During the dark period, plants do not undergo photosynthesis because they require light for this process. However, plants still continue to respire even in the absence of light. Respiration is a metabolic process where plants break down organic compounds to release energy. Therefore, option 1 would be incorrect as it includes photosynthesis, which does not occur during the dark period. Transpiration, on the other hand, is the loss of water vapor from the plant through the stomata. This process mainly occurs during the day when the stomata are open for gas exchange. Similarly, conduction is the movement of water and nutrients through the plant`s tissues, which also occurs throughout the day. Option 2 and option 3 are incorrect because they include processes that primarily occur during the day. Therefore, the correct answer is option 4, which includes respiration and conduction, the two processes that take place in plants during the dark period.