Recall that the main function of chloroplasts is to convert sunlight to chemical energy, or to carry out photosynthesis. Plant (and eukaryotic algae) cells contain these organelles, while animal cells do not, and hence, animals cannot carry out photosynthesis.
So, a lack of chloroplasts would mean that an organism would not be able to convert sunlight into chemical energy through photosynthesis.
Plants cells, and specifically the chloroplast organelle, are able to absorb sunlight, and together with CO₂ and water, produce glucose (for the plant to eat) and oxygen (which is released into the atmosphere). That glucose is further broken down by the plants' mitochondria. Animals directly consume the glucose to be broken down and converted into energy, hence why we do not have - nor need - chloroplasts in our cells.
