After reading this topic you will learn about Habitat, Structure of Colony, Sexual and Asexual Reproduction in Volvox
Volvox is found in both in freshwater and marine water. Its presence gives water green color. It appears both in spring and summer season but mostly grow in rainy season. Season also affect on Sexual and Asexual Reproduction in Volvox.
Volvox always live in colony.
The cells of volvox colony are always fixed so that is called coenobium.
Spherical in shape. The rang of each colony cells from 500-50,000.
The outside of the colony consists of mucilage.
Volvox cells have biflagellate. Flagellate found outside of colony.
The collective movement of the flagella help to move the colony.
The shape and structure of all cells of a colony have alike.
The cell is closely packed. They are organized to form polygonal shape in the volvox colony.
The mature cells wall is thick & mucilaginous.
Their cell looks like pear shaped. These cells make periphery around the colony.
The structure of volvox same as Chlaymydomonas.
Every cell has Biflagellate and attached at the outer side of the cells.
Each cell has cup shaped chloroplast. Chloroplast have one pyrenoid.
They have two contractile vacuoles that help in maintain the water balance in cell.
A nucleus found in center of cell and connected with flagella by neuromotor.
It also has eyespot near the anterior surface of colony that help in swimming in light.
REPRODUCTION (Sexual and Asexual Reproduction in Volvox):
In volvox both type of reproduction present such as asexual and sexual.
Asexual reproduction occurs when condition is favorable.
Already present colonies reproductive cells help to produce new colonies.
Only posterior side of cell take part to make new colony by asexual reproduction
The cells increase in size. They are larger in size. These are known as gonidia.
These Gonidia develop in to many pyrenoids.
There are 5 to 20 gonidia in each colony.
Each gonidia produce daughter colony.
HOW DAUGHTER COLONY DEVELOPED IN VOLVOX?
The gonidia move towards interior side of the colony. The first step gonidium divide longitudinal and this forms two cells.
In second step of division cell also divide longitudinal at right angle to the first into four cells.
The third step four cells divide longitudinal and make eight cells from four cells are central.
These eight cells arranged in curved like structure that structure is called plakea stage.
These eight cells future longitudinal divide and make 16 cells.
These arrangements look like hollow-sphere.
This hollow sphere open on exterior side as a small hole that’s called phialopore.
The cells continue divide until the cells reaches the distinctive of that species.
The last step is inversion of colony. The cells become opposite in direction, their anterior end must face the periphery of colony.
Thus, new colony comes out from paternal cells.
Sometimes it remains within the parent colony.
Sexual Reproduction Occur When Condition Are Unfavorable.
The Oogamous type of Sexual reproduction mostly present in volvox. Colony may be monoecious or dioicous.
Female gametes known as gyn gonidia and male gametes are called antheridia.
these reproductive cells commonly called gametangia.
ANTHERIDIUM OR MALE PART
The male part (gametangia) are called antheridium. The antheridium. protoplast of divides many times like asexual reproduction. It divides again and again and produces 16-128 cells. These cells named antherozoid.
When division was compete they develop new flagellum at ends point of cells.
Types of Antherozoids:
There are two types of Antherozoids cycles:
a) When cells are 128 or less after division. In this type, all the antherozoids colony are liberated in the form of mass, Mass swims and reaches to the oogonium. Then the cells of antherozoid gets detached.
b) If cell divide more than 128. In this type, antherozoids call become arranged itself into a hollow sphere shape within the antheridium. These cells undergo inversion process. After inversion antherozoids cells separate from each other. Then they are liberated fertilization.
Then female reproduction organ is Gynogonidia or oogonia. Female sex part is larger than male sex part. The protoplast of female converts into single oosphere in rounded in shape.
The male part (Antherozoids) enter oogonium through a pore. Only single antherozoid enter in female sex and zygote is formed. When Zygote formed it secretes a thick wall that become oospore. This wall consists of three layered. Oospore produces a secretion in large amount that called heamotochrome, due to this its color orange red. They release oospore and in favorable condition they germinate same as asexual reproduction.