ALGAE
ALGAE
• Aquatic, autotrophic organisms with tissues
scarsely differentiated and capable of absorbing
water and minerals with the whole body surface
(no vascular system).
• They have chlorophyll a in plastids.
• They are included in the regnum of Protoctista,
comprising eukaryotic, single-celled, colonial
and multicelluar organisms, either autotrophich
and heterotrophic.
ALGAE
• Eucaryotic algal cell (with the exception of bluegreen algae or cyanobacteria) has a wall composed
of polysaccharides (different from those of plant
cells) and plastids (normally one for each cell)
containing, beside chlorophyll a, other types of
chlorophylls and accessory pigments.
• Algal cells lack plasmodesmata so that there are not
real tissues.
Types of thallus organization
• Monadale: single-celled flagellate.
• Amoeboid : single-celled without flagella
moving by pseudopods.
• Coccoid: surrounded by a rigid wall.
• Colonial: aggregation of more organisms.
• Palmelloid: more colonies surrounded by
a mucilaginous envelope.
• Siphonal: multinucleated, single-celled
organisms.
• Siphonocladal: multi-cellular organism
with multinucleated cells.
• Filamentous: alignment of uninucleated
cells linked by plasmatic connections to
form simple or branched filaments.
• Thalloid: cells divide towards more
directions giving laminar thalli (2D) or
pseudoparenchymas (3D).
Life cycles
Variety of cycles:
• Initial meiosis (haplont organisms).
• Intermediate meiosis (two phases, haplont-
diplont, with isomorphich or heteromorphic
generations).
• Terminal meiosis (diplont organisms).
Distribution
• Algae can be found in most habitats
on Earth, although the majority
occur in freshwater or marine
environments, free or attached to
the substrate.
• Where the water is clearer, algae
can reach 200 m of depth; along the
coast, where the water is cloudy,
they live on the water surface.
• The equipment of pigments
influences the distribution: red and
brown algae live at greater depth
respect to green algae because they
have pigments capable of absorbing
short wavelenghts.
Ecological importance
• They belong to primary
producer, representing the first
ring in the food chain.
• They produce the majority of
oxygen for Earth, higher than
that of equatorial forests.
Systematics
• Classification of Algae
relies on biochemical and
structural characteristics of
plastids (type of pigments).
Pharmaceutical importance of Algae
• They have economic interest due to the
presence of polysaccharides with
thickening and gelling properties that are
used at food and pharmaceutical level.
• They contain secondary metabolites (e.g.
terpenoids, halogenated poliphenols,
nitrogen compounds) which might have
an use similar to that of equivalent
products of terrestrial plants.
• They are used in diets since they are poor
of lipids and rich of non-digestible
polysaccharides, proteins, vitamins and
minerals.
Rhodophyta (red Algae)
• A group of eukaryotic algae, red in colour, without flagella.
• They may be unicellular, but most are filamentous or membranaceous;
they never exceed 1 m in diameter.
• The majority occur in the sea, but some are freshwater or terrestrial.
• The red seaweeds are abundant in temperate and tropical regions (they
form coral reefs), but less numerous in colder regions.
• They live on the rocks, from the sea level to about 200 m of depth.
• The storage product is floridean starch (polymer of α-glucose similar to
amylopectin, in cytoplasm).
• Sexual reproduction so complicated (oogamy); vegetative reproduction by
fragmentation.
• The plastid contains chlorophyll a, d, α- and β-carotene, xanthophylls and
phycobilins (responsible for the red colour as phycoerythrin).
• Cell wall contains an outer mucilaginous layer composed of sulphur
polymer of galactose (agar and carraghen) that are useful at food and
pharmaceutical level.
• The group includes about 4000 species. They are believed to be one of the
oldest groups of eukaryotic algae.
• Plastid of red alga: phycobilins are on the external surface of
thylakoids, in special granules known as phycobilisomes.
• Some seaweeds have cell
walls impregnated of calcium
carbonate; these organisms
contributed to the formation
of coral reefs and biogene
rocks (Dolomites).
•Gelidium sp., from which is obtain agar.
•Chondrus crispus, source of carraghen. It occurs along the coasts of North Sea and of
northern America (Canada and USA).
•Porphyra, benthic organism used as a food in Orient.
Phaeophyta (brown Algae)
• A division of algae which includes no single-celled species; most of them have
thalloid organization with a great variety of shapes and dimensions, ranging
from microscopic to giants (about 70 m in lenght). They show aerocysts along
the thallus, favouring flotation.
• Almost all are marine, growing mostly in the intertidal regions, from 30 to 90 m
of depth. They are the dominant seaweeds in the colder waters of the northern
hemisphere.
• They contain in the chloroplasts chlorophyll a and c, β-carotene and
xanthophylls. They are typically olive-brown or greenish in colour owing to the
presence of the pigment fucoxanthin (a xanthophyll).
• As storage substances they present chrysolaminarine (glucan of β–glucose with
1,3 glycosidic bonds) and mannitol (a C6 polyalcohol used as diuretic,
sweetener, stabilizer, thickener, gelling and emulsifier agent). Often they
contain phloroglucinols in the vacuole. They are an abundant source of
potassium and iodine salts.
• Cell walls are impregnated of polysaccharides such as alginates and fucanes.
• Vegetative reproduction by fragmentation. Sexual reproduction by isogamy,
heterogamy and oogamy; gametes and spores with flagella.
• Great variety of life cycles (aplo-diplont or only diplont organisms).
•Fucus vesiculosus (kelp) with dichotomous thallus and aerocysts. It
grows along atlantic coasts of the English Channell and North Sea
•Laminaria saccharina and Laminaria digitata. They grow along the English Channell,
North Sea, Atlantic Ocean and southern Pacific Ocean. They show rhizine, root-like
structures usually functioning in the attachment of the thallus to the substrate.
•Macrocystis pyrifera (known as
giant kelp; it can reach 70-80 m in
lenght). It grows in the Pacific
Ocean.
•Sargassum
(sargasso),
forming
floating masses on the sea surface. It
gives the name to the Sargasso Sea
fucoxantin
mannitol
•Some costituents of brown Algae. Fucoxantin induces lypolysis in the
adipose tissue so that it is used in weight loss products and to treat obesity.
GREEN ALGAE (CHLOROPHYTA)
They are the ancestors of terrestrial plants because they show
the following features:
•chlorophyll a, b and β-carotene;
•cloroplasts with tylakoids forming grana;
•starch as the main storage product;
•cell wall mainly composed of cellulose, hemicellulose and
pectins;
•cellulose synthases in rosette;
•cytokinesis with formation of the cell plate and
phragmoplast;
•similar enzymes contained in peroxisomes involved in
photorespiration.
•colony of Volvox.
•Ulva lactuca (sea lettuce),
growing on the rocks and in the
shallow waters of the seas around
the world. It is used as a
vegetable.
•Coleochaete (Charophyceae) , showing similar features to those of plants.
•Chara (Charophyceae) , living in the shallow waters of temperate
lakes. It shows protective structures for gametes.