Kingdom Protista: Euglenoids, Slime Moulds & Protozoans | Biology Class 11 - NEET PDF Download

Biological classification is an important topic for NEET aspirants and should be well understood to develop understanding and relation between different organisms and their characteristics. Let us take a glance at one of the important topics “Kingdom Protista” in this NCERT based notes.

Euglenoids

Euglena

• Most euglenoids are freshwater organisms found in stagnant water.
• Instead of a cell wall, they have a flexible, protein-rich layer called a pellicle.
• Euglenoids possess two flagella: one short and one long.
• They are photosynthetic in the presence of sunlight but can act as heterotrophs by consuming smaller organisms when deprived of light.
• The pigments in euglenoids are similar to those found in higher plants.
• Example: Euglena.

Slime Moulds

Slime Mould

Slime moulds are a type of protist that feeds on decaying organic material. They move along decaying twigs and leaves, engulfing organic matter.

• Under favorable conditions, slime moulds form an aggregation called plasmodium, which can grow and spread over several feet.
• When conditions become unfavorable, the plasmodium differentiates and forms fruiting bodies at its tips, which bear spores.
• The spores have true walls and are extremely resistant, allowing them to survive for many years, even in adverse conditions.
• The spores are dispersed by air currents.

Protozoans

There are four major groups of protozoans:
(i) Amoeboid Protozoans:

• These organisms inhabit freshwater,seawater, or moist soil.
• They move and capture prey by extending pseudopodia(false feet), similar to the way Amoeba does.
• Some marine amoeboid protozoans have silica shells on their surfaces.
• Some species, like Entamoeba, are parasitic.

(ii) Flagellated Protozoans:

• Members of this group can be either free-living or parasitic.
• They are characterized by the presence of flagella.
• Parasitic flagellated protozoans can cause diseases, such as sleeping sickness caused by Tryptanosoma.

(iii) Ciliated Protozoans:

• These organisms are aquatic and are known for their active movement due to the presence of thousands of cilia.
• They have a cavity called a gullet that opens to the outside of the cell surface.
• The coordinated movement of cilia steers water laden with food into the gullet.
• An example of a ciliated protozoan is Paramecium.

Paramoecium

(iv) Sporozoans:

• This group includes diverse organisms that have an infectious spore-like stage in their life cycle.
• The most notorious sporozoan is Plasmodium, the malarial parasite, which causes malaria, a disease with a significant impact on the human population.

Now you can try answering the questions from Kingdom Protista asked in NEET:

Q.1. Pseudopodia help amoeboids in _______
(a) locomotion
(b) ingestion of food
(c) locomotion and ingestion of food
(d) performing metabolic reactions

Correct Answer is Option (c)
Pseudopodia help amoeboids in both locomotion and ingestion of food. Pseudopodia are temporary extensions in amoeba that help them to move to as well as intake food by surrounding it with temporary extensions.

Q.2. Amebiasis is caused due to _______
(a) Amoeba proteus
(b) Entamoeba histolytica
(c) Chaos carolinense
(d) Trypanosoma

Correct Answer is Option (b)
Entamoeba histolytica is a parasitic amoeba in humans which in turn causes Amoebiasis. Amoebiasis results in abdominal pain, diarrhoea, blood in stool, fever and loss of appetite.

Attempt this test to check your knowledge about Kingdom Protista:
Test: Kingdom Protista

Old NCERT Syllabus

Additional information on Amoeba and Entamoeba histolytica.

(a) Amoeba proteus: The Proteus Animalcule. 

• It is found in freshwater.
• Types of pseudopodia are lobopodia. 
• A contractile vacuole is present for osmoregulation. 
• Mitochondria are often seen aggregated around the contractile vacuole of the Amoeba. 
• The cytoplasm is differentiated into endoplasm and ectoplasm. 
• Endoplasm is further differentiated into plasma gel and plasmasol. 
• The body is covered by plasmalemma.
  
  Amoeba proteus
• Nutrition is holozoic. 
• The process of obtaining food by Amoeba is called phagocytosis which is done in 5 steps:
  
• 1. Ingestion: When a food particle is near the Amoeba, it forms temporary finger-like projections called pseudopodia around the food particle and engulfs it. 

  2. Digestion: The food is digested in the food vacuole with the help of enzymes.

  3. Absorption: It is then absorbed in the cytoplasm of the Amoeba by diffusion.

  4. Assimilation: The absorbed food provides energy and a part of nutrition is used for growth.

  5. Egestion: The undigested and the waste food particles are thrown out.

• Sol-gel theory of amoeboid movement was given by Hyman and supported by Pantin and Mast.

(b) Entamoeba histolytica

• Lamble (1859) discovered Entamoeba histolytica. 
• Losch (1875) discovered its pathogenic nature. 
• The life cycle of Entamoeba histolytica is monogenetic (single host life cycle). 
• It resides in the upper part of the human large intestine and repeatedly causes the disease known as amoebic dysentery or amoebiasis.
  
  E. histolytica feeding in human large intestine
• The symptoms of the disease are abdominal pain and motions with blood and mucus. 
• The parasite is generally one pseudopodium.
• The contractile vacuole is absent as there is no need for osmoregulation.
• It feeds on red blood corpuscles by damaging the wall of the large intestine and reaching the blood capillaries. It produces ulcers. 
• Multiplication is by binary fission. 
• A mature cyst is called a tetra-nucleate cyst. It has four nuclei and two chromatoid bodies.
• Tetranucleate cyst is the infective stage. 
• It is important to note that only one young amoeba with four nuclei hatches out from a cyst of E.histolytica. 
• However, a single cyst of E. histolytica produces eight amoebae. 
• The most effective medicine for amoebiasis is Metragyl or Flagyl.