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Why does a seedling shoot grow upward against gravity?

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Cluster of bright red seeds emerging from the cone-shaped fruit of a magnolia grandiflora, surrounded by large, glossy green leaves. — seed Fruit and seeds of the southern magnolia (*Magnolia grandiflora*). The fruit is an aggregate of follicles, and each follicle bears a single red seed.

A seedling shoot grows upward against gravity due to a process known as negative geotropism (or gravitropism), which is the plant's movement in response to the force of gravity.21

This upward growth is primarily regulated by auxins, a group of plant hormones that promote cell elongation. The mechanism functions as follows:23

Hormone Distribution: Auxins accumulate in higher concentrations along the lower side of the shoot.23
Cell Elongation: In the shoot, these higher concentrations of auxin stimulate the cells on the lower side to elongate more rapidly than those on the upper side.23
Vertical Orientation: This differential growth causes the shoot to bend and grow upward, effectively moving away from the soil and toward the environment most favorable for photosynthesis.13

While roots exhibit positive geotropism by growing downward, the shoot’s negative geotropic response ensures that the plant's aerial structures are correctly oriented for development.13