(1) When making I temporary slice, pinch the two blades side by side and cut quickly. In order to let the light pass through, the thinnest one should be selected and made into temporary slices for observation.

(2) As shown in the figure: 1 upper epidermis; 2 mesophyll (palisade tissue); 3 veins; 4 mesophyll (sponge tissue); ⑤ Lower epidermis; 6 stomata; Guard cells.

(3) There are many stomata on the leaves of plants, mainly distributed in the lower epidermis of the leaves. It refers to a cavity surrounded by guard cells that are opposite to each other.

(4) Vein-transporting tissues have the function of transporting substances, the conduits in plants can transport water and inorganic salts, and the sieve tubes can transport organic substances.

So the answer is: (1) is the thinnest.

(2) 1

(3)6; Stomata; 7; Guard cell

(4)3; Catheter; sieve tube