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A biologist was experimenting with a corn plant that had previously incorporated radioactive carbon into starch stored in its cells. She measured the radioactivity present in the following compounds:
Sugar extracted from the plant
CO2 producd by the plant
Alcohol, if produced by the plant

If she assumed that only aerobic respiration was occuring, where would she predict radioactivity would be found?


1 CO2 only

2 CO2 and alcohol only

3 sugar and alcohol

4 sugar and CO2 only

5 sugar, CO2, and alcohol


A student designs an experiment to produce alcohol. He includes yeast cells, water, and glucose in excess, and maintains the experiment in constant darkness, excluding oxygen. For 2 weeks he notices an increase in yeast biomass (weight of yeast) and CO2 produced. After 4 weeks he observes a decrease in biomass and very little production of CO2. Glucose is still present. For which of the following conclusions is the evidence strongest?

1 The yeast cells have totally depleted their energy source.

2 Since ATP is formed during anaerobic respiration, this ATP has poisoned the yeast cells.

3 The yeast cells have begun to utilize the CO2 and water to carry out photosynthesis.

4 The alcohol produced has inhibited the growth of the yeast cells.

5 After 4 weeks, the cells switched to aerobic respiration.

  • Bio -

    I know the answers are both 4, but i don't know why the 1st answer is 4.

  • Bio -

    I had the same question. You eliminate all the answers with alcohol because that is a product of anaerobic respiration, so it definitely wont be made by the plant cell. Therefore you eliminate choices 2,3,5. It would be choice 4 because, it states only aerobic respiration is occurring, so the starch is broken down into sugars such as glucose. And CO2 is a byproduct of this reaction. That's why.

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