Why are scientific theories modified, but seldom discarded? explain

Hello.

The original theories are based on a certain amount of truth. Now a days, theories are not accepted until there is a significant amount of evidence to back it up. If there should be new evidence that states otherwise, then the theory will be modified.  The reason that it is called a theory, is because it can't be proven yet. This means that it might still become accepted some day, but until that time, pieces of the theoretical puzzle will have to be put together gradually (modified) as new information comes in and knowledge is gained.

Have  a nice day

answer: after carbon dioxide enters the leaf through stomata it moves into the mesophyll cells where photosynthesis occurs and glucose is constructed. respiration occurs when glucose (sugar produced during photosynthesis) combines with oxygen to produce useable cellular energy.

explanation:

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.