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Living Cells As A Colony
The body of an organisms consist of separate living cells held together by mucilage. All the cells move together as a unit and the individual cells carry out some activities independently.
The group of cells are called;
There are three common Algae, which are Pandorina, Endorina and Volvox they are all colonial algae, which they are made up of cells, each similar to chlamydomonas.
Each Eudorina consists of a colony of thirty two  cells, Each Pandorina consists of a colony of sixteen  and volvox contains hundreds or even thousands of cells in a colony. When a colonial organism consists of a constant number of cells, and the cells are specifically arranged into a definite form and integrated, the colony is called A coenobium.top↑
Let use volvox to describe as an example of an organisms in which living cells form a colony.
Volvox And Pandorina
Structure Of Volvox And Pandorina
That Is the structure of a colony of pandorinatop↑
Characteristics Of Volvox
a] Habitat: Volvox lives in fresh water ponds and ditches, under favourable conditions, the organism are present in large numbers causing the Habitat to be green.
b] Sensitivity: The organisms moves towards a source of light.
c] Locomotion: Volvox moves by the means of flagella with the front end leading and the coenobium rotates about the anterior-posterior axis in an anticlockwise manner as moves.top↑
d] Reproduction : The organisms reproduces by both Asexual and sexual reproduction.
Asexual Reproduction In Volvox
Most of the cells in a colony are body cells which do not reproduce.
But few cells in the posterior part reproduce by Asexual reproduction.
So let explain this clearly....
Each asexual reproductive cell enlarges in comparison with other cells and then divides many times to produce a plate of cells.
And by continuous division and rearrangement the cells form a hollow sphere of cells. These hollow sphere of cells are the young coenobium.
The young coenobia are present or lie in the interior of the parent until the parent eventually dies and disintegrates, then they are released.top↑
Sexual Reproduction In Volvox
A reproduction is said to be Sexual when there is formation of gametes and occurrence of fertilization.
So in some species such as Volvox globator, one individual forms both male and female gametes.
While in other species, such as Volvox aureus the are male or female gametes only.
That is, only one gament is present and it maybe the male gametes or the female gametes.
A cell that will form male gametes or antherozoids divides to form many male gament which are released into the water.
While the cell that form a female gamete forms only one large female gamete.
The male gametes swim to the female gamete. One male gamete fertilises the female gamete to form a resting oospore. Which remains in the parent coenobium for sometime.
Eventually it is released and divides many times to form a new coenobium.top↑
e] Structure : Volvox is a colonial green alga.
The colony or coenobium is a hollow sphere of cells arranged in a single layer near the outer surface.
The cell are separated from one another by mucilage. The mucilage is also where all cells are stored.
This mucilage is soft at the centre of the sphere and firms near the external surface.
Also the number of cells in a colony varies from one species to another and it ranges from about 1000 to 20,000.
A colony is readily visible to the naked eye.top↑
Each cell has a chloroplast with pyrenoid, eye spot, two flagella, contractile vacuoles and nucleus.
The flagella protrude or extend through the mucilage.
There is a process called protoplasmic processes , this process is the process connecting the cells. The cell in one coenobium are similar in structure and the entire colony has a definite anterior and posterior end.
And that all on living cell as a colony,
Next class will be on living cell as a filament.
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