Scientific Method & Blood

Scientific Method & Blood

Scientific Method and Pulse experiment


In this lab you will learn to form a hypothesis, conduct experiments around that hypothesis, and collect and analyze data.

The Scientific Method

The Scientific Method is an organized way that helps scientists answer a question or begin to solve a problem. There are usually six parts to it.

Observation– something you observe in nature. It helps you to understand the problem more clearly and is designed to help you express a problem in a single question.

Question – is used to define the problem or issue you wish to learn more about.

Hypothesis – a predictionor educated guess used to answer the problem. This is usually proposed in the form of a statement. The statement needs to be testable.

Experiment –a tool you design used to test your hypothesis. It is a test or procedure used to find evidence to support or refute your hypothesis.

Analysis –data recorded during the experiment. It may be displayed as a data table, figures, or graphs. Statistics can also be used to determine the accuracy and likelihood that the data support the hypothesis.

Conclusion – This is a summary of the experiment's results, and how those results match up to your hypothesis. Your evidence either supports or refutes your hypothesis.

A few other terms you may need to know:

Independent Variable

This is the part of your experiment that you will test (manipulate) to answer your hypothesis.

Dependent Variable

This is the outcome variable. It is what you measure and what occurs in response to the changing independent variable.


The control should be the part of the experiment where you do not include the Independent Variable.

Pulse Experiment

One of the most important characteristics of modern science is its quantitative approach to solving problems. One of the first scientists to use quantitative methods was William Harvey(1578–1657), who discovered that blood circulated through the body. At the time Harvey began his work, anatomists believed that the liver produced blood from the food that the body consumed. The blood was then carried by veins to the heart, purified in the lungs, and then pumped to the various organs of the body, where it was consumed. Harvey measured that the left ventricle of the heart held roughly 60 ml of blood (convert to ounces ______oz) which is pumped/beat. He also measured that the heart beats an average of 72 times per minute (convert to beats/hour ______b/hr)forcing blood into the arteries with every movement.

Question 1

Harvey’s next question was inspired: How many ounces of blood does the heart pump every hour?


The body on average holds 5.5 liters. Convert to ounces ______.

Finding it impossible to believe that the heart could make such a quantity of blood every hour, he hypothesized that the same blood must circulate continuously throughout the body.Harvey was forced to conclude that the heart does not continually produce new blood but rather circulates or "recycles" it.


Purpose: Determine the effect of standing and breath holding on heart rate.


Watch with second hand, clock, or pulse oximeter


  1. To determine your heart rate at rest, sit quietly and take your pulse.You can find your pulse in your wrist (radial artery)or neck (carotid artery)(see figures below). Place two fingers (index and middle)on the location where you find a strong pulse and count the number of beats for 15 seconds. Then multiply this number by 4 to give you beats/minute. You and your lab partner can do this on yourselves, or each other. If you use the pulse oximeter, place it on the index finger and it will provide immediate results. Record the names of both subjects and their heart rate on DATA TABLE 1.

2. Repeat step 1 two more times for each subject. Record the data in the appropriate place on DATA TABLE 1.

3. Calculate the average pulse rate for each subject and record the results on DATA TABLE 1.


How do you think standing or holding your breath will affect your pulse rate?

Hypothesis 1: Standing will ______raise/lower_____ pulse rate in comparison to sitting at rest. (circle)

Hypothesis 2: Breath holding will ___raise/lower_____ pulse rate in comparison to sitting at rest. (circle)

Define Breath hold: A breath hold is defined as holding breath for 30 seconds and immediately taking pulse. Rest at least 1 minute between breath holds.

Define Standing: From sitting, stand and take pulse immediately after 1 minute of standing.

What is the independent variable (there may be more than one)? What is the dependent variable?

Independent Variable ______

Dependent Variable ______

4. Repeat steps 1, 2, and 3 for each subject, this time with the subjects standing or holding their breath. Record your data and calculations in the appropriate Data Table.

DATA TABLE 1: Heart rate at rest (sitting quietly)
SUBJECT / sample 1 / sample 2 / sample 3
DATA TABLE 2: Heart rate standing (stand for 1 minute)
SUBJECT / sample 1 / sample 2 / sample 3
DATA TABLE 3: Heart rate holding breath (hold breath for 30 seconds)
SUBJECT / sample 1 / sample 2 / sample 3

Conclusion: Compare the data from your experiment to your control

  1. What measurement did you use as a control in this investigation?
  1. How do your results compare with your hypothesis?
  1. What are some possible sources of error in this experiment?