Defense Department

Defense Department

Learn how the immune system helps humans and animals fight off illnesses.

About Supplies Activity Steps Test Your Knowledge Reflection Questions Investigate & Explore Related Activities Shop 4-H Home Support Corporate & Foundation Support Defense Department

About the Activity

This fun and educational activity will show kids how the body’s immune system works and how it protects animals and humans against sickness. Plus, there’s candy involved, so it should be a hit.
This is the first in a four-part educational series about preventing and treating illness in animals. View all activities at 4-H Veterinary Science: Stopping SicknessGrades: 6-8
Topic: Animal Science
Estimated Time: 60 minutes Supported by the Agriculture and Food Research Initiative, Education and Workforce Development Program.

gray and white cat

These simple materials will get you started.

  • A pencil or pen
  • Internet access to research the immune system
  • A bag of M&Ms, jellybeans or other multi-colored candy
  • A calculator
  • The downloadable activity guide with information on immune systems
supply list icon

Activity Steps
Follow these steps to complete the activity.

Before we start, think about this: Having a fever is not fun, but when you – or an animal – are sick, it’s a good sign. That’s because fevers “turn on” the immune system, helping the body fight infection. So you may feel sick when you have a fever, but that’s because your body is working hard to protect itself! 

  1. To start, read through the downloadable activity guide, glossary, and information about the immune system. There’s some pretty amazing stuff in there.Did You Know? Lymphocytes are white blood cells that support your immune system by attacking pathogens (any microorganism that can cause sickness in your body). They are found in the bloodstream and lymph nodes. Erythrocytes are red blood cells that carry oxygen from the lungs to the body’s tissues.
M&M's Read More
  1. Now it’s time for M&Ms! Open your bag of candy and sort the pieces according to color. Put the color group with the most pieces at the top of your working area; put the group with the second-most pieces below this, and continue until the group with the fewest pieces is at the bottom.Note: A typical bag of M&Ms has six colors in it, so if you don’t have enough different colors to do all eight of the blood cell types, that’s fine, the basic idea is still the same.
  2. Count the total number of “cells” you have and record this number.
  3. Assign a blood cell type name from the list in the matching activity to each color of candy.
  4. Finish performing your Complete Blood Count by counting the number of each color candy, then calculating the percent of each type of “cell.” The total of all candy percentages should equal 100.Tip: To calculate a percentage, divide the number of a specific color candy by the total number of cells. Then multiply that by 100 to convert that decimal to a %. For example, if you have 10 red pieces of candy and 36 total pieces, you would calculate the percentage as 10/36, which equals 0.27. Multiplied by 100, you get 27.7, and that’s your percentage of red candies: 27.7%
  5. Record your results in the corresponding table, then refer to the Normal Blood Count chart for different animals. Based on your totals, do you have a healthy level of blood cells for a cat? For a dog? For a cow?Tip: A cat has 6-20 white blood cells (x1000); a dog has 6-17; and a cow has 4-12.

Test Your Knowledge
See how much learned about the immune system and find great activities to try next!


[tqb_quiz id=’59118′]

Reflection Questions
Questions to deepen wonder and understanding.

  1. How does the immune system protect us against diseases?
  2. What diseases have you been vaccinated against?
  3. How can you better protect your pets or animals (if you have any) against diseases?
lightbulb icon

Investigate and Explore
Take what you’ve learned to the next level to learn more and explore the possibilities.

Humans have been studying blood for a long time. The invention of the compound microscope in 1590 made it all possible, and less than a century later the Dutch scientist Jan Swammerdam was the first person to observe red blood cells under the microscope, in 1658. Over the centuries we’ve learned a lot about how the different kinds of blood cells drive the immune system, helping it to protect the body by fighting off illnesses. And science has progressed to help the immune system support itself with the evolution of medicines and vaccines.

girl in a blue shirt with a microscope Read More

Vaccines are injections that contain the same germs that cause a disease but have been weakened so they can’t make the body sick; instead, the immune system is stimulated to produce antibodies against the vaccine and, in turn, develops immunity against the disease the vaccine was created against.

The first vaccine was used in 1796 to provide protection against smallpox, but the story of vaccines began long before that. There’s evidence to suggest that the Chinese employed smallpox inoculation – not by vaccine, but by exposing a healthy person to a smallpox scab – as early as 1000 CE. Explore more about the history of vaccines here.

There are all kinds of diseases that used to be common that, thanks to vaccines, we don’t have to worry about anymore, including polio, measles, and smallpox.

4-H'er with his project sheep

Up Next: Biosecurity Dominos

Now that you understand how the body’s immune system helps fight illness, learn how illnesses can spread and how to prevent it in the next activity, Biosecurity Dominos.

View Activity

Related Activities

If you enjoyed these activities, you can find more animal science activities on 4-H at Home.

butterfly on a yellow flower

4‑H Pollinators

STEM, Animal Science, & More Pre-K-10 Learn more about pollinators as you make simple and fun crafts with supplies you have at home.
Click Here girl with healthy vegetables from her garden

4‑H at Home Activity Guides

STEM, Crafting, & More Grades Pre-K-12 Download over 100 activities to help kids continue doing and learning all year long.
Click Here

Classify Animals

Animal Science Grades Pre-K-6 Learn how to classify animals!
Click Here animal tracks in mud

Signs of Wildlife

Agriculture & Animal Science Grades Pre-K-12 Learn how to identify signs of wildlife without actually seeing the animal!
Click Here 4-H youth with farm animals

Animal U

Animal Science Grades 3-12 Explore 85+ lessons in beef, swine, and more to learn about the science behind livestock production.
Click Here

Shop 4-H Curriculum and Products

Shop 4-H offers university-backed STEM curriculum, educational kits, products and supplies to help you continue exploring animal science and more!

Click on the tiles below to learn more and add items to your cart.

From Airedales to Zebras Veterinary Science curriculum from Shop 4-H

From Airedales to Zebras

Grades: 3-5 Introduces youth to the normal animal, basic anatomy and systems, elementary principles of disease and careers with animals. $5.75

  Veterinary Science curriculum set of 4 from Shop 4-H

Veterinary Science Set of 4

Grades: 3-12 The full set of Veterinary Science curriculum includes beginner through advanced levels and the accompanying helper’s guide. $19.50

  Animal Behavior curriculum digital download from Shop 4-H

Animal Behavior Digital Download

Grades: 9-12 Designed to be facilitated in small groups, activities cover animal care concepts and issues in biomedical research and food safety. $7.50

  Horse Science curriculum set of 2 from Shop 4-H

Horse Program Set of 2

Two of our most popular and time-tested guides that include scientific and practical horse information. Set includes one copy each of Horse Science and Horses and Horsemanship.

  All About Dogs curriculum from Shop 4-H

All About Dogs

Grades 3-8 Learn how dogs think and the meaning behind their body language, how to keep dogs happy and healthy and  the roles they play in our lives. $8.95

  Dog curriculum set of 4 from Shop 4-H

Dairy Goat Set of 4

Grades: 3-12 The full set of Dairy Goat curriculum includes beginner through advanced levels and the accompanying helper’s guide. $19.50


View the full collection of Animal and Agricultural Science curriculum on Shop 4-H.

Visit Shop 4-H

Brought to you by:

United States Department of Agriculture logo

This work is supported by the Agriculture and Food Research Initiative, Education and Workforce Development Program, grant no. 2021-67037-33376/ Project Accession No. 1024940, from the U.S. Department of Agriculture, National Institute of Food and Agriculture.

Learn About 4‑H Clubs in Your Area

Contact your local 4-H office to learn more about the great virtual and in-person programs and clubs available near you!

FIND YOUR LOCAL 4-H 4-H'er with sheep

Help 4-H Provide Equal #Opportunity4All Kids

Donate Now defense-department-hero-1920×462|defense-department-mobile-700×750|defense-department-mobile-700×750|mandms-576×432|girl-microscope-576×432|cat-576×432 In this 4-H at Home animal science activity, kids learn how the immune system helps humans and animals fight off illnesses. 60 marker s:2:”N;”; s:2:”N;”; s:2:”N;”; s:2:”N;”;