Dissection Lab teaching notes

About these lessons

Four lessons of about forty-five minutes each, for middle school life science and high school biology. Students look the frog over, sex it, open the mouth, cut the skin and then the body wall along the lab's lines, pin the flaps back, take out the chest piece, name the organs where they lie, open the heart, take out the digestive tract, and find the kidneys, the reproductive organs and the nerves. A fourth lesson goes to the leg and the nerve and muscle bench.

It is built to stand as an equal assignment for a student who opts out of the real dissection. Many states give a student that choice, and some say what the alternative must be: California's law asks that it take comparable time and effort and not be made harder as a penalty (Education Code 32255.1). So the app keeps the real lab's order, its tools and its mistakes, and the lab sheet is the same kind of sheet the class hands in. It is not offered as a replacement for dissection for the rest of the class; it works well as a pre-lab and for review.

How to read this guide

1. Say what to tell the class, in a sentence or two. Use your own words if you like.
2. Students do the steps, in order. Read them out or put them on the board.
3. On their screens what you should see when you walk round. If a screen does not look like this, that student needs you.
4. If it goes wrong what usually goes wrong at this step, and what to say.
5. Ask the question that tells you whether it landed. Let them show you on the screen.

• Button and tab names are written like this, exactly as they appear in the app.
• Times in a heading, (0 to 10), are minutes into the lesson.
• The Lab tab always shows the current step, what to find in it, and what is left to do. A student who is lost can read it there.

The lessons

Before the first lesson

• Open Dissection Lab yourself and do steps 1 to 6. It takes about fifteen minutes, and you will cut the abdominal vein once by not lifting the wall, which is the mistake your students will make.
• Open Setup and choose: middle school or high school (middle school asks fewer parts and gives a word bank), which optional steps are on (opening the chest, the nerves, the brain, the leg), the specimen (a male, a female, a female full of eggs, or any at random), plain or double injected to match your class's frogs, and the practical. Add your own questions to any step. Then share the project as a starter so every student gets your settings.
• Decide on accounts. The lab runs over several periods, so students need a free account to save it. For a single pre-lab period, no account is needed.
• Print the answer key from Setup > Print the answer key. It shows each question's full answer, built from the same sourced lines the app shows students, and marks paths and measurements right or wrong.

Lesson 1: The outside and the mouth

Students meet the frog the way the bench does: back, then belly, then the mouth. Nothing is cut except the corners of the jaw.

Lesson 1: The outside (0 to 15)

1. Say This is a preserved leopard frog. Before any cut, we look. Touch each part with the probe to find it and read what it is, what it does, and how yours compares.
2. Students do With the Probe, touch the eye, the cloudy third eyelid along its lower edge, the round eardrum behind the eye, the nostrils at the tip of the snout, the limbs, and the opening at the back end. Press Turn over to see the belly.
3. On their screens A card for each part, and the step's list filling with names. The strip under the tray counts what they have found.
4. If it goes wrong Nothing happens when they click: the probe finds a part only where it is touched. The cloacal opening is small and on the back end, between the legs.
5. Ask Where is the frog's eardrum, and where is yours?

Lesson 1: Male or female (15 to 22)

1. Say Real frogs are not labeled. You decide, and you say what you saw.
2. Students do Look at the first finger of each hand for a dark swollen pad. On the Lab tab choose male, female or can't tell yet, and tick what they saw.
3. On their screens Step 2 marked done once an answer is chosen. Can't tell yet is a real answer: the sheet asks again after the kidneys and reproductive organs are found.
4. If it goes wrong Students guess without looking. Ask them to point at the evidence before they choose.
5. Ask What evidence would change your mind later in the lab?

Lesson 1: The mouth (22 to 40)

1. Say The mouth opens the way it does at the bench: two snips at the corners of the jaw.
2. Students do Press Close up on the head, take the Scissors, and snip each corner on its mark. Press Look in the mouth. Find the tongue, the teeth on the upper jaw, the two patches on the roof, the holes beside them, the openings near the corners, the slit behind the tongue and the opening at the back.
3. On their screens The roof above and the floor below, like a lab sheet's drawing. The tongue is fixed at the front.
4. If it goes wrong The mouth will not open until both corners are snipped. A snip off the mark does not count.
5. Ask Where is the frog's tongue attached, and why does that help it catch food?

Lesson 1: Close (40 to 45)

1. Say Open the Sheet tab. Answer the questions for steps 1 to 3 in a sentence each.
2. Students do Type the answers. They save with the lab.
3. On their screens The sheet's first three sections, with the parts found listed.
4. If it goes wrong A blank answer stays blank on the printed sheet.
5. Ask What did you see that you did not expect?

Lesson 2: Opening the frog

The cuts. Skin first, then the body wall, each lifted before it is cut. This is where students learn that a cut has a depth.

Lesson 2: Pin it, cut the skin (0 to 15)

1. Say Pin the frog belly up through each arm and leg. Then cut the skin only. Lift it with the forceps first, then cut along the lines.
2. Students do With Pins, pin the four limbs. With Forceps, click the skin where a line starts, then with Scissors drag along the line: down the middle, across at the arms and across at the legs. Drag each flap outward with the forceps and pin it. Touch the inside of a flap with the probe.
3. On their screens Two flaps pinned back, their inner sides full of fine vessels.
4. If it goes wrong A cut made without lifting nicks the muscle under it; the message says so and offers Undo. A flap will not open until all three of its cuts are made, and it says which one is missing.
5. Ask Why is the inside of the skin so full of blood vessels?

Lesson 2: The body wall (15 to 30)

1. Say The same pattern through the muscle. The dark line down the middle is the abdominal vein. Cut beside it, not on it.
2. Students do Lift the wall with the forceps, cut along one of the two lines beside the vein, then across at the arms and the legs. Open and pin both flaps.
3. On their screens The organs showing through the window. The vein lies on one of the folded flaps: the one across from the cut.
4. If it goes wrong A cut down the middle cuts the vein. That is the most useful mistake in the lab: let it happen, let them undo it, and point at the log.
5. Ask Why do the handouts tell you to cut beside the middle line?

Lesson 2: The chest (30 to 40)

1. Say The heart is under the chest bones. Hold the chest up, then cut through the girdle at each arm and across the top.
2. Students do Forceps on the chest, scissors along each of the three lines, then drag the chest piece out with the forceps. It goes to the Side dish.
3. On their screens The heart and the tops of the lungs uncovered.
4. If it goes wrong A cut not held up goes into the heart or a lung.
5. Ask What were the chest bones protecting?

Lesson 2: Close (40 to 45)

1. Say Press the cuts-undone count in the strip. That is your log, and your teacher sees it.
2. Students do Read the log.
3. On their screens Each cut that went through something, and whether it was undone.
4. If it goes wrong Students worry the log counts against them. It does not: it is what happened, said plainly.
5. Ask Which mistake taught you the most?

Lesson 3: The organs and the heart

Students name the organs where they lie, lifting what covers what, then open the heart and take out the digestive tract.

Lesson 3: The organs in place (0 to 18)

1. Say Some organs hide under others. Click an organ with the forceps to lift it aside, and again to put it back.
2. Students do In a female full of eggs, snip each ovary free along its inner edge and drag it out first. Then find the fat bodies, the liver, the heart and lungs, the stomach and the small intestine. Lift the liver for the gallbladder, the stomach for the pancreas, the coils for the spleen and the large intestine.
3. On their screens The step's list filling; lifted organs drawn aside with a shadow.
4. If it goes wrong The lungs of a preserved frog are flat and partly under the liver; students take the liver for lungs. The pancreas is thin and easy to miss.
5. Ask What did you have to move to find the gallbladder?

Lesson 3: The heart (18 to 30)

1. Say Press Heart. The heart is in a thin sac. Hold it up, snip it, and name the chambers.
2. Students do Forceps on the sac, scissors down its line. Find the two atria, the ventricle, and the tube that leaves the ventricle. At high school, click the tip of the heart with the forceps to turn it up and find the sinus venosus on its back.
3. On their screens The heart opened, then its back.
4. If it goes wrong A snip not held up goes into the ventricle.
5. Ask How many chambers does the frog's heart have, and how many does yours?

Lesson 3: Take out the digestive tract (30 to 42)

1. Say Only when everything in step 9 is found. Once it is out, it is out.
2. Students do Lift the liver and snip the esophagus above the stomach; lift the bladder and snip the large intestine above the cloaca; drag the tract out. In the Side dish, cut the stomach open and look at the last meal, then drag the small intestine to uncoil it along the ruler and measure it. Measure the frog snout to vent on the tray.
3. On their screens The tract in the dish, the stomach open, the intestine stretched in rows along a ruler.
4. If it goes wrong The tract refuses to come out until step 9 is done, and says so.
5. Ask How many times longer than the body is the intestine?

Lesson 3: Close (42 to 45)

1. Say On the sheet, put the stops of a bite of food in order.
2. Students do Touch the chips in order.
3. On their screens The path, numbered.
4. If it goes wrong A wrong stop can be taken back by touching it.
5. Ask Where does digestion start in a frog, and in you?

Lesson 4: Kidneys, nerves, the leg and the Bench (optional)

The back wall of the body, the nerves, and the calf muscle and its nerve, which the Bench then runs.

Lesson 4: Kidneys and reproductive organs (0 to 12)

1. Say With the digestive tract out, the kidneys lie against the back wall.
2. Students do Find the kidneys, the testes or the ovaries and oviducts, and lift the bladder to find the cloaca. Answer the sex question on the sheet again, with the new evidence.
3. On their screens The back wall: the dark kidneys, the white oviducts along the sides in a female.
4. If it goes wrong Students say the oviducts make eggs, which one well-known handout also says. The ovaries make them; the oviducts carry them.
5. Ask Do you still agree with what you said about the sex of your frog in lesson 1?

Lesson 4: The leg (12 to 22)

1. Say Press Leg. Skin it the way the bench does, then part the thigh muscles.
2. Students do Hold the skin up, cut around the top of the thigh and down the leg, peel it off. Click the thigh muscles with the forceps to part them: the sciatic nerve and the femur lie between. Lift the calf muscle for the bone of the lower leg.
3. On their screens The muscles of the leg, the white nerve splitting above the knee.
4. If it goes wrong Nothing between the muscles until they are parted.
5. Ask What does the calf muscle do in a jump?

Lesson 4: The Bench (22 to 40)

1. Say This is a simulation of a classic experiment: the sciatic nerve and calf muscle on a stand, stimulated. Its numbers are typical shapes from teaching data, so read them as about.
2. Students do On the Bench tab, raise the voltage from zero until the muscle twitches; send two pulses close together; send trains at 5, 10, 20 and 30 a second. Then run the program, which does the whole ladder and fills a table.
3. On their screens A single twitch, then twitches that add up, then a smooth plateau.
4. If it goes wrong Students push the voltage to the top and see nothing new. Ask what changed between 10 and 30 pulses a second.
5. Ask Why does the force stop rippling at high rates?

Lesson 4: The practical (40 to 45)

1. Say Open Practical. Each station is a frog with a pin in one part. Name it.
2. Students do Name each station before the timer runs out.
3. On their screens Station by station, then a score; in practice mode, the answer after each.
4. If it goes wrong A test hides the search box and shows nothing until the end.
5. Ask Which part did you mix up, and with what?

The fetal pig

The same app has a fetal pig, near birth and about 25 cm long. Press New specimen and choose a fetal pig, or choose it in Setup before students start. It has ten steps and the same tools, sheet, practical and log. Three lessons of about fifty minutes take a student through it; the pig has no Bench.

Pig lesson 1: The outside, the mouth, tie it (0 to 50)

1. Say Look before you cut. Find each part with the probe, then turn the pig over and find the umbilical cord. What tells you whether it is male or female?
2. Students do Touch the ears, eyes, snout and a foot: count the toes. Turn over, touch the cord and a nipple. In step 2 choose male or female and tick what they saw. Close up on the head, cut back from each corner of the mouth on the marks, then Look in the mouth. Back on the tray, take Ties and touch each leg. At high school, press Cord to find the three vessels and the allantoic duct in the cut end of the cord, and Face before tying it: hold the cheek's skin up, cut round it and peel it back for the salivary glands.
3. On their screens The pig belly up with a string round each leg.
4. If it goes wrong Students call both sexes female because of the nipples. Both sexes have them: the sign is the opening just behind the cord in a male, or the small papilla below the anus in a female.
5. Ask What are the three vessels in the cut end of the cord?

Pig lesson 2: The abdomen (0 to 50)

1. Say Skin and muscle are cut together. Hold the wall up with the forceps before every cut. Behind the cord, the cuts run beside the middle, not on it.
2. Students do Forceps where a line starts, then Scissors along it, for every line on the belly. Drag each side flap outward. Find the vein running from the cord up into the liver and snip it on its short line, then drag the cord's flap back between the hind legs. Name the organs, clicking the liver, the stomach and the coils with the forceps to lift them.
3. On their screens The abdomen open, the cord's flap folded back, the bladder between two red or dark vessels.
4. If it goes wrong The cord's flap will not move: the message names the umbilical vein still holding it. A cut on the middle behind the cord goes through a male's penis; Undo is there, and the log keeps it.
5. Ask What was holding the cord's flap down, and where does that vessel lead?

Pig lesson 3: The chest, the heart, the back wall (0 to 50)

1. Say Now the chest and the neck. The throat is only skin: hold it up, or the cut goes into the thymus.
2. Students do Cut up the sternum, across the front of the chest, up the throat and across under the chin, then open the four flaps. Find the thymus, thyroid, larynx, trachea and lungs. Press Heart, snip the sac held up, name the four chambers, the aorta, the pulmonary trunk and the short ductus arteriosus between them; click the tip to see the venae cavae on the back. Back on the tray, lift the liver and the coils, snip the esophagus and the rectum on their lines, drag the tract out, and cut the stomach open in the Side dish. Then the kidneys and the reproductive organs. At high school: click the thymus with the forceps to see the carotid arteries and jugular veins; open the heart by cutting round its edge to find the foramen ovale; draw the small intestine out in the dish for the jejunum and ileum; then press Pelvis, hold the pubic bone up and cut it down the middle for the urethra and the organs around it.
3. On their screens The back wall with the kidneys, and the stomach open in the dish.
4. If it goes wrong Students mix up the thymus and the thyroid. The thymus is large, pale and on both sides of the windpipe; the thyroid is small and dark between them. A cut through the cheek's skin or the pubic bone that is not held up goes into the salivary glands or the urethra under it.
5. Ask Why does an unborn pig need a vessel that lets blood skip its lungs?

The cow eye

The same app has a preserved cow eye. Press New specimen and choose a cow eye, or choose it in Setup. It has six steps and the same tools but the pins, the same sheet, practical, log and printables. One lesson of about forty-five minutes takes a student through it.

1. Say Look at the eye from the front and the back before any cut. What is the cloudy window at the front, and what leaves the back?
2. Students do Find the cornea, the white sclera, the fat and the muscles, then Turn over for the optic nerve. From the back, snip the fat and muscles close to the white of the eye and drag them away. Press Side, make a small slit with the Scalpel on the line, then cut round the middle with the Scissors. In Both halves, drag the vitreous out, click the retina with the forceps to lift it, and find the optic disc and the shining tapetum under it. Drag the lens to the Side dish and look at the print under it. Last, Front half: cut the cornea off for the iris and the oval pupil.
3. On their screens The back half with the retina lifted aside and the blue-green tapetum showing.
4. If it goes wrong The scissors will not start the cut round the middle: the white of the eye is too tough, and a scalpel slit has to come first. A trimming snip into the optic nerve is in the log.
5. Ask Why do a cow's eyes shine in a flashlight beam at night, and yours do not?

The earthworm

The same app has a preserved earthworm, Lumbricus terrestris, the specimen most middle school classes open first. Press New specimen and choose an earthworm, or choose it in Setup. It has eight steps with the same tools, sheet, practical, log and printables. One lesson of about forty-five minutes takes a student through it.

1. Say An earthworm has no bones, no lungs and no eyes. Before any cut: which end is the head, and which side is the top? How can you tell?
2. Students do Find the prostomium, the segments, the clitellum and the anus, then Turn over for the flatter underside. Press Pores close up, find the setae and count the segments to the clitellum, then the female pores on segment 14 and the male pores on segment 15. Pin the worm top side up, one pin near the head and one behind the clitellum. Press Front end, hold the body wall up with the Forceps and cut along the line with the Scissors, just beside the middle. Click the wall with the forceps to spread it, name the organs from the head back, then lift the intestine for the nerve cord underneath.
3. On their screens The front end opened, the body wall spread to both sides, the five pairs of aortic arches around the esophagus and the gizzard behind the crop.
4. If it goes wrong A cut that is not held up, or goes too deep, goes into the gut, and a cut on the middle splits the dorsal blood vessel. Both are in the log. The front end will not open until the worm is pinned top side up.
5. Ask The worm has five pairs of aortic arches and no single heart. What does each part do that your heart does in one place?

The sheep heart

The same app has a preserved sheep heart, close to a person's heart in size and layout. Press New specimen and choose a sheep heart, or choose it in Setup. It has six steps with the same tools but the pins, and the same sheet, practical, log and printables. One lesson of about forty-five minutes takes a student through it.

1. Say Hold your fist up: your heart is about that size. Before any cut, which side of this heart is its left? It is facing you, so its left is on your right.
2. Students do Find the apex, the two auricles and the slanting groove with the coronary vessels in its fat, then Turn over for the back. Name the big vessels: the pulmonary trunk at the very front, the aorta behind it, the venae cavae and the pulmonary veins. On the front, cut with the Scissors along the line from the cranial vena cava down the right side, press Right side, and find the tricuspid valve, its strings and the papillary muscles. Hold the pulmonary trunk up with the Forceps, cut up it, spread it, and find its valve. Then the left side from the back, and up the aorta the same way.
3. On their screens The two opened sides: the thin wall of the right ventricle and the left wall, several times thicker, each folded out along its cut.
4. If it goes wrong A cut across the groove goes through the coronary vessels, and a vessel cut that is not held up cuts the valve under it. Both are in the log.
5. Ask Why is the left ventricle's wall so much thicker than the right's? Where does each one send its blood?

The lab sheet and the practical

• The Sheet fills in as students work: the parts found in each step, their first guesses if name it first is on, and the questions for each step. Paths and measurements are checked by the app; sentences are yours to grade, and the answer key gives a full answer for each, built from the app's sourced lines.
• Hand it in marks the sheet handed in; a student can take it back to change it. Print my sheet prints it, with the log line at the end and the practical's score.
• The log line is what happened, not a score: the cuts undone and what they went through, any damage left in place, a new specimen started, and any change to the setup made once the lab was under way.
• The practical's stations move each time unless Setup fixes them for everyone. Middle school names from a word bank; high school types, with spelling slips counted right unless you turn that off.

• Time on task: the sheet's log line gives the minutes worked, and the printed sheet a table by step. A click or key counts as work; a gap of more than two minutes is a break and is not counted. Useful where an alternative has to take comparable time.
• The printed sheet shows the student's own specimen as they left it, with a numbered marker on every part they found, and the heart once its sac is open.
• Hints: beside a step's parts still to find, a hint names the next one and says where it lies, without pointing at it. Each hint is in the log.
• Assisted cutting, in Setup: for a student whose plan asks for it, a click on a dashed line makes the whole cut, held up first. The order and the lines are still the student's to choose; only the drawing goes. The log marks each assisted cut.
• In Setup, Print a label-the-diagram worksheet prints a whole specimen of the lab's animal, sex and level, numbered, with blanks; Its key has the names. Good for a quiz, a review, or a student without a device that day.
• Also in Setup, Print the practical on paper prints the class's stations, one picture each with its numbered pin, three to a row; its key names each part.

Where the app differs from a common handout

• Oviducts carry eggs; the ovaries make them. One widely used handout says the oviducts are where eggs are produced.
• The skin is an important gas exchange surface. One handout calls it the major organ of gas exchange, which overstates it for an adult frog.
• The abdominal vein: handouts disagree on which side of it to cut. The app accepts either side and only marks a cut through the vein itself.

Where to go next

• Students who finished early: the Bench program box takes sentences like "When I press Stimulate, send 2 pulses 50 ms apart at 1 V", and Show as Blocks turns it into blocks.
• A study partner: the Practical tab's own stations, one line a station, like "pin the spleen and ask what it does".

More help

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