Cell membranes are not solid structures.
Many act as decomposers, breaking down the dead bodies of plants and animals and recycling the nutrients they hold. ... The fungal decay makes these nutrients and carbon dioxide available to green plants for photosynthesis, and it completes an important cycle of raw materials in the ecosystem.
The answer is: the amount of the saliva samples must stay consistent while the amount of starch must vary.
The amount of the saliva samples must stay consistent because amylase, present in the saliva, is the independent variable which affects the dependent variable - the amount of starch. So, amylase will do its job while remaining surface area of the starch will depend on the starting amount of the starch.