Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.
--------
Question: Question: What is the touch response in plants called? Answer: thigmotropism

Answer: The surface temperature of most stars is due to their size. Bigger stars produce more energy, so their surfaces are hotter. But some very small stars are very hot. Some very big stars are cool.

Question: Question: In what state of matter is butter at room temperature? Answer: solid

Answer: 6. Butter is a fat that is a solid at room temperature. What type of fatty acids does butter contain? How do you know?.

Question: Question: During adulthood, what is needed for the production of sperm? Answer: testosterone

Answer:
During adulthood, testosterone is needed for the production of sperm.