🌑 Does a bean grow taller in the dark?

My hypothesis

If I change how much light the bean plant gets, then how tall the plant grows in ten days will ______, because ______.

🔊 You fill in the blanks. Think about what a young shoot is searching for, and what it can do with only the food packed in its seed. A guess is a good because: the test finds out.

Change, measure, keep the same

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.

What you need

• 🫘 Dried beans from the grocery bag (pinto, lima or kidney): 9, all the same kind
• 🥤 Paper cups with a hole poked in the bottom: 9, all the same
• 🪴 Potting soil
• 🍽️ A baking tray or big plate: 3, one for each place
• 🚰 Water from the tap
• 🥛 A measuring cup
• 🩹 Masking tape, to mark lines
• 🖍️ Crayons or markers
• 📏 A ruler

Steps

1. Soak nine beans in a cup of water overnight.🔊
2. Fill nine cups with potting soil to 2 cm below the rim.🔊
3. Push a bean a finger deep into each cup, and water each with a quarter cup of tap water.🔊
4. Label the cups dark, shady and sunny, three of each.🔊
5. Put three cups on a tray in a dark cupboard, three on a tray in a shady room and three on a tray in a sunny window.🔊
6. Every day, give each cup the same quarter cup of water, and peek at the cupboard quickly.🔊
7. On day ten, take the cups out and stand a ruler beside each plant to measure its height.🔊
8. Write each height in your table, and write down each plant's colour and how thick its stem is.🔊
9. Draw a bar graph of the height for each place.🔊
10. Wash your hands after touching the soil.🔊

Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.

Your results table

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a bar graph, one bar for each thing you tried.

Why it works

🔊 A shoot in the dark stretches fast, using its stored food to search for light. It stays pale because a plant only makes its green colour, which catches light, when light arrives. In a bright window the plant usually grows shorter and sturdier and turns green, while the dark one soon runs out of food.

Going further (7th and up): Change a second thing: give the plants 2, 6 and 12 hours of light a day, and graph their heights against the hours of light.

Board layout

This project at your grade

From 4th grade up, the table gets a mean column. See every project for 2nd grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed how much light the bean plant gets and measured how tall the plant grows in ten days, in cm.
• What did you keep the same, and why does that matter? I kept the same kind of bean, soaked overnight and the same cups, soil and amount of water the same, so the only difference was how much light the bean plant gets.
• How many times did you test it? 3 times at each of my 3 levels.
• If you did it again, what would you change or test next? I'd give the plants 2, 6 and 12 hours of light a day, and graph their heights against the hours of light.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

• 🌱 Do plants bend toward the window?1st–5th grade · 12 days of testing · free🌦️ Growing and weather · 🌱 Outside and plants
• 🪴 Do crowded seeds grow shorter?4th–8th grade · 14 days of testing · about $2🌦️ Growing and weather · 🌱 Outside and plants