There are several vegetables that can be grown successfully hydroponically. One of the easiest and most rewarding to experiment with is Romaine lettuce.

Engage:

Did you know the world's largest tree lives right here in California? Measuring in at 36ft in diameter and 275ft tall, the General Sherman Sequoia Tree can be found at Sequoia National Park.

Where did this tree get the majority of its dry mass?*

• Trees mostly gain mass from the soil.

• Trees mostly gain mass from the air.

• Trees mostly gain mass from the sun.

*By dry mass, we are referring to the mass of the tree minus its water. The amount of water in trees varies greatly.

Explain:

Using Claim-Evidence-Reasoning (CER), provide students an opportunity to make a claim based on evidence that supports one of the three statements above.

Students then share their responses with the class.

Explore:

Take the remaining piece from a head of lettuce and place it in a bowl of shallow water. Place the bowl in a window that gets natural sunlight. Change the water every other day.

Make observations daily.

• On what day do students see the beginning of a new leaf?

• On what day do students see the beginning of a stalk?

• What color are the leaves?

• Measure the height of the lettuce.

• What other observations and measurements can you make?

Elaborate:

Now that students grew lettuce from stump once successfully, how can students redo the experiment with a new variable?

• What would happen if the lettuce was placed in a different window?

  • Does sunlight affect the growth of lettuce?

• What would happen if the lettuce was fed nutrients (similar to the packet sometimes provided with cut flowers)?

  • Is leaf color influenced by the amount of nutrients in the water?

• What else can students vary to create a new experiment?

Evaluate:

Revisit the original question: Where does the General Sherman Sequoia tree get the majority of its dry mass?

Growing vegetables hydroponically can help clear misconceptions that some students may have. For instance, it is a common believe that plants consume the soil and transform that soil into plant matter. Does growing lettuce in water demonstrate that the dry mass of a plant does not come from the ground?

Plants receive the majority of its dry mass from the air. Carbon dioxide in the air is consumed and converted into carbon for the plant and oxygen for the atmosphere.