Although pyruvate is the end product of glycolysis and no more atp is generated by fermentation of pyruvate to ethanol, yeast produce ethanol under anaerobic conditions because
a. pyruvate export requires more energy than ethanol export.
b. glycolysis substrate-level phosphorylation changes pyruvate to ethanol.
c. electrons (and protons) are then added to ethanol to make lactate.
d. pyruvate to ethanol fermentation decreases deleterious co2 levels.
e. transfer of electrons from nadh to pyruvate to make ethanol regenerates nad+, which is necessary for new rounds of glycolysis to proceed.

E. transfer of electrons from NADH to pyruvate to make ethanol regenerates NAD+, which is necessary for new rounds of glycolysis to proceed.

Explanation:

In anaerobic conditions, cells only obtain ATP from glycolysis. During this metabolic process, 2 NAD+ molecules are reduced to produce NADH.

During fermentation, pyruvate is first converted into acetaldehyde which is then reduced by the electrons provided by NADH to produce ethanol. This process regenerates the NAD+ that will be reused to continue glycolysis.

If fermentation didn't happen, the NAD+ wouldn't regenerate and glycolysis would stop, causing cell death because of lack of ATP.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!