BIOSORPTION OF Pb2+, Cd2+, & Ni2+ FROM WATERS BY ...

1.5. Algae
Living or dead algal cells are being increasingly used as biosorbents to
remove heavy metals from aqueous solutions due to their high sorption uptake and
their availibility in practically unlimited quantities in the seas and oceans (Feng and
Aldrich 2004).
Algae (singular alga) are a large and diverse group of simple, typically
autotrophic organisms, ranging from unicellular to multicellular forms (Wikipedia
2008). Seaweeds are the largest and most complex marine forms. They are
photosynthetic, like plants, and "simple" because they lack the many of the distinct
organs found in land plants. All true algae have a nucleus enclosed within a
membrane and chloroplasts bound in one or more membranes. Algae constitute a
paraphyletic and polyphyletic group: they do not represent a single evolutionary
direction or line, but a level or grade of organization that may have developed several
times in the early history of life on Earth.
Some organs that are not included in the algae are phyllids and rhizoids in
nonvascular plants, or leaves, roots, and other organs that are found in tracheophytes.
Since they are photosynthetic, so they are distinguished from protozoa. Even though
some groups contain members that are mixotrophic, deriving energy both from
photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or
phagotrophy, many are photoautotrophic. Some unicellular species rely entirely on
external energy sources and have reduced or lost their photosynthetic apparatus.
All algae have photosynthetic parts eventually obtained had origin from the
cyanobacteria, moreover they produce oxygen as a byproduct of photosynthesis,
unlike other photosynthetic bacteria such as purple and green sulfur bacteria.
Algae are most prominent in bodies of water but are also common in
terrestrial environments. However, terrestrial algae are usually rather inconspicuous
and far more common in moist, tropical regions than dry ones, because algae lack
vascular tissues and other adaptations to live on land. Algae are also found in other
situations, such as on snow and on exposed rocks in symbiosis with a fungus as lichen.
The various sorts of algae play significant roles in aquatic ecology.
Microscopic forms that live suspended in the water column (phytoplankton) provide
the food base for most marine food chains. Some are used as human food or harvested
14