At a coastal animal-feed mill, technicians grow yeast in a tall vessel using diluted molasses. The yeast cells will be dried and mixed into food for farmed ...
Question 1 Report
At a coastal animal-feed mill, technicians grow yeast in a tall vessel using diluted molasses. The yeast cells will be dried and mixed into food for farmed fish. Fig. 1 is a diagram of the vessel. Air enters near the base, and warmed water circulates through an outer jacket. Samples are removed at regular intervals to check the number of yeast cells.
(a) Name the process used by yeast cells to release energy when oxygen from the air is available. [1]
(b) Explain why air is bubbled through the liquid culture. [2]
(c) Describe how a student could use samples from the vessel to estimate the number of yeast cells per cm3. [3]
(d) Suggest two reasons why the temperature of the culture is controlled by the water jacket. [2]
(e) Explain why yeast biomass from this process can be a useful source of protein in fish food. [2]
Answer Details
(a) Yeast releases energy with oxygen by aerobic respiration. [1]
(b) Bubbling air supplies oxygen to yeast cells. They need oxygen for aerobic respiration, which releases energy for growth and cell division. [2]
(c) Take a measured volume of culture. Place it on a microscope slide or counting chamber and observe it under a microscope. Count cells in a known volume or area, then calculate the number of cells per cm3. [3]
(d) The water jacket keeps temperature near the optimum for yeast enzymes. It prevents temperatures becoming high enough to denature enzymes or low enough to make respiration and growth slow. Any two. [2]
(e) Yeast cells contain protein. Their biomass can be produced rapidly in large quantities using sugar-containing waste material and requires little land compared with producing animal protein. [2]
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