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PinkMonkey Online Study Guide-Biology

14.2 Kingdom : Protista

(Eukaryotic unicellular organisms)

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Figure 14.13 Some Protista

Protista includes all eukaryotic unicellular microorganisms, either plant-like or animal-like or showing overlapping characters of both plants and animals. Primarily they are aquatic and widely distributed all over the world, occurring in oceans, lakes, ponds and damp soils. They are autotrophic or heterotrophic. The latter are free-living or parasitic on or within multicellular organisms. Thus it reflects the lifestyles either of plants, animals or fungi. Phylogenetically they serve as the connecting link between prokaryotic Monera and complex multicellular kingdoms of plants fungi and animals. They are distinguished by the following characters:

(i) They are first eukaryotes, having a well organized nucleus and complex membranous organelles.

(ii) They are unicellular or colonial forms without distinct division of labor.

(iii) They are autotrophic or heterotrophic showing varieties of metabolic systems.

(iv) Locomotion is by pseudopodia, flagella or cilia.

(v) They show mitosis, meiosis and simplest type of sexual reproduction for the first time. Common examples are Ameba, Paramecium, Euglena, diatoms and dinoflagellates.

1. Cilia and flagella

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Figure 14.14 Cilia and Flagella

(A) Structure (B) Movement

These are microscopic, contractile, motile hair-like locomotary organelles present in ciliated and flagellated protists like Paramecium and Euglena. Cilia and flagella are similar in structure. Each arises internally from the basal body and is made up of eleven microtubules, two single ones in the center connected to nine double ones arranged along the periphery (often referred to as 9 + 2 arrangement). The outer fibrils enter cytoplasm and converge to form the basal body. The central fibrils are connected to the peripheral ones by radial lamellae, like the spokes of a wheel. Cilia are short and numerous and beat in a coordinated manner simultaneously or one after the other, while flagella are long and whip-like, showing undulating movements. Their function is to propel the cell through the surrounding liquid medium or move the surrounding medium past the cells, gathering food particles. During movements cilia beat vigorously and rapidly (effective stroke) and they recover slowly (recovery stroke). Cilia and flagella are widely distributed in gametes, unicellular plants and animals and also on cells of more complex organisms forming the internal lining of ducts, such as trachea, oviduct, etc.

Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi

Chapter 15


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