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FROG DISSECTION PRE-LAB
Why are we dissecting a frog?
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Frogs and humans are vertebrates (having a backbone or spinal cord)
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and they have very similar organ systems. Although all of the internal
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organs are not exactly the same, it is helpful to learn about anatomy through dissection. We will be
looking at several body systems and exploring the individual organs of the frog. We will be making
comparisons between the frog and yourself.
Some individuals argue that dissecting a frog is cruel. Dissection would be a cruel practice if the frogs
were mistreated. The frogs that we use in lab for our dissection were bred in Mexico for the sole
purpose of scientific study. The companies use a very safe preservative to make the frogs as safe as
possible. The frogs we are using in class have been prepared for dissection – all blood has been
drained from their bodies. We still need to wear gloves and wash our hands while working with the
frogs.
Computers can be used to simulate a dissection. This method is very popular with some students. I
do not believe that the computer experience is anywhere near as valuable as the actual dissection, but
I do think it is a good tool for preparing you for what you’ll see and experience. We will complete a
“virtual dissection” to help us prepare for our actual dissection.
The frogs we use gave their lives for science. They are “organ donors” who would like us to learn
more about them (and ourselves). In order to best use this opportunity to learn and show respect for
the frog, we must follow all instructions, including written directions and verbal instructions from the
teacher, and safety procedures. For our safety, we will wear gloves and goggles during the dissection.
Aprons are available. EVERYBODY must wash their hands before they leave the room. Hair must be
tied back. No gum chewing or eating at all.
1.
Why are we dissecting a frog?
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Characteristics of amphibians
Amphibians are cold-blooded vertebrates of the class Amphibia. They typically live on land, but breed
in water. Their aquatic larvae (tadpoles) undergo metamorphosis into the adult form. Amphibia
includes newts, salamanders, frogs, and toads. Because frogs’ eggs are not in a shell, they must
develop in a wet environment. Most amphibians do not have scales. Their skin is thin, smooth, and
moist. They do not drink water! Instead, they absorb it through their skin. This is a major reason why
most amphibians prefer to live in damp environments (or near water). Amphibians can breathe
through their lungs or through their skin.
Ecological Indicators
Amphibians are often called ecological indicators. When large numbers of amphibians begin to die or
show deformities, this may indicate a problem with the environment. Sometimes, deformities are
caused by other living organisms. Frogs are good ecological indicators because their skin is
responsible for gas and water exchange which makes them extremely sensitive to changes in air and
water quality.
2.
Frogs are amphibians and do not drink water. How do frogs get their water?
3.
Why are amphibians considered to be a good ecological indicator?
Virtual Frog Dissection
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Go to my homepage and click on the 7th Grade Life Science tab. Click
on the link for Virtual Frog Dissection.
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Below you will find questions organized by section. Use the website above to answer the following
questions. This includes an audio virtual lab. You must wear your headsets and keep them at an
appropriate level (no one else should be able to hear what you are hearing).
Introduction
Click on Introduction and answer the following questions. To move forward, click on the blinking
arrow at the bottom of the page. When you are done with a section, the arrow will no longer blink
and you can click on the appropriate link on the left side of the screen.
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4.
Why dissect? Why are frogs a good model to use when studying the digestive system (as well
as other systems)?
5.
Natural History. Frogs and humans are both vertebrates. What does this mean they both
have?
6.
Dissection Tools. Complete the chart below (you may pause the video after each tool in order
to accurately complete the chart).
Name of Tool
Purpose of Tool
Dissecting Pan
Pins
Scissors
Probe and
Tweezers
REMEMBER: Click on MENU at the bottom of the page to move to the next section. Watch for the flashing .
External Anatomy
7.
Orientation. Is it possible to tell if a frog is male or female by external appearance?
8.
Skin. What does the mucus do for the skin?
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9.
Head. Where are the frog’s eyes located and what are the benefits of this location?
10.
Head. Where are the tympanic membranes and what do they do? Do frogs have pinna?
11.
Cloaca. What materials pass through a cloaca.
12.
Legs. How many hind-leg toes does a frog have? What do the hind-legs help the frog do?
Internal Anatomy
13.
The Initial Cut. Are you supposed to push the pins in at an angle or straight down? What is the
benefit of pushing the pins in this way?
14.
The Initial Cut. Describe the first cut you will be making. Include where you will be cutting and
how deep. (Note: Our frogs do not have a slit.)
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15.
The Initial Cut. Why are there so many blood vessels in between the skin and muscle layers?
16.
Digestive System. Which organ is the pancreas located closest to?
17.
Digestive System. The movie asks you to remove the intestines. What other organ(s) is/are
removed with the intestines when you click on the tweezers?
18.
Respiratory System. What does the skin do in frogs that it does not do in humans?
19.
Respiratory System. Where are the lungs located in a frog (relative to the heart)?
20.
Circulatory (Cardiovascular) System. How many chambers does a frog’s heart have?
21.
Circulatory (Cardiovascular) System. What is a frog’s heart missing when compared to a
human’s heart (what chamber)?
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22.
Circulatory (Cardiovascular) System. Why is the three-chambered heart not as efficient as a
four-chambered heart?
23.
Reproductive System. In your own words, describe where the testes are located?
24.
Reproductive System. In your own words, describe where the ovaries are located?
25.
Excretory System. What happens to blood that enters the kidneys?
26.
Excretory System. What organ connects the kidneys to the (urinary) bladder?
27.
Nervous System. This video is long and parts have no sound. Please watch patiently. What
makes up a frog’s nervous system?
28.
Muscular System. The upper leg muscles in a frog are responsible for moving which part of the
frog’s body?
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29.
Skeletal System. How many bones are found in the axial region?
30.
Skeletal System. How many bones are found in the appendicular?
Follow-Up
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After you are done with the website portion of this pre-lab, complete
the following questions.
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31.
What is the purpose of this lab?
32.
What will we be doing during this lab to stay safe?
33.
Sketch the pattern of where you should cut to make the first
incision of your frog (cut through the integument). Draw directly
on the picture to the right.
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After you have reviewed the dissection site above, you may view any of
the following in any order you want. They are all set up as links on my
webpage.
1.
Teacher-guided video of a dissection of a rat. Rats are mammals
like humans.
2.
Colossal squid. Here you can view virtual info as well as real
photos and videos. Warning: The “Play Anatomy Interactive” is the most interesting part of
this site, but it takes a very long time to load. Be patient.
3.
Pig heart dissection video. Guides you through the dissection of a pig heart. There is blood in
this video. Great review of the heart and its chambers.
4.
Fetal pig dissection pictures. This page contains photos that are labeled with the organs they
are showing.
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