That's true. There is little variety among organisms found in pools, pounds and lakes. Despite that fact that many ponds are seasonal, lasting just a couple of month (for exemple sessile pools) while lakes can exist for more than hundred years. Lakes and ponds have limited species diversity because they are often limited from each other and from other water sources like rivers, seas and oceans.
The peas haven't start germinating, which means no leaves. They can't undergo photosynthesis to produce oxygen. At this stage they are still undergoing respiration, which produce carbon dioxide.
Because acids have a bitter taste i believe
Presumably whatever their nutrition and health requires, for instance, if a tree frog requires fruit flies to maintain a healthy and balanced diet, then the conservation center probably feeds their tree frogs fruit flies.
