PHOTOSYNTHETIC PROTISTS
These chrysophytes form the main part of phytoplanktons.
These include chrysophytes, dinoflagellates and euglenoids.
1. Chrysophytes
This group includes diatoms and golden algae (desmids).
i. Diatoms
(a) Diatoms occur in all aquatic and moist terrestrial
habitats and are also known as chief producer in the
ocean.
(b) They pile up at the bottom of water reservoirs and
form big heaps called diatomaceous earth.
(c) They are microscopic, unicellular organisms having
different shapes, such as circles, semicircles, triangular,
spindle-shaped, boat-shaped, or filamentous.
(d) The cells of diatoms are called frustules. The body
wall of the diatoms is made up of cellulose
impregnated with glass-like silica. This makes these
cells simply indestructible. The cell wall has two
overlapping halves like a soapbox. The upper half is
called epitheca and the lower half is called
hypotheca.
(e) Diatoms are variously coloured, do not possess
flagella except in the reproductive state.
(f) Each cell has a large central vacuole.
(g) Chloroplasts are yellowish brown to greenish brown.
They contain chlorophyll-a and c. Chlorophyll-b is
absent. They contain fucoxanthin that provides
brownish ting.
(h) Food is reserved in the form of oils and leucosin
(polysaccharide).
(i) The diatoms mostly reproduce asexually by binary
fission. Sexual reproduction varies from isogamy to
oogamy. Examples Navicula, Amphipleura,
Triceratium and Cymbella.
Economic Importance of Diatoms
Diatoms are economically important in the following ways
Diatoms are very important photosynthesisers.
• Diatomite deposits are often accompanied by
petroleum fields.
• These are used as a cleaning agent in toothpastes and
metal polishes and are used in filtration of oil and
syrups. They are also used to enhance night visibility.
Diatoms are used as insulation material in refrigerators
boilers and furnaces. These are also used to make
sound-proof rooms.
ii. Golden Algae (Desmids)
These are unicellular green algae. Their cell walls have
distinct halves. Sexual reproduction occurs by ‘conjugation’
(similar to Spirogyra). They are usually found in freshwater
and act as an indicators of polluted water.

2. Dinoflagellates
These are mainly marine and photosynthetic organisms
There are about 1000 species of photosynthetic protis
known to mankind.
The general characteristic features of dinoflagellates are
listed below
(i) These are important phytoplanktons. Most of them
are marine but some also occur in freshwater.
(ii) They appear yellow, green, brown, blue or red
depending on the main pigments present in their
cells.
(iii) The cell wall in dinoflagellates, if present, is
composed of number of plates made up of cellulose.
Some dinoflagellates like Gonyaulax and
Gymnodinium grow in large number in sea and
make the water look red and form ‘red tide’.
Toxins released by such large numbers may even kill
other aquatic animals.
(iv) Some dinoflagellates like Noctiluca, Pyrocystis, etc.
are phosphorescent and show bioluminescence.
(v) The cells usually possess two flagella which are of
different types (heterokont). One flagellum is
transverse arising from the anterior part. The other
flagellum arises in the vertical furrow between the
wall plates. Both these flagella beat in different
directions.
(vi) The nucleus is bigger in size, named as mesokaryon.
Chromosomes do not have histones and RNA.
(vii) The cells possess an osmoregulatory organelle called
pusule, which superficially looks like contractile
vacuole.
(viii) Dinoflagellates reproduce asexually through cell
division or by the formation of zoospores and cysts•
(ix) Reserve food is stored in the form of starch and Oils
e.g., Gonyaulax, Ceratium, Noctiluca, Peridinium an
Gymnodinium, etc.

3. Euglenoids
Euglenoids live in fresh aquatic habitats and darn
P soik’
They occur mostly in stagnant waters.
The characteristic features of euglenoids are descnk
(i) They are unicellular flagellate protists.
(ii) Body is covered by a thin protein rich layer calk
pellicle which makes their body flexible. It lack
cellulosic cell wall.
(iii) Euglenoids have two flagella, usually one long
one short.
(iv) They perform creeping movements by expansion
contraction of their body. This phenomenon i
called metaboly.
(v) Each cell possesses a mouth (cytostome) at
anterior end.
(vi) Euglenoids are autotrophic in the presence
sunlight. If deprived of sunlight, they behave lik
heterotrophs by predating on other smalla
organisms. This mode of nutrition is mixotrophk
(vii) The photosynthetic pigments include chlorophvU4
and b.
(viii) Reserve food is carbohydrate in the form of
paramylon or paramylum bodies.
(ix) Euglenoids reproduce by longitudinal binary fission
starting at the flagellar end under favourable
conditions. The palmella stage is found during
unfavourable conditions. Examples include Eggw
Perenema, Eutreptia, Phacus, etc.
Sexual reproduction is very rarely seen in euglenoids.
Fig 2.6 Euglena
Euglena is considered as plant as well as animal. It is also
called as plant animal. Plant and animal features are
• Plant Features Chloroplasts and chlorophyll are
present. It has holophytic nutrition.
Animal Features Presence of pellicle which is not
made of cellulose. Contractile vacuole is present.
Longitudinal binary fission.
Knowledge Plus
• Euglenozoa is a diverse clade that includes predatory
heterotrophs, photosynthetic autotrophs and pathogenic
parasites.
• The main feature that distinguishes protists in this clade is the
presence of a spiral or crystalline Of unknown function
inside the flagella,