Measure the Water Content of Fruits and Greens

This article shows you a simple way of measuring the water content of different types of fruits and greens. This is an excellent activity for the classroom. Spend a lesson rigging the experiment and spend 10 minutes every day for 1-2 weeks. The duration depends on what flowers you choose. Some central terms are liquid, evaporation, phase transition, water content, nutrition, and wither.

Equipment

• Flowers. Choose flowers where it’s easy to spot when they haven’t got enough water (because their heads drop)
• Different types of fruits and greens
• A scale
• A knife
• A cutting board
• Scissors

Instructions

1. Measure 100 g of each fruit and green. It should be cut into only one piece
2. Place the different pieces on a cutting board
3. Use the knife to poke a hole into the fruits
4. Make sure you have enough flowers for each of the holes
5. Place the stem of the flowers into the holes in the fruits and greens
6. Take a picture so that you can control the experiment with reference to the starting point
7. Pay attention to how the flowers are doing with the water content of the different fruits and greens in the following 1-2 weeks. What flower does the best? What flower withers first? Do the results tell you anything about the water content of the different fruits and greens?

Practical tips

You can document the experiment by regularly photographing the setup on the cutting board.

If the students leave large surfaces without any peel on the fruits and greens, some evaporation will happen, and a certain amount of the water won’t go towards the flower. This is a potential source of error in the experiment that you can discuss together. The larger the naked surface, the larger the area from which water can evaporate.

By making two setups, you can also examine how heat influences the lifespan of the flowers. Place one of the setups in a sun-filled windowsill and the other in a chiller area of the classroom. The flowers in the windowsill will most likely die sooner because the high heat leads to faster water evaporation.

What happens?

Fruits and greens contain many compounds in addition to water, such as ions and organic materials. About 96.5% of a cucumber is water. That’s the same water content as seawater! The difference is that seawater mostly consists of ions, while there are many different types of organic materials in a cucumber.

Here’s a list of the water content of common fruits and greens:

• Cucumber 96.5%
• Tomato 94%
• Water melon 93%
• Lemon 90%
• Orange 88%
• Carrot 87%
• Apple, pear and kiwi 84%
• Potato 77%
• Banana 76%
• Avocado 73%
• Almond 4%
• Walnut 3%

If your students have not yet learned about percentages, you can talk about the water content in terms of 100 g of the fruit or vegetable. For example, there are 96.5 g of water in 100 g of cucumber.