Compare and contrast an ecosystem driven by photosynthesis to an ecosystem driven by chemosynthesis.

Both chemosynthesis and photosynthesis are processes used to create food.

Photosynthesis is a process plants use to create food (glucose), in which plants convert light energy into chemical energy.  

Chemosynthesis is the process by which food (glucose) is made by bacteria using chemicals instead of light energy.

An ecosystem driven by photosynthesis requires sunlight in order to perform photosynthesis.  An ecosystem driven by chemosynthesis does not require sunlight.  instead, chemosynthesis requires bacteria or other living organisms that derive energy from reactions involving inorganic chemicals.

"do a testcross with a homozygous recessive plant."

the offspring would all be white. if the parents are both white flowers then they have the genotype rr, which when crossed results in an all white punnet square.