welcome to solsarin. today on this post we are going to find out ”is volvox prokaryotic or eukaryotic?” , we also learn about reproduction system of volvox and other aspects of volvox.
the difference between prokaryote and Eukaryotes
A prokaryote is a unicellular organism that lacks a nuclear membrane-enclosed nucleus. The word prokaryote comes from the Greek πρό (pro, ‘before’) and κάρυον (karyon, ‘nut’ or ‘kernel’). In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota.But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria (formerly Eubacteria) and Archaea (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota. In the study of the origins of life, prokaryotes are thought to have arisen before eukaryotes.
Eukaryotes (/juːˈkærioʊts, -əts/) are organisms whose cells have a nucleus enclosed within a nuclear envelope. Eukaryotes belong to the domain Eukaryota or Eukarya; their name comes from the Greek εὖ (eu, “well” or “good”) and κάρυον (karyon, “nut” or “kernel”).The domain Eukaryota makes up one of the three domains of life; bacteria and archaea (the prokaryotes) make up the other two domains. The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the now cultivated Asgard archaea.Eukaryotes represent a tiny minority of the number of organisms;however, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes.Eukaryotes emerged approximately 2.1–1.6 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs.
is volvox prokaryotic or eukaryotic?
Volvox is a eukaryotic green algae. Algae of the genus Volvox are an example of the link between colonial organisms and multicellular organisms.
Volvox, genus of some 20 species of freshwater green algae (division Chlorophyta) found worldwide. Volvox form spherical or oval hollow colonies that contain some 500 to 60,000 cells embedded in a gelatinous wall and that are often just visible with the naked eye.
Besides the absence of a nucleus, prokaryotes also lack mitochondria, or any other membrane-bound organelles that characterize the eukaryotic cell, and it was once thought that prokaryotic cellular components within the cytoplasm were unenclosed, except for an outer cell membrane. But bacterial microcompartments, which are thought to be simple organelles enclosed in protein shells, have been discovered, along with other prokaryotic organelles.
While typically being unicellular, some prokaryotes, such as cyanobacteria, may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles.
Prokaryotes are asexual, reproducing without fusion of gametes, although horizontal gene transfer also takes place.
Who discovered volvox ?
Volvox colonies were first recorded by Dutch microscopist Antonie van Leeuwenhoek in 1700 and are widely studied as a genetic model of morphogenesis (how organisms develop specialized cells and tissues). Volvox also exhibit differentiation between somatic (non-sex cells) and reproductive cells, a phenomenon considered by some biologists to be significant in tracing the evolution of higher animals from microorganisms.
The somatic cells of a Volvox
The somatic cells of a Volvox colony each feature two flagella (whiplike appendages), several contractile vacuoles (fluid-regulating organelles), a single chloroplast (the site of photosynthesis), and an eyespot used for light reception. Neighbouring cells are often joined together by strands of cytoplasm, which enable cell-to-cell communication, and the colony moves through water by the coordinated movement of the flagella. The photosynthetic colonies are usually organized so that cells with larger eyespots are grouped at one side to facilitate phototaxis (movement toward light) for photosynthesis, and the reproductive cells are grouped at the opposite side.
Reproduction system of volvox
Most species of Volvox reproduce both asexually and sexually, and some, such as Volvox carteri, switch primary modes of reproduction at least once each year. Asexual colonies have reproductive cells known as gonidia, which produce small daughter colonies that are eventually released from the parent as they mature. In sexual colonies, developing ova or spermatozoa replace gonidia, and fertilization results in zygotes that form a cyst and are released from the parent colony after its death. Thick-walled zygotes formed late in the summer serve as winter resting stages.
Volvox forms hypnozygotes with thick, ornamented cell walls that provide protection from stressful environmental conditions.
Volvox reproduces asexually through the formation of autocolonies. Special gonidium cells divide to form daughter colonies that are small versions of the parents but with the flagella facing inwards. When the cells have divided into the same number of cells as the parent colony, the hollow colonies invert through a special pore so that the flagella face outwards. The parent colony splits open to release the newly formed autocolonies.
Bymale gametes and release a glycoprotein pheromone to trigger other colonies to sexually produce either a single egg cell or a packet of 16-64 elongate biflagellate sperm. Larger gonidia reproductive cells in the colony posterior give rise to the gametes and daughter colonies. There may be only a few gonidia per colony, or as many as 50.
Most Volvox species are dioceious, although a few are monoecious. The sperm packets are released from the parent colony and make their way into a female colony where they dissociate and fertilize the egg. Unfertilized eggs can still give rise to new colonies. The resulting zygote has thick, spiny protective walls and may be reddish in color. Only a single biflagellate cell survives the meiotic processes and then divides to form a Large colony .
2. Sexual Reproduction:
The sexual reproduction in Volvox is oogamous type. Some species of Volvox e.g., V. globator are monoecious or homothallic (Fig. 3) i.e., the antheridia and oogonia develop on same colony. Other Volvox species e.g., V. rousseletii are dioecious or heterothallic i.e., antheridia and oogonia develop on different colonies.
Monoecious species are usually protandrous i.e., antheridia mature before oogonia but some species are protogynous i.e., oogonia develop before antheridia. V aureus is mostly dioecious but sometimes can be monoecious.
Reproductive cells mostly differentiate in the posterior part of colony. These cells enlarge, lose flagella and are called gametangia. The male reproductive cells are called antheridia or androgonidia and female reproductive cells are called oogonia or gynogonidia.
The genus Volvox (dark blue highlighted species), which is characterized by spheroid size (typically >500 µm diameter), large cell number (>500), and composition of mostly terminally differentiated somatic cells (Coleman, 2012), is polyphyletic with at least three separate origins.
Classification of Volvox
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.
species of freshwater Volvox
A typical volvox colony
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.
Volvox is a hollow sphere of 500 – 50,000 cells, called a colony or coenobium.
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.
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, 2-3 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. Each cell measured about 15-25 µm in length.
Importance of Volvox
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.