Chopped grass is packed tightly into a sealed silo. Bacteria on the grass keep breaking down sugars after the trapped oxygen is used up. What do those bacteria produce from the sugar?

A weightlifter's arm muscles get far less oxygen than they need during a long set of heavy curls, but the muscle cells keep contracting. Which pathway is supplying most of their ATP during the set?

A brewer bubbles nitrogen gas through a tank of grape juice to drive out the oxygen, then adds yeast. Which pathway do the yeast cells use, and what do they make?

A student sits quietly reading, and her leg muscle cells are receiving all the oxygen they need. What are those cells releasing as they break glucose down completely?

A technician grows yeast in a weak sugar solution in a shallow dish that is stirred constantly and left open to the air. Almost no alcohol forms. Why not?

When the oxygen supply to a human muscle cell runs out, the cell stops making ATP altogether.

About how many ATP molecules does a cell gain from one glucose molecule when it ferments that glucose instead of respiring it aerobically?

Two identical yeast cultures each break down 100 glucose molecules. Culture A has plenty of oxygen; culture B has none. Roughly how do their ATP totals compare?

Fermentation releases far less energy from a glucose molecule than aerobic respiration does. Why?

A sprinter cannot hold top speed for more than about 20 seconds. What does the ATP yield of fermentation tell you about why?

Which pathway releases the most ATP from a single glucose molecule?

Aerobic respiration and both kinds of fermentation begin the same way: glucose is broken down in the cytoplasm.

A cell is running fermentation because no oxygen is available. Which organelle is sitting idle that would be busy during aerobic respiration?

Yeast release carbon dioxide whether they respire aerobically or ferment. Which product forms only when they respire aerobically?

If fermentation captures so little energy, what is the point of it for a cell with no oxygen?

Muscle cells and yeast cells are both sealed in flasks with sugar and no oxygen at the same temperature, yet they end up with different products. What decides which fermentation product forms?

Bread dough made with yeast is left in a warm covered bowl and doubles in size before baking. What makes it rise?

A dairy adds bacteria to warm milk in a sealed vat. Hours later the milk has thickened and tastes sour. Which product of the bacteria explains the change?

A winemaker fits a fermenting tank with a one-way valve that lets gas out but no air in. Why must gas be allowed to escape?

Shredded cabbage held under salty brine keeps for months as sauerkraut instead of rotting. How does fermentation preserve it?