Thank you for your feedback!
AbstractSauerkraut, pickled fish, pickled vegetables, kimchi, corned beef, processed cheeses, smoked lunch meats. Do you like these high-salt foods? What about your grandparents, do they? Do your grandparents seem to like most foods to be a bit saltier than you do? Try this science fair project if you want to find out more about the incredible, edible rock known as salt, and why people vary in how much of it they like to eat.
To determine if people older than age 60 have a higher threshold of sensitivity to detecting salt than people younger than age 30.
Has this situation ever happened in your family? You're all seated around the dinner table in front of steaming plates of food. One person tastes his meal and says, "Could you please pass the salt?" While another person says, "Oh, this is so delicious! Perfect!" Everyone has a different ability to detect a salty taste, one of the five tastes that humans can sense. On top of that, everyone prefers a different level of saltiness in foods, often based on past exposures to levels of salt. If you're cooking for a crowd, this can make getting the level of saltiness "just right" tricky, if not impossible!
Taste is a complex experience. Humans can sense fives tastes: salty, sour, sweet, bitter, and savory (or umami). Sensing is done through receptor cells in taste buds on the tongue. There is genetic variability in the number of taste buds, but many people have about 10,000 of them. The receptor cells transmit signals to the brain. The experience of taste comes from these signals, combined with other information about a food's texture, viscosity, mouth feel, appearance, and aroma, as well as a person's appetite, cultural traditions, and past encounters with the food. It's no wonder there are such strong and differing feelings about which foods taste good!
A basic liking for a salty taste seems to be something humans are born with, probably because salt is essential to survival. Humans, like all animals who evolved from creatures that started in the sea, carry a small piece of the ocean inside their bodies. That bit of oceanlike water is located in the fluid in the space around cells and in the plasma, the fluid part of your blood. Plasma is kind of like the broth in a soup. It is the medium that carries proteins, carbon dioxide, clotting factors, hormones, red and white blood cells, and mineral ions all throughout your body. The mineral ion, sodium (Na+), in the plasma comes from the salt (NaCl) that you eat in your food. That sodium is what makes your blood, sweat, and tears taste slightly salty.
Sodium is vital for many body processes, like transmission of nerve impulses, muscle function, and regulation of blood volume. Many animals, including humans, must take in a small amount of sodium each day to replace the sodium that is lost through sweat and urine. The amount of sodium is kept in balance inside your body through your kidneys, which regulate how much sodium is excreted. If you take in too much sodium, for example, then your kidneys will increase the amount of sodium excreted to avoid an excessive increase in blood volume, fluid retention, and swelling (called edema).
Wild herbivores, like deer, who eat a completely plant-based diet, have to supplement their diet with salt to get the sodium they need. These animals find salt in brine springs, or in natural outcroppings of salty rock, called salt licks. Wild carnivores, or animals that eat only meat, do not have to eat salt. Their sodium needs are met through the flesh and blood that they eat. In human history, salt became highly valued as people developed farming and ate more grains and vegetables. Even when diets were supplemented with the meat of domesticated farm animals, the meat was not enough to meet all the sodium needs, so the rock known as salt became like gold! Somehow, people knew that they needed it, and that their domesticated farm animals needed it too (actually, in amounts 5-10 times that of the people). People learned that salt was an amazing preservative for their food, as well as an antibacterial and anti-fungal agent. Many cultures thought it had spiritual or magical powers. It seems strange today, but centuries ago, people were paid in salt, just like it was money, and wars were fought over salt!
Today, the modern salt industry lists about 14,000 uses for salt. In cooking, it is prized for reducing bitterness, enhancing smells, and balancing sweetness. In this science project, you'll explore this extraordinary, edible rock by looking at the threshold of sensitivity to detecting salt. You'll see at what concentration of salt in saltwater people can first identify the taste as "salty," and you'll see if age affects that threshold of sensitivity.
Terms, Concepts, and Questions to Start Background Research
This source provides an animation that describes how the salt that you eat works inside your body to transmit nerve impulses:
This source describes the effect of sodium on the physiology of the human body:
For help creating graphs, try this website:
Materials and Equipment
Shop for Supplies at Science Buddies Online Store
Science Buddies has compiled some suggestions for harder to find items in our Amazon store. The store does not include every item for every project, but it does include items that we feel work for the projects on our website. If you have comments or would like us to add items to the store, please contact us at firstname.lastname@example.org.
Making Your Salt Solutions
To conduct this experiment, you will need to make three batches of saltwater solutions, each with a different concentration of salt. The first batch of saltwater will be the control. It will contain no salt. The second batch will contain 0.05 percent salt. The third batch will contain 0.10 percent salt (double the salt concentration of the first batch).
Preparing Your Cups for Testing
Testing Your Volunteers
Analyzing Your Data
Kristin Strong, Science Buddies
If you like this project, you might enjoy exploring related careers.
Food Scientist or Technologist |
There is a fraction of the world's population that doesn't have enough to eat or doesn't have access to food that is nutritionally rich. Food scientists or technologists work to find new sources of food that have the right nutrition levels and that are safe for human consumption. In fact, our nation's food supply depends on food scientists and technologists that test and develop foods that meet and exceed government food safety standards. If you are interested in combining biology, chemistry, and the knowledge that you are helping people, then a career as a food scientist or technologist could be a great choice for you!
Life is all around you in beauty, abundance, and complexity. Biologists are the scientists who study life in all its forms and try to understand fundamental life processes, and how life relates to its environment. They answer basic questions, like how do fireflies create light? Why do grunion fish lay their eggs based on the moon and tides? What genes control deafness? Why don't cancer cells die? How do plants respond to ultraviolet light? Beyond basic research, biologists might also apply their research and create new biotechnology. There are endless discoveries waiting to be found in the field of biology!
Each time your heart beats, or you breathe, think, dream, smell, see, move, laugh, read, remember, write, or feel something, you are using your nervous system. The nervous system includes your brain, spinal cord, and a huge network of nerves that make electrical connections all over your body. Neurologists are the medical doctors who diagnose and treat problems with the nervous system. They work to restore health to an essential system in the body.