Photosynthetic cells contain chlorophyll and other light-sensitive pigments that capture solar energy. In the presence of carbon dioxide, such cells are able to convert this solar energy into energy-rich organic molecules, such as glucose.
Yes, you can add a little lemon juice or vinegar to the goat's milk to make it into a buttermilk or kefir. This will lower the pH of the milk, and allow it to release the CO2 stored in the sodium bicarbonate (baking soda), causing the bread to rise. Goat's milk generally has less fat and more vitamins.
No. Goats only have to be milked if they're dairy goats and you don't want that milk to go to waste, or that goat to dry up. If you don't have a kid (baby goat) to put on the doe and don't want her milk, you can let her dry up. The only thing is, she won't produce milk until she has her next set of kids.