氮循環示意圖白板動畫

Hand-drawn simple nitrogen cycle scene on a strip of brown soil, cut away so the underground is visible. Exactly five things: on the far left, one small grey cloud with one yellow lightning bolt; in the middle-left, one green bean plant whose roots underground carry small round pink bumps (root nodules); in the middle-right, one cow eating grass; just behind the cow, a small pile of droppings on the ground; scattered in the soil, a few tiny green dots of bacteria. Exactly four curved red arrows: one arrow pointing DOWN from the lightning bolt into the soil; one arrow pointing UP from the soil into the bean plant's stem; one arrow pointing from the bean plant across to the cow; one arrow pointing DOWN from the droppings into the soil. No arrow points up to the cloud. Nothing else in the picture, plenty of empty sky. Coloured pencil and watercolour marker, clean black ink outlines, warm off-white paper, no text.