Protista, Porifera and Cnidaria Practice Questions
20 free Protista, Porifera and Cnidaria practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which specialized cell type in Porifera is responsible for creating water currents and capturing food particles?
- A Pinacocytes
- B Choanocytes
- C Amoebocytes
- D Sclerocytes
Correct answer: Choanocytes
Choanocytes, or collar cells, possess a flagellum that beats to move water through the sponge's body. The microvilli collar traps organic particles for intracellular digestion.
In Cnidarians, the stinging organelles used for defense and prey capture are known as:
- A Cnidocytes
- B Nematocysts
- C Colloblasts
- D Statocysts
Correct answer: Nematocysts
Nematocysts are the specialized intracellular organelles (capsules) within cnidocytes that contain a coiled, thread-like tube. When triggered, they rapidly discharge to inject toxins or entangle prey.
Which of the following body forms in Cnidaria is typically sessile and reproduces asexually?
- A Free-swimming medusa
- B Ciliated planula larva
- C Sessile polyp
- D Parasitic cercaria stage
Correct answer: Sessile polyp
The polyp is the cylindrical, sessile stage in the cnidarian life cycle. It typically reproduces asexually by budding or fission, often giving rise to the free-swimming medusa stage that reproduces sexually.
Sponges are classified into different classes primarily based on the composition of their:
- A Complexity of the canal system
- B Skeletal spicule composition
- C Diversity of amoeboid cell types
- D Relative osculum diameter
Correct answer: Skeletal spicule composition
The skeletal framework of sponges is composed of spicules (calcareous or siliceous) or spongin fibers. The chemical nature and morphology of these spicules are the primary taxonomic criteria for classifying Porifera into classes.
Which Protozoan group is characterized by the presence of two nuclei—a macronucleus and a micronucleus?
- A Sarcodina
- B Mastigophora
- C Ciliophora
- D Sporozoa
Correct answer: Ciliophora
Ciliates, like Paramecium, exhibit nuclear dimorphism. The macronucleus handles day-to-day metabolic functions, while the micronucleus is involved in genetic recombination during conjugation.
The central cavity of a sponge, through which water flows before exiting, is called the:
- A Ostium
- B Spongocoel
- C Osculum
- D Coelenteron
Correct answer: Spongocoel
The spongocoel is the large central cavity of sponges. Water enters through numerous small pores (ostia) and eventually exits through the large opening known as the osculum.
Cnidarians are described as 'diploblastic' because their body develops from which two germ layers?
- A Ectoderm and Mesoderm
- B Mesoderm and Endoderm
- C Ectoderm and Endoderm
- D Epiplast and Hypoplast
Correct answer: Ectoderm and Endoderm
Cnidarians lack a true mesoderm, possessing only an outer epidermis (from ectoderm) and an inner gastrodermis (from endoderm). These layers are separated by a non-cellular jelly-like layer called mesoglea.
The 'contractile vacuole' found in many freshwater Protists is primarily used for:
- A Digestion of proteins
- B Locomotion
- C Osmoregulation
- D Storage of calcium
Correct answer: Osmoregulation
Freshwater environments are hypotonic to the protist's cytoplasm. The contractile vacuole actively collects and expels excess water to prevent the cell from bursting due to osmosis.
Which canal system is the most complex and efficient in sponges, characterized by highly folded walls and flagellated chambers?
- A Asconoid
- B Syconoid
- C Leuconoid
- D Rhagonoid
Correct answer: Leuconoid
The leuconoid system maximizes surface area for filtration by creating intricate chambers. This complexity allows leuconoid sponges to grow to much larger sizes than asconoid or syconoid types.
Obelia is a classic example of a Cnidarian that exhibits 'Metagenesis.' What does this term refer to?
- A The transformation of a tadpole larva into its sexually mature adult body form
- B Alternation between an asexual polyp generation and a sexual medusa generation
- C The capacity of an individual organism to change its biological sex during its lifespan
- D The fusion of two free-swimming medusae to produce a new colonial polyp
Correct answer: Alternation between an asexual polyp generation and a sexual medusa generation
Metagenesis in Obelia involves a diploid polyp colony that buds off medusae asexually. These medusae then reproduce sexually, releasing gametes that form a zygote that develops into a new polyp colony.
Which of the following is a characteristic feature of the Phylum Porifera?
- A Bilateral body symmetry
- B Presence of a true coelomic body cavity
- C Cellular level of organization
- D Extracellular digestion in a stomach
Correct answer: Cellular level of organization
Sponges lack true tissues and organs, representing only the cellular level of organization. Specialized cells exist but do not form integrated tissues with basement membranes or complex organ systems characteristic of higher animal phyla.
The locomotory organelles of the Protist group Sarcodina are:
- A Beating flagella
- B Rhythmic cilia
- C Pseudopodia
- D Axopodia extensions
Correct answer: Pseudopodia
Sarcodines such as Amoeba move by extending pseudopodia — temporary cytoplasmic projections driven by actin polymerization and sol-gel transitions in the cytoplasm. These extensions also engulf food particles during phagocytosis.
In the Cnidarian class Anthozoa (corals and sea anemones), which life stage is entirely absent?
- A Polyp
- B Medusa
- C Planula
- D Zygote
Correct answer: Medusa
Anthozoans exist only as polyps; the medusa stage has been lost in their evolutionary lineage. They reproduce both asexually and sexually within the polyp stage.
Which amoeboid cell in sponges is 'totipotent,' meaning it can differentiate into any other type of sponge cell?
- A Archaeocytes
- B Thesocytes
- C Lophocytes
- D Spongocytes
Correct answer: Archaeocytes
Archaeocytes are undifferentiated, amoeboid cells that migrate through the mesohyl. Their totipotency makes them essential for intracellular digestion, nutrient transport, and the regeneration of damaged sponge tissues.
The gastrovascular cavity of a Cnidarian serves which two primary functions?
- A Respiration and Excretion
- B Digestion and Circulation
- C Reproduction and Locomotion
- D Nervous coordination and Support
Correct answer: Digestion and Circulation
The gastrovascular cavity acts as a blind-gut for extracellular digestion. Because it reaches most parts of the body, it also serves as a primitive circulatory system to distribute nutrients.
Malaria is caused by a member of which Protozoan group?
- A Ciliates (e.g., Paramecium)
- B Amoebas (e.g., Entamoeba)
- C Apicomplexans
- D Flagellates (e.g., Euglena)
Correct answer: Apicomplexans
Plasmodium, the causative agent of malaria, belongs to the Apicomplexa (Sporozoa). Members of this group are obligate parasites, lack distinct locomotory organelles in adult stages, and have complex life cycles involving multiple hosts.
What is the function of the 'Gemmule' in freshwater sponges?
- A Sexual reproduction during favorable seasons
- B Filtering large food particles from water
- C Asexual survival structures for harsh conditions
- D Anchoring the sponge to the substrate
Correct answer: Asexual survival structures for harsh conditions
Gemmules are resistant internal buds containing archaeocytes surrounded by a protective spicule coat. They allow freshwater sponges to survive desiccation or freezing, germinating when favorable conditions return.
Which of the following describes the nervous system of a Cnidarian?
- A A central brain with a ventral nerve cord
- B A dorsal nerve cord with ganglia
- C A decentralized nerve net
- D No detectable nervous coordination
Correct answer: A decentralized nerve net
Cnidarians possess a simple nerve net at the base of the epidermis and gastrodermis. There is no central brain, allowing the animal to respond to stimuli from any direction.
The symbiotic algae found in the tissues of many corals, providing them with nutrients via photosynthesis, are called:
- A Cyanobacteria
- B Zooxanthellae
- C Spirogyra
- D Diatoms
Correct answer: Zooxanthellae
Zooxanthellae are endosymbiotic dinoflagellates. They provide organic carbon to the coral host, while the coral provides the algae with nitrogen, phosphorus, and a protected environment.
Which skeletal element of sponges is made of a sulfur-containing protein and gives them a 'spongy' texture?
- A Calcareous spicules
- B Siliceous spicules
- C Spongin fibers
- D Chitinous plates
Correct answer: Spongin fibers
Spongin is a modified form of collagen protein. It forms a fibrous network that provides structural support in many Demospongiae, the class to which common bath sponges belong.