Pea Shoots in Light and Dark: A Hospital Garden Test

Fresh Greens for Patients

1Northgate Children's Hospital grows pea shoots, the young stems and leaves of pea plants, in a sunny room next to its kitchen. The hospital dietitian, Ms. Farah Siddiqui, adds the tender shoots to salads and sandwiches for patients. Seventh grader Elijah Tran volunteers in the growing room on weekends, and one day he asked whether the shoots would grow just as well in a dark storage closet. Pea shoots are usually ready to harvest about 10 to 14 days after the seeds are soaked, so a test would not take long.

2Ms. Siddiqui helped Elijah set up a test. They soaked pea seeds and spread them on four trays lined with damp paper mats, with no soil and no plant food. Each tray held seeds with a dry mass of 90 g. Two trays went under grow lights that were on for 16 hours a day. The other two went into a dark closet. Both places stayed at about 21 °C, and every tray got the same amount of plain tap water each morning.

3Elijah knew that a plant can grow two ways: by taking in water, which makes it bigger and heavier, and by building new body matter such as sugar, starch and fiber. To tell these apart, a technician in the hospital lab dried small samples of shoots, roots and seeds in a low-heat oven until all the water was gone. She weighed each sample before and after drying. From the samples, she worked out the dry mass of each whole tray.

4Green leaves contain chloroplasts. In photosynthesis, chloroplasts use light energy to join carbon dioxide from the air and water into sugar, and they release oxygen. Like animals, plants also carry out cellular respiration in their cells all the time: they use oxygen to break down sugar, which releases energy for growth and gives off carbon dioxide and water.