Spirogyra is a common freshwater green alga that forms long, thin filaments. It reproduces both asexually through fragmentation and sexually through conjugation. During conjugation, projections grow out from adjacent cells in different filaments and their contents fuse, forming zygospores. The zygospores are resistant and may lie dormant before germinating into new haploid filaments.

1. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and other references: FOR
STUDENTS' additional reading purpose ONLY
1
Classification:
Class: Chlorophyceae
Order:
Zygnematales/Conjugales
Family: Zygnemaceae
Genus: Spirogyra
(Fritsch, 1935)

2. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures, books
and other references: FOR STUDENTS' additional reading purpose
ONLY
2
Spirogyra is a common free-floating green alga. It is
an unbranched, filamentous, fresh water alga. The
filament is very fine, long and slimy to touch, hence
the name 'pond silk' or water silk. It forms a green
floating mass, hence the name 'pond scum'. Each
filament, when examined under the compound
microscope, is seen to be made up of fairly long
cylindrical cells attached end to end. In each cell,
just within the cell wall, there is a lining layer of
cytoplasm enclosing a large central vacuole. The
nucleus is found in the centre of the vacuole,
suspended by fine cytoplasmic strands that arise
from the outer cytoplasmic layer.

3. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures,
books and other references: FOR STUDENTS' additional
reading purpose ONLY
3

4. The chloroplast is quite characteristic of the plant.
It is long, flat and spirally coiled inside the cell. In
each cell there may be 1-14 chloroplasts. Many
pyrenoids are embedded along the length of the
chloroplast. They contain chlorophyll and make
their food by photosynthesis. Spirogyra is a
filamentous alga. Its cells form long, thin strands
that, in vast numbers, contribute to the familiar
green, slimy ‘blanket weed’ in ponds. Seen under
the microscope, each filament consists of an
extensive chain of identical cells.
7/23/2018
This lecture slide/hand-out is not an alternative to lectures,
books and other references: FOR STUDENTS' additional
reading purpose ONLY
4

5. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures,
books and other references: FOR STUDENTS' additional reading
purpose ONLY
5
cytoplasm
nucleus
vacuole
Each cell contains a helical chloroplast, a nucleus,
cytoplasm and a vacuole enclosed in a cellulose
cell wall.
chloroplast
nucleus

6. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
6
Reproduction:
Spirogyra multiplies vegetatively, asexually
and sexually. Sexual reproduction is by
conjugation.
1. Fragmentation in Spirogyra

7. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
7
Fragmentation is a form of vegetative
reproduction where the organism is split into
new a fragment which develops into new.
Fragmentation is the normal mode of
reproduction in Spirogyra which is also known
as vegetative reproduction. Fragmentation can
occur due to mechanical injury caused by water
currents, biting aquatic animals, and or by
gelatinization of middle lamellum.

8. 7/23/2018This lecture slide/hand-out is not an alternative to lectures, books and other
references: FOR STUDENTS' additional reading purpose ONLY
8
During this process the filaments splits or break
into single cells or small lengths. Then by the
process of mitosis and through cell enlargement
each newly formed piece grows into a new
filament.
Each fragment will develop in to new filament
and splitting of filaments may or may not be
deliberate. Meiosis cell division is not present in
fragmentation. Fragmentation of algal mass of
spirogyra results in a clone which is genetically
identical to the parent algae.

9. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
9
Spirogyra Sexual Reproduction

10. 7/23/2018This lecture slide/hand-out is not an alternative to lectures, books and other
references: FOR STUDENTS' additional reading purpose ONLY
10
Sexual reproduction
only takes place under
adverse conditions, for
example, when the
pond dries up. This can
be simulated in a dish in
the laboratory by
allowing a collection dry
up gradually over a few
days.

11. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
11
Reproduction: Spirogyra reproduces both
asexually and sexually. Asexual reproduction
is by means of spore productions. There is
also vegetative reproduction in some species.
(1) Vegetative Reproduction:
it takes place due to fragmentation. The
filament may break due to mechanical injury
or due to dissoloution of middle lamella or
gelatinization of cells.

12. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and
other references: FOR STUDENTS' additional reading purpose ONLY
12

13. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and other
references: FOR STUDENTS' additional reading purpose ONLY 13
(2) Asexual Reproduction:
It takes place by means of akinetes, aplanospores and
azygospores. These are formed due to the contraction of
protoplasm and formation of new cellulose walls around it.
These spores are formed under unfavourable conditions.
During favourable conditions, they germinate to form the
new filament.
(3) Sexual Reproduction:
Sexual reproduction in Spirogyra takes place by
conjugation. It is isogamous type. Fusion of these non-
flagllate gametes is resulted in zygospore. Two methods of
conjugation have been found in Spirogyra i.e. (1) Lateral
conjugation and (2) Scalariform conjugation. These are
discussed below.

14. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and
other references: FOR STUDENTS' additional reading purpose ONLY
14
(i) Lateral conjugation:
It takes place between two cells of the same filament. Such
species are, therefore, called homothallic. Lateral conjugation
again is of three types:
(a) Indirect Lateral conjugation (b) Terminal conjugation (c)
Direct Lateral conjugation.
(a) Indirect Lateral conjugation:
In this process there is a tube-like outgrowth in-between two
adjacent cells close to the common cross walls. These
outgrowths extend laterally ultimately forming conjugation
tube. The contracted protoplasm of one cell moves to the
adjacent cell and fuses to form the zygospore. The zygospore
is diploid in nature.

15. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
15

16. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and other references:
FOR STUDENTS' additional reading purpose ONLY
16

17. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
17

18. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
18
(b) Terminal conjugation:
In this method, the so-called male gamete enters the female
gamete by perforating the septum of conjugation tube. The
conjugation tubes are produced on either side of the septum
of the two conjugating cells.
(c) Direct Lateral conjugation:
In this case, the filament is attached to the substratum by its
basal cell. Lateral conjugation takes place between two cells
placed immediately next to the basal cell. One cell swells
known as the female cell and the other cell becomes conical
known as male cell. The male gamete passes through the
septum piercing it. The nuclei are fused forming the diploid
zygospore.

19. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and
other references: FOR STUDENTS' additional reading purpose ONLY
19
(ii) Scalariform conjugation:
The scalariform conjugation takes place between the cells of
two different filaments, therefore, the species are
heterothallic. In this case, two physiologically different
filaments lie parallel to each other. Then two outgrowths arise
which are called conjugation tube. Further growth of the
conjugation tube pushes the filaments apart.
Later the conjugation tube dissolves forming a passage.
Simultaneously the protoplasm of the conjugated cells
contracts and forms gametes. The male gamete moves
through the conjugation tube into the female cell of another
filament.

20. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
20

21. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
21

22. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
22
Zygospore - The mature zygospore has three layered walls.
These zygospores are liberated by the death and decay of
the female cell wall. Zygospore germinates during favourable
condition. Each zygospore nucleus divides meiotically to
produce four haploid of which three degenerate and only one
remains functional. On germination, the zygospore gives rise
to a single haploid filament. In this way, the life cycle is
completed.
Fusion of two nuclei results in formation of diploid
zygospore. After the formation of zygospore the cell of male
filament becomes empty while the cells of the female
filament are filled with zygospore.

23. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures, books
and other references: FOR STUDENTS' additional reading purpose
ONLY
23

24. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures,
books and other references: FOR STUDENTS' additional reading
purpose ONLY
24
Two or more filaments
come to lie side by
side and projections
grow out from cells
which are in close
proximity. There is
probably some sort of
chemical message
released by
contiguous filaments
The wall between the projections starts to break
down where they meet and cell contents start to
shrink by plasmolysis (water loss).

25. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and
other references: FOR STUDENTS' additional reading purpose ONLY
25

26. 7/23/2018 This lecture slide/hand-out is not an alternative to lectures, books and
other references: FOR STUDENTS' additional reading purpose ONLY
26

27. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures, books
and other references: FOR STUDENTS' additional reading purpose
ONLY
27

28. 7/23/2018This lecture slide/hand-out is not an alternative to lectures, books and other references: FOR
STUDENTS' additional reading purpose ONLY
28

29. 7/23/2018This lecture slide/hand-out is not an alternative to lectures, books and other references: FOR
STUDENTS' additional reading purpose ONLY
29
The protoplast of one cell moves through the conjugation tube
and fuses with the protoplast of the other. This is a form of
anisogamous reproduction and is referred to as scalariform
conjugation; functionally, the protoplast that moves is a male
gamete. Both gametes are non-flagellated.
The resulting zygote develops a thick wall which is resistant
to adverse conditions and may lie dormant for some time. On
germination, the nucleus of the zygote undergoes meiosis;
four nuclei are formed (as is usual in meiosis), three
degenerate and the resulting uninucleate cell divides to form a
haploid filament.

30. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
30

31. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures, books
and other references: FOR STUDENTS' additional reading purpose
ONLY
31

32. 7/23/2018
This lecture slide/hand-out is not an alternative to lectures, books and other references: FOR STUDENTS' additional reading
purpose ONLY
32

33. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
33

34. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
34
Observe the figures carefully and label them

35. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
35
1. Give a brief account of lateral and scalariform
conjugation in Spirogyra.
2. Give an illustrated account of the life history of
Spirogyra.
3. The filaments of Spirogyra loose their colour after
conjugation. Why ?
4. Enlist the identifying characters of Spirogyra.

36. 7/23/2018
This lecture slide/hand-out is not an
alternative to lectures, books and other
references: FOR STUDENTS' additional
reading purpose ONLY
36
References
Fritsch, F.G. 1935, 1945. The Structure and Reproduction of Algae. Vol. I
& II. Cambridge Univ. Press. Cambridge. (589.3/6167, 6168)
Mauseth, J. D. (1998). Botany: An introduction to plant biology. Boston:
Jones and Bartlett.
Raven, P. H., Evert, R. F., & Eichhorn, S. E. (1999). Biology of plants. New
York: W.H. Freeman.
Sharma, O. P. (2011). Algae. New Delhi: Tata McGraw Hill.
Vashishta, B. R., & Sinha, A. K. (2014). Botany for degree students : Fungi.
New Delhi: S. Chand and Company Ltd.
Vashishta, B. R. (1960). Botany for degree students. Delhi: S. Chand.