Algae exhibit a wide range of thallus structures, from single-celled organisms to large seaweeds. Their thalli can be unicellular and motile, unicellular and non-motile, colonial, filamentous, heterotrichous, siphonous, uni-axial, multi-axial, or parenchymatous. Examples include Chlamydomonas as a unicellular motile type, Chlorella as a unicellular non-motile type, Volvox as a motile coenobial type, Spirogyra as a filamentous type, and Ulva as a thalloid type. Algae reproduce both sexually through structures

1. AlgaeAlgae
An OverviewAn Overview
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Characteristics
• Range in size from microscopic to single
celled organisms to large seaweed
• Autotrophic
• Form the reproductive structures –
gametangia or gamete chambers
• Aquatic and have flagella at some point in
life
• Often contain pyrenoids, organelles that
synthesis and store starch

3. STRUCTURE
• Thallus (haploid)
• Types of algae
–Unicellular[motile and non-motile]
–Colonial[flagellated & non-
flagellated]
–Filamentous[branched &
unbranched]
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•Heterotrichous
[different; trichomes or
branches
•Siphonous forms
•Uni axial forms
•Multi axial forms
•Parenchymatous forms

5. Forms of Green Algae
Unicellular Filamentous Colonial
Chlamydomonas
Spirogyra
Cladophora
Volvox
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6. Unicellular motile type: The simplest
unicellular plant body having rounded,
pear shaped bearing two flagella.
Example: Chlamydomonas
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7. Unicellular non-motile or coccoid type: Unicelllular
small more or less spherical, non-flagellate and
non-motile. Example: Chlorella
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8. Motile coenobial type: In this type unicellular cells with their
flagella protruded out is embedded together in a gelatinous
sheath to form a more or less rounded motile colony or
coenobium. Example: Volvox [Evolution in the Volvocine
Line]
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9. Non motile coenobial type: In this type the colony or
coenobium is composed of non-motile cells arranged in a
single layer along the long axis, e.g. Scenedesmus [Fig. a]
or cells are arranged end to end forming a pentagonal or
hexagonal meshes of net, e.g. Hydrodictyon [Fig. b] and
Pediastrum [Fig. c]
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10. Palmelloid type: It is a temporary stage formed in
Chlamydomonas under un favourable conditions.
(palmella)
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11. Filamentous type: In these types the cells are arranged one
upon the other to make the plant body filamentous which
may branched, e.g. Chladophora or unbranched, e.g.
Spirogyra.
SpyrogyraCladophora
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12. Thalloid type: In this type the plant body is
parenchymatous thallus like due to repeated cell
division in more than one plane, e.g. Ulva.
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13. Siphonaceous type: In this type the thallus is made up of
long hollow tube-like structure called coenocyte. The
coenocytic filament without partition or cell wall contains
many nuclei and is branched, e.g. Vaucheria
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14. Heterotrichous type: In this type plant body is
differentiated into a prostrate system of branched
filaments growing on the substrate and erect system away
from the substrate, e.g. Batrachospermum, Stigeoclonium.
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15. Special or complex type: The complex type of thallus
structures is shown by species of Chara ,Fucus, Laminaria,
Polysiphonia etc.
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16. IDENTIFY THE TYPE OF ALGAE
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17. CLASSIFICATION OF ALGAE
• 11 classes based on:
– COLOR
– TYPE OF CHLOROPHYLL
– FOOD-STORAGE SUBSTANCE
– CELL WALL COMPOSITION
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18. REPRODUCTION
MOST REPRODUCE BOTH
SEXUALLY AND ASEXUALLY
– Most sexual reproduction is
triggered by environmental stress
– Asexual Reproduction
• Mitosis
– Sexual Reproduction
• Meiosis
• Zoospores
• Plus and minus gametes
• Zygospore
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19. Reproduction in Multicellular Algae
• Oedogonium reproduction
– Antheridium-release
flagellated sperm that swim to
the oogonium
– Oogonium-houses the zygote
which is a diploid spore
• The spore undergoes meiosis
and produces 4 haploid
zoospores. One of the four cells
becomes a rootlike holdfast the
others divide and become a new
filament.
oogonium
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20. holdfast
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21. Spirogyra reproduce sexually by
conjugation
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22. Ulva Reproduces by Alternation of
Generations
• Two distinct
multicellular phases-
one is haploid and the
other is diploid
– Gametophyte is
haploid
– Sporophyte is diploid
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23. Class Chlorophyceae
• Green algaeGreen algae
• 7000 diverse species
• Biologist reason that green algae give rise
to land plants.
• Both green algae and land plants have
chlorophyll a and B as well as carotenoids
and store food as starch
• Both have walls made of cellulose
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24. Class Phaeophyceae
• 1500 species of BrownBrown
algaealgae
• Mostly marine and include
seaweed and kelp
• All are multicellular and large
(often reaching lengths of
147 feet)
• Individual alga may grow to a
length of 100m with a
holdfast, stipe and blade
• Used in cosmetics and most
ice creams
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25. Class Rhodophyceae
• 4000 species of RED AlgaeRED Algae
• Most are marine
• Smaller than brown algae and are often found at
a depth of 200 meters.
• Contain chlorophyll a and C as well as
phycobilins which are important in absorbing
light that can penetrate deep into the water
• Have cells coated in carageenan which is used
in cosmetics, gelatin capsules and some
cheeses
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26. Class Euglenophyceae
• 1000 species of
Euglenoids
• Have both plantlike
and animal-like
characteristics
• Fresh water
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27. Other Class Representatives
Diatoms – used in detergents,Diatoms – used in detergents,
paint removers, toothpastepaint removers, toothpaste Dinoflagellates – red tidesDinoflagellates – red tides
Important in the
formation of
petroleum
products
Golden algaeGolden algae
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28. Give an account of range of
thallus structure in algae with
the help of suitable diagrams
and example each.
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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.