27 public questions tagged with this topic.
Food vacuoles in many cells, including protists, are formed when the cell engulfs food particles. They differ functionally from the contractile vacuole, which is involved in osmoregulation and excretion.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Mitochondria Plastids Ribosomes and Other Organelles
The described organism is a euglenoid. Euglenoids have a flexible pellicle and two unequal flagella. They photosynthesise in sunlight but behave as heterotrophs by preying on smaller organisms when sunlight is unavailable.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Five Kingdom Classification and Kingdom Plantae Animalia
Kingdom Protista forms a link with the kingdoms dealing with plants, animals and fungi. Its members are single-celled eukaryotes and are primarily aquatic.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Five Kingdom Classification and Kingdom Plantae Animalia
Members of Kingdom Protista are primarily aquatic and are single-celled eukaryotes. Their cells contain a well-defined nucleus and other membrane-bound organelles.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Deuteromycetes and Economic Importance
Slime moulds are saprophytic protists that engulf organic material from decaying vegetation. Under suitable conditions they form a plasmodium, while unfavourable conditions induce fruiting bodies bearing resistant spores.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Protista - Euglenoids Slime Moulds Protozoans
Dinoflagellates may appear yellow, green, brown, blue or red depending on the principal pigments present in their cells. Most members are marine and photosynthetic.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Protista - Chrysophytes and Dinoflagellates
Protists reproduce both asexually and sexually. Their sexual reproduction involves cell fusion followed by the formation of a zygote.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Bacteria - Structure and Economic Importance
Diplomonads represent anaerobic flagellated protists within Excavata lacking classical aerobic mitochondria. Evolutionary adaptation to low-oxygen intestinal habitats led to loss of oxidative phosphorylation, electron transport chain and tricarboxylic acid cycle enzymes. Instead retains double membrane-bound mitosomes devoid of genome, involved solely in iron-sulfur cluster assembly. They possess nuclei, flagella, ribosomes but not functional ATP-generating mitochondria. Giardia lamblia exemplifies this reductive evolution, explaining absence of respiration-competent organelle and reliance on substrate-level phosphorylation in cytosol for energy. This genomic reduction reflects long-term adaptation to parasitic lifestyle within host small intestine requiring efficient iron sulfur metabolism.
Ref: NCBI Bookshelf, Microbiology: Diplomonads and Retortamonads Mitosomes; Campbell Biology 12th ed., Chapter 28 Excavata
Food vacuole biogenesis in holozoic protists occurs through phagocytosis, a receptor-mediated active engulfment of particulate matter requiring cytoskeletal remodeling. Plasma membrane extends pseudopodia around prey, forming phagocytic cup, then internalizes phagosome which fuses with primary lysosomes containing acid hydrolases. Resultant secondary phagolysosome facilitates intracellular digestion producing nutrients. Pinocytosis involves liquid droplets, diffusion and osmosis are passive molecular transports incapable of capturing bacteria or algae. Hence bulk solid ingestion strictly requires actin-dependent phagocytic machinery characterizing Amoeba and ciliates. This feature underpins diagnostic microscopy, molecular phylogenetics and evolutionary understanding crucial for NEET, CBSE and competitive examinations requiring precise conceptual clarity.
Ref: NCERT Class 11 Biology Chapter 2: Protista Nutrition; Campbell Biology 12th ed., Chapter 7 - Endocytosis and Phagocytosis
Freshwater protists like Paramecium face constant water influx due to hypotonic environment relative to cytosol. Contractile vacuole complex functions as osmoregulatory organelle, collecting excess water from cytosol via radial canals and spongiome network. Vacuole undergoes diastole collecting fluid and systole expelling it through permanent pore, maintaining cytoplasmic osmolarity and preventing lysis. This ATP-driven process expels water but also aids ion balance. It does not participate in enzymatic digestion, gas exchange or photosynthesis, which occur elsewhere in specialized compartments and organelles.
Ref: Campbell Biology 12th ed., Chapter 28: Paramecium Osmoregulation; NCERT Class 11, Biological Classification - Protista Vacuoles
Cilia and flagella share fundamentally conserved ultrastructure despite differing length, number and beat pattern across eukaryotes. Both contain nine peripheral microtubule doublets encircling two central singlets, designated 9+2 axoneme, anchored by basal body derived from centriole. Dynein arms generate sliding force hydrolyzing ATP, converted to bending by nexin links and radial spokes. Variations in waveform result from regulatory proteins, not core architecture. Protein composition overlaps heavily with tubulin and dynein, but defining similarity remains internal axonemal organization conserved from protists to mammalian epithelia.
Ref: NCERT Class 11 Biology, Chapter 8: Cell Structure - Cilia and Flagella; Campbell Biology 12th ed., Chapter 6 Cytoskeleton
Amoeboid movement represents actin-mediated cell crawling observed in Amoeba proteus, entamoebae and slime molds. Polymerization of G-actin into F-actin filaments at leading edge pushes plasma membrane forward, forming lobose or filose pseudopodia filled with endoplasm and ectoplasm. Myosin II contraction at posterior retracts cell body, coupled with sol-gel transitions of cytoplasm. This mechanism enables phagocytosis and substrate exploration without cilia or flagella, distinguishing true pseudopodial locomotion from axonemal-based systems driven by dynein-microtubule sliding, allowing directional chemotaxis toward prey. This receptor-mediated actin remodeling allows rapid engulfment of bacteria, algae and detritus particles essential for heterotrophic protists.
Ref: Campbell Biology, 12th ed., Chapter 28: Protist Diversity; NCBI Bookshelf - Cell Biology of Protists - Cytoskeleton and Pseudopodia
