when do plants grow

It’s not easy to measure how fast a plant grows. You would probably not be too keen to take measurements every few hours – and especially not overnight. There are ways, however, of seeing whether a plant grows best in the light or the dark.
You can attach a position sensor to a plant to record its growth. And you can measure for a longer period of time using a data logger to take the readings – rather than run a computer all that time.

What you need
Clamps and stands, plant, such as a growing bean and thread, data logger and position sensor. A light sensor will record day and night.

Set up the position sensor and plant. Use thread to tie the plant to the position sensor. If the sensor is placed the ‘other way’ round, the graph will develop in the opposite direction.
Connect the sensor to the data logger.
Press a data logger button to start it recording.
After you have recorded for sufficient time, a week say, you can stop recording. You then need to connect the data logger to the computer to transfer the readings you have connected. Get the software to get data from the data logger.


  • How does the graph show plant growth?
  • What does the graph tell you about plant growth? Is it steady – or does it change during the day or night?
  • How could the graph tell you if the plant grows faster at night?
  • What are the sources of error in this experiment?
  • Teacher question
  • This experiment takes a very long time and it needs to be set up so that it will not be disturbed in this time. What tips can you offer for doing this? Which plant would you use?

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