Transpiration
Transpiration is how plants release water through tiny holes in their leaves into the air.
A wet sponge sits on a tray in a warm room. The sponge holds water inside it. Over time, water moves out through the tiny holes in the sponge and floats into the air as vapor. Plants do the same thing — water exits through small pores in their leaves and joins the air around them.
Explaining transpiration by grade level
Plants drink water from the soil. The water moves up the stem to the leaves. Then the water goes out through tiny holes in the leaves. That is how a tomato plant stays cool.
Projects that explore transpiration
Which plant releases the most moisture through its leaves? To find out, you build a plastic bubble around each of six different plants, trapping the water vapor they give off. Each plant gets equal water and sunlight for seven days. When the time is up, the coleus plant has released the most moisture at 71.7 mL. The strawberry plant comes second at 60.8 mL. The tomato plant places third at 56.4 mL — despite having the largest leaf surface area. Lettuce releases the least, at only 18.5 mL.
Do plants with bigger leaves lose more water through their stomata? To test this, you place ivy, a money plant, and an elephant ear in separate beakers, each filled with 100 ml of water. A fourth beaker with no plant serves as the control. After five days, you measure how much water remains in each beaker. The results may surprise you: despite their very different leaf sizes, the three plants lose similar amounts of water. That means leaf size alone does not determine how much water a plant releases.