Chrysophytes are a group of microscopic, photosynthetic organisms mainly found in freshwater and marine environments. They belong to the kingdom Protista and are commonly known as golden algae because of their characteristic golden-yellow colour. This colour is due to the presence of pigments like chlorophyll a, chlorophyll c, and xanthophylls (especially fucoxanthin).
Classification of Chrysophytes
It has been classified into three groups: diatoms (Bacillariophyceae), golden-brown algae (Chrysophyceae), and yellow-green algae (Xanthophyceae).
1. Bacillariophyceae (Diatoms)
- Diatoms are members of the division Bacillariophyta.
- They are unicellular eukaryotic organisms found mainly in aquatic environments.
- The cell wall of diatoms is made of silica and consists of two overlapping halves, called a frustule.
- The two-part cell wall of diatoms is the inspiration for the name of these organisms.
Examples: Dinoflagellates, diatoms, euglenoids, slime moulds, and protozoans.
2. Chrysophyceae (Golden brown algae)
- Golden algae, also called golden-brown algae, include about 33 genera and nearly 1,200 species of algae.
- They are found in both freshwater and marine (saltwater) environments.
- Golden algae belong to the class Chrysophyceae.
- Most species are unicellular and biflagellate, meaning each cell has two different flagella.
- They contain the pigment fucoxanthin, which gives them their golden-brown color.
- Their food reserve is mainly stored as oil droplets.
- Many species are protected by a silica cyst called a statocyst (or statospore).
- The surface ornamentation of the statocyst helps in distinguishing between different species.
- They reproduce asexually by producing motile and non-motile spores.
Examples: Chrysococcus, Dinobryon, Synura.
3. Xanthophyceae (Yellow Brown Algae)
- Their yellow-green colour is due to the absence of the pigment fucoxanthin.
- The cell wall is mainly made of cellulose.
- They are found mostly in freshwater, but some species occur in terrestrial and marine environments.
- They may occur in different forms such as unicellular, filamentous, or colonial forms.
Examples: Vaucheria, Tribonema
Characteristics of Chrysophytes
- Mostly consist of Unicellular Organisms
- Free-floating (Planktonic) in water
- Two unequal flagella.
- The colour of golden yellow is caused by an auxiliary pigment(Fucoxanthin).
- Silica and cellulose are used to make cell walls.
- Found in both freshwater and marine environments.
- Chrysophytes are photosynthetic.
Cell Structure and Metabolism
- No uniform cell structure among all chrysophytes
- Some species are amoeboid and lack a cell wall
- Others have cell walls composed of cellulose and silica
- One or two flagella may be present; if two, they are usually unequal
- Mainly photosynthetic (autotrophic)
- Some golden algae become heterotrophic or mixotrophic in low light or nutrient-rich conditions
Reproduction of Chrysophytes
- In chrysophytes, reproduction happens by cell division.
- Chrysophytes generate spores and reproduce asexually.
- The spores move around, have flagella, and are known as zoospores.
- Flagella are only present during reproductive stages
- Only diatoms exhibit sexual reproduction.
Significance of Chrysophytes
- Chrysophytes are autotrophs that produce a large amount of oxygen by photosynthesis.
- Chrysophytes are also useful. Diatomaceous earth is used to filter and polish oils. As a biofuel.
- They are particularly important in lakes, where they may serve as the zooplankton's main food source.
- It decomposes dead stuff and distributes these nutrients to another part of the water body.
- It supports the maintenance of biodiversity.
- Chrysophytes produce oils or the polysaccharide laminarin as a food storage product.