How Much Water Is in a Fruit?
The cells and tissues that make up living organisms are mostly water. For example, water comprises about 90% of the weight of a tomato, 80% of the weight of an earthworm, 70% of the weight of a tree, and 70% of the weight of a human body.
In this activity, students will investigate the amounts of water in two different fruits and use measures of weight and volume. The activity also introduces students to the concept of drying (or removing water) as a means of preserving foods. Drying can be traced back to ancient times, and was an important method of food preservation used by American Indians and early settlers in North America. When foods are dried, most of the moisture is removed. Drying makes many grains, meats and vegetables much less suitable environments for the growth and reproduction of molds, bacteria and insects.
Dehydration also makes foods lighter, and easier to store and transport. Other methods for preserving food that involve dehydration include smoking—which is faster and more effective because the absorbed smoke is toxic to many microorganisms—and salting, which draws moisture out of the food items.
Session 1: How much liquid does an orange have?
- While holding a bag of oranges in front of the class, ask, How much water do you think is in this bag? Lead a class discussion about the amount of water in an orange. Ask the students to predict the amount of water contained in one orange. Make sure they equate orange juice with water.
- Show the students how to measure the volume of an orange by observing and measuring “how much space it takes up.” Fill a prepared beaker with 800 mL of water. Record the number of mL in the beaker on the board. Then place an orange into the water. Hold it down gently, so that the whole orange is submerged. Ask, Did the water level go up or down? How much? Why? To help students understand the concepts of displacement and volume, talk about what happens to the water when someone gets into a bathtub.
- On the board, subtract the original volume of water in the container from the volume in the container after the orange was added. Calculate and record the difference. Ask, What does the difference represent? (A standard juice orange will displace about 140–150 mL and will yield 40–50 mL of squeezed juice.)
- Have each group measure the volume of an orange by submergence, as you demonstrated. Ask the students to suggest ways to measure the amount of juice inside their oranges.
- Show the students how to squeeze the juice out of an orange. Have them cut their oranges in half using serrated plastic knives. Use the top and bottom portions of soft drink bottles as “juicers,” purchased plastic juicers (see PDF), or let students devise their own ways to squeeze out the juice. Have each group squeeze the juice out of one orange. Make sure the students save the remainders of their oranges.
- Have each group measure the amount of juice obtained by pouring it into a 250-mL beaker. Ask, How can the remaining material be measured? If students suggest weighing, have them consider the conversions necessary to equate the weight information with their earlier measurement in mL. Have students place the remaining orange pieces without juice into the beaker prepared with of 800 mL water and read the new volume. Ask, Has the amount of water displaced changed? Why? What was the volume of the entire orange? What is the volume of the remaining “stuff”? What fraction of the orange was water? Have students record the values they obtained on the “How Much Juice Is in an Orange” observations sheet.
Keywords: body | cells | chromatography | dehydrate | dehydration | evaporation | excretion | health | kidney | life science | transpiration | water | lesson
- Moreno, N., Tharp, B., and Dresden, J. (2011) The Science of Water Teacher’s Guide. Baylor College of Medicine: Houston.
- Photo © Valentyn Volkov. Licensed for use.
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Funded by the following grant(s)
My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932
Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education