Important Questions and Answers

How to Use This Section

Animal Kingdom is examined in two ways and almost never in a third. Either you are given a set of characters and asked for the phylum or class, or you are given a name and asked for its character. Everything below is built for those two moves.

The 46 items are organised in three tiers:

1. Concept Checks - the six fundamental features, the two digestive patterns, the two circulatory patterns, and the definitions that questions quote word for word.
2. Application and Scenarios - an unnamed animal to place, a specimen to work through, a column to match.
3. Analytical and Multi-Concept - trends that run across phyla, and the traps built out of look-alike facts.

Every item is set as a Question with a worked Answer, written the way you would write it in the exam.

Coverage of the chapter-end exercises

Every chapter-end exercise is worked here, so this section is the one place to check that you have covered the textbook in full.

The Facts These Items Draw On

Fundamental features. Level of organisation - cellular (sponges), tissue (coelenterates, ctenophores), organ (platyhelminthes), organ-system (platyhelminthes in the comparison table, and every phylum from aschelminthes onwards). Symmetry - asymmetrical, radial (coelenterates, ctenophores, adult echinoderms), bilateral. Germ layers - diploblastic with mesoglea, triploblastic with mesoderm. Coelom - coelomate, pseudocoelomate (aschelminthes), acoelomate (platyhelminthes). Segmentation - metameric, first in Annelida. Notochord - mesodermally derived, defines Chordata.

Digestion. Incomplete - single opening. Complete - mouth and anus, first in Aschelminthes.

Circulation. Open - blood pumped out, tissues bathed directly (arthropods, hemichordates). Closed - blood in vessels (annelids, chordates).

Signature structures. Choanocytes and spongocoel - Porifera. Cnidoblasts - Coelenterata. Comb plates - Ctenophora. Flame cells - Platyhelminthes. Muscular pharynx and excretory pore - Aschelminthes. Nephridia and parapodia - Annelida. Malpighian tubules, chitinous exoskeleton, jointed appendages - Arthropoda. Radula, mantle cavity, calcareous shell - Mollusca. Water vascular system, calcareous ossicles - Echinodermata. Proboscis gland, stomochord - Hemichordata.

Vertebrate classes. Cyclostomata - jawless, 6-15 pairs of gill slits, ectoparasitic. Chondrichthyes - cartilaginous, placoid scales, no air bladder, claspers. Osteichthyes - bony, operculum, air bladder, cycloid or ctenoid scales. Amphibia - moist scaleless skin, three-chambered heart, cloaca. Reptilia - dry cornified skin, three-chambered but four-chambered in crocodiles. Aves - feathers, pneumatic bones, air sacs, four-chambered. Mammalia - mammary glands, hair, pinnae, four-chambered, viviparous with few exceptions.

Tier 1 - Concept Checks

Question 1

Q. On what fundamental features is the classification of animals based?

Answer. On the features animals share whatever their habit and habitat: the arrangement of cells (level of organisation), symmetry, the presence or absence of a coelom, the germ layers, segmentation, the notochord, and the patterns of the digestive, circulatory and reproductive systems.

Question 2

Q. What is the cellular level of organisation, and which animals show it?

Answer. The cells are arranged as loose cell aggregates, with some division of labour among them. Sponges show it.

Question 3

Q. Which animals show the tissue level of organisation?

Answer. Coelenterates and ctenophores, in which the cells performing the same function are arranged into tissues.

Question 4

Q. Where does the organ level first appear, and where the organ-system level?

Answer. The organ level appears in Platyhelminthes, where tissues are grouped to form organs, each specialised for a particular function. The organ-system level appears from Aschelminthes onwards - aschelminthes, annelids, arthropods, molluscs, echinoderms, hemichordates and chordates - where organs associate to form functional systems. The comparison table also credits Platyhelminthes with organ and organ-system, so that is the phylum to name when a question asks where the level appears first.

Question 5

Q. Distinguish between an incomplete and a complete digestive system.

Answer. An incomplete digestive system has only a single opening to the outside of the body, which serves as both mouth and anus. A complete digestive system has two openings, mouth and anus, so food travels one way through the gut.

Question 6

Q. Distinguish between an open and a closed circulatory system.

Answer. In an open system, the blood is pumped out of the heart and the cells and tissues are directly bathed in it. In a closed system, the blood is circulated through a series of vessels of varying diameters - arteries, veins and capillaries.

Question 7

Q. Define radial symmetry and name the groups that show it.

Answer. An animal is radially symmetrical if any plane passing through the central axis of the body divides the organism into two identical halves. Coelenterates, ctenophores and adult echinoderms show it.

Question 8

Q. Define bilateral symmetry.

Answer. An animal is bilaterally symmetrical when the body can be divided into identical left and right halves in only one plane. It runs from Platyhelminthes onwards, the one exception being adult echinoderms, which are radial.

Question 9

Q. What does diploblastic mean, and which animals are diploblastic?

Answer. An animal is diploblastic when the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm. An undifferentiated layer, the mesoglea, is present in between. Coelenterates are diploblastic.

Question 10

Q. What does triploblastic mean?

Answer. An animal is triploblastic when the developing embryo has a third germinal layer, the mesoderm, in between the ectoderm and the endoderm. Platyhelminthes to chordates are triploblastic.

Question 11

Q. Define coelomate, pseudocoelomate and acoelomate with one example each.

Answer.

• Coelomate - the body cavity is lined by mesoderm; a true coelom. Example: annelids.
• Pseudocoelomate - the mesoderm is present as scattered pouches in between the ectoderm and endoderm, so the cavity is not lined by mesoderm. Example: aschelminthes.
• Acoelomate - the body cavity is absent. Example: platyhelminthes.

Question 12

Q. In which phylum is metameric segmentation first observed, and what does the term mean?

Answer. In Annelida. The body is externally and internally divided into segments with a serial repetition of at least some organs - as in the earthworm.

This is one of the chapter-end exercises.

Question 13

Q. What is the notochord and what is it made of?

Answer. The notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Animals with a notochord are chordates; those without one are non-chordates.

Question 14

Q. Distinguish between intracellular and extracellular digestion.

Answer. Intracellular digestion takes place inside the cell - the food is taken in and broken down right there. That is the pattern in sponges, and it is one of the two routes used by coelenterates and ctenophores. Extracellular digestion takes place outside the cells, in a cavity or gut, and the products are then absorbed. Coelenterates and ctenophores use both.

This is one of the chapter-end exercises.

Question 15

Q. What is the difference between direct and indirect development?

Answer. In direct development, the young one resembles the adult when it is born or hatched, and simply grows. In indirect development, the young one is a larva that differs from the adult and must pass through metamorphosis to reach the adult form. Reptiles and birds show direct development; amphibians and echinoderms show indirect development.

This is one of the chapter-end exercises.

Question 16

Q. What separates a chordate from a non-chordate in five lines?

Answer. Notochord present against absent; central nervous system dorsal, hollow and single against ventral, solid and double; pharynx perforated by gill slits against gill slits absent; heart ventral against dorsal if present; post-anal tail present against absent.

Tier 2 - Application and Scenarios

Question 17

Q. An aquatic animal has a body with pores called ostia, a central cavity, choanocytes lining its canals, and a skeleton of spicules. Name the phylum and one example.

Answer. Porifera. Water enters through the ostia into the spongocoel and leaves through the osculum; the choanocytes or collar cells line the cavity, and digestion is intracellular. Example: Sycon.

Question 18

Q. An animal has stinging cells on its tentacles, a central gastro-vascular cavity with a single opening on a raised hypostome, and exists as a sessile cylindrical form and a free-swimming umbrella-shaped form. Identify the phylum and name both forms.

Answer. Coelenterata (Cnidaria). The stinging cells are cnidoblasts containing nematocysts. The two body forms are the polyp (sessile, cylindrical) and the medusa (free-swimming, umbrella-shaped).

Question 19

Q. A dorso-ventrally flattened endoparasite has hooks and suckers, absorbs nutrients through its body surface, and uses flame cells for osmoregulation. Name the phylum and two examples.

Answer. Platyhelminthes. Examples: Taenia (tapeworm) and Fasciola (liver fluke).

Question 20

Q. An animal is circular in cross-section, pseudocoelomate, has a complete gut with a muscular pharynx, and separate sexes with females longer than males. Name the phylum.

Answer. Aschelminthes. Examples: Ascaris, Wuchereria, Ancylostoma.

Question 21

Q. A metamerically segmented coelomate has longitudinal and circular muscles, nephridia, a closed circulation and a double ventral nerve cord. Name the phylum and one terrestrial example.

Answer. Annelida. Terrestrial example: Pheretima, the earthworm.

Question 22

Q. An animal has a chitinous exoskeleton, a body of head, thorax and abdomen, jointed appendages, compound eyes and malpighian tubules. Which phylum, and what fraction of named species does it hold?

Answer. Arthropoda. Over two-thirds of all named species on earth are arthropods, which is why it is the largest phylum.

Question 23

Q. An unsegmented animal has a calcareous shell, a muscular foot, a visceral hump under a mantle, and a radula in its mouth. Name the phylum and two examples.

Answer. Mollusca, the second largest phylum. Examples: Pila (apple snail) and Loligo (squid).

Question 24

Q. A marine animal has an endoskeleton of calcareous ossicles, a radial adult body, a bilateral larva, a water vascular system and no excretory system. Name the phylum and two examples.

Answer. Echinodermata. Examples: Asterias (star fish) and Cucumaria (sea cucumber).

This is one of the chapter-end exercises.

Question 25

Q. A worm-like marine animal has a body of proboscis, collar and trunk, an open circulatory system and a proboscis gland for excretion. Which phylum does it belong to now, and which one did it once belong to?

Answer. Hemichordata, now a separate phylum under non-chordata. It was earlier considered a sub-phylum under Chordata, because the stomochord in the collar region was taken to be a notochord.

Question 26

Q. Two marine chordates are given. In the first, the notochord is present only in the larval tail; in the second, it runs from head to tail and persists all life. Name each subphylum with an example, and say what the two are collectively called.

Answer. The first is Urochordata (Tunicata) - Ascidia, Salpa, Doliolum. The second is Cephalochordata - Branchiostoma. Together they are the protochordates, and both are exclusively marine.

Question 27

Q. If you were given a specimen, what steps would you follow to classify it?

Answer. Work down the fundamental features in a fixed order, because each answer removes a large block of phyla.

1. Level of organisation - cellular, tissue, organ or organ-system.
2. Symmetry - asymmetrical, radial or bilateral.
3. Germ layers - diploblastic or triploblastic.
4. Body cavity - acoelomate, pseudocoelomate or coelomate.
5. Segmentation - present or absent.
6. Notochord - present or absent; if present, the animal is a chordate.
7. Digestive system - complete or incomplete; circulatory system - open or closed.
8. Finally check the signature structure - choanocytes, cnidoblasts, comb plates, flame cells, nephridia, malpighian tubules, radula, water vascular system - to fix the phylum.

For a chordate, keep going: jaw present or absent, then fins or limbs, then the class-level characters.

This is one of the chapter-end exercises.

Question 28

Q. How useful is the study of the nature of body cavity and coelom in the classification of animals?

Answer. Very useful. There are only three possible answers, and each one cuts the animal kingdom cleanly, so this is one of the sharpest single tests available.

• Acoelomate - no body cavity at all; Platyhelminthes.
• Pseudocoelomate - a cavity present but not lined by mesoderm, the mesoderm lying as scattered pouches; Aschelminthes.
• Coelomate - a cavity lined by mesoderm; Annelida onwards, including all chordates.

So one observation drops the animal into one of three groups. And because it is a feature of the body plan, not of habit or habitat, it does not shift with the environment the way colour or size might. It also marks a real structural advance - a true coelom lets the gut move independently of the body wall and leaves room for organs to develop.

This is one of the chapter-end exercises.

Question 29

Q. What difficulties would you face if the classification of animals did not take common fundamental features into account?

Answer. Classification would fall back on habit and habitat, and those are misleading.

1. Unrelated animals would be grouped together. A whale, a shark and a squid all swim in the sea; on habitat alone they would sit in one group, although they are a mammal, a cartilaginous fish and a mollusc.
2. Closely related animals would be separated. A bat flies, so it would be filed with birds instead of with mammals; Ichthyophis, which is limbless, would end up nowhere near the other amphibians.
3. No stable framework would exist, because habit and habitat change with the environment while level of organisation, symmetry, germ layers, coelom, segmentation and the notochord do not.
4. Any newly discovered animal would have nowhere definite to go, and you could not compare groups with each other at all.

This is one of the chapter-end exercises.

Question 30

Q. Match the following: (a) Operculum, (b) Parapodia, (c) Scales, (d) Comb plates, (e) Radula, (f) Hairs, (g) Choanocytes, (h) Gill slits - with Ctenophora, Mollusca, Porifera, Reptilia, Annelida, Cyclostomata and Chondrichthyes, Mammalia, Osteichthyes.

Answer.

It is also the single best half-hour of revision in the chapter - every entry is a signature structure.

This is one of the chapter-end exercises.

Tier 3 - Analytical and Multi-Concept

Question 31

Q. Arrange these phyla by body cavity and state what each step gains: Platyhelminthes, Aschelminthes, Annelida.

Answer.

• Platyhelminthes - acoelomate. No cavity; the organs are packed in solid tissue.
• Aschelminthes - pseudocoelomate. A cavity appears, but the mesoderm lies as scattered pouches and does not line it. This is also where the complete alimentary canal first appears.
• Annelida - coelomate. The cavity is lined by mesoderm, and metameric segmentation appears in the same phylum.

Every phylum after Annelida is coelomate, so this three-step ladder is worth reciting in order.

Question 32

Q. Give the excretory structure of Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata.

Answer.

The two that get answered wrongly most often are Echinodermata - absent and Mollusca - the gills themselves.

Question 33

Q. Which of these have an open and which a closed circulatory system: Arthropoda, Annelida, Hemichordata, Chordata?

Answer. Open - Arthropoda and Hemichordata. Closed - Annelida and Chordata. The pair worth memorising is Annelida closed against Arthropoda open, because the two phyla sit next to each other in the chapter and the contrast is asked constantly.

Question 34

Q. Which group changes its symmetry during its life, and why does that matter in an examination?

Answer. Echinodermata. The larvae are bilaterally symmetrical while the adults are radially symmetrical. It matters because a question that asks for "the symmetry of echinoderms" cannot be answered with one word - a bare "radial" ignores the larva, and a bare "bilateral" ignores the adult. It also means that a description mentioning a bilateral larva with a radial adult is pointing at Echinodermata and at nothing else.

Question 35

Q. List the animals from this chapter that are parasitic on human beings.

Answer.

Note the pattern - the parasites of human beings come from four phyla, and the flatworms and roundworms supply most of them.

This is one of the chapter-end exercises.

Question 36

Q. Why was Hemichordata removed from Chordata, and what would it need in order to be a chordate?

Answer. Hemichordates have a stomochord, a rudimentary structure in the collar region, and people once read it as a notochord. It is not a true notochord, so the group is now placed as a separate phylum under non-chordata. To count as a chordate the animal would need the whole set - a true notochord, a dorsal hollow nerve cord, paired pharyngeal gill slits and a post-anal tail. Hemichordates do have gills, which is part of why the confusion lasted so long, but gills are not what define a chordate - the group was moved out because that collar structure is a stomochord, not a true notochord.

Question 37

Q. Complete the table of firsts: where does each of these appear for the first time in the chapter's sequence - tissue level, organ level, organ-system level, complete digestive system, true coelom, metameric segmentation, notochord?

Answer.

Platyhelminthes and Annelida each carry two firsts, which is exactly why those two phyla are asked more often than their length in the book suggests.

The one row that gets answered two different ways. The descriptive account says organs associate into functional systems in annelids, arthropods, molluscs, echinoderms and chordates - that is the list to write when a question asks you to describe the organ-system level, or to name the groups that have organ systems. The comparison table starts crediting the level earlier: Platyhelminthes is listed as organ and organ-system, and Aschelminthes onwards as organ-system. So when an objective question asks which phylum shows the organ-system level first, answer from the table - Platyhelminthes.

Question 38

Q. Give the respiratory arrangement of Porifera, Platyhelminthes, Arthropoda, Mollusca, Echinodermata, Amphibia and Aves.

Answer.

Question 39

Q. Build the shortest possible key that separates Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia.

Answer.

1. Skeleton cartilaginous, no operculum, no air bladder - Chondrichthyes. Otherwise go on.
2. Bony skeleton, four pairs of gills under an operculum, air bladder present - Osteichthyes. Otherwise go on.
3. Skin moist and scaleless, respiration also through the skin, three-chambered heart - Amphibia. Otherwise go on.
4. Skin dry and cornified with scales or scutes, no external ear openings - Reptilia. Otherwise go on.
5. Feathers, forelimbs as wings, pneumatic bones - Aves.
6. Hair, mammary glands, external pinnae - Mammalia.

Notice how the key uses body covering at almost every step. That is the fastest single character in the vertebrate classes.

Question 40

Q. Name the look-alike pairs in this chapter that cost the most marks, and separate them.

Answer.

1. Mesoglea against mesoderm - the mesoglea is the undifferentiated layer between ectoderm and endoderm in diploblastic animals; the mesoderm is a true third germ layer in triploblastic animals.
2. Pseudocoelom against coelom - in the first the mesoderm lies as scattered pouches; in the second the cavity is lined by mesoderm.
3. Flame cells against nephridia against malpighian tubules - Platyhelminthes, Annelida and Arthropoda in that order.
4. Comb plates against cnidoblasts - Ctenophora against Coelenterata.
5. Open against closed circulation - Arthropoda open, Annelida closed.
6. Placoid against cycloid or ctenoid scales - Chondrichthyes against Osteichthyes.
7. Three-chambered against four-chambered heart - amphibians and most reptiles against crocodiles, birds and mammals.
8. Oviparous against viviparous - reptiles and birds are oviparous; mammals are viviparous with few exceptions, and Ornithorhynchus is that exception.

The Chapter-End Exercises

These are the textbook's own exercises, worked in full. Every one of them is mapped in the coverage table at the top of this section.

Question 41

Q. What are the peculiar features that you find in parasitic platyhelminthes?

Answer. They are mostly endoparasites found in animals including human beings, and everything about the body is built for that life.

1. Hooks and suckers are present in the parasitic forms, so the worm can hold on inside the host.
2. Some of them absorb nutrients from the host directly through their body surface, so a mouth and a gut are not needed for feeding.
3. The body is dorso-ventrally flattened, which keeps every cell close to the surface and gives a large area for that absorption.
4. They are acoelomate, with organ level of organisation.
5. Flame cells are present and carry out osmoregulation and excretion.
6. Sexes are not separate, fertilisation is internal, and development passes through many larval stages, which raises the chance that at least one larva reaches a new host.

Taenia, the tapeworm, and Fasciola, the liver fluke, are the examples.

This is one of the chapter-end exercises.

Question 42

Q. How important is the presence of the air bladder in Pisces?

Answer. The air bladder regulates buoyancy. A bony fish can adjust the gas inside it and so hold its position in the water column without swimming, and it can rise or sink by changing that gas. That saves a great deal of energy and lets the fish stay still to feed or rest.

The importance shows most clearly where the bladder is missing. Chondrichthyes have no air bladder, and because of that they have to swim constantly to avoid sinking. Presence or absence of the air bladder is also one of the quickest characters for separating Osteichthyes from Chondrichthyes.

This is one of the chapter-end exercises.

Question 43

Q. Prepare a list of the modifications observed in birds that help them fly.

Answer. Almost every system of a bird has been altered for flight, and the answer is best given system by system.

1. Body covering. The body is covered with feathers, which give the flight surface and streamline the body, and the forelimbs are modified into wings.
2. Skeleton. The endoskeleton is fully ossified and the long bones are hollow with air cavities - they are pneumatic - so the skeleton is strong but very light.
3. Respiration. Respiration is by lungs, and air sacs connected to the lungs supplement it, which keeps up the heavy oxygen supply that flight muscles need.
4. Circulation. The heart is completely four-chambered, so oxygenated and deoxygenated blood never mix and the flight muscles get fully oxygenated blood.
5. Body temperature. Birds are warm-blooded, or homoiothermous, so they can hold a constant body temperature and their activity does not drop when the air is cold.
6. Skin. The skin is dry and without glands except the oil gland at the base of the tail, which keeps weight down while the oil keeps the feathers in condition.
7. Digestion. The mouth carries a beak and no teeth, and the digestive tract has the extra chambers crop and gizzard, so food is gathered fast and ground inside the body rather than in a heavy head.
8. Hind limbs. The hind limbs are scaled and modified for walking, swimming or clasping tree branches, which handles landing, perching and take-off.

This is one of the chapter-end exercises.

Question 44

Q. Could the number of eggs or young ones produced by an oviparous and a viviparous mother be equal? Why?

Answer. No, they are usually very different.

An oviparous mother lays her eggs outside her body. Once laid, the eggs face predators, drying, and changes of temperature, with nothing from the mother to protect them, so only a small fraction hatch and survive. To leave any offspring at all she has to produce a very large number of eggs.

A viviparous mother keeps the developing young inside her body, where they are protected and nourished until they are ready to be born. The survival rate is therefore much higher, and a small number of young ones is enough.

So the number produced matches the risk that each mode of development carries - high risk outside the body means many eggs, low risk inside means few young.

This is one of the chapter-end exercises.

Question 45

Q. What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?

Answer. Arthropoda holds over two-thirds of all named species on earth. No single feature explains that; several act together.

1. The chitinous exoskeleton. It protects the body, supports it and cuts water loss, and it is that last property which let arthropods occupy dry land as completely as they occupy water.
2. Jointed appendages. The same basic appendage is modified for walking, swimming, feeding, sensing or mating, so one body plan serves an enormous range of ways of life.
3. A divided body. The body is divided into head, thorax and abdomen, so each region can specialise instead of every part doing everything.
4. A wide range of respiratory organs. Gills, book gills, book lungs and a tracheal system are all found in the phylum, so the group is not tied to one medium.
5. Well-developed sense organs. Antennae, compound and simple eyes, and statocysts for balance let them find food, mates and shelter in almost any surroundings.
6. Development that avoids competition. They are mostly oviparous, and development may be direct or indirect. Where it is indirect, the larva feeds differently from the adult, so the young and the adults do not compete for the same food.
7. Small size and short generation time. Small bodies need little food and little space, and quick generations mean large populations and rapid adaptation to new conditions.

This is one of the chapter-end exercises.

Question 46

Q. "All vertebrates are chordates but all chordates are not vertebrates." Justify the statement.

Answer. The statement is true, and it turns on the difference between having a notochord and having a vertebral column.

Every vertebrate is a chordate. Members of the subphylum Vertebrata possess a notochord during the embryonic period, and they also have the other chordate characters - a dorsal, hollow, single nerve cord, paired pharyngeal gill slits and a post-anal tail. Having the full set, every vertebrate answers the definition of a chordate.

Not every chordate is a vertebrate. In vertebrates the notochord is replaced by a cartilaginous or bony vertebral column in the adult, and they carry three further features - a ventral muscular heart with two, three or four chambers, kidneys for excretion and osmoregulation, and paired appendages, fins or limbs. The protochordates never develop any of that. Urochordata - Ascidia, Salpa, Doliolum - keep the notochord only in the larval tail, and Cephalochordata - Branchiostoma - keeps it from head to tail all its life without ever replacing it with a vertebral column.

So Urochordata and Cephalochordata are chordates that are not vertebrates, which is exactly what the statement claims.

This is one of the chapter-end exercises.