AP Biology Final: Squid Dissection

Squid Dissection

Background Information

There are more than 300 species of squid identified throughout the world, in the deeper parts of freshwater and saltwater. All are characterized by soft, elongated, tubular bodies, compact heads, and ten arms. Two of those arms are longer and have suckers with horned rings used for catching prey. They range greatly in size, the smallest being ¾ inch and the largest being 65 feet.

Like fish, squid use gills on the sides of their heads to process needed oxygen from the water. Their heads also feature large eyes on both sides. These eyes are believed to be as complex as those of humans. They do, after all, need to watch out for predators in the dark reaches of the ocean, almost near the ocean floor. Squid can be considered the prey of many other animals because of their soft bodies.

When threatened, squids will squirt out a jet-black ink. If they’re not so lucky, other animals will digest the entirety of the squid except for its hard beak. The inside of the squid is also composed of a tough, horny material.

Major Internal and External Anatomy

Mouth: consumes small organisms that will travel to the esophagus to be digested

Beak: the buccal mass is the muscular casing around the beak; tears food into small pieces; attached to the esophagus.

Gill heart: also called a brachial heart; one is located at the base of each gill to pump blood from the body to the gills

Gill: a respiratory organ that exchanges oxygen and carbon dioxide between the blood and the sea water

Pen: the remnant of the shell that is found within the mantle on the dorsal side; functions as support for the mantle; colored by a dark ink

Stomach: small oval structure located over the caecum; breaks down food

Incision Guide

On the dorsal side of the squid, begin the incision on the superior portion and down the medial plane to the inferior portion.

Remove the beak by cutting along the highlighted circle.

Open the flaps you've created and view the pen, gills, gill hearts, and stomach.

If you flip over the main portion of the squid, you can view the vein that runs from proximal to distal ends.

If you're just curious, you may want to cut the flaplike areas off and cut them in half to reveal the veins running through them. Proceed to cut the rest of the squid to find the remaining parts.

Dissection Procedure

AP Biology Final Project: Frog Dissection

Frog Dissection

Background Information

Frogs are members of the class amphibia because they live both in and out of water. There are approximately 4,740 different species of frogs throughout the world, 90 of which are found in the U.S. They are found in the highest concentration in warmer tropical climates. Frogs eat insects along with some types of small animals, including earthworms and minnows.

The way frogs breathe can be considered unique. When they are tadpoles, they breathe through internal gills and their skin. Through development, they develop the lungs necessary to respiration on land, and their gills are lost. Like humans, frogs take in air through their nostrils with their mouths closed before exhaling with body contractions. Tiny blood vessels, capillaries, under the outer skin layers also help frogs breathe through their skin.

Frogs range widely in appearance and size. Some of the tiniest frogs are smaller than a dime, while the largest frogs can grow to be longer than a foot. A species called the “Glass Frog” has skin so translucent an observer can see its heart beating.

Major Internal and External Anatomy

Tympanum: an eardrum-like structure that receives sound waves

External nares: anterior openings for the exit or entry of air

Eye: allows the frog to see

Nictitating membrane: a transparent part of a frog's lower eyelid that moves over the eye to clean it and protect it

Glottis: opening through which air enters the trachea

Eustachian tubes: openings in the mouth that lead to tubes that connect to the middle ear to equalize air pressure

Tongue: the muscular structure attached to the front of the mouth which is extended to catch insects 

Pharynx: a tubelike structure that serves as the passageway for food, liquid, and air

Esophagus: a muscular tube that connects the mouth to the stomach

Maxillary teeth: sharp teeth in the maxilla of a frog's mouth that function in holding captured prey

Internal nares: openings for the intake of air

Vomerine teeth: small projections in the top of a frog's mouth that function in holding prey

Liver: secretes bile and processes digested food molecules

Fat bodies: masses of fat in the body cavities of frogs which are needed for hibernating and mating

Sperm ducts: site of sperm secretion in male reproductive system

Testes: male sex organs which produce sperm

Kidney: two long excretory organs that lie along the back; filter wastes from the blood and excrete them in the urine

Small intestine: the principal organ of digestion and absorption of digested food

Large intestine: posterior organ of the digestive system which stores undigested food

Pancreas: gland which secretes digestive enzymes into the next part of the digestive system

Spleen: organ through which the products of the frog's digestive and urogenital system pass when discharged from the body

Lung: receives air coming through the windpipe and serves as the site of oxygen absorption

Heart: the organ of the circulatory system which pumps blood throughout the frog

Stomach: stores food and mixes it with enzymes to begin digestion 

Incision Guide

First, cut the hinges of the frog's mouth to open it wider and to see the back of the mouth as indicated by the purple portions below.

Cut along the medial orientation. Then, near the cranial end, cut from the medial line down under the frog's axilla. Repeat with the caudal end, cutting from the medial line above its hind legs. Pin each skin flap so it is out of the way and so the liver is exposed.

Pull the liver aside, revealing the stomach and the small intestine.

If not already exposed, cut deeper into the cranial end to pull the skin back to reveal the heart and the esophagus. The lungs are found visceral to the heart.

In order to locate the kidneys, pancreas, and large intestine, the stomach and the small intestine must be moved. Our frog was male, so there were sperm ducts and testes on the kidneys seen by moving the intestines. To do this, pick the small intestine up with tweezers and let the mesenteries rip from the intestines.

Dissection Procedure

AP Biology Final Project: Starfish Dissection

Starfish Dissection

Background Information

Starfish are actually considered “sea stars” by today’s marine biologists because these creatures are not actually fish, but echinoderms. They are related to sand dollars, sea urchins, and sea cucumbers, and all of these organisms have five-point radial symmetry. There are five main sections to their anatomy that are arranged around a central disk. Thus, the most common type of sea star is one with five arms. Some varieties come with numbers of arms in multiples of five, with maybe ten, twenty, thirty arms or more. The thousands of varieties of sea stars are found in all types of ocean environments-from the deep ocean floor to rocky land bordering the water.

Sea stars eat mussels, clams, small fish, snails, and barnacles. The way they consume their prey is interesting: multiple arms of a sea star will work to pull bivalves open, then the stomach is pushed through the sea star’s mouth to envelop the other organism before it retreat back into the sea star’s body. Sea stars are not oxygenated and do not possess blood. Instead, sea water is taken in through their sieve plates to extend the tube feet.

Some fun facts about sea stars concern their unique limbs. If an arm is cut off by a predator, the vital organs in the lost arm and some parts of the central disk may be enough to regrow an entirely new sea star. The individual arms also possess “eye” on the very tips. These cannot see visually are humans do, but they can feel around the sea floor and tell the difference between light and dark.   

Major Internal and External Anatomy

Central disk: provides structures to the central portion of the starfish
Eye spots: sensory organs of the starfish, sense between dark and light and feel the ocean floor
Madreporite: where water enters the water vascular system
Spines: protect the starfish from predators

Mouth: spot through which food enters the starfish and the stomach may exit the organism to consume prey
Podia (tube feet): organ of locomotion of a starfish; expands with intake of water and retracts on its own
Ambulcaral groove: contains the tube feet on the oral side and is used to pry open the shells of bivalves

Pyloric caeca: synthesize enzymes to digest food in the stomach
Stomach: digest food into usable nutrients

Gonads: reproductive organs of starfish, either testes or ovaries
Ring canal: canal in which filtered water enters through the madreporite and branches out into the radiated canals
Ossicles: provide structure to each of the five arms
Lateral canal: canal running the length of the arm; receives water from annular canal and passes it into the tube feet

Incision Guide

First, cut off the tip of a ray. Take note of the tube feet which are attached to the long, zipper-like ridge that extends the length of the ray. The top of the tube feet is the ampulla, which helps to create suction that makes the starfish stay in one place or adjust its position.

Using scissors, then cuts along either side of the skeletal structure extending almost to the central portion of the starfish. Cut across these lines to remove a rectangular flap of skin from the center of that arm.

Remove the somewhat circular flap of skin above the ring canal. This connects the five lateral canals from the five arms. The flap may need to be extended beyond a circular shape to be removed. 

Carefully remove the crumbly brown material on either side of the skeletal plates, or ossicles. These are the pyloric caeca. These are the digestive glands that secrete enzymes for digestion. The gonads, sexual reproductive structures of testes or ovaries, look similar to the pyloric caeca but are somewhat ridged in appearance. 

Dissection Procedure

AP Biology Final Project: Clam Dissection

Clam Dissection

Background Information

Clams are bivalve mollusks. The term bivalve applies to these creatures because they possess two shells which are held together by a hinge in the middle. Clams are unique in that they possess two adductor muscles on opposite ends of the organism along with a hard structured foot that helps it move. The insides fo the shells are usually pearly, and small pieces of sand that may enter the clam may slowly take on a pearly surface. There are approximately 15,000 different species of bivalves, and they are usually found buried just below the surface or up to two feet under sandy or muddy freshwater or ocean bottoms.

Clams filter water for breathing and food through two different siphons, inhalant and exhalant. The inhalant siphon takes in water and food particles. The exhalant siphon releases water with waste.
Species of clams range widely in size. The largest species, appropriately named the giant clam, has been found to reach widths of 5 ft and weights of 500 lbs.

Major Internal and External Anatomy

Growth rings: mark the stage of development or age of the clam

Umbo: the point on the shell at which growth begins; marks one of the earliest stages of development

Hinge ligament: helps the shell open and close at the meeting of the two shells

Posterior/anterior adductor muscle: bridges the gap between the halves of the shell to hold them together

Mantle: membranous tissue that covers entire body; yellow/cream color, secretes shell material

Gills: folded, ridged tissue with microscopic cilia; aids in respiration and the gas exchange

Foot: hatched-shaped and hard, provides locomotion and movement to the organism

Labial palp: leaflike structures between gills and anterior adductor that direct water carrying food into the mouth

Inhalant/exhalant siphons: folds in the mantle that regulate flow of water into and out of the clam

Mouth: slit between palps that is the site of the passage of food into the digestive system

Digestive gland: light green mass surrounding stomach that secretes enzymes into the digestive system

Anus: end of intestine near exhalant siphon; removes undigested food

Reproductive organ: spongy reddish mash ventral to the palps that produces eggs and sperm in clams of their respective genders

Intestine: coiled tubule from stomach through body to anus; site of the absorption of digested food

Incision Guide

At the dorsal end of the clam, there is a hinge ligament that needs to be cut before the clam is cracked open. There should be care not to go too deep, however, because the heart is in close proximity in the interior of the clam.

Once the clam is cracked open, mantel should be pulled away to view the inhalant and exhalant siphons.

There may be some difficulty in cutting open the tough muscle of the foot to reveal the reproductive organs, stomach, and digestive gland. The intestine is mostly in the foot but partially out of it, and the anus follows it.

Dissection Procedure