Some friends are trying to make wine in their basement. theyve added yeast to a sweet grape 36) juice mixture and have allowed the yeast to grow. after several days they find that sugar levels in the grape juice have dropped, but there's no alcohol in the mixture. the most likely explanation is that a) the yeast used the alcohol as a carbon source. b) the mixture needs more sugar, because yeast need a lot of energy before they can begin to produce alcohol. c) the mixture needs more oxygen, because yeast need oxygen to break down sugar and get enough energy to produce alcohol d) the mixture needs less oxygen, because yeast only produce alcohol in the absence of oxygen 37) natural selection 37) . a) creates beneficial mutations c) completely eliminates harmful mutations b) is a random process d) can favor beneficial mutations 38) what is the source of energy that provides the boost for electrons during photosynthesis? 38) a) atp c) light b) cellular respiration d) electromagnetism 39) plasma membranes are selectively permeable. this means that 39) a) anything can pass into or out of a cell as long as the membrane is intact and the cell is healthy b) plasma membranes must be very thick. c) the plasma membrane allows some substances to enter or leave a cell more easily than others. d) glucose cannot enter the cell.