Volvox
Classification
Sub-division —_ Algae
Class — Chlorophyceae
Order a Volvocales
Family — Volvocaceae
Genus — Volvox
{I] Thallus, External features of a colony.
{II} Asexual reproduction. Daughter colonies.
{III} Sexual reproduction. Sex organs and the zygote.
- Stain a few colonies in safranin, wash in water and mount in glycerine to study the external features of a Colony and structure of a cell.
- Thallus is multicellular, motile and coenobial colony.
- Colonies are mostly spherical, rounded or oval in shape.
- It is hollow in the Centre and cells are arranged in a single layer towards the periphery. Layer of cells is surrounded by a gelatinous mass which forms the outer and firm limiting layer.
- The number of cells in a colony varies from 500-6,500 according to the species.
- Each cell of the colony is connected with a few of the neighboring cells by thin and delicate cytoplasmic strands.
- Each cell is enveloped by an _ individual gelatinous sheath.
- All the cells of a colony are typically chlamydomonad
in shape, size and structure. Each vegetative cell is biflagellate, motile and
ovoid. The two flagella are anteriorly inserted. Two contractile vacuoles are situated
near the base of flagella, one each at the base of each flagellum. Cup-shaped chloroplast
occupies much of the posterior part in which is situated a single pyrenoid. In the
cavity formed by cup-shaped chloroplast lies a single nucleus, surrounded by
cytoplasm. Cytoplasm is rich in volutin grains. Eyespot or stigma occupies
antero-lateral position.
[II] Asexual reproduction
1. Asexual reproduction takes place by the formation of daughter colonies.
2. Daughter colonies are formed mostly in the formed mostly in the posterior part of the colony.
3. Many small daughter colonies remain embedded in the parent colony. These appear similar to parent colony except its smaller size.
4. Daughter colonies are liberated by the gelatinization of the wall of the parent colony.
[III]Sexual reproduction
1. Colonies may be monoecious or dioecious.
2. Sexual reproduction is oogamous.
3. Antheridia and oogonia are developed most! in the
posterior part of the colony.
4. Antheridium produces biflagellate antherozoids,
while non-motile oogonium develops a single egg.
5. As a result of fertilization oospore or zygote is
produced.
6. Zygote is orange-red in colour because of the presence
of haematochrome.
7. Zygote is a thick-walled structure. The wall is
made up of two or three layers, Outermost layer is thick and may be smooth or ornamented.
👉Life cycle of volvox, Sexual Reproduction in Volvox,
👉Protista Kingdom प्रोटिस्टा जगत
Identification
Sub-division—Algae, (1) Thallus simple, (2) Presence of chlorophyll, (3) Cell wall of cellulose.
Class—Chlorophyceae. (1) Chloroplasts green. (2)
Photosynthetic product starch, (3) Motile cells flagellated, (4) Flagella equal
in length.
Order——Volvocales. (1) Vegetative cells flagellated,
(2) Thallus motile.
Family—Volvocaceae. (1) Thallus colonial, (2) Division
of cells in longitudinal plane.
Genus—Volvox. (1) Colony spherical or sub-spherical, (2)
Number of cells at least 500.
Hints for collection- It can be collected from
freshwater and permanent ponds and pools where it occurs as small green balls
on the surface layer. The alga grows abundantly during spring and disappears
during Summer.
👉Life cycle of volvox, Sexual Reproduction in Volvox,
👉Protista Kingdom प्रोटिस्टा जगत