particularly in adverse conditions, because it allows a single organism to produce many offspring at once, increasing its chance of continuing its species.

Consider a tree that produces many seeds at once, like a dandelion. Each seed has the potential to grow into a new plant, increasing the chances that at least some will survive and thrive in the environment. Similarly, Plasmodium's ability to produce many daughter cells means that even if some encounter difficulties, many have the chance of survival.

Yeast, on the other hand, can put out small buds that separate and grow further, as we saw in Activity 7.1.

Yeast employs a different asexual reproductive strategy known as budding. Instead of splitting evenly like bacteria do, yeast grows smaller buds off of itself. Once these buds become large enough, they detach from the parent organism and develop into new, independent yeast cells. This allows yeast to reproduce and colonize new environments more effectively.

Imagine a tree that produces fruit. Each fruit can be seen as a bud that can grow into a new tree when it's planted. In the same way, when a yeast bud separates, it is like planting a new seed, ensuring the yeast species can spread and thrive in various locations.

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