Question

digging deeper: van helmonts experiment
plants within the genus tillandsia are commonly known as air plants. within this category are 500 - 600 different species of plants. air plants are epiphytic (\epi\= upon; \phyte\= plant), meaning they live on other plants. they are not parasitic because they only use the host plant for physical support, rather than deriving nutrition from it.
because air plants don’t live in the ground, they have tiny root systems. in fact, the nutrients absorbed by an air plant don’t come through the roots at all. instead, the plants have specialized hair - like cells on their leaves called trichomes. these help the plant absorb water and minerals from the humid air around them.
since the 1600s, scientists have known that plants get most of their nutrition from the air rather than the soil. a physician named jan van helmont tested this theory. he took the mass of a seedling and a pot of dry soil. after watering the seedling regularly for 5 years, it grew into a small tree and had gained about 75 kg. the mass of the soil, however, was nearly unchanged.
questions:

1. what question was van helmont trying to answer with his experiment?
2. how do the roots on an air plant validate the results of van helmont’s experiment?
3. what purpose do trichomes serve?

Explanation:

1. Van Helmont's experiment was about determining the source of a plant's mass - whether it came from soil or elsewhere. He measured the mass of a seedling and soil at the start, watered the seedling for 5 years, and noted the plant's significant mass gain with little soil mass change.
2. Air plants have tiny root systems that don't absorb nutrients from the host plant or soil. This supports Van Helmont's finding that plants don't get most of their nutrition from soil, as air plants survive without relying on soil - based nutrients through their roots.
3. Trichomes are specialized hair - like cells on air plant leaves that help the plant absorb water and minerals from the humid air around them.

Answer:

1. Does a plant get most of its mass from the soil?
2. Air plants have tiny roots and don't get nutrients from soil, validating that plants may not rely on soil for nutrition.
3. They help the plant absorb water and minerals from the air.