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## Biological Classification ### 2.2.1 Chrysophytes - This group includes diatoms and golden algae (desmids). - They are found in fresh water as well as in marine environments. - They are microscopic and float passively in water currents (plankton). - Most of them are photosynthetic. - In diatoms...

## Biological Classification ### 2.2.1 Chrysophytes - This group includes diatoms and golden algae (desmids). - They are found in fresh water as well as in marine environments. - They are microscopic and float passively in water currents (plankton). - Most of them are photosynthetic. - In diatoms the cell walls form two thin overlapping shells, which fit together as in a soap box. - The walls are embedded with silica and thus the walls are indestructible. - Therefore, diatoms have left behind large amounts of cell wall deposits in their habitat; this accumulation over billions of years is referred to as 'diatomaceous earth'. - Being gritty, this soil is used in polishing, filtration of oils and syrups. - Diatoms are the chief 'producers' in the oceans. ### 2.2.2 Dinoflagellates - These organisms are mostly marine and photosynthetic. - They appear yellow, green, brown, blue, or red depending on the main pigments present in their cells. - The cell wall has stiff cellulose plates on the outer surface. - Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates. - Very often, red dinoflagellates (Example: Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides). - Toxins released by such large numbers may even kill other marine animals such as fishes. ### 2.2.3 Euglenoids - Majority of them are freshwater organisms that are found in stagnant water. - Instead of a cell wall, they have a protein-rich layer called pellicle which makes their body flexible. - They have two flagella, a short and a long one. - Though they are photosynthetic in the presence of sunlight, when deprived of sunlight, they behave like heterotrophs by predating on other smaller organisms. - Interestingly, the pigments of Euglenoids are identical to those present in higher plants. - Example: Euglena ### 2.2.4 Slime Moulds - Slime moulds are saprophytic protists. - The body moves along decaying twigs and leaves, engulfing organic material. - Under suitable conditions, they form an aggregate mass called a plasmodium which may grow to several centimeters in diameter. - The plasmodium has a multinucleate structure without a cell wall. - The plasmodium ingests food by phagocytosis. - It produces spores that can germinate into new slime moulds. This image shows two types of protists: Euglena (a) and a slime mould (b).