Introduction to the Algae

20141101159

Ram Hari Dahal

• The algae are a heterogeneous group oforganisms.

• They are major contributors to global bio-diversity, with estimated numbers of speciesranging from 36,000 to more than 10 million.

• As a result of photosynthetic activities they areproducing enormous quantity of organic carbon

• Algae can be used to produce bio-fuels, used inaquaculture and also can be used to remove

pollutants from sewage and agricultural effluents.

Contents1. Defining the Algae

2. Algal Body Types

a) Microalgae

b) Macroalgae

3. Algal Reproductive Types

a) Asexual Reproduction

b) Sexual Reproduction

4. A Survey of Algal Diversity

5. An Overview of Algal Photosynthesis

a) The General Process of Photosynthesis

b) The light- Acquisition Problem

c) The Photoprotection Problem

d) The Carbon-Fixation Problem

6. Societal Issues Involving Algae

1. Defining the Algae

• 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 photosyhnthetic

species.

2. Algal Body Types

• Algal bodies can be divided into microalgae and macroalgae

a) Microalgae• Their bodies are so small that microscope is needed to

observe them.• They occur as solitary cells, known as unicells.• They occur in a variety of shapes viz. coccoid, colonies,

flagellates etc• Microalgae may also occur in the attached periphyton, may

swim or float in the open waterband are collectively known as phytoplankton.

• When the phytoplankton populations become very large they form algal blooms.

b) Macroalgae

• Algal bodies are large enough to be seen with the unaided eye.

• The macroalgae known as giant kelps have parenchymatous bodies that may reach 50m in length.

• Most coenocytic, parenchymatous, andpseudoparenchymatous algae can be seenwithout the use of microscopic method.

3. Algal Reproductive Types• Algae reproduce by both asexual and sexual methods.• Some algal species reproduce only asexually, but many

reproduce by both sexual and asexual processes.a) Asexual Reproduction• Populations of many unicellular species increase by

longitudinal and transverse cell division.• They reproduce by means of flagellate unicells known

as zoospores, or non-flagellate aplanosores or autospores.

• Akinetes are specialized asexual cells that develop from actively growing cells when environmental signals indicate impending conditions for growth and during favourable condition they germinate.

b) Sexual ReproductionAmong sexually reproducing algae, gametesmay be more or less differentiated, dependingon the species.• Isogamous reproduction describes the

situation when mating gametes areoften biochemically differentiated.

• Anisogamous reproduction involves themating of two gametes that differ in size orbehavior.

• Oogamous reproduction occurs when aflagellate or non-flagellete male gametes fuseswith a larger, non-motile egg cell.

4. A survey of Algal DiversityThe algae can be classified into a dozen or solineage. The details are given in table.

5. An Overview of Algal Photosynthesis

• The diversity survey shown that the oxygenic photosynthesis is a defining feature of the algal lineages, present in half or more of the species

a) The General Process of Photosynthesis

• Photosynthesis is the process by which light energy is harnessed to produce organic compound.

• 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 carbondioxide, there by forming organic compounds in a process known as carbon fixation.

b) 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 maynot be sufficient to supply the needs of algal photosynthesis.

• The algae perform photosynthesis and acquire exogenous organicnutrients. So they are termed as mixotrophs.

c) The Photoprotection Problem

• Algae may encounter fast irradiance changes when current transportdeep-dwelling phytoplankton cells into bright surface light or when areceding tide exposes shoreline macroalgae.

• 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.

d) 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.

6. Societal Issues Involving Algae

• Algae provide the organic carbon that is the basis for aquatic food chains, influencing the quality of fisheries.

• Human is cultivating algae for food and other products.

• They help to meet the fuel needs.

• Some algal blooms produce toxins that poison animals and when they decay, much of the oxygen in the water is consumed, killing fish and shellfish.

• Algal blooms are responsible for the global spread of “dead zones”