(2) No. 1 test tube and No. 2 test tube control, the experimental variable is saliva, No. 1 test tube is a control group, indicating that water does not have a digestive effect on starch. 1 test tube and No. 2 test tube is a control, indicating that salivary amylase digestion of starch.
(3) The temperature at which digestive enzymes work best is the same as that of the human body, which is about 37 degrees Celsius. Therefore, in the experiment, the device should be placed in warm water at 37℃. At that temperature, the digestive enzymes are most active． The control inquiry is also applied．
(4) the experiment in the test tube No. 2 added saliva, saliva salivary amylase in the starch decomposition into maltose, so the drop of iodine solution does not change blue; No. 1 test tube added to the water on the starch is not digested, the starch is not broken down, the drop of iodine solution turns blue.
(5) The experiment proved that salivary amylase has a digestive effect on starch.
The answer is: (1) saliva;
(2) control;
(3) 37 ℃; suitable for the oral temperature, 37 ℃ is the optimal temperature for salivary amylase to play a catalytic role;
(4) blue; not blue;
(5) saliva has a digestive effect on starch.