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.
Goat's milk does contain lactose and it has almost as much as cow's milk. Cheeses made from both cow's milk and goat's milk will have a reduction in the amount of lactose due to the fermentation process. For this reason many people who are lactose intolerant are able to eat cheeses.