DINOFLAGELLATES - “PROTISTS WITH TWO FLAGELLA”
1. Dinoflagellates are mainly marine. They are found on the surface of water. These are golden brown in colour.
2. In Dinoflagellates, the nutrition is mainly holophytic, because they have chloroplast. Example - Noctiluca, Ceratium, Gonyaulax, Gymnodinium, Pyrocystis.
Note: It is also classified in protozoa due to its holozoic mode of nutrition and colourless body.
(i) Mainly Asexual – Binary fission.
(ii) 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.
Some informations of Dinoflagellates
1. Maximum Dinoflagellates (eg. - 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 night. This is known as "bioluminescence.
So these dinoflagellates are also known as 'night light'.
2. Gonyaulax spreads on the surface of seawater, through rapid multiplication due to which the sea water appears red. It is called as red tide. It is also responsible for water bloom.
3. 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 food chain. These algae also affect the marine animals.
4. Noctiluca is known as 'sea - ghost' because it glows at night.
5. Dinoflagellates are also called "fire algae" because they appear as glowing light due to bioluminescence.
Division - Chrysophyta/Bacillariophyta - DIATOMS
DIATOMS - "GOLDEN ALGAE OR JEWELS OF SEA"
The members of Division - Bacillariophyta are known as Diatoms. Diatoms means-"Cut in to 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 of Diatoms include Navicula, Cyclotella, Pinnularia.
1. They are found in different shapes such as circular, rectangular, triangular, elongated and boat-shaped.
2. The cell wall of diatoms is made up of cellulose in which silica particles are embedded at many places, due to which the cell wall appears to be made up of silica. This silicate cell wall is called "shell" or "frustule".
3. 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 epitheca and the other basal part is known as hypotheca. The place where the two parts overlap each other is called 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 sea, very huge rocks of dead diatoms are formed which are known as "diatomite" or "diatomaceous earth" or "kieselguhr".
4. Diploid nucleus is present in Diatom.
5. Their cells have chloroplasts, in which pigments are present, Chlorophyll 'a', Chl 'c', and xanthophyll (fucoxanthin). Due to these pigments it appears golden coloured.
6. Stored food – Leucosin (Chrysolaminarian) & fats (Oil).
7. Movement – They are immotile, because flagella are absent. They float on the surface of water with the help of low molecular weight stored fats.
(i) Mainly asexual– binary fission.
(ii) Sexual reproduction- Very rare - by gametic meiosis.
(iii) The zygote formed during sexual reproduction is called as "Auxospore"- Auxospare is an asexual structure.
Use of Diatoms:–