Lettuce Cells in a Vertical Farm

Lettuce Without Soil or Sun

Isla Thorne's class toured a vertical farm inside an old warehouse. Lettuce grows there on shelves stacked eight levels high under rows of LED lights. There is no soil and no sunlight. Each plant sits in a foam plug with its roots hanging into a tray of flowing water mixed with nutrients. A pump bubbles air into the water in every tray.

The farm manager, Dmitri Solano, shared two sets of records. During one growing period, the air pump on Rack 2 broke and was not replaced for the full three weeks. Everything else about Rack 1 and Rack 2 was the same, including the lights, the water, the nutrients and the lettuce seeds. At harvest, the staff weighed the heads of lettuce and checked their roots.

For a second test, Dmitri sealed one fresh lettuce leaf in each of two clear boxes with carbon dioxide sensors. One box sat under an LED light, and the other sat in a dark cabinet at the same temperature. A third box held a piece of white lettuce root of the same mass, under the light. The sensors recorded the carbon dioxide level in parts per million (ppm) every 10 minutes.

Back at school, the class looked at thin pieces of lettuce leaf and root under a microscope. Both kinds of cells had a cell wall, a cell membrane and a nucleus. The leaf cells were packed with green chloroplasts, but the root cells had none. Their textbook explains that mitochondria are found in nearly all plant and animal cells, but they are too small to see clearly with a school microscope.