Introduction to Animals Worksheet

Introduction to Animals Worksheet

Circle the correct response.

1. Animals are [ heterotrophs / autotrophs ]

2. [ All / Most ] animals are multicellular.

3. The cells in the skin of your hand are [ bigger than / the same size as ] the cells in your heart.

4. Organisms that have 2 copies of each chromosome are [mobile / diploid ]

5. The absence of a cell wall allows animals [ mobility / diploidy ]

6. A hollow ball of cells that forms after fertilization is called a [ blastula / mesoderm ]

7. In all animals except [ humans / sponges ] a zygote undergoes divisions to become a blastula.

8. The cells of animals are organized into functional units called [ blastula / tissues ]



9. ______ Ectoderm a. lining of the digestive tract, digestive organs


10. ______ Mesoderm b. outer layer of skin and sense organs


11. ______ Endoderm c. most of the skeleton, muscles Match the body plan to its description
12. ______ radial d. body that is irregular shaped


13. ______ bilateral e. has a distinct right and left half


14. ______asymmetry f. body parts arranged around a central axis, like the spokes of a bicycle wheel



What symmetry do these animals have?

15. ______________

16. ____________________  

17. Segmented animals are constructed from a series of repeating units called [segments /vertebrates]

18. Evidence of segmentation in human beings can be seen in the [ skin / backbone ]

Match the name of the Phylum to the organism:


a. vertebrates

b. segmented worms

c. flatworms

d. jellyfish

e. sea stars

f. sponges

g. clams

h. roundworms

i. insects

19. _____ Cnidaria

20. ______ Mollusca

21. _____ Annelida

22. _____ Chordata

23. ______Nematoda

24. ______Platyhelminthes

25. ______ Porifera

26. ______Arthopoda

27. ______Echinodermata




Animal Body Systems

For each term below, indicate what body system it relates to. Body Systems


28. Gastrovascular Cavity ___________________________

29. Ganglia ____________________________

30. Hermaphrodite ____________________________

31. Blood vessels ____________________________

32. Exoskeleton ____________________________

33. Gills

34. Anus

35. Nerve Net ____________________________

36. Hydrostatic ____________________________

37. Gametes ____________________________

38. Flame cells

39. radula

40. trachea & spiracles




Support (skeletal)







Revised from :


Introduction to Animal

Introduction to Animals

All Materials © Cmassengale


  • All multicellular (metazoans) & eukaryotic
  • Cells lack cell walls & come in a variety of shapes
  • Ingestive heterotrophs (take in food & internally digest it)
  • Store food reserves temporarily as glycogen in the liver
  • Have some type of skeletal support
  • Exoskeletons found in arthropods cover the outside of the body but limit size
  • Endoskeletons found in all vertebrates are found inside the body & are made of cartilage &/or bone
  • Worms have fluid-filled internal cavities giving them skeletal support
  • Sponges have the simplest skeleton 
  • May be sessile (attached & non-moving) or motile (able to move around)
  • Muscular tissue provides energy for movement
  • Reproduce sexually
  • Show levels of organization including cell, tissue, organ, & system
  • Most show division of labor among cells
  • Cells are specialized for particular functions
  • Cell junctions hold individual cells in a tissue together
  • Most vertebrates have a backbone or spine made of repeating bones called vertebrae that protect the spinal cord
  • Some show cephalization (have a head with sensory organs concentrated there)

Invertebrate Groups

  • Simplest animals
  • Contains the greatest number of animal species
  • Most found in water
  • Do not have an backbone
  • Includes sponges, cnidarians, flatworms, roundworms, annelids (segmented worms), mollusks, arthropods, & echinoderms

Vertebrate Groups

  • More complex animals
  • Most have a backbone
  • Includes fish, amphibians, reptiles, birds, & mammals

Body Areas

  • Dorsal is the back or upper surface
  • Ventral is the belly or lower surface
  • Anterior head or front end
  • Posterior is the tail or hind end opposite the head
  • Oral surface in echinoderms is where the mouth is located (underside)
  • Aboral surface in echinoderms is the surface opposite the mouth (top side)





Body Symmetry

  • Symmetry is the arrangement of body parts around a central plane or axis
  • Asymmetry occurs when the body can’t be divided into similar sections (sponges)
  • Radial symmetry occurs when similar body parts are arranged around a central point like spokes on a wheel (echinoderms)
  • Most animals with radial symmetry are sessile (attached) or sedentary (move very little)
  • Bilateral symmetry occurs when animals can be divided into equal halves along a single plane (right & left sides that are mirror images)
  • Animals with bilateral symmetry are more complex, usually motile organisms, such as worms, arthropods, and all vertebrates
  • Animals with bilateral symmetry show cephalization & have anterior & posterior ends





  • Occurs whenever animal bodies are divided into repeating units or segments
  • Found in more complex animals
  • Earthworms show external segmentation, while humans show internal segmentation (vertebrae of the backbone)
  • Segments may be fused together such as cephalothorax covering chest & head of a crayfish

Tissue Development

  • All animals reproduce sexually, but some also reproduce asexually (sponges bud & flatworms fragment)
  • Zygote is the fertilized egg all animals form from
  • Zygote undergoes rapid cell divisions known as cleavage to become hollow ball of cells called blastula
  • Blastocoel is the central cavity of the blastula
  • Blastula invaginates (folds inward at one point) to form an opening & two cell or germ layers; process called gastrulation
  • New cup-shaped structure with 2 cell layers is called the gastrula
  • Archenteron is the deep cavity of the gastrula that forms the primitive gut
  • Inner germ layer called endoderm & outer germ layer called ectoderm
  • Opening may become the mouth or the anus
  • Protostomes (mollusks, arthropods, & annelids) develop mouth from blastopore, while deuterostomes (echinoderms & vertebrates) develop an anus from blastopore
  • Some animals form a third germ layer in the middle called mesoderm
  • Cells differentiation during development changing their shapes to fit their function ( neurons or nerve cells become long to conduct messages)


  • Protostomes have spiral cleavage in which embryonic cells divide in a spiral arrangement
  • Deuterostomes have radial cleavage or embryonic cell division parallel or perpendicular to the vertical axis of the embryo

  • Protostomes have determinate cleavage ( embryonic cells can’t form a new organism if separated)
  • Deuterostomes have indeterminate cleavage ( embryonic cells can form other organisms if separated such as identical twins)

Germ Layers

  • Form the tissues, organs, & systems of an animal
  • Found in the embryo of all animals except sponges (have specialized cells but no tissues)
  • Ectoderm (outer) forms skin, nerves, & sense organs
  • Endoderm (inner) forms the digestive & respiratory organs & systems
  • Mesoderm (middle) forms muscles, circulatory system, reproductive & excretory systems

germ layers

Larval Forms

  • Some animals have indirect development & go through an immature larval form that does not resemble the adult
  • Planula is the larva of cnidarians (jellyfish, corals, & sea anemones)
  • Trochophore is the larva of mollusks (squid & octopus)
  • Dipleurula is the larva of echinoderms (starfish & sea urchins)


  • May be complete or incomplete
  • Usually found in arthropods
  • Incomplete metamorphosis (egg –> nymph –> adult)
  • Complete metamorphosis ( egg –> larva –> pupa –> adult)





Body Cavities

  • Coelom is an internal body cavity lined with mesoderm

  • Animals with a coelom are called coelomate animals (annelids, mollusks, arthropods, & vertebrates)
  • Acoelomate animals do not have a body cavity but have solid bodies (sponges, flatworms, & cnidarians )
  • Pseudocoelomate animals have a body cavity only partially lined with mesoderm (roundworms)

  • Schizocoely occurs in protostomes where the coelom develops when mesoderm masses split
  • Enterocoely occurs in deuterostomes

Body Layers

  • Sponges have specialized cells but no tissues or organs
  • Cnidarians (jellyfish, coral, sea anemone) have 2 body layers (ectoderm & endoderm) with a jellylike layer called mesoglea between for support
  • Cnidarians have one body opening into a large cavity called gastrovascular cavity
  • All worms, mollusks, arthropods, echinoderms, & vertebrates have 3 cell layers (ectoderm, mesoderm, & endoderm)

Mouth & Anus Development

  • Blastopore is the opening in the gastrula formed when blastula folds inward
  • Protostomes are animals that the blastopore develops into the mouth ( earthworms, mollusks, arthropods)
  • Deuterostomes are animals that the blastopore develops into the anus (echinoderms & vertebrates)

Support Systems

  • Sponges are supported by spicules, while limestone cases support corals

  • Hydrostatic skeletons in worms consist of a fluid-filled body cavity surrounded by muscles
  • Arthropods have external exoskeletons that prevent water loss but must be molted for growth to occur
  • Echinoderms & vertebrates have internal endoskeletons that grow with the organism

Digestive Systems

  • All animals are heterotrophs
  • Sponges have specialized cells to capture & digest their food
  • Cnidarians have one opening into their gastrovascular cavity where food enters & wastes leave; called a two-way digestive system
  • Annelids, arthropods, & vertebrates have a one-way digestive system in which food enters the mouth, is digested,  & wastes leave through the anus

Circulatory System

  • Transports oxygen and nutrients to cells & carbon dioxide and wastes away from cells
  • Sponges, cnidarians, & flatworms don’t have a circulatory system
  • In closed systems, blood remains in blood vessels at all times until it reaches cells (earthworms & vertebrates)
  • In open systems, blood isn’t always contained in blood vessels (arthropods)

Respiratory System

  • Oxygen is needed & carbon dioxide must be eliminated
  • Sponges, cnidarians, flatworms, & roundworms exchange gases by diffusion
  • Mollusks & fish use gills to exchanges gases, while terrestrial vertebrates use lungs

Nervous System

  • Cephalization occurs in animals that have a distinct head at the anterior end where sensory organs are concentrated
  • Cephalization is found in more complex animals 
  • Sponges have specialized nerve cells, while cnidarians & flatworms have a nerve net
  • Ganglia are clusters of nerve cells found in more complex animals
  • Nerve cells may specialize to detect, light, sound, etc.
  •  Brain interprets nerve impulses & sends a response

Body Coverings

  • Integument is the outer covering of an animal
  • Terrestrial vertebrates have water-tight outer coverings
  • Integuments of amphibians allow gas exchange through the skin
  • Adaptations of integuments include scales, fur, hair, & feathers to protect and insulate the body

Excretory System

  • Rid animals of wastes, help conserve water, & filter wastes from the blood
  • Ammonia is a toxic waste that must be gotten rid of by an animal’s body
  • Kidneys filter blood in vertebrates

Reproductive System

  • All animals reproduce sexually, but some also use asexual reproduction
  • Budding is asexual reproduction in which an outgrowth on the parent organism breaks off to form a new individual (hydra)

hydra with bud 3.JPG (83198 bytes)

  • Sponges, flatworms, & cnidarians asexually reproduce by fragmentation (separating into pieces & each piece making a new organism)
  • Some insects develop from unfertilized eggs by parthenogenesis
  • Hermaphrodites are animals that produce both sperm & eggs (earthworms – cross fertilize & tapeworms self fertilize)
  • Echinoderms, arthropods, mollusks, & vertebrates have separate sexes & exchange sperm
  • Internal fertilization occurs inside the body of the female & larger numbers of sperm & eggs are produced
  • External fertilization occurs inside the body of the female & fewer eggs & sperm are produced

Eye Model Labeled

External Right Eye Model


1.Frontal Bone9.Superior Rectus
2.Nasal Bone10.Trochlea of Superior Oblique
3.Maxillary Bone11.Lacrimal Gland
4.Lacrimal Bone12.Sclera
5.Zygomatic Bone13.Iris
6.Inferior Rectus14.Pupil
7.Inferior Oblique15.Nasolacrimal Duct
8.Lateral Rectus16.Lacrimal Punctum



Frog Dissection


Frog Dissection
Pictures:  Modern Biology, Holt

As members of the class Amphibia, frogs may live some of their adult lives on land, but they must return to water to reproduce. Eggs are laid and fertilized in water. On the outside of the frog’s head are two external nares, or nostrils; two tympani, or eardrums; and two eyes, each of which has three lids. The third lid, called the nictitating membrane, is transparent. Inside the mouth are two internal nares, or openings into the nostrils; two vomerine teeth in the middle of the roof of the mouth; and two maxillary teeth at the sides of the mouth. Also inside the mouth behind the tongue is the pharynx, or throat.

In the pharynx, there are several openings: one into the esophagus, the tube into which food is swallowed; one into the glottis, through which air enters the larynx, or voice box; and two into the Eustachian tubes, which connect the pharynx to the ear. The digestive system consists of the organs of the digestive tract, or food tube, and the digestive glands. From the esophagus, swallowed food moves into the stomach and then into the small intestine. Bile is a digestive juice made by the liver and stored in the gallbladder. Bile flows into a tube called the common bile duct, into which pancreatic juice, a digestive juice from the pancreas, also flows. The contents of the common bile duct flow into the small intestine, where most of the digestion and absorption of food into the bloodstream takes place.

Indigestible materials pass through the large intestine and then into the cloaca, the common exit chamber of the digestive, excretory, and reproductive systems. The respiratory system consists of the nostrils and the larynx, which opens into two lungs, hollow sacs with thin walls. The walls of the lungs are filled with capillaries, which are microscopic blood vessels through which materials pass into and out of the blood. The circulatory system consists of the heart, blood vessels, and blood. The heart has two receiving chambers, or atria, and one sending chamber, or ventricle. Blood is carried to the heart in vessels called veins. Veins from different parts of the body enter the right and left atria. Blood from both atria goes into the ventricle and then is pumped into the arteries, which are blood vessels that carry blood away from the heart.

The urinary system consists of the frog’s kidneys, ureters, bladder, and cloaca. The kidneys are organs that excrete urine. Connected to each kidney is a ureter, a tube through which urine passes into the urinary bladder, a sac that stores urine until it passes out of the body through the cloaca. The organs of the male reproductive system are the testes, sperm ducts, and cloaca. Those of the female system are the ovaries, oviducts, uteri, and cloaca. The testes produce sperm, or male sex cells, which move through sperm ducts, tubes that carry sperm into the cloaca, from which the sperm move outside the body. The ovaries produce eggs, or female sex cells, which move through oviducts into the uteri, then through the cloaca outside the body.

The central nervous system of the frog consists of  the brain, which is enclosed in the skull, and the spinal cord, which is enclosed in the backbone. Nerves branch out from the spinal cord. The frog’s skeletal and muscular systems consist of its framework of bones and joints, to which nearly all the voluntary muscles of the body  are attached. Voluntary muscles, which are those over which the frog has control, occur in pairs of flexors and extensors. When a flexor of a leg or other body part contracts, that  part is bent. When the extensor of that body part contracts, the part straightens.


Describe the appearance of various organs found in the frog.
Name the organs that make up various systems of the frog.

In this lab, you will dissect a frog in order to observe the external and internal structures of frog anatomy.


• safety goggles, gloves, and a lab apron
preserved frog
dissecting pins (6–10)
dissecting tray and paper towels
plastic storage bag and twist tie
marking pen
dissecting needle


  1. Put on safety goggles, gloves, and a lab apron.
  2. Place a frog on a dissection tray. To determine the frog’s sex, look at the hand digits, or fingers, on its forelegs. A male frog usually has thick pads on its “thumbs,” which is one external difference between the sexes, as shown in the diagram below. Male frogs are also usually smaller than female frogs. Observe several frogs to see the difference between males and females.
  1.  Use the diagram below to locate and identify the external features of the head. Find the mouth, external nares, tympani, eyes, and nictitating membranes.

  1. Turn the frog on its back and pin down the legs. Cut the hinges of the mouth and open it wide. Use the diagram below to locate and identify the structures inside the mouth. Use a probe to help find each part: the vomerine teeth, the maxillary teeth, the internal nares, the tongue, the openings to the Eustachian tubes, the esophagus, the pharynx, and the slit-like glottis.

  1. Look for the opening to the frog’s cloaca, located between the hind legs. Use forceps to lift the skin and use scissors to cut along the center of the body from the cloaca to the lip. Turn back the skin, cut toward the side at each leg, and pin the skin flat. The diagram above shows how to make these cuts
  2. Lift and cut through the muscles and breast bone to open up the body cavity. If your frog is a female, the abdominal cavity may be filled with dark-colored eggs. If so, remove the eggs on one side so you can see the organs underlying them.
  3. Use the diagram below to locate and identify the organs of the digestive system: esophagus, stomach, small intestine, large intestine, cloaca, liver, gallbladder, and pancreas.


  1. Again refer to the diagram below to identify the parts of the circulatory and respiratory systems that are in the chest cavity. Find the left atrium, right atrium, and ventricle of the heart. Find an artery attached to the heart and another artery near the backbone. Find a vein near one of the shoulders. Find the two lungs.

  1. Use a probe and scissors to lift and remove the intestines and liver. Use the diagram on the next page to identify the parts of the urinary and reproductive systems. Remove the peritoneal membrane, which is connective tissue that lies on top of the red kidneys. Observe the yellow fat bodies that are attached to the kidneys. Find the ureters; the urinary bladder; the testes and sperm ducts in the male; and the ovaries, oviducts, and uteri in the female.

  1. Remove the kidneys and look for threadlike spinal nerves that extend from the spinal cord. Dissect a thigh, and trace one nerve into a leg muscle. Note the size and texture of the leg muscles.
  2. Dispose of your materials according to the directions from your teacher.
  3. Clean up your work area and wash your hands before leaving the lab.
Click here for worksheet


Frog Dissection Worksheet


Frog Dissection Worksheet
    1. What do you think is the function of the nictitating membrane, and why?
    2. A frog does not chew its food. What do the positions of its teeth suggest about how the frog uses them?
    3. Trace the path of food through the digestive tract.
    4. Trace the path of blood through the circulatory system, starting at the right atrium.
    5. Trace the path of air through the respiratory system.
    6. Trace the paths of sperm in a male and eggs in a female.
    7. Trace the path of urine in both sexes.
    8. Which parts of the frog’s nervous system can be observed in its abdominal cavity and hind leg?
    9. Suppose in a living frog the spinal nerve extending to the leg muscle were cut. What ability would the frog lose? Why?
    10. The abdominal cavity of a frog at the end of hibernation season would contain very small fat bodies or none at all. What is the function of the fat bodies?


  1.  Structures of an animal’s body that fit it for its environment are adaptations. How do the frog’s powerful hind legs help it to fit into a life both in water and on land?
  2. During one mating of frogs, the female lays some 2,000 to 3,000 eggs in water as the male sheds millions of sperm over them. How do these large numbers relate to the frog’s fitness for life in water?