In the problem (1), 100W bulb is used as the light source to continuously increase the distance between the bulb and the device. It can be seen that the deflection of the pointer, that is, the intensity of photosynthesis is changing, so the light intensity is the independent variable.

(2) From the question (1), we can see that the distance between bulbs is getting bigger and bigger, so photosynthesis is gradually weakened. Moreover, the deflection of pointer at point B decreases, indicating that photosynthesis is slow, so the photosynthesis of plants at point A is strong, and the pointer begins to shift after point C, indicating that photosynthesis at point C is equal to respiratory intensity. Because the respiratory intensity after point C is greater than the intensity of photosynthesis, that is, the negative growth of organic matter. Therefore, point C accumulates more organic matter than point D. 。

(2) After reaching point C, the pointer began to deviate backwards, indicating that oxygen has been consumed from the device at this time, so the intensity of photosynthesis and respiration at point C is equal.

(3) Compared with point A, at point D, the illumination is weakened, the photoreaction is weakened, and ATP and [H] provided for dark reaction are reduced, so the amount of C3 reduction is reduced, the concentration of carbon dioxide is unchanged, the synthesis rate is unchanged, the C3 content is increased, and the C5 content is reduced due to the reduction of three carbon compounds. The CD segment indicates that the balance pointer begins to deviate backwards, indicating that respiration is greater than photosynthesis at this time. Photosynthesis at point A is greater than respiration. By the way, point D is with point A..

(3) Because rice plants can carry out photosynthesis under the condition of light, it is necessary to measure the respiratory intensity of their seedlings, and the device should be shaded. If the temperature of the water bath drops at this time, the deflection of the pointer will be affected. From the internal analysis, it is because the temperature affects the activity of respiratory enzymes.

So the answer is: (1) the light intensity changes the distance between the light bulb and the equipment.

(2)①A？ C

② equals ③ increase or decrease? correct

(3) Shading or darkness? Temperature affects the activity of respiratory enzymes.