Dinoflagellates – Class 11 | Chapter – 2 | Short Notes Series PDF

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

Dinoflagellates Structure

Mic-UK: Dinoflagellates

  • Dinoflagellate are mostly marine but also found in freshwater. Their distribution is related to the temperature, pH and depth
  • Dinoflagellate are unicellular having a eukaryotic cell
  • They can be red, blue, green, yellow or brown depending on the pigment present in the cell
  • The complex covering of their cell is called amphiesma, it has flattened vesicles
  • Flattened vesicles known as alveoli are present inside the plasma membrane
  • Alveoli of Dinoflagellate contain cellulose plates, which are impregnated with silicates
  • Dinoflagellate typically have two flagella. One of the flagella wraps around the transverse groove like a belt and the other flagellum projects behind the cell and present in the longitudinal groove, that is perpendicular to the transverse groove
  • Dinoflagellate move like a spinning top with the help of flagella
  • The cell of Dinoflagellate has all common membrane-bound organelles such as mitochondria, Golgi bodies, rough and smooth endoplasmic reticulum and food vacuoles
  • The nucleus of the Dinoflagellate is called dinokaryon.
  • Dinokaryon nucleus has chromosome attached to the nuclear membrane and condensed throughout. They lack histones and have a fibrillar appearance.
  • The mitosis is closed type, i.e. the nuclear envelope does not break during mitosis. The mitotic spindle is extranuclear
  • Rapid multiplication gives rise to sudden population explosions, or blooms, which is responsible for the red colour of the sea, the famous Red Tide. The toxins released by the blooms may kill fishes and reach humans, who eat those fishes
  • Many Dinoflagellate are bioluminescent and emit blue-green light
  • Dinoflagellate also produce lipids and sterols. One of the sterols is known as dinosterol

Dinoflagellate Nutrition

  • Dinoflagellate are mostly photosynthetic autotrophs.
  • Heterotrophic Dinoflagellate ingest other microorganisms and protozoans to get nutrients
  • They are also present as endosymbionts in marine invertebrates such as corals, jellyfishes, etc.
  • The photosynthetic endosymbionts are called Zooxanthellae, they provide carbohydrate to their hosts
  • Endosymbiont Dinoflagellate, which lack pigments are dependent on their hosts and live like a parasite
  • Dinoflagellate are important producers in the marine ecosystem
  • The chloroplast of Dinoflagellate is bound by three membranes and originated from engulfing algae.
  • It contains chlorophyll a, c and may contain various accessory pigments such as peridinin, fucoxanthin, etc.
  • Some Dinoflagellate are photosynthetic as well as heterotrophic, they are known as mixotrophic

Dinoflagellates Reproduction

  • Reproduction in dinoflagellates is primarily asexual through binary fission. The cells are haploid.
  • Sexual reproduction occurs by fusion to form a zygote. The zygote may form a resting stage known as dinocyst or may remain motile
  • The zygote later undergoes meiosis to form haploid cells
  • In unfavourable conditions, vegetative cells of dinoflagellates fuse together to form Planozygote. It takes in excess fat and oil, its shell becomes harder and size increases, the stage is known as Hypnozygote, that is very similar to the hibernating stage. Sometimes even spikes are formed
  • Under favourable conditions, dinoflagellates break out the shell and present in a temporary stage known as Planomeiocyte. They quickly reorganise to their actual shape as a dinoflagellate

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