They do not have a mouth to eat from and do not have an anus to excrete from. Instead, the Volvox eats mainly through photosynthesis. This means that Volvox are capable of converting sunlight into energy as primary producers. Because of their photosynthetic tendencies, the Volvox is rarely observed living in heavily shaded areas.
Their mobility allows them to seek out sunlight. Likewise, they are not often found in deep waters where the sunlight cannot reach them. There are two types of photosynthesis that may occur: oxygenic photosynthesis and anoxygenic photosynthesis. Volvox convert sunlight into usable energy mainly through oxygenic photosynthesis. During this process, sunlight transfers electrons within water and carbon dioxide to produce sugars or carbohydrates.
Carbon dioxide is released in the process while oxygen is created. Humans breathe oxygen, while plants breathe carbon dioxide. Each part of the Volvox structure is explained below:. All life on earth is classified into unique groups depending upon distinguishing characteristics. Each group can further be subdivided into smaller groups. The classification system for organisms can be broken down into seven different levels: kingdom, phylum, class, order, family, genus, and species in that order.
Kingdoms are the most basic classification of living things. There are five kingdoms in total. A phylum is the first attempt at narrowing down the list of organisms based on a physical similarity, which suggests that there is a common ancestry among similar organisms.
Classes, orders, families, and genus are all narrowed down even further based on similar traits until we finally get to a single species. Since Volvox is a genus, they can further be broken down into species. Each classification is further explained below as it related to the Volvox:. Volvox are commonly found within deep ponds, lagoons, puddles, ditches, swales, and more.
They tend to thrive in areas that receive a large amount of rainwater. They choose to live within nutrient-rich water and grow rapidly in the warmth. Volvox are commonly observed in pond scum. Volvox are widely regarded in the scientific community as a model species thanks to their unique reproductive tendencies.
They have the ability to reproduce both sexually and asexually. Asexual reproduction is the most common means of reproduction amongst the Volvox. Favorable or unfavorable environmental conditions will result in either asexual reproduction or sexual reproduction.
In the wild, it is unknown what the ratio is between asexually reproduced Volvox and sexually reproduced Volvox. A sex-inducing pheromone is also capable of triggering an asexual or sexual reproduction. The pheromone is mostly given off as a result of heat shock which is facilitated by oxidative stress. The sex-inducing pheromone is thought to have been key in the Volvox surviving through long periods of drought and extreme heat. Lastly, the pheromone may also be given off if the Volvox is wounded.
Asexual colonies of Volvox consist of both somatic and gonidia cells. The somatic cells are vegetative and completely incapable of reproduction. Although not capable of reproduction, somatic cells are mobile and serve their own unique purpose.
The gonidia, on the other hand, are not mobile. They are responsible for producing life to new colonies as they rapidly and repeatedly divide.
During sexual reproduction, both monoecious and dioecious colonies are brought to life. Monoecious colonies have both male and female reproductive organs and are hermaphrodites. Dioecious colonies have a sex assigned to them, whether male or female. The male colonies release sperm into the surrounding water while the female colonies have specialized cells that enlarge and become eggs. The sperm then fertilizes the eggs, and the eggs are released back into the water until they hatch and mature.
Colony inversion, as discussed previously, is the unique way in which the embryo of the reproductive cells invert. During their first stage of division, they form a mushroom cap or cupped appearance. Volvoxes are free-floating single-cellular algae but typically stay together as spherical colonies or balls of , cells. They can live in a variety of freshwater habitats, including ponds, pools, and ditches.
Under a microscope, volvoxes look like green marbles slowly rotating, making them one of the most adorable microscopic organisms. Volvox is a polyphyletic genus of Chlorophyte green algae in the family Volvocaceae. Volvox is classified in the class Chlorophyceae due to the presence of chlorophyll. Common species are Volvox aureus , Volvox globator , Volvox carteri , and Volvox barberi , etc. Photo source: Microbe wiki.
A typical volvox colony consists of a hollow sphere of cells. Each ball, or coenobium , is formed by a single layer of superficial cells joined together. Each cell is surrounded by a thick mucilaginous wall, forming a gelatinous layer that holds the hollow ball together.
In some volvox species, these mucilaginous walls may fill up the internal space of the sphere. These superficial cells are also called vegetative cells or somatic cells. Each vegetative cell sitting on the surface of the sphere bears two flagella. These flagella face the side of the surrounding water and beat to propel the whole colony through the water. This is why a volvox moves like a rolling ball.
The hollow ball consists of a layer of cells. Each cell has a pair of whip-like flagella. The flagella beat in synchrony, allowing the colony of cells to swim. Image modified from cronodon. Two flagella and one red eyespot are visible. Photo source: microscopy-uk. Other than flagellated somatic cells, a mature Volvox colony also contains reproductive germ cells.
The number of germ cells are less than somatic cells and locate in the center of the sphere. Inside the vegetative cell, there is a nucleus, a cup-shaped chloroplast , several contractile vacuoles water-regulating , and other cell organelles. Each vegetative cell has a red eyespot stigma which can sense light. Volvox, like other green algae, is photosynthetic and it swims toward the light called phototaxis to keep itself illuminated.
If the light is too strong, volvoxes also move away from very bright lights that may damage their chloroplasts. The Volvox ball has a preferred front-end and cells in the front of the sphere have larger eyespots than the rest.
These eyespots guide the movement of the volvox colony. The reproductive cells are grouped at the rest side. The anterior pole possesses a photosensitive eyespot and two flagella that make it possible for the colony to move towards the light.
The base of the flagella bears single cup-shaped chloroplasts. Volvox cell is enclosed by a cell wall and plasma membrane. The central cytoplasm possesses a central nucleus, contractile vacuoles, several mitochondria, endoplasmic reticulum, Golgi apparatus sometimes called dictyosomes in plant cells , ribosomes, etc. Contractile vacuoles act as excretory organs to regulate the water level of the cell. Pyrenoid is a protein body in the chloroplasts of algae that produce and store starch.
To coordinate the movement of flagella between individual volvox cells to beat in unison, all the vegetative cells on the surface are connected to their nearest neighbors by protoplasmic bridges.
In fact, the cell junction functions in the same way between our heart muscle cells to make our heart beating as a whole! The cell cluster in the center is a group of reproductive germ cells. All Volvox species are able to make their own nutrients through photosynthesis. Volvoxes are green because their cells contain chloroplasts which hold the green pigments, called chlorophyll.
The chlorophyll molecules absorb the sunlight and convert it into biological energy. At the same time, photosynthesis also consumes carbon dioxide CO 2 and produces oxygen O 2. Because of the plant-like activities, Volvoxes and all other green algae are autotrophic organisms.
Volvoxes are an important part of the aquatic ecosystem. They are part of the food chain which makes them an important component of the food items for many aquatic organisms such as fish. However, the overgrowth of Volvox aureus could result in a harmful algal bloom. An algal bloom is more frequent in warm waters having a high nitrogen content. Photo credit:: Flickr. A volvox ball or colony is usually a cluster of , cells.
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