This is possible because when a star dies, it basically expands to its maximum (explodes). Therefore, the materials of the exploded star mix with the primeval hydrogen of the Universe. Later, other stars are formed out of this mixture. Thats also how the sun was formed. :)
Explanation: Photosynthesis removes CO2 from the atmosphere and replaces it with O2. Respiration takes O2 from the atmosphere and replaces it with CO2.
Well because death by starvation would be far more agonizing than death by predators. Starving to death would last longer and the death would be more excruciating.
