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🌱 How does a seed know which way is up?

Statoliths settle with gravity and auxin bends roots down and shoots toward light.

lessons

~10 min

to learn

🔬 Science

subject

Adults

level

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What you’ll learn

Gravity is the teacherExplain gravitropism via statoliths and auxin-driven differential growth.Dense plastids settle with gravity; auxin shifts; organs bend by growing unevenly. Roots down, shoots up.
Light joins the argumentAdd phototropism and multi-cue integration.Shoots chase light with related hormone logic. Gravity works in the dark. Other tropisms fine-tune paths.
From seed stores to autotrophyConnect seed reserves and space experiments to orientation success.Packed nutrients fund the search for light and water. Orbit experiments confirm gravity’s role. Garden practice rides the same physics.

Questions this course answers

What do statoliths do in gravitropism?

Dense starch plastids settle and contribute to gravity sensing that guides auxin-mediated bending.

Order a simplified root gravitropic bend

Sense gravity, move hormone, grow unevenly, reorient.

Why can seedlings orient correctly even in total darkness?

Gravity sensing works without photons; light cues matter more after emergence.

Grounded in trusted sources

Taiz and Zeiger Plant Physiology — tropism chapters
NASA plant space biology education pages
University botany labs on gravitropism and auxin
Classic Cholodny-Went tropism hypothesis educational summaries

Every Wunder lesson is built from real, reputable sources — never invented.

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