Doc: Dinoflagellates, Red Tides NEET Notes | EduRev

Biology Class 11

NEET : Doc: Dinoflagellates, Red Tides NEET Notes | EduRev

The document Doc: Dinoflagellates, Red Tides NEET Notes | EduRev is a part of the NEET Course Biology Class 11.
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What are Chrysophytes?

Chrysophytes are plant-like protists that can be found in marine and freshwater environments which are often low in calcium.

  • There are three main types of chrysophytes: Diatoms (Bacillariophyta), Golden-brown algae (Chrysophyceae), and Yellow-green algae (Xanthophyceae).
  • Although many are unicellular and free swimming, some chrysophytes, like the dinobryon above, join together and form colonies.
  • There are over 1000 described species of Chrysophytes, and, because there are so many species, there is no common cell structure shared by them. 
  • Some species have cell walls made of cellulose strengthened by silica compounds, while others are amoeboid without any cell walls.

Doc: Dinoflagellates, Red Tides NEET Notes | EduRevSome Members of Chrysophytes

Methods of Feeding, Movement, and Reproduction

  • Since chrysophytes are plant-like and have chloroplasts, they are mainly autotrophic
  • If there is inadequate lighting, they can become heterotrophic, especially in areas with high dissolved foods concentrations. 
  • Chrysophytes are mainly non-motile, but they do have two flagella for movement in harsh conditions.
  • Most chrysophytes reproduce asexually through meiosis, but diatoms reproduce sexually, dividing and exchanging parts under certain conditions.

Chrysophyta: Relatives, Affect on Humans, and Role in Food Chain

  • Chrysophyta is algae, so their closest relatives are the six other divisions of algae: Euglenophyta, Pyrrophyta, Chlorophyta, Rhodophyta, Phaeophyta, and Xanthophyta. 
  • Being the main components of plankton and nanoplankton, diatoms and Chrysophyceae are the foundation of the marine food chain, functioning as the producers. 
  • Chrysophyta can be considered helpful to humans. We use them in toothpaste, scouring products, and filters. 
  • As autotrophs, they provide a substantial amount of oxygen in the atmosphere, as well.
  • Also, because chrysophytes store their food as oils, they can be used for biofuel. 
  • Diatoms are especially effective in biobutanol production because of their small size.

Doc: Dinoflagellates, Red Tides NEET Notes | EduRev


Additional Information: Chrysophytes
Diatoms - Golden Algae or Jewels of the Sea
  • The members of Division - Bacillariophyta are known as Diatoms. Diatoms mean-"Cut into two". This name is based on the cell wall of diatoms, which is divided into two parts. They have Holophytic mode of nutrition because they possess chloroplast.
    Examples: Navicula, Cyclotella, Pinnularia.
Structure
  • They are found in different shapes such as circular, rectangular, triangular, elongated and boat-shaped.
    Doc: Dinoflagellates, Red Tides NEET Notes | EduRev
  • The cell wall of diatoms is made up of cellulose in which silica particles are embedded in many places, due to which the cell wall appears to be made up of silica. This silicate cell wall is called "shell" or "frustule".
  • Their cell wall is made up of two halves, which are arranged like the lids of a soapbox. These half parts are collectively known as theca. The part which is present on the upper side acts as the lid and known as the epitheca, and the other basal part is known as the hypotheca. The place where the two parts overlap each other is called a girdle.

Note: Their cell wall has silica in very large quantity. Due to this reason, their cell wall is hard. The cell wall does not get destroyed after their death so, at the bottom of the sea, very huge rocks of dead diatoms are formed which are known as "diatomite" or "diatomaceous earth" or "kieselguhr".

Try yourself:Diatom frustule/shell is made of
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  • The diploid nucleus is present in Diatom.
  • Their cells have chloroplasts, in which pigments are present, Chlorophyll 'a', Chlorophyll 'c', and xanthophyll (fucoxanthin). Due to these pigments, it appears golden coloured.
  • Stored food: Leucosin (Chrysolaminarian) & fats (Oil).
  • Movement: They are immotile because flagella are absent. They float on the surface of the water with the help of low molecular weight stored fats.
Reproduction
  • Mainly asexual: Binary fission.
  • Sexual reproduction: Very rare - by gametic meiosis.
  • The zygote formed during sexual reproduction is called as "Auxospore". Auxospore is an asexual structure.
Try yourself:Leucosin (Chrysolaminarin) is a carbohydrate which is stored as reserve food in case of
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Use of Diatoms
  • Soundproofing
  • Filtration of oils and syrups.
  • Stone polishing.
  • As "Heat insulator" in steam boilers, i.e. they are used as thermostat because the kieselguhr is a bad conductor of heat.

Dinoflagellates: Protists With Two Flagella

  • Dinoflagellates are mainly marine. They are found on the surface of the water. These are golden brown in colour.
    Doc: Dinoflagellates, Red Tides NEET Notes | EduRev
    Dinoflagellates
  • In Dinoflagellates, nutrition is mainly holophytic, because they have chloroplast.
    Example Noctiluca, Ceratium, Gonyaulax, Gymnodinium, Pyrocystis.
  • Ceratium: It is also an exception because its, mode of nutrition is mixotrophic.
  • Noctiluca is an exception in Dinoflagellates because:
    (i) It is colourless.
    (ii) Chloroplast is absent.
    (iii) Photosynthesis is absent in it. Therefore, it has a holozoic mode of nutrition.
    (iv) But yet it is placed in Dinoflagellates because two flagella are present.
    (v) Plated cell wall is present.

Note: It is also classified in protozoa due to its holozoic mode of nutrition and colourless body.

Try yourself:Which is not a feature of dinoflagellates?
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Structure
  • Their cell wall is divided into plates, which is made up of cellulose. Therefore the covering of Dinoflagellates is seen as armoured, so they are called as Armoured algae.
  • Dinoflagellates have two flagella - one is transverse and other is longitudinal. Dinoflagellates show a special type of movement which is like whorling whips. Therefore they are also known as "Whorling whips".

Doc: Dinoflagellates, Red Tides NEET Notes | EduRevParts of Dinoflagellates

  • Dinoflagellates are haploid. Histone proteins are absent. Due to this reason Dinoflagellates are called as Mesokaryote.
  • They have an osmoregulatory structure called 'Pusule'.
  • Dinoflagellates are yellow-brown or golden brown in colour. These colour of Dinoflagellates are due to the pigments present in them - Chlorophyll 'a', Chlorophyll 'c' and Xanthophylls (Dinoxanthin & Didinoxanthin).
  • They have starch as stored food.

Reproduction

  • Mainly Asexual – Binary fission.
  • Sexual reproduction is very rare. Dinoflagellates are haploid, so they reproduce by Zygotic meiosis. Therefore, their life cycle is haplontic type.

Note: Exceptionally Noctiluca is diploid so it reproduce by gametic meiosis, therefore its life cycle is Diplontic type.

Additional Information: Dinoflagellates
  • Maximum Dinoflagellates (Example: Noctiluca, Gonyaulax, Pyrocystis) show 'bioluminescence'. Their protoplasm has photogenic granules. These granules are made up of luciferin protein. 
  • Energy is released by the oxidation of luciferin. This energy is liberated in the form of light during the night. This is known as "bioluminescence. So these dinoflagellates are also known as 'night light'.
  • Gonyaulax spreads on the surface of seawater, through rapid multiplication due to which the seawater appears red. It is called red tide. It is also responsible for water bloom.
  • Both Gymnodinium & Gonyaulax are toxic. They secrete toxins, which are known as "saxitoxin". These toxins can cause paralysis in human beings. Humans acquire these toxins through the food chain. These algae also affect marine animals.
  • Noctiluca is known as 'sea - ghost' because it glows at night.
  • Dinoflagellates are also called "fire algae" because they appear as glowing light due to bioluminescence. Division - Chrysophyta/Bacillariophyta - DIATOMS.
Try yourself:Sea water glows during night mainly due to occurrence of
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