Reproduction of Algae | Vegetative reproduction, Asexual reproduction & Sexual reproduction

2. REPRODUCTION OF ALGAE
Algae reproduce by various methods, as follows;
o Vegetative
o Asexual
o Sexual

3. VEGETATIVE REPRODUCTION
 The type of reproduction, in which the whole new plant is
produced from an organ (or vegetative part of the plant)
which is not involved in sexual reproduction is called
Vegetative reproduction.
 Vegetative reproduction is a form of asexual reproduction
in which specialized organs formed by the parent, become
detached and generate new individuals.
 In algae, the vegetative reproduction is widespread and
commonly seen among filamentous members.

4. TYPES OF VEGETATIVE
REPRODUCTION
1. Fragmentation
2. Hormogonia
3. Budding
4. Propagules / Bulbils
5. Akinetes
6. Cell division
7. Fission
8. Abscissed Pinnules / Proliferous shoot
9. Amylum stars / Protonema like outgrowth

5. FRAGMENTATION :
In this process, the fragments or pieces of the parent
become detached and grow into new individuals.
Eg; Hormidium, Nostoc
HORMOGONIA :
In cyanophyta, the short lengths or small fragments of
trichomes are cut off by the occurrence of simple breaks
in the filaments. Thes are called are Hormogonia. They
may also form after the formation of the intercalary cells
called necridia or seperation disc.
Eg; Oscillatoria, Nostac

6. BUDDING :
A lateral bud is formed by the vesicles by the formation of
a cell wall in some genera of green algae. This bud
seperates and develops into another vesicle with its own
rhizoid. Eg; Protosiphon
PROPAGULES / BULBILS :
Some wedge-shaped modified branches develop in some
genera, as in Sphacelaria. They bear two or more short
processes called propagules or bulbils. These are rich in
food material, and on being detached they develop into
new plant.

7. AKINETES :
The formation of thick walled cells containing large
quantity of food reserves is very common in sevral algae.
These cells are called Akinetes. They can withsatnd
unfavourable conditions and thus help in perennation.
Each akinete can germinate into a new plant.
Eg; Anabaena
CELL DIVISION :
In desmids and diatoms, cell division is a common
method of vegetative reproduction. In desmids, cell
division occurs when a set size is attained by the algae. In
diatoms, vegetative or mitotic cell division starts after a
period of increase in cell volume, thus resulting in a
progressive reduction cell size.

8. FISSION :
In unicellular flagellates, the vegetative reproduction
takes place by longitudinal fission of the cell along with
the simultaneous reformation of organelles which have
not divided, Fission usually starts at the anterior end
progresses downward. Eg; Euglena.
ABSCISSED PINNULES :
Abscission of older pinnules in Bryopsis and proliferous
shoots in Caulerpa are also the means of vegetative
reproduction. These abscissed pinnules or shoots
germinate into new plant.

9. AMYLUM STARS :
These are found in Chara. Star like aggregates of cells
developing on the lower nodes are called amylum stars.
They are filled with starch. Sometimes, Protonema like
outgrowths also grow on the lower nodes in Chara. Both
these vegetative structure give rise to new plant.

10. ASEXUAL REPRODUCTION
 Asexual is a type of reproduction from one individual,
without the fusion of sex cells from two different parents.
 Therefore, the asexual reproduction may also be defined as
“any form of reproduction not depending on a sexual
process or on a modified sexual process”.
 In some aspects, asexual reproduction is very similar to
certain forms of vegetative reproduction, particularly in
flagellate algal groups.
1. Zoospores.
2. Non motile asexual spores.

11. ZOOSPORES – The motile asexual spore
 The zoospores are unicellular, flagellated and motile
structures, each with a small amount of protoplast.
 These are known from Chlorophyceae, Prasinophyceae,
Xanthophyceae, Chrysophyceae, Dinophyceae,
Prymnesiophyceae, Eustigmatophyceae and
Phaeophyceae.
 The zoospores are usually biflagellate structures devoid
of a cell wall.
 In general, the production of zoospores, as of other
asexual spores, is preceded by mitotic divisionof the
nuceli followed by partion of protoplast. Resulting into
the formation of 2, 4, 8 or more zoospores formed by
longitudinal cleavage of the parent cell wall.

12.  The entire cell thus functions as a sporangium called
zoosporangium, from which zoospores escape by rupture
or lysis of the parental wall.
 Zoospores swim for some time, settle down on some
sustainable substratum, attain a cell wall and each
develops into a new plant.
 In many members of Ectocarpales, zoospores from
plurilocular sporangia regenarate the sporophyte
generation, as in Ectocarpous, Laminariocolax and
Giffordia.

13. NON-MOTILE ASEXUAL SPORES
1. Aplanospores: The protoplast released from the algal
cell as non-motile and non-flagellate spore is called an
aplanospores. Eg; Ulothrix, Vaucheria.
2. Autospores: Such aplanospores which the same
morphological features as that of parent cell are called
autospores as in Chlorerlla.
3. Hypnospores: Aplanospores with very thick wall are
called hypnospores, as in Chlamydomonas.
4. Tetraspores: In some Rhodophyta and Phaeophyta
instead of mitosis, the spores are also formed after
meiosis, and these are called tetraspores.

14. 5. Exospores: In Chamaesiphon and some other epiphytic
blue-green the cell membrane bursts at the apex,
exposing the protoplast, which soon becomes
fragmented into spherical spores called exospores.
6. Endospores: In Dermocarpa calvata and some other
blue-green algae, the successive divisions of cell
contents in three planes result in the formation of
endospores.
7. Monospores: In Tilopteris, chantransia stage of
Batrachospernum and some other brown algae and red
algae non-motile spore developing singly in a
sporangium is called monospores.
8. Carpospores: These are non-motile spores formed by
the divisions of the zygote in some red algae, Eg;
Batrachospernum, Polysiphonia. They are formed in the
carposporangium of carposporophyte.

15. 9. Neultral Spores: The vegetative cells in the some algae
transform directly into the spores called neutral spores.
10. Bispores: In some red algae, two spores develop in a
sporangium. These are called bispores developing in a
bisporangium.
11. Polyspores: In some red algae more than four spores are
formed in a sporangium after reduction division. These
haploid spores are called polyspores or paraspores.
12. Statospores: Smooth walled or partially ornamented
thick-walled internal cysts or statospores are found in
some members of Bacillariophyceae, Chrysophyceae.
13. Cysts: Cysts are the resulting stages of many algae, in
Vaucheria, amoeba like multi-nucleate cysts develop,
which, on liberation, germinate into new thalli.

16. SEXUAL REPRODUCTION
 Sexual reproduction is a type of reproduction which
involves the fusion of two cells and their nuclei from two
parent individuals, so that the offspring receives the
genetic material from both parents.
 Fusion actually means the joining together of two
gametes to form a zygote.
 A gamete is a haploid sex cells, whose functions is to
join with a gamete of opposite sex to form a diploid
zygote.
 Zygote is, therefore, a diploid cell which is produced by
the fusion of two haploid gametes.

17.  A fertilized ovum is a zygote, and it develops first into an
embryo and then into a sporophyte. Blue-green algae and
bacteria lack sexual reproduction.
 In many genera of Chrysophyta and Bacillariophyta, the
sexual reproduction has been rarely observed, although it
is probably a feature of the life history of most of the
species.
 In algae, the sexual reproductive units may vary in their
morphology and behaviour. Due to this, the sexual
reproduction in algae may be of three different types, viz.
isogamous, anisogamous and oogamous.

18. ISOGAMY
 When two fusing gametes of the opposite sex are
morophologically identical and have same size, they are
called isogametes and their process of fusion is called
isogamy.

19. ANISOGAMY
 When two fusing gametes of the opposite sex are
morophologically dissimilar and have different size, they
are called anisogametes and their process of fusion is
called anisogamy.

20. OOGAMY
 When two fusing gametes are extremely dimorphic, the
larger, non-motile and called egg, and the smaller, motile
by flagella and sperm or male gamete, the gametes are
called oogamous, their process of fusion is called oogamy.