Biology BIOLOGICAL CLASSIFICATION

Kingdom - Protista

All the organism included in Protista are unicellular (acellular) eukaryotes. Members of protista are primarly aquatic. This kingdom forms a link with the others dealing with plants, animals and fungi.

Living organisms included in Protista are as follow :-
[ Dinoflagellates, Chrysophytes, Euglenoids , Slime molds, Protozoans ]

Reproduction :-
Protists reproduce Asexually and Sexually.

1. Asexual Reproduction :
This is the most common method of reproduction in protists. It is of following types-

(a) Binary fission :Two daughter cells are formed by division of one mother cell. After this each daughter cell grows to form a normal organism.
eg- Dinoflagellates, Chrysophytes, Euglenoids.

(b) Spore formation : Some protists have special structure known as sporangia. Spores are formed in this sporangia. The sporangia bursts after sometime and all the spores become free. These spores form a new cell after germination.
eg- Slime-moulds (false fungi).

2. Sexual Reproduction :
Sexual reproduction was first of all seen in protists. In sexual reproduction two haploid gametes fuse to form a diploid zygote. This process is known as Syngamy.
Syngamy is of three types -
(a) Isogamy : It is the easiest way of sexual reproduction. In isogamy the fusing gametes are morphologically (i.e. shape, size, structure) similar but physiologically (i.e. functionally or genetically) they may be similar or dissimilar. When fusing gametes are physiological dissimilar, process called physiological anisogamy.

(b) Anisogamy : The fusing gametes are morphologically dissimilar ( smaller - larger ) but physiologically they may b similar or dissimlar (usually).

(c) Oogamy : It is developed form of anisogamy. Male gamete is small and motile while female gamete is large and non-motile. This female gamete is known as egg. In it the formation of male and female gamete takes place in sex organs.

Patterns of Life

(1) Life cycle showing zygotic meiosis :
When Protist is haploid and meiosis occurs in zygote then it is known as zygotic meiosis.
In this type of life cycle during sexual reproduction gametes are formed by mitosis. These gametes are haploid. These gametes fuse to form a diploid zygote.
After that meiosis takes place in zygote, as a result haploid cells are formed again.
Note: In this type of life cycle the zygotic phase is only diploid and remaining all the phases are haploid so this type of life cycle is known as haplontic life.
eg- Dinoflagellates.

(2) Life cycle showing gametic meiosis :
When protists is diploid and meiosis takes place during gamete formation, then it is called gametic rneiosis. In this type of life cycle during sexual reproduction meiosis takes place in diploid cell, due to which haploid gametes are formed. Now haploid gametes fuse to form diploid zygote. And after that mitosis takes place in zygote, due to which diploid cells are formed again.
Note : In this type of life cycle only gametic phase is haploid and remaining all phases are diploid so this type of life cycle is known as diplontic life cycle.
eg- Diatoms

 
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