(1) The appearance of red apricot is a manifestation of phototaxis of plants, because under the irradiation of unilateral light, auxin is transported laterally to the adverse light side, resulting in uneven distribution of auxin, and the distribution on the adverse light side is much more than that on the light side; Auxin can also promote the growth of plants, so plants grow by bending to the light source.

(2) Falling red refers to that the flowers and leaves of plants fall off, and under the decomposition of soil microorganisms, the organic substances contained in them are decomposed into inorganic substances, which are then absorbed by plants.

(3) The food chain includes producers and consumers, so the food chain includes rice → pests → frogs.

(4) "Weeding" can not only loosen the soil, enhance the respiration of crop roots, but also help the roots to absorb mineral elements; It can also eliminate weeds, reduce the competition between weeds and crops, and make more energy flow to crops, thus increasing crop yield.

So the answer is:

(1) Under the irradiation of unilateral light, the distribution of auxin is uneven, and the distribution on the backlight side is much more than that on the light side, and the plants grow curved towards the light source.

(2) decomposer organic matter? inorganic matter

(3) Rice → Pest → Frog

(4)① In order to loosen the soil and enhance the respiration of crop roots, it is beneficial for the roots to absorb mineral elements.

② In order to eliminate weeds, reduce the competition between weeds and crops, and let more energy flow to crops.