🪱 Earthworm Cardiovascular Investigation

🔗 Why Study Earthworm Hearts?

You've been learning about the human cardiovascular system—a complex network of chambers, valves, and vessels that keep you alive. But what if we could see a simpler version working in real-time? Earthworms have a visible circulatory system that pumps blood through their transparent bodies, giving us a window into cardiovascular function without high-tech equipment.

Key Similarity: Both use closed circulatory systems with muscular pumps that push blood through vessels. The earthworm's 5 aortic arches function like simple hearts, contracting rhythmically to create pulses you can actually see!

📺 Background Videos

Before you begin, watch these videos to understand earthworm anatomy and the observation technique:

🧰 Materials Needed (per group)

🔬 Investigation Procedure

Part 1: Baseline Pulse Observation

1. Prepare your workspace: Clear your lab table surface. If you have a dark background (notebook cover, folder, etc.), place it down to help you see the earthworm's blood vessel more clearly.
2. Obtain your earthworm: Gently remove one earthworm from the soil. Use the dropper to rinse it lightly with water to remove excess dirt. Keep it moist throughout the investigation by adding drops of water as needed.
3. Position the earthworm: Gently stretch the earthworm on your work surface (don't overstretch—just enough to keep it from rolling). Orient it so the anterior (head) end is to your left and posterior (tail) end is to your right.
4. Apply the plastic wrap: Cut a piece of plastic wrap slightly longer than your earthworm. Gently press it down over the earthworm, creating light tension. The wrap should hold the earthworm in place without crushing it.
5. Locate the dorsal blood vessel: Look at the dorsal (top) surface of the earthworm. You should see a dark line running along the length of the body—this is the main blood vessel. The aortic arches are located near segments 7-11 (about 1/3 from the head).
6. Observe the pulse: Watch carefully for rhythmic contractions of the aortic arches. You should see wave-like movements as blood is pumped from the posterior to the anterior end. It may help to dim the lights or use a flashlight at an angle.
7. Count the pulse rate: Once you can clearly see the contractions, count how many pulses occur in 30 seconds. Record this in your data table. Repeat this measurement 3 times and calculate the average.
8. Convert to beats per minute: Multiply your 30-second count by 2 to get beats per minute (bpm).

Part 2: Effect of Vibration (Optional Challenge)

1. Create a vibration stimulus: While keeping the earthworm under the plastic wrap, gently tap the table surface near (but not touching) the earthworm. Use consistent force—about the same as tapping a pen on a desk.
2. Observe and record: Count the pulse rate for 30 seconds during the vibration stimulus. Record this in your data table.
3. Allow recovery: Wait 2 minutes for the earthworm to return to baseline. Count the pulse again to confirm it has returned to resting rate.
4. Return your earthworm: Carefully remove the plastic wrap, use the dropper to add water to re-moisten the earthworm, and return it to the soil container.

� Record Your Data in Your Notebook

Create these data tables in your science notebook:

Part 1: Baseline Pulse Data

Draw a table with 3 columns and 4 rows:

• Column 1: Trial (Trial 1, Trial 2, Trial 3, Average)
• Column 2: Pulses in 30 seconds
• Column 3: Beats per Minute (bpm) - multiply your 30-second count by 2

Collect 3 trials and calculate the average pulse rate.

Part 2: Vibration Response (Optional Challenge)

Create a second table with these rows:

• Baseline (resting) pulse rate
• Pulse rate during vibration
• Pulse rate after 2-minute recovery
• Calculate the change: Did the pulse increase or decrease during vibration?

📝 Written Analysis (3-5 sentences)

In your notebook, write a paragraph describing:

• What you observed during the investigation
• How the earthworm's pulse compared to human heart rate
• Any challenges you faced in counting the pulse
• What you learned about circulatory systems from this activity

💭 Discussion Questions - Write Answers in Your Notebook

Write complete answers (3-5 sentences each) to these questions in your science notebook:

🎯 Learning Objectives & Standards

This investigation addresses the following concepts:

• Structure and Function: Relate the structure of circulatory systems to their function
• Comparative Anatomy: Compare simple and complex circulatory systems
• Homeostasis: Understand how organisms respond to environmental stimuli
• Evolution: Recognize shared features across phyla (closed circulatory systems)
• Scientific Inquiry: Design observations, collect quantitative data, and draw evidence-based conclusions

🚀 Extension Challenges

For advanced students or additional investigation time:

• Size comparison: Compare pulse rates of small earthworms vs. large nightcrawlers. Does body size affect heart rate?
• Graph your data: Create a bar graph comparing baseline vs. vibration pulse rates. Include error bars if you collected multiple trials.
• Research project: Investigate how other invertebrates (insects, mollusks, crustaceans) circulate blood. Create a comparison chart showing open vs. closed systems.
• Calculate cardiac output: Research the approximate blood volume of an earthworm and estimate how much blood is pumped per minute based on your pulse data.
• Video analysis: With teacher permission, record slow-motion video of the pulse and analyze frame-by-frame to identify the exact location of the aortic arches.