It can be seen from the figure: ① represents the cell wall, ② represents the cell membrane, ③ represents the chloroplast, ④ represents the nucleus, ⑤ represents the vacuole; ⑥ represents the cytoplasm.

(7) Various substances are dissolved in the cell fluid inside the vacuole. The sweet and delicious substance of watermelon comes from watermelon cells, the cell fluid in the vacuoles in the cytoplasm.

(8) The picture has a cell wall, chloroplast, and vacuole structure. From this, it can be seen that the picture is a diagram of a plant cell; animal cells do not have a cell wall, chloroplast, and vacuole structure.

So the answer is : ① represents the cell wall, ② represents the cell membrane, ③ represents the chloroplast, ④ represents the nucleus, ⑤ represents the vacuole; ⑥ represents the cytoplasm. (7) Cell fluid. (8) Cell wall, chloroplast, vacuole