How Gemmules Form and Ensure Sponge Survival
Gemmules are found in sponges, gemmules are internal buds (embryonic shoot), which plays a significant role in asexual reproduction. In other words, you can define what are gemmules as a cluster of cells capable of growing into an adult sponge.
Now that you are familiar with what are gemmules, let us proceed with what is gemmule formation?
Gemmule Formation in Sponges
Gemmule formation occurs in freshwater by several sponges like Spongilia and some water species such as sea sponges, figuline ficus, and various other types of poriferans. The organisms give out gemmules, which further give birth to new sponges.
Archaeocytes or totipotent cells are filled with food material in the form of lipoprotein or glycoprotein amalgamate to become a mass. Further, an amoebocyte moves around the archaeocyte to provide a surrounding layer. This amoebocyte releases solid chitin, which becomes a layer around archaeocytes.
Freshwater sponges usually die during the autumn season but leave behind a lot of gemmules. These produced internal buds can even withstand and live in winters and summers' adverse and unfavourable conditions. Further, these grow to become new sponges when they find an abundant quantity of water.
Structure of Gemmules
A completely formed gemmule features a standard size, and the structure of the same is similar to a hardball. Alongside reproductive cells, you can also see a food mass embedded in membranes on a grown gemmule.
Plus, gemmules have a tiny opening, which is scientifically termed as a micropyle. When the conditions are favorable for development, cells come out from this opening.
Parts of a Gemmule
Inner layer
Spicule
Micropyle
Archaeocytes
Outer pneumatic layer
Gemmules Classification
In general, there are two categories of gemmules, and the names are:
Single or double-layered coats enclosed by mono or binucleate cells
Triple-layered coats enclosed by binucleate cells
Features of Gemmules
Gemmules can survive without oxygen.
They are the same as a bacterium's endospore.
Gemmules can live in adverse conditions, where sponges may not be able to survive.
Characteristics of Gemmules
Although there isn’t much definition and structure to gemmules, they possess the following characteristics:
i. Gemmules are resistant to drying up, they are resistant to desiccation due to weather, temperature, etc.
ii. They are resistant to freezing, even in winters during the low temperatures.
iii. They are also resistant to anoxia, which means that they can survive even in extreme shortages of oxygen.
iv. They can survive and lie around for long periods of times, which means that they do not degrade, spoil, or rot.
v. Gemmules resemble the endospore of bacteria.
vi. They are composed of amoebocytes.
vii. They are surrounded by a thin layer of spicules for support and to deter the predators.
viii. These gemmules are super degrading resistant and can survive extreme environmental conditions that could even kill fully grown sponges.
ix. The gemmules only resume growing after the environment has become less hostile.
Gemmule Reproduction among Sponges
Do you know that these internal buds show resistance towards freezing and dehydration? Yes, it is true. In fact, gemmules can even live in the absence of oxygen. The exterior gemmule layer is surrounded by endospore, further surrounded by spicule, which also protects. As a result, gemmules can grow into freshwater sponges.
Do it Yourself
a) Write down the parts of a gemmule.
b) Formation of gemmule in sponges is beneficial for:
(i) Sexual reproduction
(ii) Dissemination
(iii) Parthenogenesis
(iv) Asexual reproduction
By now, you must have acquired considerable knowledge related to gemmules. Nevertheless, for more such topics, please prefer to download the Vedantu app today!
FAQs on Gemmules: Key to Asexual Reproduction in Sponges
1. What are gemmules in sponges?
Gemmules are internal buds produced by sponges, primarily freshwater species, as a method of asexual reproduction. They are essentially tough, dormant clusters of embryonic cells, mainly archaeocytes, enclosed in a protective coat. This structure allows the sponge to survive harsh environmental conditions like freezing or drying out. When conditions become favourable again, a gemmule can develop into a new, genetically identical adult sponge.
2. What are the different parts of a gemmule and their functions?
A typical gemmule has a highly organised structure designed for survival. Its main parts include:
- Archaeocytes: A central mass of totipotent cells that are undifferentiated and contain all the genetic material to form a new sponge.
- Inner and Outer Membranes: These layers enclose and protect the archaeocytes from environmental stress.
- Spicules: Often, a layer of spicules (like amphidiscs) is embedded between the membranes, providing structural reinforcement and defence against predation.
- Micropyle: A small opening or pore in the outer coat through which the archaeocytes exit to begin forming a new sponge once conditions are suitable.
3. How does a new sponge develop from a gemmule?
The development of a new sponge from a gemmule, a process also known as hatching, begins when environmental conditions become favourable (e.g., return of water, optimal temperature). The mass of undifferentiated archaeocytes inside the gemmule becomes active and streams out through the micropyle. Once outside, these cells begin to differentiate and organise themselves into the various cell types needed to form a new, functional sponge that is a clone of the parent.
4. Under what conditions do sponges produce gemmules?
Sponges produce gemmules in response to the onset of unfavourable environmental conditions that could be lethal to the adult organism. The primary triggers for gemmule formation are:
- Extreme temperatures, particularly freezing during winter.
- Desiccation, which is the drying out of their aquatic habitat during a drought.
- Anoxia, or a significant lack of oxygen in the water.
- Changes in water salinity or pH levels.
5. Why is gemmule formation considered a crucial survival strategy for sponges?
Gemmule formation is a crucial survival strategy because it allows the sponge lineage to achieve dormancy and persist through periods of extreme environmental stress. The gemmule's tough, multi-layered coat effectively shields the vital archaeocytes from freezing, drying, and oxygen deprivation. This ensures that even if the entire adult sponge population dies off, the species can repopulate the habitat once favourable conditions return, making it an essential adaptation for life in unstable environments like freshwater ponds.
6. How does asexual reproduction via gemmules differ from budding in Hydra?
While both are forms of asexual reproduction, they differ significantly. Budding in Hydra is an external process where an outgrowth develops on the parent's body and matures before detaching. In contrast, gemmule formation is an internal process in sponges. The key difference is purpose: budding in Hydra is for propagation in favourable conditions, whereas gemmulation is a defensive, survival mechanism to endure unfavourable conditions. The parent sponge often disintegrates to release the gemmules, which is not the case in Hydra's budding.
7. What are archaeocytes, and what is their specific role in gemmule formation?
Archaeocytes are totipotent amoeboid cells found in sponges. 'Totipotent' means they are undifferentiated and can develop into any type of specialised sponge cell. Their role in gemmule formation is central: they are the very cells that are aggregated and packed into the core of the gemmule. Loaded with food reserves (glycoprotein), these archaeocytes remain dormant and protected within the gemmule, carrying the complete genetic blueprint to create a new individual.
8. What would likely happen to a freshwater sponge population if it lost the ability to form gemmules?
If a freshwater sponge population, such as *Spongilla*, lost the ability to form gemmules, it would face a high risk of local extinction. Freshwater habitats frequently experience seasonal freezing or drying. Without gemmules to act as a survival pod, the entire population would perish during winter or a drought, as the adult sponges cannot withstand these conditions. Gemmules are their primary mechanism for overwintering and surviving harsh periods, so losing this trait would eliminate their resilience to environmental change.
9. Can you provide an example of a sponge that commonly reproduces using gemmules?
A classic example of a sponge that heavily relies on gemmule formation is the freshwater sponge, *Spongilla*. This genus is commonly found in ponds, lakes, and slow-moving streams—environments prone to significant seasonal temperature shifts and potential drying. *Spongilla* typically produces gemmules in the autumn, which allows the species to survive the harsh winter and repopulate the water body in the spring.
10. Is gemmule formation a type of sexual or asexual reproduction? Explain the reason.
Gemmule formation is a definitive type of asexual reproduction. The reason is that it involves only a single parent and does not require the fusion of gametes (sperm and egg). The new sponge that develops from a gemmule is genetically identical to its parent, essentially a clone. This lack of genetic recombination and involvement of only one parent are the defining characteristics of asexual reproduction.
