Phyccology

FACULTY OF NATURAL AND COMPUTATIONAL SCIENCE
DEPARTMENT OF BIOLOGY
COURSE TITLE: PHYCOLOGY
COURSE CODE: Biol2031
Prepared by: Yitayeh Alemu (MSc. in botany)
1

1. Introduction
• The word phycology is derived from the Greek word “phykos”, which means
“seaweed.”
• Phycology (algology) is the study of algae
• The algae are thallophytes (plants lacking roots, stems, and leaves) that have
chlorophyll a as their primary photo synthetic pigment
• Algae are primary photo-synthetic organisms in freshwater and marine food
chains.
• Used as a food source for zooplankton and filter feeding shellfish, the algae are an
extremely important group organisms.
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• They are aquatic both marine and freshwater and occur on and within soil and on
moist stones and wood as well as in association with fungi and certain animals.
• It is thought that 90 percent of the photosynthesis on earth is carried on by aquatic
plants.
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2.General characteristics and ecology
2.1. General 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
 Primitive plants
 No true roots, only attachment structures (Holdfasts)
 Produce spores (not seeds)– motile or non-motile
 Most have sexual and asexual reproduction
 Non-vascular, do not possess an internal transport system. 4

2.2. Ecology of Algae
2.2.1. Planktonic algae
• The term ‘planktonic algae’ refers to the forms found floating or freely swimming in water.
• Among the freshwater planktonic algae, forms such as Chlorella, Chlamydomonas, Volvox
and Eudorina of Chlorophyceae.
2.2.2. Benthic algae
• The term ‘benthic algae’ refers to aquatic algae found attached to one or the other
substratum.
• Among the freshwater forms, Cladophora, Pithophora, Chara, Nitella etc.
• And among marine forms most members of Phaeophyceae and Rhodophyceae are the
common examples. 5

2.2.3.Thermal Algae
• Some algae withstand or tolerate a very high temperature and these are often called
thermal algae.
• Such forms are known to grow up to 85°C, nearly boiling water.
• Majority of thermal algae belong to Myxophyceae, e.g., Synechococcus elongates.
2.2.4.Soil algae
• Such forms of algae that grow on or in soil are called soil or terrestrial algae or
edaphophytes.
• Vaucheria, Botrydium, Zygnema, Oedogonium, Microcoleus, Nostoc, Oscillatoria etc.
occur on soils.
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2.2.5. Crybophytes
• Certain algae are found growing on snow covered peaks of high mountains imparting
attractive colors to snow.
• Common examples are—Haematococcus nivalis, Chlamydomonas yellowstonensis.
2.2.6. Lithophytes
• The algae growing attached to stones and rocky surfaces are called lithophytes.
• These may be of two types:
(i) Epilithic: These include algae living on surface of rocks, e.g., Calothrix, Rivularia,
Polysiphonia etc.
(ii) Endolithic: These include algae which live inside the rocks, e.g., Dalmatella and
Podocapsa. 7

2.2.7. Epiphytes
• Some algae grow attached on the other plants and are called epiphytes.
• Such algae do not obtain the food from the plants on which they grow rather require support only.
• Eg. Bulbochaete.
2.2.8. Halophytes
• Certain algae inhabit in water with high percentage of salt, Eg. Dunaliella and Stephanophora.
2.2.9. Symbionts
• A pretty large number of algae live in association with dissimilar organisms for their mutual
advantage and are called symbiotic algae.
• Lichens are the best examples of symbiosis where the association lies in between algae and fungi.
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2.2.10. Endozoic Algae
• Endozoic algae inhabit the protoplasm of other organisms.
• Eg. Chlorella like algae are found living within Paramecium.
2.2.11. Parasitic algae
• Some algae, for their food, are dependent on other plants and are termed as parasitic
forms.
• The common intercellular parasite Cephaleuros(Chlorophyceae) grows on the leaves of
angiosperms like Magnolia, Rhododendron.
• Polysiphonia fastigata is a semi parasite occurring on another algae.
• Ascophyllum nodosum (Phaeophyceae), Some blue green algae Anabaeniolum,
Oscillatoria and Simonosiella are found as parasite on man and in the intestines of
animals.
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3. Cellular and thallus organization
• Thallus refers to the body plan of the algae
Blade (fronds)---- the leaf of the algae but not true leaf
Stipe------the stem of the algae but not true stem
Holdfast ----- the root of the algae but not true root
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3.1.Unicellular
• They are single celled algae.
• They may be motile flagellated.
• example: Chlamydomonas.
Figure 3.1.1. Chlymadomonas
• They may be non-motile coccoid.
• example: Chlorella
Figure 3.1.2. Chlorella
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Colonial Thallus
• In this form daughter cells which arise as a result of cell division, remain loosely
held together in common gelatinous mass.
• These forms are of two types
i) Coenobial Forms
 Colonial form with definite number of cells arranged in definite manner.
Coenobium are of two types.
a)Motile
 They have flagella on their body and are able to move e.g. Volvox, Eudorina,
Pandorina etc.
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b)Non-motile
 They lack flagella e.g. Hydrodictyon, Pediastrum, Scenedemus, etc.
Colonial non-motile algae
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II) Cell Aggregation
• The daughter cells are not aggregated in a definite manner in the colony thus the
colonies are not of constant size and shape. They are of following types
a)Palmelloid Forms
• Cells remain irregularly arranged in a common gelatinous matrix.
• They function as independent entities.
• These forms may be temporary (Chlamydomonas) or permanent (Tetraspora) other
e.g. Asterococcus, Aphanocapsa.
b) Rhizopodial Forms
 In these colonial forms, cells are aggregated with each other through rhizopdia e.g.
Chrysidiastrum. 16

C) Dendroid Forms
• Cells are aggregated with each other in a branching pattern through
mucilagenous strands arising from the base of each cell.
• Such colonies look like a microscopic tree.
E.g Ecballocystis, Chrysodendron etc.
Cell aggregation
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3. Siphonaceous Coenocytic Forms
• Plant body is unicellular and elongated tubular structure (e.g. Charium) or
umbrella shaped uni-nucleate body e.g. Acetabularia.
• In more advanced siphonaceous algae, thallus is aseptate and multinucleate
structure known as coenocyte.
• Septa develop only to delimit the reproductive organs to seal off the damaged
parts e.g. Protosiphon Botrydium, Vaucheria, Caulerpa
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4. Filamentous Thallus
A thread like multi-cellular thallus is known as filamentous thallus.
These are of following types
i) Simple Unbranched Thallus
The thallus is simple is simple and unbranced and may be free floating as in Spirogyra or may be
attached to substratum with the help of rhizodial cells, e.g. Ulothrix, Oedogonium, Zygnema, Nostoc,
Anabaena, Oscillatoria etc.
ii)Branched Filamentous Thallus
• Thallus give rise to lateral outgrowth or branches which may be true or false branches.
a)True Branches
True branches arise as a result of occasional cell division in a second plane e.g. Cladophora.
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b) False Branches
 False branches arise in blue-green algae e.g. Scytonema due to breakage and
resumption of growth by trichomes in mucilagenous sheath of filaments.
iii) Heterotrichous Thallus
 Highly evolved filamentous habit where thallus is differentiated into
creeping prostrate and upright erect systems, e.g. Ectocapus, Fritscheilla,
Stigoclonium, Coleochaete.
Unbranched filamentous thallus 21

Unbranched filamentous thallus
22

Branched filamentous thallus
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5. PARENCHYMATOUS THALLUS:
• It is multicellular where cell division take s place in two or more planes.
• If cell division occur in one plane only, flat foliaceous structure are
formed as in Ulva.
• If cell division takes place in more than two plane, tubular (in Codium,
Scytosiphon etc.) or complex structure (as in Sargassum)may be formed
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2. Reproduction and life cycles
Reproduction is the biological process by which new individual organisms
"offspring" are produced from their "parents".
Reproduction is a fundamental feature of all known life; each individual organism
exists as the result of reproduction.
There are three common methods of reproduction found in algae.
1.Vegetative Reproduction
2. Asexual Reproduction
3. Sexual Reproduction
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1. Vegetative Reproduction
 The vegetative reproduction in algae includes those methods of
propagation in which portion of the plant body become separated off to
give rise to individuals.
 Process does not involve the meiosis, fusion of nuclei and production of
spores.
 Very common mode of multiplication.
 Vegetative reproduction take place by different methods.
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i) By Cell Division
oThe mother cells divide and the daughter cells are produced, which
become new plants.
oIt is sometime known as Binary Fission.
oThis type of reproduction is found in Diatoms , Euglena.
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ii) Fragmentation
 The plant body breaks into several parts or fragments and each such
fragment develops into an individual.
 This type of vegetative reproduction is commonly met within filamentous
forms, e.g., Ulothrix, Spirogyra etc.
 The fragmentation of colonies also takes place in several blue green algae,
e.g. Aphanothece, Nostoc etc.
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iii) Budding
oBud like structure has been reported to develop on the thalli of
Protosiphon.
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iv) Amylum Stars
 They are starch filled, star shaped, cell aggregates present on the lower
node of member of Charophyceae.
 They germinate into new plant bodies.
v) Tubers
 Tuber like structure develop on the rhizoids of Cladophora and Chara.
 They accumulate food materials.
 When detached, germinate into new plants.
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vi) Adventitious Branches
• Adventitious Branches are formed in some large thalloid forms of algae.
• These branch when get detached from the parent thallus develops into
new plant .
• Adventitious branch like protonema formed on the internodes of Chara
• E.g Dictyota , Fucus .
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vii) Hormogone formation
• When the trichome's break in small pieces of two or more cells, such pieces
are called ‘hormogones’
• In some Blue green algae the fragments undergoes a gliding movement
which are called ‘Hormogones’.
• Each hormogone develops into a new plant, e.g., Oscillatoria, Nostoc etc.
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2. Asexual Reproduction
• Asexual reproduction is a mode of reproduction by which offspring arise
from a single organism, and inherit the genes of that parent only.
• It is reproduction which almost never involves ploidy or reduction.
• The offspring will be exact genetic copies of the parent, except in the
specific case of automixis.
• It involves the rejuvenation of the protoplasts.
• Asexual reproduction occur through following methods
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i) By Zoospores
• These are motile and naked reproductive bodies developed inside special structures
known as zoosporangia.
• They possess two, four or many flagella and are able to swim in water.
• Each zoosporangium may produce only one (Oedogonium), in multiple of four
(Ulothrix) or many (Cladophora) zoospores inside them.
• Flagella may be present at he interior end (green algae) or on the lateral side (brown
algae).
• They are always formed in favourable conditions.
• The zoospores are always motile.
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 On the basis of number of flagella present on their bodies they are of
following types
• i)Biflagellate: Having two flagella, e.g. Chlamydomonas, Ectocarpus.
• ii) Quardiflagellate : Having four flagella e.g. Macrozoospores of
Ulothrix
• iii)Octaflaellate: Having eight flagella, e.g. Polyblepharis.
• iv)Multiflagellate: having many flagella e.g. Oedogonium,
Synzoospore of Vaucheria.
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2. Aplanospores
• These are non motile spores produced inside sporangia.
• Mostly these are produced by terrestrial algae (e.g. Vaucheria) but also by
Microspora and Ulothrix (aquatic forms)
• For their formation, protoplast of the cell rounds off and develop its own
wall to become aplanospore, also considered as arrested zoospore.
• Sometimes aplanospores are similar to their parents (Chlorella,
Scenedesmus) in all aspect except size and are known as autospore.
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• Vaucheria produces minute size spore in large numbers inside sporangium,
known as microaplanospores.
3. Hypnospores
 These are thick walled, non-motile aplanospores produced by some algae to
tide over the unfavourable conditions,
e.g. Chlamydomonas nivalis, Pediastrum, etc. on return of favourable
conditions, hypnospore germinate into new plant bodies.
Chlamydomonas nivalis walls become red due to deposition of
haematochrome, responsible for Red Snow phenomenon. 38

4) Akinetes or Cyst:
It is the types of reproduction very common in the blue green as well as green
algae.
These akinetes are a type vegetative cell which is thick walled and will
overcome the unfavourable condition.
Sometimes they are formed in chain.
In Protosiphon, akinetes are formed multinucleate protoplast to form
coenocysts.
• They are known as statospore in diatoms.
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5.Monospores
 These are haploid, naked, non-motile and uninucleate spores produced singly inside
the monosporangia during chantrantia stage in member of class Rhodophyceae.
 They are liberated after the rupturing of cell wall.
6.Tetraspore
• These are non-motile spores produced in groups of four, inside specialized cells
known as tetrasporangia.
• Tetraspores are sexual spores known as gonospores and meiospores produced after
meiotic division in diploid nucleus of tetrasporangium.
• found in Phaeophyceae and some member of Rhodophyceae
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7.Neutral Spores
Prouduced by direct transformation of the protoplast of a vegetative cell
into a single spore, e.g. Ectocarpus.
8.Carpospores
 (Karpos= fruit +Sporo= seed) are non- motile spores produced on short
filament arising from carpogonium following fertilization.
 They are feature of red algae, e.g. Polysiphonia, Batrachospermum etc.
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3. Sexual Reproduction
Conditions for sexual reproduction
(a) The sexual reproduction takes place after considerable accumulation of food
material and the climax of vegetative activity is over.
(b) The bright light is the major factor for the production of the gametes.
(c) A suitable pH value is required.
(d) The optimum temperature is necessary.
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Sexual reproduction is of following types:
• i)Autogamy
• ii) isogamy
• iii) Heterogamy
a)Anisogamy
b) Physiological Anisogamy
iv) Aplanogamy or conjugation
v) Parasexuality
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Autogamy
Is the fusion of two sister gametes produced inside the same mother
cell.
In this process, only karyogamy takes place.
It is important feature of diatoms.
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(i) Isogamy:
• Isos=equal, alike, +gamos=marriage)is the fusion of two morphologically and
physiologically similar gametes.
• Fusing gametes are known as isogametes.
• The fusion of similar motile gametes is found in many species.
• Usually the gametes taking part in fusion come from two different individuals or
filaments, sometimes these gametes come from two different cells of the same
filament.
• they cannot be classified as "male" or "female." Instead, organisms undergoing
isogamy are said to have different mating types, most commonly noted as "+" and
"-" strains, e.g. many spp. of Chlamydomonas spp., Ulothrix etc. 47

(ii) Heterogamy
 The fusion of dissimilar gametes is called heterogamy.
 There are two main types : (a) Anisogamy: (b) Physiological Anisogamy a)
Anisogamy: (Gr. Aniso = unequal+gamos= marriage) is the fusion of two
morphologically and physiologically dissimilar gametes.
 Fusion gametes are known as anisogametes.
 Male gametes are smaller and more active, while the female gametes are
larger and less active,
e.g. Chlamydomonas braunii, Pandorina etc.
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(b) Physiological Anisogamy
• when the fusing gametes are morphologically similar but exhibit different
physiological behavior, the sexual reproduction is known as phisiological
anisogamy.
• In this case one gamete is more active and other is sluggish e.g.
Chlamydomonas monoica, Spirogyra, Ectocarpus.
• In E. siliculosus, the sluggish (female) gamete is surrounded by a large number
of more active (male) gametes this type of fusion is known as clump
formation.
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iii) Oogamy
 (Gr. Oion= egg + gamos = marriage) is the fertilization of a large, non-
motile female gamete by small, motile male gamete.
 It is most advanced and highly evolved mode of sexual fusion and occur in
highly evolved algae, e.g. Chlamydomonas coccifera, C. ooganum, Volvox,
Oedogonium, Chara, Fucus etc.
 In red algae Polysiphonia and Batrachospermum where male gametes are
also non- motile, oogamy is more specialized.
 Here male gametes are known as spermatia and female as carpogonia.
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Iv) Conjugation Or Aplanogamy
 Is the fusion of two similar, non-motile gametes or cells which facilitate the
transfer of genetic material from one cell to another.
The fusing gametes are known as aplanogametes.
e.g. Spirogyra, Zygnema etc.
V) Parasexuality
• The genetic recombination without the involvement of sexual reproduction is
known as parasexuality
e.g. Anacytis, Anabaena and Cylindrospermum.
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 Life Cycle In Algae
• The growth and development of algae passes through a number of
distinct morphological and cytological stages in definite orderly manner.
• This sequence of orderly changes is called as life cycle or life history.
• It comprises the sequence of events from zygote of one generation to the
zygote of next generation.
• There are five distinct types of life cycle as found in algae.
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Five types of Life cycle
• Haplontic life cycle
• Diplontic
• Haplodiplontic
• Haplobiontic
• Diplobiontic
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Haplontic cycle
• Most common type of life cycle in algae
• It is the most primitive and simplest type of life cycle
• Life cycle is diphasic
• The prominent phase is haploid gametophytic phase
• The diploid phase in the life cycle is represented by the zygote
• Zygote is formed by the fusion of haploid male and female gametes
• Zygote immediately undergo meiosis to produce haploid zoospores
• Zoospores germinate and grow by mitosis to produce the haploid
gametophytic generation
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• Gametophytic plant produce male and female gametes by mitosis
• Ex. Chlamydomonas and Ulothrix
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Diplontic life cycle
• This type is just a reversal of the haplontic type of life cycle
• Life cycle is diphasic, but the prominent phase is diploid sporophytic
phase
• Haploid gametophytic phase in the life cycle is represented only by the
gametes
• Here gametes are produced in the gametangia by meiosis
• Moreover zygote do not undergo meiosis, rather it develop into a diploid
sporophytic phase by mitosis
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Haplodiplontic life cycle
• Life cycle is diphasic
• One phase is haploid gametophyte and the other is diploid sporophyte
• Sporophytic plant produce sporangia which produce haploid zoospores
by meiosis
• Zoospores develop into haploid gametophytic generation
• Gametophyte produces gametes
• Male and female gametes fuse to form the diploid zygote
58

• There are two types of haplodiplontic life cycle
a.isomorphic
 gametophytic and sporophytic phase are morphologically similar [eg. Ulva,
Chaetophora]
b.Heteromorphic
 Gametophytic and sporophytic phase are morphologically dissimilar
[eg. Laminaria, Urospora]
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Haplobiontic life cycle
• Here the life cycle is triphasic [three phases]
• One diploid and two haploid phases
• The three phases are:
A. Gametophyte phase [n]: haploid phase 1
B. zygote [2n]: diploid phase
C. Carposporophyte phase [n]: haploid phase 2
• Gametophyte phase produce haploid gametes
61

 Male and female gametes fuse to form zygote which is diploid
 Zygote upon reduction division produces haploid spores which germinate
in to a intermediate haploid phase called Carposporophyte
Carposporophyte reproduce asexually by carpospores [n]
 Carposopores germinate and develop into haploid gametophytic
generation
Eg. Rhodophyceae members
62

Diplobiontic life cycle
 Most complex and advanced type of life cycle in algae
 Life cycle is triphasic with one haploid phase and two diploid phase
 The life cycle includes
A. Carposporophyte – diploid [2n]
B. Gameophyte – haploid [n]
C. Tetresporophyte – diploid [2n]
 Diploid zygote develop mitotically to diploid carpospophytic phase
 Carposporophyte produce diploid carpospores [2n]
64

oCarposporophyte germinate into diploid tetrasporophytic phase
oTetrasporophyte produce haploid tetraspores by meiosis
oTetraspore germinate into the haploid gametophytic generation
oGametophytic generation produce male and female gametes
oGametes fuse to form diploid zygote
oThus in haplo-diplontic life cycle, two diploid phase [carposporophyte
and tetrasporophyte] alternate with haploid gametophytic phase
Eg. Rhodophyceae - Polysiphonia
65

3.Ecology and distribution of algae
3.1.Origin, evolution and adaptation of algae
• It is believed that the first organism on earth is anaerobic prokaryotes 4 billion years ago
• From anaerobic prokaryotes there may be evolution of photosynthetic and aerobic
prokaryotes
• Later the aerobic prokaryotes (mitochondria) were engulfed by other prokaryotes and
gave raise for primitive eukaryote which may responsible for the evolution of animal
like protists, fungi and animals.
• The photosynthetic prokaryotes may be cyanobacteria (chloroplast) gave raise for plant
like protists (algae) and plants.
• So, it is believed that algae are originated from endosymbiosis relationship between
photosynthetic bacteria with aerobic primitive eukaryotes. 67

• The endosymbiotic theory is the idea that a long time ago, prokaryotic cells engulfed
other prokaryotic cells by endocytosis.
• This resulted in the first eukaryotic cells.
Evidence in support of the endosymbiotic theory:
Similarities between mitochondria, chloroplasts, & prokaryotes:
1. Circular DNA
2. Ribosomes
3. Binary fission 68

Continou…
• Terrestrial plants evolutionary monophyletic and arose from a green algal ancestor.
• This is because :
• They both have same photosynthetic pigments (Chlorophyll a & b, carotenes, etc.)
• Both use starch to store photosynthetic products
• Both have cellulose in their wall
• Both have ‘alternation of generations’
• Cells divide similarly
69

Adaptation of algae
• Develop gas bladder for Buoyancy and ease obtaining sunlight
• Algae (including Cyanobacteria) are aquatic organism and ubiquitous in distribution.
• They are found not only in fresh and marine waterbodies but also on terrestrial habitats such
as soil, tree trunk and man-made substrates.
• As they heavily depend on water, it becomes a limiting factor for their survival.
• Algae are poikilohydric organisms and don’t have control over their water balance.
• However, algae are found growing abundantly in extreme habitats indicating their adaptation
to the harsh environment.
70

Continou…
• The response of algae to desiccation stress is producing specialized spores that would
remain dormant during harsh period and revive once the favorable conditions return.
• Their thick cell walls would have further protective layers of chemical substances
and also mucilage sheath which helps in the delay of desiccation.
• Algae produce and accumulate varieties of organic osmolytes that protect them from
desiccation, high irradiation and UV light.
• Algae occurring in colder habitats have substances in their cells that would withstand
sub-zero temperatures.
• Algae growing in saline habitats accumulate salt and maintain ionic balance with the
cellular concentration.
71

4.Classification of algae
• Algae are generally classified on the basis of the following characteristics:
Chemical and physical feature of the cell walls
Nature and properties of pigments that contribute to photosynthesis
Morphological characteristics of cells and thalli.
Habitat
Food-storage substance
Flagella number and the location of their insertion in motile cells.
Reproductive behavior and
Color
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4.1.Major divisions of algae
 The major division of algae are the following
• Division:
o Cyanophyta (Blue green algae)
o Chlorophyta (Green algae_
o Phaeophyta (Brown Algae)
o Rohodophyta (Red Algae)
o Charophyta (the Stone worts)
o Euglenophyta(Euglenoids)
o Bacillariophyta(Diatoms)
o Pyrrophyta (Dinofllagellates) 73

 Division Cyanophyta
• Are commonly called cyanobacteria or blue-green algae.
• Represent with single class Cyanophyceae.
• It may believed that cyanobacteria are the first oxygen producer and first algae to evolve
on the earth.
• Only autotrophic prokaryotes that release O2 by splitting water during the light reactions
• First terrestrial photosynthetic organism of any kind
• Cyanophyta thought to be the endosymbiont(s) that led to chloroplasts in other algal groups
• Most common algal group in terrestrial systems and symbiotic relationships.
74

Ecology of Cyanophyta
• Cyanobacteria are genetically highly diverse and are found
in a wide range of habitats: including
Ponds
Lakes
Rivers
Oceans
Temperate soils
Geothermal waters
Desert soils
Rocks
75

Continou…
• Polar regions and hypersaline waters
• Occasionally they are found in certain life-threatening habitats like:
Thermal springs
Hot deserts and Antarctica.
• Many fresh water cyanobacterial species can tolerate and grow from 0 °C under
ice to 26–35 °C in tropical zone.
• The optimum temperature for thermophilic cyanobacteria may be 45 °C or more.
• A few are endosymbionts in lichens, plants, various protists, or sponges and
provide energy for the host.
76

 Body form of Cyanophyta
• Filamentous vs. non-filamentous types
• Within filamentous:
oSimple or
oBranched
False branching
True branching
• Colonies
77

Reproduction of Cyanophyta
• Vegetative and asexual mode of reproduction is present.
• Vegetative reproduction accomplish by cell division, fragmentation and hormogonia
formation.
• Unicellular forms exhibit binary fusion, while filamentous multicellular forms and
colonial forms exhibit disintegration, in which sections of the organism become separated
from the parent, drift away, and mature into new individuals.
• Exospores and endospores are products of successive bipartition and are characteristic of
the chamaesiphonales and pleurocapsales.
78

• The liberated endospores germinate immediately without a resting periods.
• Besides, a variety of asexual bodies such as hormogonia, hormocysts, nannocytes and
akinetes also facilitate their vegetative propagation
• Sexual reproduction is absent (Sex organs, gametes and flagellated zoospores are
altogether absent), however, in some species (e.g., Anabaena , Nostoc , Synechoccus and
Cylindrospermum ) genetic recombination has been reported.
• Conjugation has not been observed in cyanobacteria.
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Division Chlorophyta
• Commonly known as Green 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 cell walls made of cellulose
80

• The green algae originated by an endosymbiosis event in which a
heterotrophic eukaryotic host cell that already contained a mitochondrion,
captured a photosynthetic prokaryote that ultimately turned into a
photosynthetic plastid.
• This endosymbiosis event happened between 1 and 1.5 billion years ago
and marked the origin of green algae, the most primitive oxygenic
photosynthetic eukaryotes.
81

Ecology of Chlorophyta
• Chlorophyta inhabit freshwater, marine and terrestrial habitats.
• Conditions for survival include light, carbon, essential nutrients, water quality, temperature
and tidal exposure.
• Certain intertidal species such as the ulva, or sea lettuce, can tolerate a range of
temperatures and survive drying at low tide.
• While most chlorophyta are aquatic.
82

Thallus Organization of Green Algae
• Green algae are a heterogeneous group exhibiting a wide range in their thallus structure and
morphology.
• Beginning from simple microscopic motile unicellular forms through multicellular
flagellated or non flagellated colonies, Palmelloid forms, dendroid forms, filamentous
forms, heterotrichous forms, siphonous forms and well developed parenchymatous thalli to
a thallus with well differentiated tissues which bear leaf and stem like structures and
resemble land plants.
• Unicellular thallus is the simplest type of construction within green algae.
83

 Reproduction in Chlorophyta
• There are three common ways of reproduction in green algae: vegetative, asexual and sexual.
• In the vegetative mode of reproduction, the algal body cuts off or break and gives rise to new
individuals.
• This process is known as fragmentation.
• In the colonial Dictyosphaerium and in some filamentous forms, fragmentation is common.
• Multiplication by ordinary cell division is a characteristic feature of some Chlorophyceans.
• Asexual reproduction by zoospores is widespread in Ulothrix, Chlorococcum.
• In some cases, the zoospores are non-motile and are known as arrested zoospores or
aplanospores.
84

• These spores in some forms have thickened wall and are capable of
• enduring prolonged desiccation and these are called hypnospores.
• In a number of algae, production of zoospores never takes place, although reproductive cells are
formed.
• The cell contents divide and new cell walls are formed around the divided protoplasts.
• These cells acquire all the distinctive features of the parent, while still enclosed in the parent cell.
• These bodies are known as autospores.
• The formation of autospores is common in Chlorococcales.
• Sexual reproduction in green algae takes place by fusion of gametes or by exchange of genetic
information through conjugation.
85

Division Phaeophyceae
• Commonly called Brown algae
• 1500 species.
• 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.
86

Thallus Organization of brown algae and
ecology
• Most of brown algae are lithophytes , which require stable hard substrata for attachment,
and a number of the filamentous, smaller species are epiphytes.
• Unicellular, colonial and unbranched filaments are absent in pheophyceae.
• The freshwater Phaeophyta species are simply filamentous and smaller in size unlike their
marine counterparts which have complex gigantic (big) thalli.
87

• Their size ranging from small filamentous forms like Ectocarpus and Hinskia,
which are few millimeters to massive intertidal (b/n low and high tides) weeds
such as Ascophyllum and Fucus , to subtidal (below low tides) large kelps and
the largest seaweed known Macrocystis pyrifera.
• They have higher morphological and anatomical differentiation compared to
the other algae.
• The size range vary greatly, from crustose (brown algae grows tightly
appressed to a substrate) form which may be 1–2 mm, macroscopic
filmentous tufts (cluster of algae) 2–10 mm, subtidal kelp forests that might
be as tall as 20–60m. 88

 Reproduction of brown algae
Vegetative Reproduction
• Several species of brown algae show vegetative reproduction via fragmentation.
Asexual Reproduction
• All brown algae reproduce asexually with exceptions of Tilopetridales, Dictyotales and
Fucales.
Sexual Reproduction
• In Pheophyceae sexual reproduction takes place by the formation of flagellate gametes
that are formed inside gametangia.
89

Division Rhodophyta
• Commonly known as red algae
• 4000 species
• 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.
90

Thallus Organization of red algae
• Most of the red algal thalli are beautiful, soft and slimy.
• The thallus ranges from simple unicellular to complex multiaxial form.
• Thalli are usually multicellular, filamentous or non-filamentous, cylindrical or flattened,
branched or unbranched.
91

Continou…
• Morphological forms of the group ranged from the unicellular species such
as, Porphyridium sp. to the filamentous types such as Polysiphonia species.
• Other unicellular forms are Chroothece , Rhodosorus , Rhodospora while
some other filamentous forms are Goniotrichum , Bangia , Rhodochaete
• The thalli of some red algae such as Porphyra Sp. are parenchymatous in
nature.
92

Reproduction in red algae
• In red algae, reproduction takes place by vegetative, asexual or sexual modes.
• Vegetative propagation is confined to the unicellular members of the
Porphyridiales,
• Although in filamentous members of the other orders, fragments of the algae
may grow into new thalli.
• While in multicellular forms both asexual and sexual reproduction is more
common.
93

Ecology of red algae
• The occurrence of red algae varies from genus to genus and their growth forms can
be divided into three major types.
• That is aquatic forms, terrestrial forms, epiphytic and parasitic forms.
94

 Physiology of Algae
Nutrition
• Most algal groups are considered photoautotrophs; prepare their own food using their
photosynthetic apparatus, sunlight as the source of energy, CO2 as the carbon source and
water to produce carbohydrates and ATP.
• Most algal divisions contain colorless heterotrophic species that can obtain organic carbon
from the external environment either by taking up dissolved substances (osmotrophy) or by
engulfing bacteria and other cells as particulate prey (phagotrophy).
• Other algae use a complex spectrum of nutritional strategies, combining photoautotrophy and
heterotrophy, which is referred to as mixotrophy.
95

• The relative contribution of autotrophy and heterotrophy to growth within a mixotrophic
species varies along a gradient from algae whose dominant mode of nutrition is
phototrophy, through those for which phototrophy or heterotrophy provides essential
nutritional supplements, to those for which heterotrophy is the dominant strategy.
• Some mixotrophs are mainly photosynthetic and only occasionally use an organic energy
source.
• Other mixotrophs meet most of their nutritional demand by phagotrophy, but may use some
of the products of photosynthesis from sequestered prey chloroplasts.
• Heterotrophy is important for the acquisition of carbon when light is limiting and,
conversely, autotrophy maintains a cell during periods when particulate food is scarce.
96

On the basis of their nutritional strategies, algae are classified into four groups:
Obligate heterotrophic algae
• They are primarily heterotrophic, but are capable of sustaining themselves by
phototrophy when prey concentrations limit heterotrophic growth
e.g. Gymnodium gracilentum.
Obligate phototrophic algae
• Their primary mode of nutrition is phototrophy, but they can supplement
growth by phagotrophy and/or osmotrophy when light is limiting
e.g. Dinobryon divergens.
97

Facultative mixotrophic algae
• They can grow equally well as phototrophs and as heterotrophs
e.g. Fragilidium subglobosum
Obligate mixotrophic algae
• Their primary mode of nutrition is phototrophy, but phagotrophy and/or
osmotrophy provides substances essential for growth (photoauxotrophic
algae can be included in this group) (e.g., Euglena gracilis, Euglenophyta).
98

• The algae are mostly photosynthetic species that produce oxygen and live in aquatic
habitats.
• This includes both photosynthetic protists, which are eukaryotes, and the prokaryotic
cyanobacteria, also known as blue-green algae.
• Though the algae is photosynthetic but it has exception also, as non-photosynthetic protists
are also included among the algae as they are closely related to photosynthetic species.
• Photosynthesis is the process by which light energy is harnessed to produce organic
compound.
99

• This reaction takes place in thylakoid membranes, in pigment protein
assemblages known as photosystems I and II.
• During this process sunlight is used to oxidize water to molecular oxygen.
• ATP and NADPH are used to reduce carbon dioxide, there by forming
organic compounds in a process known as carbon fixation.
100

The Light-Acquisition problem
• Land plant receive full-spectrum sunlight but full-spectrum sunlight is
unavailable for aquatic algae.
• The amount of light that chlorophyll of aquatic algae can absorb may
not be sufficient to supply the needs of algal photosynthesis.
• The algae perform photosynthesis and acquire exogenous organic
nutrients.
• So they are termed as mixotrophs.
101

The Photoprotection Problem
• Algae may encounter fast irradiance (light rays) changes when current
transport deep-dwelling phytoplankton cells into bright surface light or
when a receding tide exposes shoreline macro algae.
• Some algae live in extremely high-irradiance habitats due to which the
excess light destroys the essential protein and chlorophyll causing the
formation of destructive oxygen radicals.
102

The Carbon Fixation Problem
• The problem occurring in the aquatic algae is the acquisition of carbon
dioxide, which makes up less than 0.05% of Earth’s atmosphere and
diffuses 10,000 times more slowly in water than air.
• Algae have evolved diverse carbon concentration mechanisms (CCMs)
that help them to obtain sufficient carbon dioxide for photosynthesis.
103

 Growth in algae
Basically there are two types of algal growth pattern in algae. They are-
• Diffused or generalized growth pattern.
• Localized growth pattern.
Diffuse or Generalized Growth
• Growth of algae where all portion of algae grow similarly is diffuse kind of growth.
• It is a primitive type of growth pattern.
• In this case, growth or cell division occurs on every part of the algae rather at a specific
place.
• Here every cell of the thallus is capable of cell division.
104

There are four types of Diffuse or Generalized Growth in algae. These are:
1. Transverse
2. Transverse and longitudinal
3. Transverse and oblique (slash)
4. Heterotrichous
1. Transverse division
• Transverse division results in the growth of the algae in length.
• Cells divide transversely which causes the length increase.
• This pattern is generally seen in filamentous algae.
• E.g Spirogyra, Oscillatoria, Ulothrix etc. 105

2.Transverse and longitudinal division
• This type of division results into leaf like structure.
• Two types of arrangement in cell under microscope are seen.
• They cause increase in both length and width i.e. they grow both longitudinally and
transversely.
106

3.Transverse and oblique division
• Cladophora and Pithophora show this kind of growth.
• The transverse division causes increase in length and the oblique division
forms oblique branches in thalloid body of the algae.
4. Heterotrichous division
• In this pattern of growth, both erect and prostrate part arise.
• E.g. Stigeoclonium, Coleochaete, Fritschiella, Haplosiphon etc.
107

Localized Growth Pattern
• In case of localized pattern of growth, growth is restricted to certain parts of the body.
• This pattern is more advanced type because growth remains restricted.
• These are five types.
1. Apical
2. Basal
3. Intercalary
4. Trichothallic
5. Marginal
108

1. Apical growth
• When growth occurs only by means of apical cell by dividing to form the thallus beneath it, its
apical growth. E.g Dictyota, Dictyopteris, Fucus, Chara.
2. Basal growth
• Growth is brought about from the basal cell of bulbose structure of the pointed tip. E.g.
Bulbochaete.
3. Intercalary growth
• Growth is localized neither at the base nor at the tip but at one or several loci.
• E.g. Oedogonium, Laminaria.
• Growth results in increase of filament in length.
• New cell arises by cell division which initiates in between two cells that means intercalary.
109

4. Trichothallic growth
• Here cell divides to form a hair like structure above and thallus below the cell.
• It is special type intercalary growth that results into indefinite growth. E.g
Gloeotrichia.
5. Marginal growth
• Marginal growth results in the increase of algae in diameter.
• E.g Lithothamnion.
• Marginal meristematic cells give rise to new cell towards the outer side thus
increase in diameter.
110

 Nitrogen fixation by algae
• Certain blue-green algae, such as Aulosira, Tolypotlrrix, Anabaena,
Cylindrospermum, Nostoc and Mastigocladus possess the capacity to convert
(or fix) elementary nitrogen found in the air to useful nitrogenous compounds
which can be assimilated by other organisms.
• Such species contribute greatly to the fertility of rice fields in tropical
countries.
111

• A number of blue-green algae are found in symbiotic association with other plants and
the nitrogen fixed by them may be largely responsible for the success of the partnership.
• The nitrogen fixed by blue-green algae can be assimilated by themselves as well as by
other organisms.
112

Economic importance of algae
Beneficial effects
oAs Food
• People of coastal countries, like China and Japan, have long been using seaweeds and certain
other algae as a source of food.
• Some of the more commonly used are Porphyra, Vlva, Alaria, Chlorella, Chondrus,
Rhodymenia and Nostoc.
• These not only form an important ingredient of soups but are also used for flavoring meat.
• Sometimes the blades and stipes of seaweeds are eaten after frying, with or without salt.
• Besides being rich in organic iodine, which serves as prevention of goiter.
113

• Vitamins B, C, folic acid, and niacin are also found in them.
• They are, however, poor in protein content.
• Among all the edible seaweeds the most important is the red alga Porphyra
tenera which is cultivated in shallow sheltered seacoasts on a commercial scale
in Japan.
• Chemical analyses of the processed alga by several Japanese scientists
established that it is very rich in proteins (30-35%) and carbohydrates (40-45%).
Fairly high concentrations of vitamins A, B, C and niacin were also detected.
114

oFor Fodder
• The brown algae Ascophyllum, Laminaria and Fucus are used as stock feed for sheep and
cattle in maritime districts.
• In Ireland and Scotland there are established industries for processing them into a
commercial feed.
• The seaweed meal is very nutritious because of its high vitamin and mineral content.
• The milk produced by cows that feed on such meals is richer in fat content than by those fed
on conventional fodder.
• Likewise, hens fed with seaweed meal produce eggs rich in iodine.
115

ALGAE IN INDUSTRY
• Many products of commercial and pharmaceutical importance have been
derived from algae.
Agar-Agar
• Agar is obtained commercially from species of Gelidium, Gracilaria and
condrus.
• Japan and South East Asia are the main production centers of Agar.
• The greatest use of agar is in food, Pharmaceutical and cosmetic industry.
• It is used for almost a century as stiffening agent in culture media. 116

Carrageenan
• Carrageenan is obtained from the cell walls of Chondrus crispus and Gigartina stellata.
• Carrageenan is used in stabilization of emulsions in paints and cosmetics.
• In alcohol and sugar industry it is used as a clearing agent.
• It is also utilized in the textile, leather and brewing industries.
ALGINATE
• These are salts of algainic acid which occur in the cell wall of the brown algae belonging to
the order Laminariales.
• Alginate are non-toxic and viscous and readily form gel, useful as thickener, emulsifier and
gelling agent.
• Flame proof fabrics are also prepared from alginates.
117

Agricultural
• The species of Nostoc, Syctonema, Aulosira, Lyngobya, Microcoleus, Aphanothece and
Anabaena can fix atmospheric nitrogen and increase the soil fertility.
• Due to their mucilaginous sheath, they are able to prevent soil erosion by binding the soil
particles firmly.
• Nostoc, Oscillatoria, scytonema, Spirulina, etc. are used as fertilizers to rice fields.
• Cultivation of Spirulina is gaining importance as feed for fish, poultry and cattle.
118

ALGAE IN MEDICINES
• Many algae such as chlorella, Polysiphonia, Laminaria synthesis antibiotic
substances.
• Antibiotic Chlorellin is extracted from Chlorella Vulgaris, which inhibits the
growth of certain bacteria and a few algae.
• Some algae, like Gelidium are used for treatment of Kidney, Bladder and Lung
diseases.
• Antibiotic and pharmaceutical compounds from Cyanophyta: Cyanophyta
currently used against: herpes, pneumonia, HIV and antifungal drugs.
• Some compounds used in cancer treatment (reduce tumor growth rates). 119

 Harmful effect of algae
• Cyanobacterial blooms = death and destruction
• Swimmer’s itch = Lyngbia releases chemicals
• Cyanotoxins: released by animal ingestion neurotoxins (e.g. Anabaena,
Oscillatoria) and hepatotoxins (e.g. Microcystis, Nostoc) (death to mammals,
birds and fishes).
120

 Control method
Biological Control
• The virus, cyanophage infect various blue-green algae and could possible to control their growth in
surface water since they cause lysis.
• Recently, the eucaryotic algae Chlorella and Sirodotia have also been reported to be attacked by
phycoviruses.
• Addition of virus particles to cultures of susceptible algae results in considerable increase in virus
titers and rapid fall in algal cell numbers.
• A better method for algal control consists in introducing suitable crustaceans or fish into the water
body.
• These animals feed on algae either directly or indirectly, and may be harvested for food at maturity.
121

CHEMICAL CONTROL
• The growth of algae in reservoirs and lakes is controlled by appropriate
applications of algaecide cop per sulphate which selectively kills the algae.
• Chlorophenyl dimethyl urea, a photosynthetic inhibitor, has also been found
effective in checking the growth of planktonic algae.
• Besides, there are other promising algaecides such as antibiotics, quinones,
substituted hydrocarbons and phenols.
• But they are not in common use because of their higher cost.
122

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