VOLVOX
(Volvere to roll)
Common Indian Species: Volvox globator, V. prolificus, V. africanus and V. mereli.
Systematic Position :-
Sub-division : Algae
Class : Chlorophycene
Order : Volvocales
Family : Volvocacene
Genus Volvox
Common Occurrence: Commonly occurs in fresh water pools and ponds in rainy season, in the form of small balls, of the size of a pin-head.
Work to be done
Study external morphology, daughter colonies, sex organs and zygote with the help of given material and permanent slides, and identify the genus.
External Morphology
Take a few colonies, stain them with safranin,wash in water, mount in glycerine and study under low power and then under high power of microscope:-
1. Coenobium (a colony with definite number of cells) is a hollow sphere of mucilage made of many cells.
2. All the cells are arranged in the periphery of mucilaginuous sphere in a single layer.
3. Number of cells in a colony varies from 500 to 60,000 in different species.
4. Cells are connected with each other by the cytoplasmic strands, which form a net-like structure in the colony.
5. All somatic cells are green in colour and show a typical Chlamydomonad structure, i.e., similar to that of Chlamydomonas. Cells in Volvox globator are Sphaerella type.
6. Each cell remains surrounded by its individual mucilaginuous sheath.
7. Two flagella of equal length are present in each cell.
8. Two to six contractile vacuoles are present in each cell.
9. A single nucleus, cup-shaded chloroplast, with one or more pyrenoids and eyespot are also present in each cell.
Asexual Reproduction
Study the slide of daughter colonies:
1. Asexual reproduction is with the help of daughter colonies, which develop in parent colony.
2. Daughter colonies are present in the posterior side of the colony and formed by various divisions in some of the cells.
3. The number of daughter colonies in a parent colony varies from a few to as many as twenty.
4. Daughter colonies move for some time within parent colony. 5. Daughter colonies come out by rupturing the parent colony and behave as individual colonies.
Sexual Reproduction Study the slides of sex organs:-
1. Sexual reproduction is oogamous and coenobia may be homothallic or hetero- thallic.
2. Homothallic species are always protandrous, i.e.. antheridia develop first and oogonia later on.
3. Sex organs are present in the posterior half of the coenobium.
4.Antherozoids are formed in an enlarged cell (male gametangium), the contents of which divide into 32 to 256 parts.
5. Egg is present singly in female gametangium or oogonium which remains undivided.
6. Zygote is formed after fertilization, which takes place in the presence water
7. Zygote in rrounded by a three-layered smooth or spiny wall. It contains an orange red pigment called haematochrome
Read more:- Comments on CHLORELLA
Post a Comment