First of all, there is no photosynthesis before the first tender leaf is germinated, but only respiration, because photosynthesis is carried out in chloroplasts, while soybean seeds have no cells containing chloroplasts, only the leaves or green stems of plants contain chloroplasts (chlorophyll exists in chloroplasts, so cells with chloroplasts are green).

Second, after the first tender leaf is produced, it begins to carry out photosynthesis and has respiration (if it is soybean sprouts we eat, there is no such stage, soybean sprouts are white, and the part we eat is an elongated hypocotyl).

The above is the general process. Let's talk about the changes in the process of soybean germination in detail:

When the seed germinates, it absorbs water and swells, the seed coat softens, and the respiration gradually increases. Nutrients stored in cotyledons or endosperm are gradually decomposed and transformed into substances that can be absorbed and utilized by cells, and transported to the embryo, hypocotyl and radicle (at this time, the nutrients in seeds are gradually reduced, but the weight of bean sprouts is increased relative to that of soybeans, and the increased part is mainly the weight of water absorbed by soybeans). The radicle breaks through the seed coat to form roots, the embryo forms stems and leaves, and the hypocotyl forms the part connecting the stems and leaves (if bean sprouts are eaten, the embryo has not yet formed stems and leaves).

If it is in nature, after the germ forms stems and leaves, it can carry out photosynthesis to synthesize organic matter, so that the content of organic matter increases gradually, and at the same time, plants are breathing, consuming organic matter and generating energy needed by plants for life activities.