Phycology lecture

Instructor: Duretti Ensarmu (MSc.)

August, 2024
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• General characteristics and ecology

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 Qns4. Why are Algae Important (why we study about Algae?

 They are key (crucial) to the functioning of the planet.

 They are oxygen producers; they dominate the world‟s oceans and
account for the production of a major fraction of the world‟s oxygen.

 They contribute approximately 40 to 50% of the oxygen in the

atmosphere, or the oxygen in every other breath we breathe.

 Algae are the original source of fossil carbon found in crude oil and
natural gas.

 Algae, for practical purposes, are the only primary producers in the
oceans an area that covers 71% of the Earth‟s surface.

 Microscopic algae and seaweeds directly or indirectly support most life

in the seas
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• Unicellular Forms of Algae

• They are single-celled organisms.

• These algae can be found in diverse environments, including
freshwater, marine, and terrestrial ecosystems.
• Many of them are solitary cells, with or without flagella,
– hence motile or non-motile.
– Eg. Nannochloropsis (Heterokontophyta) is non-motile
unicell,
– while Ochromonas (Heterokontophyta) is motile unicell.
 Colonial forms of Algae

• This types of algae exist as aggregates of several single

cells held together loosely or in a highly organized
fashion (colony).
– In these types of aggregates, the cell number is
indefinite,

– growth occurs by cell division of its components,

– there is no division of labor, and each cell can
survive on its own.

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When the number and arrangement of cells are determined at the
time of origin and remain constant during the life span of the
individual colony, colony is termed coenobium.

– Eg. Volvox (Chlorophyta) has spherical colonies and motile

coenobium,

– Pediastrum (Chlorophyta) has flat colonies of cells characterized

by spiny protuberances and non-motile coenobium.
 Flagella
• Flagella can be defined as motile cylindrical appendages found in

widely divergent cell types throughout the plant and animal kingdom,

– which either move the cell through its environment or

– move the environment relative to the cell.

• The flagella of the green alga Chlamydomonas have been used as a

model of flagellar structure.

• The flagellar membrane may have;

– hairs on its surface (tinsel or hairy or pantonematic or

Flimmergeissel).

– no hairs (mastigonemes) on its surface (whiplash or acronematic

flagellum)
• Algal cells can have different arrangements of flagella,

 If the flagella are of equal length, they are called isokont flagella;
 if they are of unequal length, they are called anisokont flagella;
 if they form a ring at one end of the cell, they are called
stephanokont flagella.
  Heterokont refers to an organism with a hairy and a smooth
flagellum.

• Motile green algal cell are typically of biflagellate, or although quadric-

flagellate

• A tri-flagellate (type of zoospore) and the uni-flagellate (few) forms are

also found.

• Intermediate cases exist, which carry a short second flagellum,

– where it is reduced to a stub in some species, or

– reduced to a nonfunctional basal body attached to the functional one

in other species.
• Flagella can be of different length in the same cell.

• This is controlled by intraflagellar transport, defined as

– the bi-directional movement of particles along the
length of the flagellum between the axoneme and
the flagellar membrane.
 Filamentous Algae
• Filamentous (piece of hair) result from cell division in the plane perpendicular
to the axis of the filament and,
» have cell chains consisting of daughter cells connected to each
other by their end wall.
• Filaments can be simple as in Oscillatoria (Cyanophyta),
» Spirogyra (Chlorophyta), or Ulothrix (Chlorophyta),
» have false branching as in Tolypothrix (Cyanophyta) or
» true branching as in Cladophora (Chlorophyta).
• Filaments of Stigonema ocellatum (Cyanophyta), consists of a single layer of
cells and are called uniseriate, and
• those of Stigonema mamillosum (Cyanophyta) made up of multiple layers are
called multiseriate.
 Siphonous Algae

 They are characterized by a siphonous or coenocytic

construction,

– consisting of tubular filaments lacking transverse cell

walls.
 These algae undergo repeated nuclear division without
forming cell walls;
– hence, they are unicellular, but multinucleate (or
coenocytic).

 Eg. sparsely branched tube of Vaucheria

(Heterokontophyta) is coenocyte or apocyte, a single cell
containing many nuclei.
 Parenchymatous Algae
• These algae are mostly macroscopic with
undifferentiated cells and originate from a meristem
with cell division in three dimensions.

• In the case of parenchymatous algae, cells of the

primary filament divide in all directions and any
essential filamentous structure is lost.

• This tissue organization is found in Ulva

(Chlorophyta) and many of the brown algae.
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 Life cycle of Algae
• Sequential changes of the different phases through which an organism
completes the life process,

starting from zygote/diploid of one generation to the zygote of the

next generation though gamete/haploid is called the life cycle.
• Algae exhibit four different life cycles with variation within different
groups.

• The main difference is that, the point at which meiosis occurs and the
type of cells it produces.
 1. Haplontic/ monogenic/ Zygotic Life
Cycle
• The Haplontic Life Cycle is a diphasic cycle and considered as the
simplest and most primitive type of lifecycle.

• There is two-stage in haplontic life cycle such as:

– gametophyte (haploid) and

– sporophyte (diploid) which is represented only by zygote.

• The Haploid gametes are developed within the gametangium of the

gametophytic plant.

• Then two haploid gametes are fused and formed a zygote and enter to
the diploid stage  is sporophytic phase of the life cycle.
 Cont’…
• This cycle is characterized by a single predominant haploid vegetative
phase;

– with the meiosis taking place upon germination of the zygote.

– Then the zygote divides into haploid (n) zoospores, which are then
developed into haploid plants.

• this is known as the gametophyte (haploid) stage.

• Example: Chlamydomonas,

» Ulothrix,

» Oedogonium and

» Spirogyra.
• This cycle has a single predominant vegetative diploid phase, and

– the meiosis gives rise to haploid gametes.

– At first, the sporophytic plant body develops sex organs.

– Then sex organs undergo meiosis processes and develop gametes.

– These gametes represent the gametophytic stage.

– After that, the gametes are fertilized and form a zygote.

– This zygote forms a sporophytic plant body.

 Eg. Bacillariophyceae, Sargassum, Fucus Phaeophyceae.

 3. Diplohaplontic or Sporic Life Cycles
• These cycles present an alternation of generation between two different phases
consisting in a haploid gametophyte and a diploid sporophyte equally.

– The gametophyte produces gametes by mitosis;

– the sporophyte produces spores through meiosis.

• Alternation of generation in this life cycles can be;

– Isomorphic/homologous, in which the two phases are morphologically

identical as in Ulva (Chlorophyta) or

– heteromorphic/heterologous, with the predominance of the sporophyte as

in Laminaria (Heterokontophyta) or

– with the predominance of the gametophyte as in Porphyra (Rhodophyta).

 4. Triphasic Life Cycle
• In this type, there is a succession of three distinct generations.

• The triphasic life cycle is two types such as;

• 4a) Haplobiontic Type

• The gametophytic (haploid) phase in this type is elaborate/decorative,
dominant and persists for a long time as compared to the sporophytic
(diploid) phase which is represented only by zygote

• Haplobiontic type is when two successive haploid generations are

interrupted only by the diploid zygote stage indicate its triphasic
nature.
 Cont‟…
• The gametophytic plant body were develops the sex organs which are
then forms male (spermatium) and female (egg) gametes.
• These gametes are fused and form a zygote.
• After that, the zygotes undergo meiosis and form a haploid
gametophytic plant, the carposporophyte*.
• Then the carposporophyte form carposporangium which is then develop
a haploid carpospores.
• After that a new free living gametophytic plant is developed by the
germination of carpospores.
• It has three phases such as Haploid carposporophyte, Haploid
gametophyte, and Diploid zygote.
• Diplobiontic Type consists of one gametophytic phase and two
sporophytic phases which indicate its triphasic nature.

• In this type, the sporophytic phase is more elaborate and persists for long
duration as compared to the gametophyte i.e., diplobiontic type.

• This life cycle is observed in Polysiphonia, a member of Rhodophyceae.

• The gametophytic phase in Polysiphonia is represented by two different types of
gametophytic plants
– male plants which bear spermatangium and
– female plants, which bear carpogonium.

• The male and female gametes fuse and produce zygote (2n) which develops into
a diploid carposporophytic phase, and diploid carpospores are formed within the
carposporophyte.

• After that, the carpospores are germinated and form diploid tetrasporophytic
plants.
 Cont‟…
• Next, a diploid tetrasporangia is developed from the
tetrasporophytic plant and each diploid tetrasporangia
produces four tetraspores (n) by meiotic division.

• Among these four tetraspores two develop male gametophyte

and the other two develop female gametophyte.

• There are three phase in Diplobiontic Type such as Haploid

gametophyte, Diploid carposporophyte, and Diploid
tetrasporophyte.
 Adaptation of Algae
• They have a variety of adaptations that help to survive including body
structure, defense mechanism and reproductive strategies.

• Some algae have holdfasts that attach to the sea floor & anchor them
down much.
 4. CLASSIFICATION OF ALGAE
 For the first time, Aristotle and his pupil (learner) Theophrastus, the father of
Botany, classified the plants into three groups; trees, shrubs and herbs.

 This classification was based on form and texture of the plants.

 In 18th century, Linnaeus proposed his artificial sexual system of classification.
 In 1880, A.L.de Jussieu divides cryptogamic plants into three major groups;
1. Thallophyta (algae, fungi and bacteria),
2. Bryophyta and
3. Pteridophyta.
 The major groups of algae are classified on the basis of their,
 pigmentation,
 chemical nature of photosynthetic storage product,
 thylakoids organization and other features of the chloroplasts,
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  chemistry and structure of cell wall,
 number, arrangement, and ultra structure of flagella (if any),
 occurrence of any other special features, and mode of reproduction.
• The standard botanical classification system is used in the systematics of the
algae ( International Code of Botanical Nomenclature; ICBN):

• Phylum –phyta

• Class – phyceae

• Order – ales

• Family – aceae

• Genus – a Greek name

• Species – a Latin name

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 4.1 Division Cyanophyta (Blue-green algae)
 Also called Myxophyceae include primitive forms known as blue green
algae.
 This group though classically considered as algae, lack eukaryotic cell
organization and show greater similarity with bacteria.
 Cyanophyceae is characterized by the following features;
– Lack of pigment bearing cell or structure ( chromatophore), the
pigments are localized in unstacked photosynthetic lamellae
(thylakoids) in peripheral cytoplasm.
– Presence of two chrxs phycobilin pigments (c-phycocyanin and c-
phycoerythrin
– Absence of nucleus and other membrane bound organelles in cells.
– Cell wall made up of peptidoglycons coverd by gelatinous sheath
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 – Food reserves stored in the form of cyanophycean starch that is similar to
glycogen.
– No sexual reproductions, flagellated spores or reproductive bodies.

Pigments and photosynthesis;

 Chlorophyll a, blue and red phycobilins (phycoerythrin, phycocyanin,
allophycocyanin, and phycoerythrocyanin), and carotenoids are the pigments.
 Normal photosynthesis is accomplished by water splitting with coupling of
photosystem II and I operating as per the „Z‟ scheme.
 Under anaerobic conditions, only PsI functions through cyclic
photophosphorylations with electron donors.
Reproductions;
 Reproduce asexually through the production of non-motile spores and,
– vegetatively by cell division and hormogonia formation.
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 In some filamenteous cyanobacteria, the death of an intercalary (a meristem
situated b/n zones of permanent tissue) cells leads

 to the formation of fragments.

 The fragments, which come out of the sheet and float on the surface of water,
are called hormogonia.

 Hormogonia are distinguished from, vegetative filaments by their

 gliding motility,

 the small size of their cells and,

 the absence of heterocysts.

• A gas vacuole is composed of gas vesicles, or hollow cylindrical tubes with

conical ends, in the cytoplasm,

• Which controls the buoyancy of hormogonia.

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 The membrane is permeable to gases, allowing the contained gas to
equilibrate with gases in the surrounding solution.

 The membrane, must however, be able to exclude water.

 It have been postulated that the inner surface must be hydrophobic,

– thereby preventing condensation on it of water droplets, and

– restraining, by surface tension, water creeping through the pores.

 At the same time, these molecules must present a hydrophilic surface at

the outer (water-facing) surface in order to minimize the interfacial
tension,

– which would otherwise result in the collapse of the gas vacuole.

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 4.2 Division Chlorophyta (Green algae)
 The class Chlorophyceae is the largest class among algae.

 They are Popularly called grass-green (green) algae and are chrxz by the
presence of the;

– Chloroplasts with pyrenoid in cell.

– Chlorophyll a, b, carotene and xanthophyll pigments as in the higher plants.

– Starch as food reserve.

– Their cell wall made up of cellulose.

– Flagellated reproductive cells having isokontous flagella.

– sexual reproduction.

 Chloroplasts are surrounded only by the double-membrane chloroplast

envelope, with no chloroplast E.R.

 Thylakoids are in stacks of 2-6 or more. 45

 They are primarily freshwater (90%); only about 10% of the species are
marine.

 Flagella dependent motility is common.

 Flagella are equal, usually apically inserted, and typically two in number.

 They lack hairs, but may be covered with a delicate fur or scales.

 Asexual reproduction, the spores when produced through mitosis (mitospores),

when through meiosis (meiospores).

 fragmentation of colonies into two or more parts, each part becoming a new
colony.

 Zoospores; is flagellated (motile)

 Aplanospores is non-flagellated and have a wall distinct from the parent cell
wall.

 Autospores; are aplanospores that have the same shape as the parent cell.46
 Autospores are usually formed in a multiple of two in the parent cell.

 Aplanospores that is thick walled and which is resting stage is called

hypnospore.

 Coenobia are colonies with a definite number of cells arranged in a specific

manner (e.g., Volvox).

 Sexual reproduction, may be isogamous, anisogamous or oogamous with the

general line of evolution occurring in the same direction.

 If the species is isogamous or anisogamous, the gametes are usually not formed
in specialized cells,

 although in the oogamous species, gametes are normally formed in

specialized gametangia.

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 4.3 Division Phaeophyta (Brown Algae)
 The term Phaeophyceae is derived from Greek „phyaios’-brown,

– is to the dominance of brown accessory pigments that give thalli brownish

appearance.

 Phaeophyta have the following chrxs;

 Highly evolved branched, multicellular macroscopic thallus ranging from

heterotrichous to pseudoparenchymatous habit.

 Chloroplasts are yellowish-brown to dark brown in color and have

chlorophyll a, c1, c2, and β-carotene and several xanthophylls.

 Uninucleate, chloroplast surrounded by two additional membranes of

chloroplast E.R and have three thylakoids per band.

 The food reserves are laid down mostly as laminarin with some manitol
rarely some fats. 48
 The cell wall has two layers (outer is mucilaginous containing fucinic acids and
alginic acids, and inner consists of cellulose arranged in a parallel manner).

 The cell wall consists of mannan and xylan in addition to cellulose .

 Motile reproductive cells usually have two heterokontous laterally inserted

flagella ( posterior whiplash and anterior tinsel).

 Either have distinct alternation between sporophytic and gametophytic

generations with isomorphic and heteromorphic life cycle,

 (or no alternation of generation cyclosporic life cycle where the haploid

phase is reduced to gametes only).

 Cyclosporic; in this type, an independent free living gametophyte is lacking.

 They are found almost exclusively in the marine habitat, there being only four
genera containing freshwater.
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 Sexual reproduction ranges from isogamous to anisogamous and oogamous.
 Meiosis occurs in unilocular sporangia, which are unicellular and form from four to
many usually motile spores.
 Multicellular (plurilocular) structures produce asexual spores or gametes by mitotic
division.

4.4 Division Rhodophyta (Red Algae)

 Commonly known as red algae, most of the genera are exclusively marine.
 Morphologically, they are diverse, but all of them have the following chrxc;
 There is no flagellated stages in their life cycle.
 Photosynthetic pigments are chlorophyll a and rarely chlorophyll d, a and ß
carotene and two phycobilins: r-Phycoerythrin, r-Phycocyanin.
 The presence of xanthophyll (lutein) and the phycobilin r-Phycoerythrin is
responsible for red colourations.
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  The food reserves are laid down in the form of Floridean starch (a-
1,4-glucan) and oil.

 Mitosis is closed, that is, the nuclear envelop does not breakdown
during nuclear division.

 Dughter cells in multicellular forms have pit connection (consists of a

proteinaceous plug core in between two thallus cells).

 Sexual reproduction is highly specialized.

 Morphology ranges from unicells (rare) to filamentous and pseudo

parenchymatous and parenchymateous forms.

 There is no truly parenchymatous growth.

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 The class Rhodophyceae, usually divided into two subclasses based on sexual

reproduction and thallus structure;

 Sub-class – Bangioideae and

 Sub-class – Florioideae.

Sub-class - Bangioideae
 Their thallus can be unicellular, colonial, filamentous, or pseudoparenchymatous
as in poryphra.

 The growth of thallus is intercalary, have no cytoplasmic connection between

cells (pit connection).

 Carposporophyte is not formed and zygote divides by vertical and transverse

division to form the spore (carpospores).

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 The number of cells may be 2, 4 and 16.

 Carpospores germinate to form conchocelis like plant.

Sub-class - Florioideae
o Produce Carposporophyte.

o elaborates post fertilization changes.

o The growth of thallus is strictly apical.

o The Carpospores are formed indirectly from the zygote.

o The cells of species have a large pole-like opening in the wall between adjacent
cells with cytoplasmic strand, connecting the two protoplasts which is called pit
connection.

o Pit connections are formed at mitosis.

o They are more advanced Rhodophyaceae.

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 Reproduction in red algae
 Red algae do not reproduce vegetatively except unicellular forms which increase

by cell division.

 All of them produce one or more kinds of non flagellated asexual spores,

– monospores and neutral spores in Bangioideae and

– Carpospores, biospores, tetraspores, polyspores and paraspores in

Florioideae.

 Sexual and asexual- multicellular forms.

Sexual reproduction
• The sexual reproduction is always oogamous.

 The sex organs of red algae have a distinguished terminology.

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 Male sex organs (spermatangia)
 Male sex organs are spermatangia (Antheridial mother cell)

 Is formed by repeated division of vegetative cell.

 The liberated naked uninucleate protoplast of each spermatangium is called

spermatum.

 On liberation, the spermatia, are carried passively by the water currents in all
directions and some of them may be drifted to and lodged against carpogonia.

 Easily distinguished as it‟s colorless

 Produced on short branches of limited growth (Batrachospermum) or special

trichoblast in Polysiphonia.

 From each spermatangium a single non-motile uninucleate spermatium is

formed.

 They are dependent for their movement upon the mercy of water currents.
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 Female sex organ (carpogonium)
 Is formed by slight modification of ordinary vegetative cells of the female
thallus.

 It increases in size; the swollen (enlarged) cell undergoes no division and its
protoplast function directly as an egg.

 In certain species, the ellipsoid carpogonium extends to the thallus surface at

one or both ends,

 by giving out a small papillate out growth that is considered as a

rudimentary trychogyne.

 In the species, which lack bulge or trichogyne, the spermatium itself puts forth a
narrow process containing a thin stream of cytoplasm.

 It establishes a connection between the spermatium and the carpogonium.

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 The spermatial nucleus migrates through it in to the carpogonium to fuse with the
egg nucleus.

 Carpogonia are produced terminally on small branches.

 It is single-celled, but terminally prolonged into a club-shaped structure called

trichogyne, which has no nucleus.

 Nucleus is situated in the basal part only.

Formation of carpospores
• After fertilization, zygote nucleus undergoes meiosis and form four haploid
nuclei,

– then the four haploid nuclei undergoes mitosis and form 8, 16, or 32 nuclei.

• The cleavage of the protoplast at each nuclear division leads to the formation of
a group 8-32 uninucleate haploid meiospores known as carpospores.
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• The matured naked, non-flagellated carpospores are released by the

breakdown of the surrounding cell walls when the female thallus is

submereged by the incoming tide.

• In monoecious species, the male areas are segregated from the female

areas.

• The former are yellowish white or white and the later purple.

• The carpospores has a stellate chromatophore.

Germination of carpospores
• The liberated naked carpospore becomes amoeboid.

• It exhibits slow amoeboid movements of two or three days.

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• Then, it comes to rest, becomes spherical, secretes a cell wall and
germinates to produce a branched filamentous,

– which is some species resembles an alga known as Conchocelis

rosea.

• The conchocelis stage produce monospores whose function is

unknown.

• They may serve to multiply the conchelis stage or germinate to

form plate like porphyra thallus.

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 Fertilization
 Spermatia produced in large number and float in the waters passively and by
chance contact with trichogyne of female organs.

 The membrane of spermatium and the wall of the trichogyne at point of mutual
contact dissolve, forming an open passage into base of carpogonium.

 Nucleus of spermatium (only one) migrates to the base of carpogonium and fuses
with female nucleus.

 After fertilization, the trichogyne shrivel and gets cut off ( disintegrates) from the
basal part of the carpogonium.

 The process of sexual reproduction up to fertilization is more or less similar in

Rhodophyaceae,

– but post fertilization changes are complex and bases for classification.

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 Post fertilization changes (Floriodae)
• The diploid carposporophyte which develops attached to the gametophyte of
Polysiphonia becomes differentiated into several distinct regions.

• Apically growing cells of the meristematic gonimoblast, some of which

eventually develop into diploid carpospores, are observed to contain only lightly
pigmented proplastids.

• As growth continues, the inner cells of the gonimoblast cease dividing and
undergo considerable cytoplasmic change prior to incorporation into the
expanding fusion cell.

• Cells appear active in protein synthesis while proplastids and nuclei break down.

• A limited number of adjacent gametophyte cells are likewise added to the fusion
cell, a structure which is devoid of both plastids and nuclei.

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 All cells of the differentiating carposporophyte are interconnected by morphologically
distinct transfer connections, which differ from normal red algal pit connections in that
they are intracellular rather than extracellular.

 Transfer connections may enhance the transport of nutritive materials within the
carposporophyte and toward the meristematic cells at the margin.

 Diploid fused nucleus produce two daughter nucleus which are haploid by meiosis.

 Fertilized carpogonium produces a lateral outgrowth and this is the first initial of
gonimoblast filament.

 Haploid daughter nucleus passes to it.

 The second nucleus remains within the carpogonium and divides repeatedly by mitosis,
provides haploid nuclei to successive initials of gonimoblast filament.

 then each initial give rise to gonimoblast filaments.

 Cystocarp or carposporophyte is haploid, and is said to be parasitic on the female

gametophyte.
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• Carposporangium give rise to a single carpospores:

– thus, several carpospores are liberated from carposporangia.

• Carpospore settle down, germinate and produce an elongated process

which gets transversely divided by a septum into two cells.

• These develop into the prostrate system which later produces the erect
filaments (chantransia).

• From chantransia stage, adult shoots arise either from the prostrate or
erect system and

– the adult shoots show the growth of main axis by means of an apical
cell which finally develops into Batrachspermum plant.

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 4.5 Division Charophyta (the Stone worts)
• The Charophyceae are primarily freshwater organisms, although a few species
may occur in brackish water.
• That they diverged very early from the Chlorophyaceae is evident from the
fossil record;
– charophytes are known from the Palaeozoic era, as far back as the Silurian
period (435- 460 million years ago).
• This is the line of algal evolution, which led to the development of land plants.
• The class contains a single order and seven living genera.
Characteristic features;
• The Stone worts are usually occur in still and clear waters in attached condition
to the mud of the bottom of the pools.
• They found in less oxygenated water and best survive in clear and hard water.
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 The thallus is attached to the mud by a rhizoidal system, the plant body is
erect and possesses nodes and internodes,
– secondary laterals also called leaves arise from nodes which are of
limited growth.
– The leaves may or may not be differentiated into nodes and
internodes.
 Reproduction takes place by vegetative and sexual.
 Asexual reproduction is absent.
 Vegetative takes place by means of special vegetative bodies such as
amylum stars, bulbils, secondary protenema.
 Sexual reproduction is oogamous and takes place by oogonia (nucule)
antheridia (globule).
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 The zygote nucleus divides reductionally producing four haploid nuclei.

– Out of these 4 haploid nuclei, one is functional and the others are degenerate.

– The functional nucleus divides into two cells, the lower cell is rhizoidal and
the upper one gives rise to main thallus.

 Cell walls are composed of cellulose and are frequently heavily calcified;

– this feature leads to the deposition of marl (CaCO3 and MgCO3) in

freshwater habitats where charophytes abundant.

 Calcified remains also fossilize readily, especially the female organ,

– which is termed a gyrogonite in the fossilized state.

 Cell division occurs by a phragmoplast.

 Cells are uninucleate and typically contain numerous ellipsoidal chloroplasts

arranged in twisted, longitudinal and parallel rows.
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 The chloroplasts are enclosed by a double membrane and lack an additional
membrane of ER;

– thylakoids are in stacks of 2-6 or more.

 The chloroplast contains chlorophyll a and b, β - carotene and some

xanthophylls.

 Morphologically, they are parenchymateous with nodal and internodal regions.

 The motile Charophyceae, have laterally or subapically inserted flagella.

 The flagella are, found only in the male gamete, two in numbers, isokontan and
acronematic.

 The starch is being the most important storage product.

 whorls of branches are formed from the node, and the internodes are composed
of a single enlarged cell that may be corticated (e.g. Chara).

67
• The term antheridium and oogonium not being appropriate,

– because the sexual reproductive structures include both a sex organs and

– a multicellular sheath derived from cells beneath the sex organs.

• The male sex organs are spherical and called globules.

– It has antheridial filament and each filament may have up to 200 cells.

• The female sex organs are oval and called nucule.

– It has corona of cells (group of 5 cells that serve as cover) and tube cells
(spirally coiled cells serve as sterile jacket).

• Globule and nucules are born on internodes, usually on the same plant.

• In chara, the nucule is above the globule.

68
• Of the bryophyte-like features in this group,

– notable are the reproductive bodies which are enclosed within a sterile
envelope (otherwise unique in the algae),

– have rhizoids with oblique septa and the formation of the protenema stage.

4.6 Division Euglenophyta (Euglenoids)

• Euglenoid flagellates occur in most freshwater habitats:

– puddles, ditches, ponds, streams, lakes, and rivers,

– particularly waters contaminated by animal pollution or decaying organic

matter.

• Euglenoid cells are surrounded by a pellicle that has four main components:

– the plasma membrane,

– repeating proteinaceous units called strips,

69
 – subtending microtubules, and

– tubular cisternae of endoplasmic reticulum.

• The strips are arranged in parallel, are characteristic of the species, and

– are composed primarily of the proteinaceous articulins.

– below each strip is a set of parallel microtubules, where each microtubule

occupies a discrete position relative to the strip.

• The cisterna of E.R is also intimately associated with each strip and appears to
function as a reservoir for calcium.

• Two membranes of the chloroplast envelope plus one membrane of chloroplast

E.R surrounds the euglenoid chloroplasts;

– the latter membrane is not continuous with the nuclear membrane.

• The chloroplasts are usually discoid or plate-like with a central pyrenoid.

70
• The thylakoids are grouped into bands of three, with two thylakoid
bands traversing the pyrenoid.
• The photosynthetic pigments are chlorophyll a and b, ß-carotenes and
xanthophylls.
• Euglenoid are unicellular in morphology.
• The cells have two basal bodies and one or two emergent flagella.
• The flagella are similar to those of trypanosomes in having a
paraxonemal rod (paraxial rod),
– that runs the length of the flagellum inside the flagellar membrane.
• The one emergent flagellum in Euglena has helically arranged fibrillar
hairs (no microtubules) attached along the length of the flagellar
membrane.
71
• The fibrillar hairs are of two lengths:

– there is a single helical row of long hairs and

– two helical rows of short hairs in Euglena.

– other genera have flagella similar to Euglena.

– have paramylon as the storage product in the cytoplasm.

– No sexual and asexual reproduction, they can reproduce vegetatively by

cell division.

4.7 Division Bacillariophyta (Diatoms)

• The Bacillariophyceae or the diatoms probably evolved from a scaly member of

the Chrysophyceae.

• The diatoms are unicellular, sometimes colonial algae found in almost every
aquatic habitat as ;
72
 – free-living photosynthetic autotrophs,

– colorless heterotrophs, or

– photosynthetic symbiotes.

 They may occur as plankton or periphyton, with most brownish-green

films on substrates such as rocks or aquatic plants being composed of
attached diatoms.

 The characteristic feature of the Bacillariophyceae is their ability to

secrete an external wall composed of silica, the frustule.

 It is constructed of two almost equal halves,

– the smaller fitting into the larger like a Petri dish.

– The outer of the two half-walls is the epitheca and the inner the
hypotheca. 73
 – Each theca is composed of two parts,

• the valve, a more or less flattened plate, and

• the connecting band, attached to the edge of the valve.

• The two connecting bands, one attached to each valve, are called the girdle.

• The siliceous material of the frustule is laid down in certain regular patterns that

leave the wall ornamented.

• The ornamentation of diatoms can be divided into four basic types:

(1) Centric and radial, where the structure is arranged according to a central point.

(2) Trellisoid, where the structure is arranged uniformly over the surface without

reference to a point or line.

74
(3) Gonoid, where the structure is dominated by angles.

(4) Tennate, where, structure is symmetrically arranged upon either side of

a central line.

• Two membranes of the chloroplast envelope surround the chloroplasts,

– outside of which the two membranes of the chloroplast E.R. are, the outer
membrane being continuous with the outer membrane of the nuclear
envelope.

• The thylakoids within the chloroplast are grouped three to a band, and in
most chloroplasts there is a more or less central pyrenoid.

• The pyrenoid is usually crossed by widely spaced bands of thylakoids,

which in some cases are reduced from the normal three thylakoids per
band to two.
75
• The chloroplasts contain chlorophylls a, c1, and c2, β carotene and
fucoxanthin is the principal carotenoid, giving the cells their golden-brown
color.

• Fucoxanthin is an efficient carotenoid in the transfer of energy to chlorophyll a

and is part of photosystem II of photosynthesis.

• Bacillariophyceae is unicellular, colonial and filamentous in morphology.

• Only the sperm cells have one pantonematic flagella.

• The storage product is chrysolaminarin, which is located in vesicles in the cell.

• Chrysolaminarin differs from the laminarin found in the Phaeophyceae by

lacking a terminal mannitol residue at the reducing end of the polysaccharide.

• Reproduction is vegetatively (cell division) and sexually (isogamous and

oogamous).

76
 4.8 Division Dinophyta (Dinoflagellates)
o The members of this division are typical unicellular flagellates, but can be
also nonflagellate, ameboid, coccoid, palmelloid, or filamentous.

o Dinoflagellates have two flagella with independent beating pattern,

o one training and the other girdling that confers characteristic rotator
swimming whirling motion.

o Flagella are apically inserted (desmokont type) or emerge from a region

close to the midpoint of the ventral side of the cell (dinokont type).

o Most of them are characterized by cell-covering components that lie

beneath the cell membrane.

o Around the cell, there is a superficial layer of flat, polygonal vesicles,

which can be empty or filled with cellulose plates. 77
o Dinoflagellates possess chlorophylls a, b, c1, and c2, fucoxanthin, other
carotenoids, and xanthophylls such as

o peridinin, gyroxanthin diester, dinoxanthin, diadinoxantin, and

fucoxanthin.

o Three membranes surround the chloroplasts, (if present).

o Within the chloroplasts, the thylakoids are for, the most part united in a stack of
three.

o The chloroplasts DNA is localized in small nodules scattered in the whole

chloroplast, with typical pyrenoids.

o A complex photoreceptive system is present in the dinophytes such as

o Warnowia polyphemus, Warnowia pulchra, or Erythropsidinium

agileconsisting of a “compound eye” composed of a lens and a retinoid.
78
Most dinoflagellates are distinguished by a dinokaryon,

a special eukaryotic nucleus involving fibrillar chromosomes that remain

condensed during the mitotic cycles.

The principal reserve polysaccharide is starch, located as grains in the

cytoplasm,

but oil droplets are present in some genera.

At the surface of the cell, there are trichocysts,

which discharge explosively when stimulated.

Besides photoautotrophy, dinoflagellates exhibit an amazing diversity of

nutritional types,

because about half of the known species lack plastids and are therefore
obligate heterotrophic.

79
 Physiology of Algae
NUTRITION
 Algae are a diverse group of photosynthetic organisms that play a crucial role
in aquatic ecosystems.
 Their physiology, particularly regarding nutrition, varies widely among
different types of algae,
 but there are some common features and mechanisms by which they
obtain nutrients
 Ex. most Algal groups are photoautotrophs, that is, depending entirely upon
their photosynthetic apparatus for their metabolic necessities,
 using sunlight as the source of energy, and CO2 as the carbon source to
produce carbohydrates and ATP.

 They contain colorless heterotropic species that can obtain organic carbon
from the external environment either by
 taking up dissolved substances (osmotrophy) or
 engulfing bacteria and other cells as particulate prey (phagotrophy).
 Auxotrophic: Algae that cannot synthesize essential components such as the
vitamin B12 complex or fatty acids, so they have to import them.
80
 Cont’…
Mixotrophy: combining photoautotrophy and heterotrophy.
Some mixotrophs are mainly photosynthetic and only
occasionally/sometimes 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
sequester prey chloroplasts.
Photosynthetic fixation of carbon and use of particulate food
as a source of major nutrients and growth factors can
enhance growth, especially in extreme environments where
resources are limited.
Heterotrophy is important for the acquisition of carbon
when light is limiting and,
Autotrophy maintains a cell during periods when
particulate food is scarce.

81
 Cont’…
 Because 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.
 Obligate phototrophic algae: they are primarily phototrophy, but they can
supplement growth by phagotrophy and/or osmotrophy when light is
limiting.
 Facultative mixotrophic algae: they can grow equally well as phototrophs and
as heterotrophs
 Obligate mixotrophic algae: they are primarily phototrophy, but phagotrophy
and/or osmotrophy provides substances essential for growth.
 photoauxotrophic algae can be included in this group.
82
 Photosynthesis
 Algal photosynthesis account for almost half of the photosynthetic C fixed
every year.

 Algae's efficiency at pulling inorganic C out of the environment is dependent

on growth condition which implies the presence of an inducible CO2
concentrating mechanism in algal cells.

 Carbonic anhydrase is an enzyme that interconverts carbon dioxide and

hydrogen-carbonate which supply Rubisco with CO2 from the pool of
HCO3−.

 Antenna complexes are proteins with many bound antenna pigments which
are important in absorbing light energy.
 Algal photosynthesis is thought to increase with increase in nutrient, that is,
N, P and Fe availability.
83
 Cont’…
 If the algal photosynthesis would increase more CO2 would be removed from
the environment.

 Algae grow faster and are very efficient in absorbing and converting solar
energy into chemical energy which is mainly in the form of triacylglycerol.

Chloroplasts
 photosynthesis occurs within photosynthetic compartment called chloroplasts.

 Inside the double membrane that surrounds the chloroplast known as the
chloroplast envelope.

 light is harvested and converted into a series of photochemical and

enzymatic reactions by pigment protein complexes and associated
proteins found in membrane structures called thylakoids. 84
 Cont’…
 In Prokaryote, thylakoids are free within the cytoplasm, while in eukaryotes
they are enclosed within bounding membranes to form the chloroplast.
 The colorless matrix of the chloroplast is known as, stroma.

 Inside the chloroplast, thylakoids are organized into two different

compartments,
 granal thylakoids, stacked into hollow disks termed grana; and
 stromal thylakoids forming multiple connections between the grana.

 Chloroplasts contain nucleic acids and ribosomes.

 DNA is naked, that is, not associated with proteins, and occurs in two
configurations:
 scattered, but not connected, small nucleoids or
 as a peripheral/outeral ring. 85
 happen in the thylakoid membrane of the chloroplast.

 involve the capture of the light energy and its conversion to energy currency as

NADPH and ATP.

 These reactions are absorption and transfer of photon energy, trapping of this

energy, and generation of a chemical potential.

 The latter reaction follows two routes:

 1st, generates NADPH due to the falling of the high-energy excited

electron along an electron transport system,

 2nd, generates ATP by means of a proton gradient across the thylakoid

86
membrane.
 Water splitting is the source of both electrons and protons.

 Oxygen is released as a by-product of the water splitting.

Light-Independent reaction
 involve the sequence of reactions by which this chemical potential is used to fix
and reduce inorganic carbon in triosephosphates.

87
 The fixation of CO2 takes place during the light independent phase using the
assimilatory power of NADPH and ATP in the chloroplast of stroma
(eukaryotic algae) or in the cytoplasm (prokaryotic algae).

 It do not occur in the dark; rather they occur simultaneously with the light
reactions, however, light is not directly involved.

 It commonly referred to as the Calvin Benson Bassham cycle (CBB cycle)

after the pioneering work of its discoverers.

88
Algae can grow in virtually any environment that has

carbon dioxide,

sunlight,

minerals and

enough water.

The limiting factor in algal growth is often sunlight or minerals.

When sunlight is limited, some kinds of algae can take in organic substances,

like plant matter, as food.

89
 Nitrogen Fixation

Means N2 from the atmosphere, is fixed by organism having the

nitrogenase enzyme into NH4+ using ATP as a source of energy.

All known N2-fixing organisms are prokaryotes.

Cyanobacteria are diazotrophs (able to fix atmospheric N2).

Algal cells are natural fertilizer and now a days it is used worldwide,
without any side effect
algal cells have specific cells (Heterocyst) and are the site of N2 fixation.

90
 Cont’…
 Algae are able to convert unavailable N2 into bio-available NH4.

 The process is one of the most metabolically expensive processes in biology,

requiring 16 ATP for each molecule of N2 fixed.

 Nitrogenase enzyme is very sensitive to inactivation by O2.

• Cyanobacteria have evolved three different mechanisms designed to exclude

oxygen from the area of the cells containing nitrogenase:

1. Heterocystous cyanobacteria: it fix N2 in heterocysts.

 Heterocysts are surrounded by a glycolipid layer which is impermeable to

O2.
91
 Cont’…
 It lack photosystem II and, therefore, the ability to evolve O2.

 It have cyclic photophosphorylation and can produce the ATP,

• Which is necessary for N2 fixation.

 It also have a form of myoglobin called cyanoglobin that scavenges oxygen

 Under anaerobic conditions, in an atmosphere of N2 and CO2, both

vegetative cells and heterocysts can fix nitrogen.

2. Non-filamentous cyanobacteria (that fix nitrogen in the dark): these

cyanobacteria fix N2 in the dark when photosynthesis is not producing
nitrogenase inhibiting O2.

3. Trichodesmium and Katagnymene: these cyanobacteria are the major bloom-

forming organisms.
92
 Cont’…
 It is responsible for fixing one-quarter of the total N2 in the oceans of
the world.
 They do not have heterocysts yet fix nitrogen in the light under aerobic
conditions.
 Within the filaments, 10 to 15% of the cells (called diazocytes) are
specialized to fix N2 ,
 while the others do not fix the N2

 Cells that fix N2 are adjacent to one another and have a denser
thylakoid network with fewer gas vacuoles and cyanophycin
granules.
93
 7. Economic and Ecological
importance of algae
1. Beneficial effects
Economic
There are importance of algae
companies in Europe and North
 Algae includeAmerica
a wide range
(e.gof Earthrise
prokaryotic and eukaryotic
Farms) that marine and fresh
cultivate
water organisms which are engaged
Spirulina in the process
at large scalesof photosynthesis.
for human
 As source
consumption.
of human food supplements and animal feed
 Man has used a number of algae as food for thousands of years.

 Nowadays, algae like Chlorella, Anabaenopsis and Spirulina are being

Spirulina
cultivated at large scales for humanisconsumption.
rich in
proteins, vitamins
(vitamin B12- cyanocobalamin), rare fatty
acids and iron.
94
 As a source of pharmaceuticals
 Varieos types of algae have proved
Are to beagainst
effective sourcesthe
ofHIV1-
compounds
virus with
antibiotic and anticancer activity.
This enzyme plays a role as a therapeutic agent
 Sulfolipid from Spirulina-for cancer and other disease.

 Superoxide dismutase (SOD) -

 SOD is a scavenger of free radicals, which are known to cause

Are effective against a wide range of bacteria.
damage to proteins, DNA, membranes and organelles.

 Antibiotics-called cyanobacterins are obtainable from some blue-

green algae like Nostoc, Scytonema hofmani produces antibiotics

95
 As a source of varies chemicals
 Iodine- from Laminaria and Porphyra

 Gelling or solidifying agent

 Agar, Carageenan- from red algae, e.g. Glaciralia

 Alginic acid -from brown algae

 Phycocyanin- coloring agent for food and cosmetics.

 Vitamin A, B, and C- from porphyra.

96
 Ecological importance
 Enrichment of aquatic and terrestrial environments with
nitrogen sources

• Some cyanobacteria (blue green algae) are capable of converting

gaseous nitrogen (N2) to ammonia using their unique enzyme complex
called nitrogenase in a process called nitrogen fixation.

• The nitrogen fixed benefits other aquatic algae and plants (e.g Azolla)
and many terrestrial plants including the liverwort Blasia, the hornwort
anthoceros, cycads, wheat and rice plants and many lichens.

97
 Algae as primary producers
 Algae form the bases of aquatic food chains.

 Through photosynthesis, algae generate organic compounds on

which the lives of aquatic and terrestrial animals including man
depend.

 Zooplankton and herbivorous fish feed on algae called

phytoplankton and the former in their turn serve as food for other
aquatic animals including carnivorous fish.

 Man also uses fish as food.

98
 Oxygenation of the atmosphere
 Cyanobacteria and their descendents have been generating oxygen
for at least 2.7 billion years.

 Oxygen derived from their photosynthesis gradually accumulated

in the atmosphere, eventually reaching its present levels, about
21%.

 Oxygen is required by aerobic organisms for cellular respiration.

99
 Algae in biotic associations

 Algae are involved in a variety of biotic interactions. Algae are known to live in
intimate associations with invertebrates, fungi, bryophytes, and vascular plants.

 The association produces an integrated unit with greater biological fitness.

 Lichens-fungi + algae, anabaena- azolla, cycad coralloid roots-nostoc,

chlorella= hydra or paramecium, dinoflagellates =sea anemones and corals,
platymonas+ convolute (marine flat worm).

100
 Algae as biomonitors ( bioindicators,
ecological indicators)
 By providing early warning of possible environmental deterioration
(contamination with nutrients
Means reducing and toxic
the health substances)
of the since they are more
environment
sensitive than animals and other autotrophic organisms.
and influencing algal growth in addition to Total
Micro algae in animal aquaculture systems
nitrogen (TN), total phosphorus (TP), water,
 Microalgae are used as food for herbivorous animals- shellfish (mollusks such
temperature, and light intensity.
as clams, oyster) and fish.

Algae in waste treatment plants

 Algae play two important roles in waste-treatment systems.

 They serve as oxygenators in aerobic decomposition of organic matter.

 They also remove nutrients like nitrogen and phosphorus and heavy metals from waste-
water. 101
 7.2. Harmful effects
• A) Changes in physico-chemical conditions of aquatic ecosystems resulting

from Blooms

 Algal blooms- because of increased concentration of nutrients like nitrogen and

phosphorus, algae grow luxuriously leading to the coloring of water bodies.

 As a result of algal blooms,

affects the growth of
 Penetration of light is reduced
submerged macrophytes.
 Sedimentation of accumulated decomposable organic matter

leads to the creation of anoxic

condition, which drastically
affects animals like fish-fishkill.
102
 B) Toxicity
 Many algae particularly dinoflagellates and cyanobacteria produce a variety of
potent toxins that capable of sicken and killing other organisms that prey on
these algae such as animals including humans.

 Indeed, this probably was the reason that these algae are selected for in the
evolutionary process since it reduced predation by grazers.

 Filter-feeding shellfish can accumulate large quantities of these toxins as

they filter the algae out of the water, consumption of these shellfish by man,
birds, and animals results in sickness and death.

103
 Cont’…
 Cyanophyceae produce neurotoxins (anatoxin and saxitoxin) that block the
transmission of signal from neuron to neuron and affect NS.
 These alkaloids (nitrogen containing compounds) bind to voltage-activated Na ion -
channels and block influx of Na ion, thereby preventing the generation of an action
potential (affect the NS).

 Hepatotoxins (microcystin and nodularin), are inhibitors of protein

phosphatases, which then affect the liver.

 Dermatotoxins– affect the skin as a result of the toxicity of algal blooms,

aquatic and terrestrial animals die, Fishkill often occurs.
 Because of toxic blooms of Microcystis aeruginosa, death of wild and domestic
animals occurs.
104
 Dinophyceae (dinoflagellates)
 produce Paralytic shellfish poisoning caused by saxitoxin and approximately
two dozen naturally occurring analogues.

 The saxitoxins bind to voltage activated Na ion-channels, blocking influx of Na-

ion and preventing the generation of an action potential.

 Saxitoxins are retained primarily inside cells with very little excretion or
leakage from cells.

 These highly water-soluble, but stable, compounds must be released during

senescence or cell lysis, which coincides with the decline of a bloom.

 Spirolide poisoning, this group of cyclic imines include the spirolides,

gymnodimine, pteriatoxin and pinnatoxins.

105
 Cont’…
 The imine ring gives the molecules their toxic properties. They are “fast-acting toxins”,
causing death of mice within minutes after oral application.

 Shellfish-clam, oyster, and mussels eat paralytic shellfish poisoning- toxic

dinoflagellates. Humans as result of whom they are paralyzed consume the shellfishes.
This disorder in humans is known as paralytic shellfish poisoning.

C) Production of dimethyl sulfuide (DMS) and acidic precipitation

 Red algae, Raphidophytes (naked flagellates) and some haptophytes (e.g.
phaeocystis) produce a volatile sulfur- containing compound called DMS that
contributes to acidic precipitation up on oxidation to sulfate.

106
107