Why Are Dinoflagellates Vital in Marine Biology?
The dinoflagellates species are included in the Kingdom Protista. The dinoflagellates are phototrophic organisms. They are also known as photosynthetic organisms. They are single-cell eukaryotes and are present in the phylum Dinoflagellata. Most of the dinoflagellates are marine planktons, and are therefore known as dinoflagellates plankton. They are also found in freshwater habitats. Most of them are mixotrophic and some of them are considered photosynthetic. When there are changes in the temperature, salinity, and depth of the water body, the population of dinoflagellates water changes. The dinoflagellates species are the largest group of marine eukaryotes. We will learn more about what are dinoflagellates, different colours of dinoflagellates, such as red dinoflagellates, and about the kingdom Protista.
Protista
As we read previously, there are organisms called eukaryotes too. They are unicellular in nature. They are colonial and are present without much cellular differentiation. The body organisation at the tissue level is not present in these protists. They are mostly aquatic in nature. As they are eukaryotic in nature, they have the presence of all kinds of membrane-bound organelles. 80S cytoplasmic ribosomes are also present in them. Some of them may also possess cellulosic cell walls (9+2) of the microtubule, the pattern is followed by their cilia and flagella. Their cilia and flagella consist of tubulin protein. Flagella, cilia, and pseudopodia are the means by which these cells show movement. Among all these three modes, the ciliary mode is the fastest. The modes of nutrition of these protists can be photosynthetic, holozoic, saprobic, and parasitic. They also have mixotrophic nutrition. This means that they have both photosynthetic and saprobic type of nutrition as it is present in euglena. Both asexual and sexual modes of reproduction are present in them. They show two types of life cycles that are zygotic meiosis and gametic meiosis. The protists basically comprise decomposers, photosynthetic, or parasites. Dysentery, malaria, and sleeping sickness are some of the diseases that can be caused by them. They comprise diatoms, dinoflagellates, euglenoids, slime moulds, and protozoans. Now, we will thoroughly learn about the dinoflagellates.
Dinoflagellates Characteristics
These features will let us know more about dinoflagellates. They are also known as golden brown photosynthetic protists. They belong to the class Dinophyceae. Dinophyceae is also known as Pyrrophyta. Some are present in freshwater, and mostly, all are present in marine forms. They have pigments present in their cells that are known as red, yellow, green, brown, or blue. Some characteristics are as follows:
They are unicellular organisms. They are motile in nature and are biflagellate. Though some of their forms are non-motile in nature.
They are found in both marine and freshwater, though mostly in the marine form.
Theca or lorica is a rigid coat present on their body. It consists of two or more articulated or sculptured plates of cellulose and pectin. Due to this feature, they are called armoured dinoflagellates.
In their theca, they have two grooves. One is the sulcus and the other is the cingulum. The sulcus is longitudinal and the cingulum is a transverse groove.
They have a heterokont flagella. This means that they are different. Their flagella pass out from the pores of the lorica and lie in the grooves. The longitudinal flagellum is narrow and the transverse flagellum is in the shape of a ribbon. Both of their flagella are present at right angles to each other. Due to this, they are also called whirling whips. These are the dinoflagellates flagella.
Carbohydrates and oils are their reserve food material.
Due to the presence of chlorophyll a, c, and xanthophyll, they have different types of colours, such as red, brown, and green. Their plastids are surrounded by 3 layered structures.
Their nucleus is larger in size. They have condensed chromosomes in interphase. Their chromosomes do not have histones. At the time of cell division, their nuclear envelope and nucleolus remain present. This organisation is called mesokaryon.
They possess trichocysts and cnidoblast cells. These are also present in coelenterates.
Pusule is a non-contractile vacuole that is present in them. It is present near the flagellar base. It takes part in floatation and osmoregulation.
The most common mode of reproduction is asexual. It occurs through cell division.
Some of them have reported sexual reproduction too. It is of anisogamous and isogamous type of sexual reproduction.
Zygotic and gametic meiosis occurs in their life cycle.
Interesting Facts about Dinoflagellates
Some Interesting Facts about Dinoflagellates are as follows:
Some of their species show bioluminescence. This means that they emit light. Due to their phosphorescence quality, the sea glows at night time. Red dinoflagellates cause the red sea.
Gonyaulax is some of their species that produce saxitoxin. This toxin is released into the sea and is very poisonous in nature. It can kill fishes and other aquatic animals. The shellfish consumes these dinoflagellates and then accumulates this poison into its shell. Thus, it is not harmful to shellfish.
The red tide is caused by Gymnodinium and Gonyaulax species. These are thus known as red dinoflagellates.
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FAQs on Dinoflagellate: Definition, Characteristics & Examples
1. What are dinoflagellates as per the Class 11 syllabus?
Dinoflagellates are unicellular, eukaryotic organisms belonging to the Kingdom Protista. As per the NCERT syllabus for Class 11, they are primarily marine and photosynthetic. Their name is derived from their characteristic whirling motion, which is caused by the presence of two dissimilar flagella.
2. What are the main characteristics of dinoflagellates?
The main characteristics of dinoflagellates are:
Cell Wall: They have a rigid outer covering called the theca, which is made of stiff cellulose plates.
Flagella: They possess two flagella; one lies longitudinally and the other transversely in a furrow between the cell plates.
Pigmentation: They appear in various colours like yellow, green, brown, blue, or red, depending on the main pigments (chlorophyll a, c, and carotenoids) in their cells.
Nucleus: They have a unique nucleus called a mesokaryon, where chromosomes are condensed and lack histone proteins.
Nutrition: Most are photosynthetic, but some are heterotrophic or mixotrophic.
3. Which dinoflagellate is known for causing red tides and what is this phenomenon?
The dinoflagellate most famously known for causing red tides is Gonyaulax. A red tide is an example of an algal bloom, which occurs when these organisms undergo rapid multiplication under favourable conditions. Their massive population density makes the sea appear red. This phenomenon is significant because many red-tide dinoflagellates release toxins that can kill other marine animals such as fish.
4. How are the two flagella of a dinoflagellate arranged and why is it significant?
The arrangement of flagella in dinoflagellates is unique and crucial for their movement. One flagellum is transverse, wrapping around the cell in a groove called the cingulum, which causes the cell to spin. The other is longitudinal, located in a groove called the sulcus, which propels the cell forward. The combination of these two movements results in the characteristic whirling or spinning motion for which they are named (Greek 'dinos' means whirling).
5. Why are dinoflagellates considered to have both plant-like and animal-like features?
Dinoflagellates exhibit a fascinating mix of features that blur the line between plants and animals. They are considered plant-like because many are photosynthetic, containing chlorophyll and other pigments to produce their own food. They are considered animal-like because they possess flagella for active movement (motility) and some species are heterotrophic, meaning they ingest other organisms for nutrition. This dual nature makes them a prime example of the diversity within Kingdom Protista.
6. What makes the nucleus of a dinoflagellate, known as a mesokaryon, unique among eukaryotes?
The dinoflagellate nucleus is called a mesokaryon because it has features intermediate between a prokaryotic nucleoid and a typical eukaryotic nucleus. Its uniqueness comes from two main aspects:
Lack of Histones: Unlike almost all other eukaryotes, their DNA is not organised by histone proteins.
Condensed Chromosomes: Their chromosomes remain permanently condensed and visible throughout the entire cell cycle, not just during mitosis as seen in other eukaryotes.
7. What is the importance of bioluminescence in some dinoflagellates?
Bioluminescence in dinoflagellates, such as Noctiluca (also known as 'sea sparkle'), is a defence mechanism. When the water is disturbed, a chemical reaction involving the enzyme luciferase produces a flash of light. The importance of this is to startle potential predators, a phenomenon known as the 'burglar alarm' effect. This flash can attract a larger predator to prey on the organism that disturbed the dinoflagellate, thereby protecting it.
