Where the shape comes from
A millet plant growing: the tree-shape 木 for stalk and roots, with a stroke laid across the top for the ear bending under its own weight. That drooping head is the whole difference between 禾 and the arrow 矢. It marks crops, harvest and the reckoning that goes with them: 秋 the season, 种 to sow and a kind, 科 a branch of study, 私, 秒, 稻.
汉字 filed under 禾
No published character on HSK Guide is filed under this radical yet. 汉字库.