Animals whose embryos form only two germ layers, ectoderm and endoderm, are described as what?
Diploblastic
✓
Triploblastic
Eucoelomate
Pseudocoelomate
Correct Answer
Diploblastic
Diploblastic animals develop from just two germ layers, ectoderm and endoderm, and include radially symmetrical groups such as cnidarians. Triploblastic animals add a third layer, the mesoderm. Eucoelomate describes an animal with a true body cavity formed within mesoderm. Pseudocoelomate describes an animal whose body cavity is only partly lined by mesoderm.
Category: Body Plans and Phylogeny
Question 2
In which group of animals does the blastopore develop into the anus?
Mollusks
Echinoderms
✓
Annelids
Arthropods
Correct Answer
Echinoderms
Echinoderms are deuterostomes, so the first opening of the embryonic gut becomes the anus and the mouth forms later. Mollusks are protostomes, in which the blastopore becomes the mouth. Annelids are also protostomes. Arthropods are protostomes as well.
Category: Body Plans and Phylogeny
Question 3
What kind of body cavity do roundworms (nematodes) have?
A true coelom
No body cavity
A pseudocoelom
✓
A spongocoel
Correct Answer
A pseudocoelom
Roundworms are pseudocoelomates: their body cavity is lined partly by mesoderm and partly by endoderm. A true coelom forms entirely within mesoderm and is found in animals such as earthworms and vertebrates. No body cavity describes acoelomates such as flatworms. A spongocoel is the central water-filled cavity of a sponge.
Category: Body Plans and Phylogeny
Question 4
What shared trait unites nematodes and arthropods in the clade Ecdysozoa?
A body built of repeated segments
Five-part radial symmetry as adults
A shell secreted by a mantle
Molting an outer cuticle or exoskeleton
✓
Correct Answer
Molting an outer cuticle or exoskeleton
Ecdysozoans grow by periodically shedding and replacing a tough outer covering, the cuticle in nematodes and the exoskeleton in arthropods. A body built of repeated segments describes annelids and is not shared by nematodes. Five-part radial symmetry as adults is a trait of echinoderms. A shell secreted by a mantle is a mollusk trait.
Category: Body Plans and Phylogeny
Question 5
Which sponge cell type beats a flagellum to draw water through the body and traps food particles on a collar?
Choanocyte
✓
Amoebocyte
Cnidocyte
Flame cell
Correct Answer
Choanocyte
Choanocytes, or collar cells, line the inner surface of a sponge; their flagella pull water through the body and food caught on the collar is engulfed by phagocytosis. An amoebocyte moves through the mesohyl, carries nutrients and secretes spicules. A cnidocyte is the stinging cell of cnidarians. A flame cell is part of the flatworm excretory system.
Category: Sponges and Cnidarians
Question 6
Through which large opening near the top does water leave a sponge?
Ostium
Osculum
✓
Spicule
Mesohyl
Correct Answer
Osculum
Water enters a sponge through many small pores and exits through the osculum, a large opening at the top of the body. An ostium is one of the small pores in the body wall where water enters. A spicule is a tiny needle-like structural element. Mesohyl is the jelly-like layer between the sponge's two cell layers.
Category: Sponges and Cnidarians
Question 7
In jellies and sea anemones, the stinging organelle called the nematocyst is housed inside which cell type?
Choanocyte
Amoebocyte
Cnidocyte
✓
Gastrodermal cell
Correct Answer
Cnidocyte
Cnidocytes are stinging cells concentrated on the tentacles and around the mouth, and each contains a nematocyst with a coiled thread that fires toxin when triggered. A choanocyte is a flagellated collar cell of sponges. An amoebocyte is a mobile sponge cell that carries nutrients and builds spicules. A gastrodermal cell lines the gastrovascular cavity and is involved in digestion, not stinging.
Category: Sponges and Cnidarians
Question 8
Which cnidarian class, which includes corals and sea anemones, lives only in the polyp form with no medusa stage?
Scyphozoa
Cubozoa
Hydrozoa
Anthozoa
✓
Correct Answer
Anthozoa
Members of Anthozoa, such as sea anemones and corals, exist only as polyps. Scyphozoa are the true jellies, in which the medusa is the dominant stage. Cubozoa are box jellies with a square, bell-shaped medusa. Most Hydrozoa have both polyp and medusa forms in their life cycle.
Category: Sponges and Cnidarians
Question 9
Flatworms regulate dissolved salts and remove nitrogenous wastes using which structures?
Flame cells
✓
Metanephridia
Malpighian tubules
Contractile vacuoles
Correct Answer
Flame cells
Flatworms have a branching network of excretory tubules containing flame cells, whose beating cilia move waste fluid out of the body. Metanephridia are the paired excretory organs found in each segment of annelids. Malpighian tubules are the excretory organs of insects. Contractile vacuoles expel excess water from single-celled organisms such as many protists.
Category: Worms and Arthropods
Question 10
Which structure anchors a tapeworm to the intestinal wall of its host?
Proglottid
Scolex
✓
Clitellum
Radula
Correct Answer
Scolex
The scolex is the tapeworm's head region, armed with suckers and often hooks that attach it to the host's intestine. A proglottid is one of the repeating body segments that carries reproductive organs. A clitellum is the glandular band of an earthworm used in reproduction. A radula is the scraping feeding structure of many mollusks.
Category: Worms and Arthropods
Question 11
The arthropod exoskeleton is composed mainly of which substance?
Cellulose
Keratin
Chitin
✓
Collagen
Correct Answer
Chitin
Chitin is a tough nitrogen-containing polysaccharide that forms the bulk of the arthropod exoskeleton, and some crustaceans harden it further with calcium carbonate. Cellulose is the main structural polysaccharide of plant cell walls. Keratin is the protein of vertebrate scales, hair and feathers. Collagen is a protein found in animal connective tissues, not the main component of the exoskeleton.
Category: Worms and Arthropods
Question 12
Bony fishes adjust their buoyancy in the water using which gas-filled organ?
Lateral line
Operculum
Ampullae of Lorenzini
Swim bladder
✓
Correct Answer
Swim bladder
The swim bladder is a gas-filled sac that lets a bony fish control its depth, and sharks lack one. The lateral line is a sense organ that detects movement and vibration in the water. The operculum is the bony flap covering the gills. The ampullae of Lorenzini are electroreceptors found in sharks and rays.
Category: Vertebrates
Question 13
Spiders, scorpions and horseshoe crabs belong to which arthropod subphylum?
Chelicerata
✓
Crustacea
Myriapoda
Hexapoda
Correct Answer
Chelicerata
Chelicerata is named for the chelicerae, the first pair of appendages, which serve as mouthparts and in spiders often deliver venom; spiders, scorpions and horseshoe crabs are all chelicerates. Crustacea includes mostly aquatic animals such as crabs, lobsters and shrimp. Myriapoda includes millipedes and centipedes. Hexapoda includes insects and their six-legged relatives.
Category: Worms and Arthropods
Question 14
What does the radula do in the mollusks that have one?
Secretes the shell
Scrapes or rasps food
✓
Pumps water over the gills
Anchors the animal in place
Correct Answer
Scrapes or rasps food
The radula is a tongue-like ribbon covered with tiny teeth that scrapes food, for example algae off a rock, in many mollusks such as snails. Secreting the shell is the job of the mantle. Pumping water over the gills is not a radula function. Anchoring the animal is done by the muscular foot.
Category: Mollusks and Annelids
Question 15
Which mollusk class, which includes octopuses and squid, has a closed circulatory system?
Gastropoda
Bivalvia
Cephalopoda
✓
Polyplacophora
Correct Answer
Cephalopoda
Cephalopods are active predators with a closed circulatory system, and octopuses and squid have three hearts. Gastropoda, the snails and slugs, have an open circulatory system. Bivalvia, such as clams and mussels, also have open circulation. Polyplacophora, the chitons, have open circulation as well.
Category: Mollusks and Annelids
Question 16
Annelid bodies are built from a series of repeated segments, each with repeated internal and external features. What is this condition called?
Metamorphosis
Cephalization
Ecdysis
Metamerism
✓
Correct Answer
Metamerism
Metamerism is the division of the body into repeating segments, which allows different segments to become specialized; it is a defining trait of annelids. Metamorphosis is a change in body form during development, as when a larva becomes an adult. Cephalization is the concentration of nerve tissue and sense organs at the head end. Ecdysis is the shedding of an exoskeleton or cuticle.
Category: Mollusks and Annelids
Question 17
In sea stars, the water vascular system uses hydrostatic pressure to move which structures used in locomotion and feeding?
Tube feet
✓
Parapodia
Chaetae
Pseudopodia
Correct Answer
Tube feet
Tube feet extend through openings in the endoskeleton and are expanded or retracted by water pressure in the water vascular system, giving slow but powerful movement and grip. Parapodia are paired fleshy appendages of polychaete worms. Chaetae are the chitinous bristles of annelids. Pseudopodia are temporary cytoplasmic extensions used by amoeboid cells.
Category: Echinoderms and Chordates
Question 18
Which chordate feature do adult tunicates retain after metamorphosis?
Notochord
Pharyngeal slits
✓
Dorsal hollow nerve cord
Post-anal tail
Correct Answer
Pharyngeal slits
Adult tunicates are sessile suspension feeders that keep their pharyngeal slits and use them to filter food from the water. The notochord is lost during metamorphosis. The dorsal hollow nerve cord is also lost when the larva settles and transforms. The post-anal tail is lost at metamorphosis too.
Category: Echinoderms and Chordates
Question 19
What major advantage did the amniotic egg give reptiles, birds and mammals?
Embryos could breathe through gills
Eggs could be fertilized outside the body
Embryos could develop away from water
✓
Larvae could feed as filter feeders
Correct Answer
Embryos could develop away from water
The membranes of the amniotic egg enclose the embryo in its own fluid, handle gas exchange and store wastes, freeing amniotes from depending on water for reproduction. Embryos breathing through gills describes aquatic larvae such as tadpoles. Fertilization outside the body is typical of many fishes and amphibians and does not work for a shelled egg. Filter-feeding larvae are found in groups such as lampreys and amphibians.
Category: Vertebrates
Question 20
Which group of mammals, including the platypus and the echidnas, lays eggs?
Marsupials
Eutherians
Rodents
Monotremes
✓
Correct Answer
Monotremes
Monotremes are the only egg-laying mammals, and they secrete milk from a ridge of mammary tissue rather than from nipples. Marsupials give birth to underdeveloped young that usually continue developing in a pouch. Eutherians, the placental mammals, nourish the embryo through a complex placenta. Rodents are a group of placental mammals and give birth to live young.
Category: Vertebrates