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Cardiovascular, Respiratory, & Digestive Systems Lesson for Middle School Biology

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I am a Christian. I was an 8th-grade American History teacher. I am currently a freelance writer, public speaker, & homeschooling mom of 9.

Middle School Biology Lesson on the Cardiovascular, Respiratory, & Digestive Systems

Middle School Biology Lesson on the Cardiovascular, Respiratory, & Digestive Systems

This is the 6th lesson in a series of 32 hands-on lessons covering middle school biology. This lesson covers the cardiovascular, respiratory, & digestive Systems. In this lesson we dissect a heart, use a lung model to learn about the respiratory system, and create a hands-on tour of the digestive system. I used this plan while teaching a 55 minute middle school biology class. Each lesson plan includes homework assignments and a variety of hands-on activities to make each lesson engaging & memorable. Use these fun lessons with your classroom, homeschool, after-school program, or co-op!

These lessons are written for a class that meets once a week. If your class meets 5 days a week, simply do this lesson one day a week and use the homework assignments (at the bottom of the page) for the work for the other days of the week.

Quickly sketching the heart before dissecting it

Quickly sketching the heart before dissecting it

Homework Review & Heart Observation

1. Hand out extra credit tickets to anyone who did the extra credit. Go over the homework questions from the book. (I give out tickets for students who volunteer to answer the questions.)

2. Use a picture to show how your heart is in the middle of your chest, only slightly to the left. What is it protected by? (ribs & sternum).

You will need:

  • a picture or illustration showing where the heart sits in relation to the other organs in your body

3. Have everyone sketch the heart. As they sketch the heart, ask them what they notice. Some things they might note include:

  • "Tubes" going into the heart. These are blood vessels, which is how blood travels to and from the heart. They're like large interstate highways leading to and from a large city. The one in the middle is the aorta, which takes oxygenated blood from the left ventricle to the rest of the body. The superior vena cava brings blood from the top half of the body to the right atrium. The inferior vena cava brings blood from the lowers tissues. (Superior just refers to the upper body and inferior refers to your lower body.) The pulmonary vein brings blood from the lungs into the left atrium.
  • It's covered in "white stuff," which is fat. Why do you think it would have so much fat around it? It provides cushioning. It also provides your ready with a ready supply of energy because your heart needs lots of energy to do what it does.
  • There are blood vessels on the outside. They're called coronary blood vessels and they provide a blood supply for your heart itself as it needs lots of oxygen to do what it does.

You will need:

  • at least 1 heart (either purchased from a site such as for about $5/sheep heart or gotten from a hunter who has recently killed a deer) - In the past I have gotten them from hunters. The heart freezes and thaws out nicely just like a beef steak. This time I bought one for each group of 4 students.
Explaining the parts of the heart before we begin the dissection

Explaining the parts of the heart before we begin the dissection

External Heart Observation

4. Point out the parts of the heart using a diagram like the one above. Share that:

  • Is the left atrium & ventricle on your left? Why not? This isn't your heart. It belongs to the sheep that is facing you. It was the sheep's left side.
  • [Students should put on disposable gloves or at least 1 glove.] Push the right side and the left side. Which one is firmer? (the left) Does everyone agree the left side is firmer? Why do you think that is case? (The left side is stronger because it pumps the blood to the entire body. The right side only has to pump blood to the lungs.) When we cut it open, we'll be able to see a big difference between how thick the left side and the right side are. Which side do you think will be thicker? (the left)
  • Shove your fingers down in the blood vessel openings. What do you feel? What do you think it will look like when you cut it open?
  • Use an item to shove down each of the blood vessel openings. Where do they lead to? (The aorta leads to the left ventricle. The pulmonary artery leads to the right ventricle. The superior vena cava leads to the right atrium.
  • [Pour water into one of the blood vessels.] Have the students gently pump the heart. Where did the water come out of?
  • [Pour water into a different blood vessel.] Have the students gently pump the heart. Where did the water come out of?

You will need:

  • disposable gloves for students (at least 1 glove per student plus more), which are sold at Walmart in the pharmacy section
  • probing items such as a craft stick, pencil, or the handle of a dissection tool
  • a small disposable bottle of water
Dissecting the heart

Dissecting the heart

Internal Heart Observation

5. Allow students to dissect their hearts by cutting open the pulmonary artery. Make sure each group has 1 student willing to cut the heart. If you'd like a step-by-step guide, you can follow the one provided by or you can follow my script below, which came partly from that script and also from the below video:

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  • The heart is a muscle, so it's kind of like cutting up a raw steak. Some people eat hearts. They grind them up into their ground beef or ground venison. You wouldn't want to eat this one, though, because it has chemicals in it to preserve it.
  • Notice the difference in thickness between the left and right sides of the heart. Why again is that the case?
  • Notice the semi-lunar valves, which prevent blood from going backwards from the ventricle into the atrium. When your blood is pumped up, some of it is going to fall back down because gravity still does have an effect on that blood. Those pockets fill up & push together to create a seal which prevents any blood from falling back down.
  • Look for the stringy tendons. They are papillary muscles called chordae tendinae or "heartstrings." Even though they don't look like much, they actually prevent your valves from inverting every time your heart contracts, pushing the blood out of it. Have you ever heard the expression that someone is tugging at your heartstrings? If someone is making your heart beat faster, they really are making your heart pull on those heartstrings a bit harder.
  • Now cut away whenever you'd like. Inspect what you find. After a few minutes I'm going to ask each group to tell us something neat they discovered. [As students cut away at their hearts, I did try to answer questions when they asked me what various parts were.]

You will need:

  • a tray for cutting, such as the dissection tray soldby or a hard plastic disposable plate (the kind used for eating)
  • a dissection knife or scissors such as the dissection scalpel sold by or a kitchen paring knife (which you should only use for dissections after using it for this)
  • a cover for the table, such as a plastic tablecloth or newspapers
Sharing what they discovered during their heart dissections

Sharing what they discovered during their heart dissections

Sharing Heart Dissection Discoveries & Clean Up

6. Allow each group to share something they found of interest while continuing their dissections.

7. Clean up. Students can help wash off tools using soapy water while they wash their hands. Use Clorox wipes if needed on the tables. Throw away the hearts and table coverings. (I more thoroughly cleaned the tools after I got home.)

You will need:

  • soap & water
  • Clorox wipes (optional)
  • a box or plastic bags to hold dissection tools after they've been rinsed
Lung models made from plastic bottles and balloons

Lung models made from plastic bottles and balloons

Respiratory System

8. Discuss the respiratory system: The heart sits between your 2 lungs. Why is it so close to your lungs? What is the main relationship between your heart and lungs? (Your lungs breath in oxygen, & your heart pumps that oxygen throughout your body via the red blood cells. Your lungs also exhale carbon dioxide, which the waste product of your body that is picked up by the red blood cells from the rest of your body & deposited into your lungs to get rid of each time you exhale.)

9. What causes your lungs to inhale and exhale? (your diaphragm) How does it work?

  • Demonstrate using two lung models created ahead of time. Allow students to each have a turn pulling on the balloon diaphragm.
  • To make a lung model, watch the video below or follow my directions: Cut the neck off a balloon & stretch it over the bottom of the bottle (the part that was cut off). Place a second balloon in the open top of the bottle and fold the open part of the balloon over the top of the bottle. If desired, add a straw to the balloon to act as a trachea & hold it in place using play-doh or clay. By pushing and pulling the bottom balloon (the diaphragm), the balloon inside the bottle (the lung) will fill with air and lose air. The plastic water bottle can be compared to the protective rib cage.

You will need:

  • at least 2 working models of a lung as described above
Digestive System Demo

Digestive System Demo

Digestive System

10. In order for your heart and lungs and the rest of your body to work, they need energy and nutrients, which is why we need the digestive system.

  • What body breaks down your food? Most people think the process begins in the stomach, but it actually begins in your mouth.
  • Not only does mechanical digestion begin in the mouth as you chew up your food, but so does chemical digestion. Mechanical digestion is chewing food into smaller pieces.
  • Let the students chew up and swallow a cracker. Chemical digestion is breaking down food into small chemical components so your body can use it.
  • Amylase in your saliva starts to break down the starches in sugars. Have the students suck on a cracker without chewing it. Let it dissolve. Does it taste a little sweeter? You body is breaking down the carbohydrates into a sugar called glucose.
  • Do you think this happens with all foods. Sugar/carbohydrates will dissolve partly in your mouth from your saliva, but proteins like meat and cheese have to be chewed to digest it.

You will need:

  • 2 crackers (such as saltine crackers) per student
Peristalsis demo with a sock (esophagus) and a ball (bolus)

Peristalsis demo with a sock (esophagus) and a ball (bolus)

Esophagus and Peristalsis

11. Discuss how your esophagus works.

  • Ask if anyone has ever laughed so hard that they had milk come out of their nose or if they swallowed something quickly and then had to cough it up because "it went down the wrong pipe." This usually doesn't happen because under normal circumstances after you swallow your food, your epiglottis closes up over your windpipe/trachea that leads down to your lungs and your soft palate lifts up to block the way to your nose. Have everyone use their tongues to feel their soft palate on the roof of their mouth.
  • How do you think food travels down through your esophagus? It's not gravity. If anyone has a bottle a water, get a mouthful of water, touch your toes (so you're upside-down), and swallow your water. Could you swallow the water? Of course! You can still swallow when you're upside-down. Food travels through your digestive system by peristalsis, which is wave-like muscle contractions.
  • Demonstrate peristalsis by putting 1-3 balls in the foot of a long sock and then pushing them down through the sock.

You will need:

  • a few bottles of water (if students don't have them)
  • a long sock (such as a soccer sock or tube sock)
  • 1-3 balls that fits snugly in the sock (such as baseballs)
Chyme in the stomach made using vinegar and crackers and a sandwich bag

Chyme in the stomach made using vinegar and crackers and a sandwich bag


12. Discuss how your stomach works:

  • Your stomach is like a bag that is small but can grow bigger. The inside has lots of wrinkles. [Show a picture of the inside of a stomach.] Why do you think it has all those wrinkles? [Quickly fold up a paper back and forth to make ridges and valleys like a fan-style. Then expand and shrink down the paper.] God created those wrinkles to do this so that they can expand to a large size when you eat an entire pizza and then shrink back down after you'd digested that tasty stuffed-crust pie.
  • [Hold up a sandwich bag that has some vinegar & water in it.] Your stomach is like this plastic bag. When it's empty, it's like this crumpled up bag. [Crumple up the plastic bag.] When food enters it, your stomach unfolds and opens up. [Open the plastic bag & drop in a few crackers.] The stomach also has 2 holes just like the plastic bag. The holes are called sphincters. The one at the top lets the bolus in, and the one at the bottom lets the digested bolus (now called chyme) into the small intestine.
  • Did you notice there's a liquid in this bag? Your stomach lining produces gastric juices, which you've tasted when you threw up. Who knows what I'm taking about? Some of the gastric juices include hyrdochloric acid and protein-digesting pepsin. Not only do the gastric juices further digest the food, but they also kill harmful bacteria so that they don't make you sick.
  • By the way, bases offset acids. Your stomach has acids in it. When you have an upset stomach, it may be due to your stomach producing too much acid. That's why a cup of milk or an anti-acid tablet like Tums, which is high in calcium, might help.
  • [Mash up the crackers] We now have something we call chyme.
  • Remember that I said your stomach has 2 holes or sphincters? One is the at the top and is connected to the esophagus. What is the bottom one connected to? Your small intestine. I'm going to make that second sphincter by cutting a hole in the bottom corner of this bag. Before I open up that second sphincter, I want to show you something.

You will need:

  • a sheet of scrap paper
  • a plastic ziplock bag with about 1 Tbsp. vinegar + 1/4 c. water
  • 5 crackers
Holding a piece of yarn that is 20 feet to show the length of the small intestine

Holding a piece of yarn that is 20 feet to show the length of the small intestine

Length of Your Small Intestine

13. About how long do you think your small intestines are?

  • Ask for 2 volunteers to hold each end of a piece of yarn that is about 20 feet long. You small intestines are about 20 feet long!
  • How does that fit inside your body? It's all wrapped up.
  • Your large intestine is about 5 feet long. Why is your small intestine called "small"? It has a smaller diameter compared with your large intestine. Your small intestine is divided into 3 parts: the duodenum (the first food which is where most of the chemical digestion occurs), jejunum (the next 8 feet), and the ileum. The jejunum and ileum are where most of the nutrients are absorbed into your blood.

You will need:

  • a piece of yarn, rope, or string that is about 20 feet long with a string tied to it to mark the first foot (to show the length of the duodenum) & a string tied to it to make 8 feet later (to show the length of the jejunum)
Small intestine demo using pantyhose or a sock

Small intestine demo using pantyhose or a sock

A duster glove with "fingers" can show what villi would look like

A duster glove with "fingers" can show what villi would look like

Small Intestine

14. Discuss how your small intestines work:

  • Now it's time to open up that sphincter & release the chime into your small intestine. [Cut a hole in the bottom corner of the bag and let the liquid pour into the sock or pantyhose.]
  • Your small intestine absorbs the nutrients after your stomach and pancreas have broken them down. Dump the sandwich bag of chyme into the pantyhose or sock. Your small intestines are lined with villi, which are absorbing the liquids and then distributing the nutrients throughout your body. Again, your food mush is moved through the intestines by peristalsis.
  • The villi are kind of like absorbent fingers. [If you have a duster with fingers, like the one in the photo, you can show it so they can get an idea of what villi would look like.]

You will need:

  • scissors
  • pantyhose or sock
  • a duster with "fingers" (optional)
Large intestines absorbing the water

Large intestines absorbing the water

Large Intestine

15. Discuss the large intestine:

  • What is left moves through the large intestine, where water is removed and whatever is leftover (feces) is stored until you have a bowel movement.
  • Take a few sheets of paper towels and absorb the water from the disposable bowl. This water will go back into your body.
  • What is left will go into the toilet. A trash can will represent the toilet, so I'm putting this bowl and leftover slime in the "toilet."

You will need:

  • a few paper towels

16. (Optional) Pass out miniature Baby Ruth candy bars to represent the feces.

You will need:

  • miniature Baby Ruth candy bars

Looking for More Depth: What We're Reading at Home

A Beka's Science: Order & Design

A Beka's Science: Order & Design


Page numbers refer to the pages in A Beka's Science: Order & Design.

  • Friday: Read pp. 79-83 (skipping Check it Out). Read questions #1-6 on p. 92 & answer 3 questions of your choice.
  • Monday: On a chart list at least 5 types of joints in your body. Describe each joint and list an example. Make a display of real-life objects that resemble at least 2 of these joints. (Hint: Dig through your toys & craft supplies.)
  • Tuesday: Read pp. 84-87 (skipping both Check it Outs). Read questions #7-11 on p. 92 & answer 3 questions of your choice.
  • Wednesday: Read pp. 89-90. Answer questions #12-15 on p. 92.
  • Extra credit #1: Sketch the other half of the skeleton* (*For the skeleton, I folded this skeleton picture in half & photocopied one half of it so they can sketch the mirror image.
  • Extra credit #2: Color the muscles from the Human Muscles Worksheet
  • Extra credit #3: Color, assemble, & wear this Brain Hemisphere Hat

© 2018 Shannon

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