Basis of Animal Classification Practice Questions
20 free Basis of Animal Classification practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following levels of organization is characterized by cells arranged as loose cell aggregates without forming tissues?
- A Cellular level
- B Tissue level
- C Organ level
- D Organ system level
Correct answer: Cellular level
Sponges (Phylum Porifera) exhibit the cellular level of organization where cells perform specific functions but do not form integrated tissues. Some division of labor exists among the cells.
In which phylum do cells performing the same function arrange into tissues for the first time?
- A Porifera
- B Coelenterata
- C Platyhelminthes
- D Aschelminthes
Correct answer: Coelenterata
Coelenterates (Cnidarians) and Ctenophores exhibit the tissue level of organization. In these animals, the arrangement of cells is more complex than in sponges, forming distinct tissues.
Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm, are called:
- A Triploblastic
- B Diploblastic
- C Coelomate
- D Pseudocoelomate
Correct answer: Diploblastic
Diploblastic animals, such as coelenterates, possess only two primary germ layers. An undifferentiated layer called mesoglea is present between the ectoderm and the endoderm.
An undifferentiated layer, mesoglea, is present in between the ectoderm and the endoderm in:
- A Platyhelminthes
- B Aschelminthes
- C Coelenterata
- D Annelida
Correct answer: Coelenterata
In diploblastic animals like Coelenterates and Ctenophores, the mesoglea serves as a non-cellular jelly-like layer between the two germ layers. Triploblastic animals replace this with a cellular mesoderm.
Radial symmetry is observed in which of the following phyla?
- A Annelida, Arthropoda and Chordata
- B Coelenterata, Ctenophora and Echinodermata
- C Mollusca, Chordata and Annelida
- D Porifera, Platyhelminthes and Aschelminthes
Correct answer: Coelenterata, Ctenophora and Echinodermata
Radial symmetry—where any plane through the central axis divides the body into equal halves—is characteristic of Coelenterata (Cnidarians), Ctenophora, and adult Echinodermata. These groups lack distinct left and right sides, unlike bilaterally symmetrical animals.
When the body can be divided into identical left and right halves in only one plane, the symmetry is called:
- A Radial symmetry
- B Bilateral symmetry
- C Spherical asymmetry
- D Biradial symmetry
Correct answer: Bilateral symmetry
Bilateral symmetry, where the body can be divided into identical left and right halves along only one plane, is typical of complex animals such as Annelids and Arthropods. It promotes cephalization—concentration of sense organs and nervous tissue at the anterior end—and more directed movement.
The body cavity which is lined by mesoderm is called:
- A Hemocoel
- B Pseudocoelom
- C True coelom
- D Blastocoel
Correct answer: True coelom
A true coelom is a fluid-filled body cavity situated between the body wall and gut wall that is entirely lined by mesoderm-derived peritoneum. Animals possessing this structure—such as Annelids, Molluscs, and Chordates—are called coelomates.
In some animals, the body cavity is not lined by mesoderm; instead, the mesoderm is present as scattered pouches. This is known as:
- A Acoelom
- B Pseudocoelom
- C Schizocoelom
- D Enterocoelom
Correct answer: Pseudocoelom
A pseudocoelom is found in Aschelminthes (roundworms). Because the cavity is not fully lined by mesoderm, these animals are categorized as pseudocoelomates.
Which of the following phyla is characterized by the absence of a body cavity (acoelomate condition)?
- A Annelida
- B Platyhelminthes
- C Aschelminthes
- D Echinodermata
Correct answer: Platyhelminthes
Platyhelminthes (flatworms) are acoelomates: the space between the body wall and digestive tract is filled with solid parenchyma tissue rather than a cavity. Despite being triploblastic, they lack a true body cavity, distinguishing them from coelomates and pseudocoelomates.
Metameric segmentation (metamerism) is a characteristic feature of:
- A Mollusca
- B Porifera
- C Annelida
- D Platyhelminthes
Correct answer: Annelida
Metamerism involves the serial repetition of similar body segments, both externally and internally. This is most prominently seen in Annelids like the earthworm.
The notochord is derived from which germ layer?
- A Ectoderm
- B Endoderm
- C Mesoderm
- D Mesoglea
Correct answer: Mesoderm
The notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Its presence distinguishes chordates from non-chordates.
Animals that do not possess a notochord are called non-chordates. This group includes phyla from:
- A Porifera to Hemichordata
- B Porifera to Echinodermata
- C Coelenterata to Chordata
- D Aschelminthes to Echinodermata
Correct answer: Porifera to Hemichordata
Non-chordates lack a notochord throughout their life cycle. This broad group encompasses all phyla from Porifera through Hemichordata.
In an open circulatory system, the blood is:
- A Circulated through a series of vessels of varying diameters
- B Pumped out of the heart into open spaces called sinuses
- C Contained entirely within capillaries
- D Absent and replaced by water
Correct answer: Pumped out of the heart into open spaces called sinuses
In an open system, found in Arthropods and Molluscs, tissues and organs are directly bathed in blood. Closed systems, conversely, keep blood confined to vessels, allowing for higher pressure and regulation.
An incomplete digestive system has:
- A Two separate openings for mouth and anus
- B One opening serving as both mouth and anus
- C No opening at all (absorption through skin)
- D A mouth opening but no intestine present
Correct answer: One opening serving as both mouth and anus
Phyla like Platyhelminthes have an incomplete digestive tract where a single opening functions for both ingestion and egestion. A complete digestive system must have two distinct openings.
Which of the following show organ-system level of organization?
- A Sponges (Porifera)
- B Hydra (Cnidaria)
- C Tapeworms (Platyhelminthes)
- D Arthropods (Arthropoda)
Correct answer: Arthropods (Arthropoda)
In higher animals like Arthropods, Annelids, and Chordates, organs associate to form functional systems. Tapeworms show organ level, while Hydra shows tissue level.
Choose the correct match regarding symmetry:
- A Sponges - Always bilateral
- B Ctenophores - Radial
- C Adult Echinoderms - Bilateral
- D Annelids - Radial
Correct answer: Ctenophores - Radial
Ctenophores (comb jellies) exhibit radial symmetry. Sponges are mostly asymmetrical, adult echinoderms are pentamerous radial, and annelids are bilateral.
Triploblastic animals possess three germ layers. These are:
- A Ectoderm, Endoderm, Mesoglea
- B Ectoderm, Mesoderm, Endoderm
- C Epiblast, Mesoderm, Endoderm
- D Ectoderm, Mesenchyme, Endoderm
Correct answer: Ectoderm, Mesoderm, Endoderm
Starting from Platyhelminthes to Chordata, all animals are triploblastic. The addition of the mesoderm allows for the development of complex organs and true body cavities.
The presence of a true coelom allows for:
- A Space for organ growth and flexibility
- B First appearance of a nervous system
- C The ability to photosynthesize
- D Intracellular digestion as the sole method
Correct answer: Space for organ growth and flexibility
The coelom acts as a cushion for internal organs and allows them to move and grow independently of the outer body wall. It also provides a hydrostatic skeleton in some soft-bodied animals.
Animals belonging to phylum Aschelminthes are:
- A Acoelomates
- B Pseudocoelomates
- C True coelomates
- D Diploblastic organisms
Correct answer: Pseudocoelomates
Aschelminthes are unique as the only phylum categorized as pseudocoelomates. Their body cavity is a remnant of the embryonic blastocoel and is not lined by mesodermal epithelium.
Which feature primarily distinguishes a crab from an earthworm in animal classification?
- A Presence of a mouth opening
- B Level of body organization
- C Presence of jointed appendages
- D Pattern of embryonic germ layers
Correct answer: Presence of jointed appendages
Both crabs and earthworms are bilaterally symmetrical coelomates at the organ-system level of organisation and both are triploblastic, so none of those features can separate them. Jointed appendages are the defining character of Arthropoda, to which the crab belongs, while earthworms are annelids and have no jointed limbs.