The northern hemisphere is warmer in the summer than the winter because the northern hemisphere are pointing toward the sun. Because of this the rays hit us more directly making is hotter. So during the winter when the northern hemisphere is not pointing toward us, it makes is colder. It also depends on the tilt of the axis. When it is more direct it makes the temperature hotter.
Answer:
Either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.
The plant pigments that are involved in photosynthesis are chlorophyll pigments, mostly chlorophyll A. They are found in chloroplasts.
Yes, it's important to prevent damage to the nerve cells because if they were to get damaged you could get paralyzed. When your nerve cells are damaged the signals to move different parts of your body don't make it through to the muscles which leads to paralysis.