Book 4, Question 5
Why Do Roots Grow Down?
Roots grow down because they follow gravity. Down is where soil holds moisture, and where a plant can anchor itself. So wind does not tip it over!
From the book
Page from A Million Whys Book 4
More fun facts
- Roots grow toward the pull of gravity. Scientists call this gravitropism.
- Stems do the opposite and grow up, away from gravity.
- A plant chemical called auxin collects on the lower side of a sideways root and slows its growth there, so the root bends down.
- In a sideways stem, auxin on the lower side speeds growth instead, so the stem curves up.
- Tiny heavy grains inside root cells sink downward and help the plant sense which way is down.
- Roots growing down help a plant find water and hold it firmly in place.
Sources: BBC, BBC, Scientific American
Questions kids ask
How does a root know which way is down?
Tiny heavy grains in its cells settle downward, which helps the root sense gravity.