Final answer:
A membrane-bound sac with digestive enzymes and a lower pH than the surrounding cytoplasm is known as a lysosome. It plays a crucial role in digesting cellular waste and pathogens, and its acidic environment is maintained by proton pumps that transport hydrogen ions into the lysosome.
Step-by-step explanation:
A membrane-bound sac containing only digestive enzymes in an environment with a lower pH than the surrounding cytoplasm is called a lysosome. These organelles are pivotal in the digestion and recycling of cellular waste, including macromolecules and non-functioning organelles. Lysosomes are equipped with acid hydrolases, enzymes that thrive in acidic conditions with an optimal pH of around 4.5. They play a critical role in cellular processes like autophagy and the immune response, in which they break down pathogens engulfed by phagocytosis.
The low pH environment required for lysosomal enzymes to function is maintained by proton pumps that actively transport hydrogen ions into the lumen of the lysosome. This compartmentalization allows the enzymes to be synthesized and transported in an inactive form, preventing damage to other cellular components before they reach the lysosome.
In essence, the lower pH and the presence of digestive enzymes are crucial for the functioning of lysosomes, which are the cell's breakdown and recycling centers. This safeguards the cell by ensuring that hydrolytic reactions occur within a contained environment.