Protista (Unicellular eukaryotes) Questions in English

(N/A) $\rightarrow$ Habitat: These organisms are mostly marine and photosynthetic.
$\rightarrow$ Body organization: They appear yellow,green,brown,blue,or red depending on the main pigments present in their cells.
$\rightarrow$ Cell wall: The cell wall has stiff cellulose plates on the outer surface.
$\rightarrow$ Flagella: Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.
$\rightarrow$ Special features: Very often,red dinoflagellates (e.g.,$Gonyaulax$) undergo such rapid multiplication that they make the sea appear red (red tides). Toxins released by such large numbers may even kill other marine animals such as fishes.
$\rightarrow$ Reproduction: Dinoflagellates reproduce asexually through cell division or by the formation of zoospores and cysts.
$\rightarrow$ Reserve food: Reserve food is stored in the form of starch and oils. Examples include $Gonyaulax$,$Ceratium$,$Noctiluca$,$Peridinium$,and $Gymnodinium$.

(N/A) $\rightarrow$ Habitat: Majority of them are freshwater organisms found in stagnant water.
$\rightarrow$ Body organization: Instead of a cell wall,they have a protein-rich layer called pellicle,which makes their body flexible.
$\rightarrow$ Flagella: They have two flagella,one short and one long.
$\rightarrow$ Mode of nutrition: Nutrition is holophytic,saprobic,or holozoic. This mode of nutrition is called mixotrophic.
$\rightarrow$ Photosynthesis: Though they are photosynthetic in the presence of sunlight,when deprived of sunlight,they behave like heterotrophs by preying on other smaller organisms.
$\rightarrow$ Pigments: The pigments of euglenoids are identical to those present in higher plants,including chlorophyll '$a$' and '$b$'.
$\rightarrow$ Feeding: Prey such as bacteria and small flagellates are ingested through a cytostome,supported by microtubules.
$\rightarrow$ Reserve food: Reserve food is stored as carbohydrates in the form of paramylon or paramylum bodies.
$\rightarrow$ Reproduction: Euglenoids reproduce by longitudinal binary fission under favourable conditions.
$\rightarrow$ Unfavourable conditions: The palmella stage is found during unfavourable conditions.
$\rightarrow$ Examples: Euglena,Peranema,Eutreptia,Phacus,etc.

(N/A) $\rightarrow$ Slime moulds are saprophytic protists.
$\rightarrow$ The body moves along decaying twigs and leaves,engulfing organic material.
$\rightarrow$ Under suitable conditions,they form an aggregation called $Plasmodium$ which may grow and spread over several feet.
$\rightarrow$ During unfavourable conditions,the $Plasmodium$ differentiates and forms fruiting bodies bearing spores at their tips.
$\rightarrow$ The spores possess true walls.
$\rightarrow$ They are extremely resistant and survive for many years even under adverse conditions.
$\rightarrow$ Body organization: The body of slime moulds is covered with mucilage having a gelatinous consistency; they do not have chlorophyll.
$\rightarrow$ They are surrounded by a plasma membrane. However,the spores have cellulosic cell walls.
$\rightarrow$ Special features: Anton De Bary related them to animals and called them $Mycetozoa$.
$\rightarrow$ These are also named as 'fungus animals' because they share common characters of both animals and fungi due to their protistian nature.
$\rightarrow$ They are like protozoa in their amoeboid plasmodial stage and similar to true fungi in spore formation. Acellular slime moulds ($Plasmodial$ slime moulds) are commonly found on dead and decaying plant matter.
$\rightarrow$ The cellular slime moulds occur in all humus-containing upper layers of damp soil.
$\rightarrow$ When the food supply is short or conditions are not favourable,the amoeboid cells form an aggregate without any fusion.
$\rightarrow$ This aggregated mass is called $pseudoplasmodium$.
$\rightarrow$ Examples of cellular slime moulds are $Dictyostelium$ and $Polysphondylium$.
$\rightarrow$ Economic importance: Slime moulds are beneficial as they cause the decomposition of organic matter in the soil.
$\rightarrow$ Examples: $Physarum$,$Stemonitis$,$Comatricha$,$Trichia$.

(N/A) $\rightarrow$ All protozoans are heterotrophs and live as predators or parasites.
$\rightarrow$ They are believed to be primitive relatives of animals.
$\rightarrow$ They were first studied by Leeuwenhoek.
$\rightarrow$ They can cause several diseases in humans and animals.
$\rightarrow$ General characteristics of protozoans:
$\rightarrow$ They are microscopic,unicellular,and colourless organisms with diverse shapes.
$\rightarrow$ Locomotion occurs with the help of finger-like pseudopodia,flagella,or hair-like cilia.
$\rightarrow$ Respiration occurs through the general body surface.
$\rightarrow$ Reproduction occurs by binary fission,multiple fission,or budding.
$\rightarrow$ Sexual reproduction occurs by syngamy and conjugation.
$\rightarrow$ Amoeboid protozoans: These organisms live in freshwater,seawater,or moist soil. They move and capture prey by extending pseudopodia (false feet),as in Amoeba. Marine forms often have silica shells on their surface. Nutrition is holozoic. Some,such as Entamoeba,are parasites.
$\rightarrow$ Flagellated protozoans: Members are either free-living or parasitic. They possess flagella for locomotion. Nutrition is holozoic,saprobic,or parasitic. Examples include Trypanosoma (sleeping sickness) and Leishmania (kala-azar).
$\rightarrow$ Ciliated protozoans: These are aquatic,actively moving organisms due to the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. Examples include Paramecium.

(D) Amoeba and Paramecium are both unicellular eukaryotic organisms belonging to the kingdom Protista,specifically classified as protozoans. Both organisms primarily reproduce asexually through the process of binary fission,where a single cell divides into two identical daughter cells. Therefore,all the given statements are correct.

(B) Protozoans are classified under the kingdom $Protista$ because they are unicellular eukaryotes.
Kingdom $Animalia$ consists of multicellular,eukaryotic organisms that lack cell walls.
Since protozoans are single-celled,they do not meet the criteria for being classified as animals.
They are heterotrophs and live as predators or parasites,and are divided into four major groups: $Zooflagellata$,$Sarcodina$,$Sporozoa$,and $Ciliata$.

(A) The organism $X$ is $Gonyaulax$,which is a type of dinoflagellate $(Y)$.
These organisms multiply rapidly in the ocean,causing a phenomenon known as 'red tides' due to their red pigments.
These blooms release toxins that can kill large marine animals,such as fishes $(Z)$.

(A) Haeckel created the kingdom $Protista$ to include all unicellular eukaryotic micro-organisms.
They possess a typical eukaryotic structure with membrane-bound organelles and a well-defined nucleus.

(D) In protists,reproduction occurs through both asexual and sexual methods.
Asexual reproduction includes processes such as binary fission (e.g.,$Euglena$),budding,and the formation of spores or cysts (e.g.,$Entamoeba$).
Sexual reproduction involves the fusion of cells (syngamy) and conjugation,leading to the formation of a zygote.
Therefore,all the mentioned processes are involved in the reproduction of protists.

(C) Chrysophytes are a group of organisms that include diatoms and golden algae (desmids).
These are microscopic,photosynthetic protists.
Their cell walls are embedded with silica,forming two thin overlapping shells that fit together like a soap box.

(D) Amoeboid protozoans are organisms that live in fresh water,sea water,or moist soil.
They move and capture their prey by putting out pseudopodia (false feet),for example,$Amoeba$.
Some of them,such as $Entamoeba$,are parasites.
Therefore,$Entamoeba$ is an example of an amoeboid protozoan.

(C) Protozoans are single-celled microscopic eukaryotic organisms that are classified based on their mode of locomotion:
$1$. Amoeboid protozoans: These move using pseudopodia, e.g., $Amoeba$ $(A-III)$.
$2$. Ciliated protozoans: These possess thousands of cilia for movement, e.g., $Paramecium$ $(B-I)$.
$3$. Flagellated protozoans: These possess flagella for movement, e.g., $Trypanosoma$ $(C-IV)$.
$4$. Sporozoans: These include organisms that have an infectious spore-like stage in their life cycle, e.g., $Plasmodium$ $(D-II)$.
Therefore, the correct matching is $A-III, B-I, C-IV, D-II$.

(D) Sporozoans are characterized by having an infectious spore-like stage in their life cycle and they do not possess locomotor organelles like cilia or flagella in their mature stage. Hooks and suckers are specialized attachment structures typically found in parasitic helminths (worms),not in protozoan sporozoans. Therefore,option $D$ is incorrectly matched.

(C) Chrysophytes belong to the kingdom $Protista$. Examples include diatoms and golden algae (desmids). $A$ key characteristic of chrysophytes is that their cell walls form two thin overlapping shells,which fit together like a soap box. These walls are embedded with silica,making them indestructible and leading to the accumulation of large amounts of cell wall deposits in their habitat over billions of years.

(C) Dinoflagellates are mostly marine and photosynthetic organisms. They appear yellow,green,brown,blue,or red depending on the main pigments present in their cells. Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the cell plates.

(C) Dinoflagellates are primarily marine,photosynthetic,and biflagellated protists.
$(i)$ Incorrect: Soap box-like structure is a characteristic of diatoms (Chrysophytes).
$(ii)$ Correct: They are mostly marine and possess two flagella (biflagellated).
$(iii)$ Correct: They appear yellow,green,brown,blue,or red depending on the main pigments present in their cells.
$(iv)$ Correct: Their cell wall is characterized by stiff cellulose plates on the outer surface.
$(v)$ Incorrect: Dinoflagellates are typically photosynthetic,not saprophytic or parasitic.
Therefore,the correct statements are $(ii), (iii),$ and $(iv)$.

(B) The characteristics described in the statements correspond to $Chrysophytes$.
$1$. $Chrysophytes$ include diatoms and golden algae (desmids).
$2$. They are microscopic and float passively in water currents,hence they are known as plankton.
$3$. Most of them are photosynthetic.
$4$. In diatoms,the cell walls form two thin overlapping shells which fit together as in a soap box. Since these walls are embedded with silica,they are indestructible. Thus,diatoms have left behind large amounts of cell wall deposits in their habitat; this accumulation over billions of years is referred to as 'diatomaceous earth'.

(D) The characteristics described belong to $Euglenoids$.
$1$. $Euglenoids$ are primarily freshwater organisms found in stagnant water.
$2$. Instead of a cell wall,they possess a protein-rich layer called a $pellicle$,which provides flexibility to their body.
$3$. They typically have two flagella,one short and one long.
$4$. They exhibit mixotrophic nutrition; they are photosynthetic in the presence of sunlight but act as heterotrophs by preying on smaller organisms in the absence of sunlight.

(C) The given statements describe the characteristics of slime moulds.
$(i)$ Slime moulds are saprophytic protists that feed on decaying organic matter.
$(ii)$ Under suitable conditions,they form an aggregation called a plasmodium,which can grow and spread over several feet.
$(iii)$ During unfavourable conditions,the plasmodium differentiates and forms fruiting bodies,which bear spores at their tips. These spores possess extremely resistant walls and survive for many years even under adverse conditions.

(C) Cholera,Typhoid,and Tetanus are bacterial diseases,not viral.
Dinoflagellates,Euglenoids,and Slime moulds are classified under the kingdom Protista,not Monera.
Members of the kingdom Protista are primarily aquatic,forming a link with plants,animals,and fungi.
Diatoms are the chief producers in the oceans,not Dinoflagellates.

(B) Slime moulds exist in both haploid and diploid states during their life cycle.
Dinoflagellates are typically motile,possessing two flagella.
Euglena possesses a protein-rich layer called a pellicle,which makes its body flexible.
Protozoans are heterotrophs and live as predators or parasites; they lack a rigid cell wall,which is a characteristic feature of this group.

(D) The characteristics of dinoflagellates are as follows:
$\bullet$ Their cell wall typically has stiff cellulose plates on the outer surface.
$\bullet$ Many species,such as $Gonyaulax$,release toxins that can kill marine animals.
$\bullet$ Rapid multiplication of certain species (like $Gonyaulax$) causes 'red tides' in the sea.
$\bullet$ They are mostly marine and photosynthetic organisms.
Therefore,the statement that they are mostly fresh water and non-photosynthetic is incorrect.

(D) Slime moulds are saprophytic protists. Their body moves along decaying twigs and leaves,engulfing organic material. Under suitable conditions,they form an aggregation called plasmodium,which may grow and spread over several feet. During unfavorable conditions,the plasmodium differentiates and forms fruiting bodies bearing spores at their tips.

(B) Euglenoids are unique organisms that exhibit mixotrophic nutrition.
In the presence of sunlight,they perform photosynthesis like plants due to the presence of chlorophyll.
However,in the absence of sunlight,they behave as heterotrophs by predating on other smaller organisms.
Therefore,the correct option is $B$.

(C) Diatoms are microscopic algae that have cell walls composed of silica $(SiO_2)$.
When these organisms die,their cell walls accumulate at the bottom of oceans and lakes over millions of years.
This accumulation forms a sedimentary rock known as diatomaceous earth,which is rich in silicon.

(B) The phenomenon of bioluminescence,where sea water appears to glow at night,is primarily caused by marine dinoflagellates. Among the given options,$Noctiluca$ (often called the 'sea sparkle') is a well-known dinoflagellate capable of bioluminescence. While $Gonyaulax$ is also bioluminescent,$Noctiluca$ is the most classic example associated with this phenomenon in marine biology.

(D) Diatoms have a rigid cell wall made of silica,which restricts their growth. When a diatom reaches a minimum size due to repeated cell divisions,it undergoes sexual reproduction to form a specialized cell called an auxospore. The auxospore is diploid and serves to restore the original size of the diatom cell. Therefore,the rejuvenescent spore of a diatom is diploid and an auxospore.

(A) The reserve food material in various protists is as follows:
$1$. Diatoms: Store food in the form of Leucosin $(Chrysolaminarin)$ and oils.
$2$. Euglena: Stores food in the form of Paramylon granules.
$3$. Dinoflagellates: Store food in the form of carbohydrates and oils.
$4$. Paramoecium: Stores food in the form of glycogen granules.
Therefore,Leucosin is the reserve food found in Diatoms.

(D) The flagellation in $Euglena$ is characterized by the following features:
$1$. $Euglena$ possesses two flagella of unequal lengths,which is referred to as $Heterokont$.
$2$. The flagella are of the $Stichonematic$ type,meaning they have a single row of mastigonemes (fine hair-like projections) on one side of the flagellum.

(B) The eye-spot (stigma) in $Euglena$ and various Crustaceans contains a specialized red-colored carotenoid pigment known as $Astaxanthin$.
This pigment is responsible for the characteristic red appearance of the eye-spot,which functions as a photoreceptor to help the organism detect light intensity and direction.

(B) The paraflagellar body is a specialized structure located at the base of the flagellum in $Euglena$.
It acts as a photoreceptor,which is sensitive to light.
This structure works in conjunction with the stigma (eyespot) to help the organism detect light intensity and direction,facilitating phototaxis.

(A) In the life cycle of cellular slime moulds (e.g.,Dictyostelium),individual amoeboid cells exist in the somatic phase $(n)$.
When food becomes scarce,these cells secrete a chemical signal,cyclic $AMP$ $(cAMP)$.
This chemical signal induces chemotactic movement,causing the individual cells to aggregate together.
This aggregation of cells forms a multicellular,slug-like structure known as a Pseudoplasmodium.

(A) Myxamoebae are amoeboid cells formed during the life cycle of acellular slime moulds,such as $Physarum$. These cells are produced by the germination of spores and can function as gametes or undergo division.

(B) The Red Sea gets its name due to the presence of the cyanobacteria $Trichodesmium$ $erythraeum$,which imparts a reddish color to the water.
$A$ red tide is a phenomenon caused by the rapid multiplication (bloom) of certain marine protists,specifically dinoflagellates like $Gonyaulax$ and $Gymnodinium$,which make the sea appear red.

(D) Acellular slime moulds (Myxomycetes) exhibit the following characteristics:
$\bullet$ They possess a diploid vegetative stage known as the plasmodium.
$\bullet$ They form a structure called capillitium which helps in the dispersal of spores.
$\bullet$ They undergo sporic meiosis,where meiosis occurs during the formation of spores.
$\bullet$ They exhibit isogamous sexual reproduction.
Therefore,the correct features are $b, c, e,$ and $f$.

(C) Slime moulds are saprophytic protists that exhibit characteristics of both plants and animals.
- The vegetative phase is animal-like because the body consists of a naked mass of protoplasm (plasmodium) without a cell wall.
- The reproductive phase is plant-like because they produce spores that possess true cell walls (made of cellulose).
- Therefore,the statement in the Reason is reversed; the vegetative phase is animal-like and the reproductive phase is plant-like.

(A) Slime moulds are saprophytic protists. Under suitable (favourable) conditions,they form an aggregation called plasmodium,which may grow and spread over several feet. When conditions become unfavourable,the plasmodium differentiates and forms fruiting bodies bearing spores at their tips. Therefore,both the Assertion $(A)$ and the Reason $(R)$ are correct statements.

(C) The Assertion is correct because holophytic protistans (like diatoms and dinoflagellates) are major producers in aquatic ecosystems,contributing significantly to global photosynthesis.
The Reason is incorrect because holophytic protistans are photoautotrophs that use $H_{2}O$ as the source of electrons and protons during photosynthesis,not non-sulphur organic compounds. Chemosynthetic organisms use inorganic chemical energy,which is not the primary mode of nutrition for these protists.

(A) The contractile vacuole is a sub-cellular organelle found primarily in protists (e.g.,$Amoeba$) and unicellular algae.
It is primarily responsible for osmoregulation and excretion.
It functions by collecting excess water and dissolved metabolic wastes from the cytoplasm and expelling them into the external environment through a process of contraction.
This periodic cycle of expansion (filling) and contraction (emptying) helps the organism maintain its internal water balance and remove waste products.

(B) Pseudopodia are temporary extensions of the cell surface found in certain protozoans like $Amoeba$.
These structures are formed by the streaming of the protoplasm (specifically the cytoplasm) within the cell.
This movement is often referred to as amoeboid movement,which involves the sol-gel transition of the cytoplasm,allowing the organism to change its shape and move.

(N/A) $\rightarrow$ In chrysophytes, specifically diatoms, the cell wall forms two thin overlapping shells that fit together like a soap box.
$\rightarrow$ The cell walls are embedded with silica, making them indestructible.
$\rightarrow$ Due to this, diatoms have left behind large amounts of cell wall deposits in their habitat over billions of years, which is known as "diatomaceous earth".

(N/A) $\rightarrow$ They appear yellow,green,brown,blue,or red depending on the main pigments present in their cells.
$\rightarrow$ The cell wall has stiff cellulose plates on the outer surface.
$\rightarrow$ Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates.

(N/A) $\rightarrow$ Nutrition in $Euglena$ is holophytic (photosynthetic),saprobic,or holozoic. This diverse mode of nutrition is known as mixotrophic.
$\rightarrow$ Although they are photosynthetic in the presence of sunlight,they behave as heterotrophs by feeding on smaller organisms when sunlight is absent.
$\rightarrow$ The pigments of euglenoids are identical to those present in higher plants,including chlorophyll '$a$' and '$b$'.
$\rightarrow$ Prey,such as bacteria and small flagellates,are ingested through a cytostome (cell mouth),which is supported by microtubules.
$\rightarrow$ Reserve food is stored as carbohydrates in the form of paramylon or paramylum bodies.

(N/A) $\rightarrow$ Slime moulds are saprophytic protists.
$\rightarrow$ The body moves along decaying twigs and leaves,engulfing organic material.
$\rightarrow$ Under suitable conditions,they form an aggregation called $Plasmodium$,which may grow and spread over several feet.
$\rightarrow$ During unfavourable conditions,the $Plasmodium$ differentiates and forms fruiting bodies bearing spores at their tips.

(N/A) $\rightarrow$ These organisms live in freshwater,seawater,or moist soil.
$\rightarrow$ They move and capture their prey by extending $Pseudopodia$ (false feet),as seen in $Amoeba$ (since a mouth is absent).
$\rightarrow$ Marine forms often have silica shells on their surface.
$\rightarrow$ Nutrition is holozoic.
$\rightarrow$ Some species,such as $Entamoeba$,are parasites.
$\rightarrow$ Asexual reproduction occurs by binary fission,multiple fission,or spore formation,while sexual reproduction occurs by syngamy.
$\rightarrow$ Examples: $Amoeba$,$Entamoeba$,$Radiolarians$,$Pelomyxa$,$Foraminiferans$,and $Heliozoans$.

(N/A) $\rightarrow$ The members of this group are either free-living or parasitic.
$\rightarrow$ They possess flagella for locomotion,as their name suggests.
$\rightarrow$ They can be aquatic,free-living,parasitic,commensals,or symbiotic.
$\rightarrow$ Nutrition is holozoic,saprobic,or parasitic.
$\rightarrow$ Asexual reproduction occurs by binary fission.
$\rightarrow$ Sexual reproduction is observed in some forms only.
$\rightarrow$ Example: $Trypanosoma$ $brucei$,which causes sleeping sickness.

(N/A) $\rightarrow$ They possess a cavity (gullet) that opens to the outside of the cell surface.
$\rightarrow$ The coordinated movement of rows of cilia causes water laden with food to be steered into the gullet.
$\rightarrow$ Many ciliates live as free-living individuals in fresh and marine water (e.g.,$Paramecium$).
$\rightarrow$ Nutrition is holozoic,except in some parasitic forms.
$\rightarrow$ The body is covered with a flexible pellicle.
$\rightarrow$ There are definite regions for ingestion (cytostome) and egestion (cytoproct).
$\rightarrow$ Ciliates possess a large macronucleus and a smaller micronucleus.
$\rightarrow$ They have small ejectable trichocysts for defense.
$\rightarrow$ Osmoregulation occurs via contractile vacuoles.

(N/A)

Dinoflagellates	Euglenoids
$(1)$ They are mostly marine.	$(1)$ They are freshwater forms found in stagnant water.
$(2)$ They have a cell wall with stiff cellulose plates on the outer surface.	$(2)$ They lack a cell wall but possess a protein-rich layer called pellicle,which makes their body flexible.
$(3)$ They are typically photoautotrophic.	$(3)$ They are photoautotrophic in the presence of sunlight but behave as heterotrophs when deprived of sunlight.
$(4)$ They have two flagella: one lies transversely and the other longitudinally.	$(4)$ They have two flagella,both of which are located at the anterior end.

(N/A) Diatoms possess a unique,shining,two-valved cell wall made of silica,known as a frustule.
Due to this distinctive,glass-like,and shimmering appearance of their cell walls,they are often referred to as the 'pearls of the ocean'.

(N/A) $1$. $Euglena$ is considered a taxonomic puzzle because it exhibits both plant-like and animal-like characteristics.
$2$. The absence of a rigid cell wall is an animal-like feature,while the presence of chloroplasts for photosynthesis is a plant-like characteristic.
$3$. $Euglena$ exhibits mixotrophic nutrition. In the presence of sunlight,it performs photosynthesis to produce its own food (autotrophic),and in the absence of sunlight,it acts as a heterotroph by preying on other smaller organisms.