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.

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.

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

For the first question, the biologist would predict that radioactivity would be found in the sugar, CO2, and alcohol. So the answer is option 5 - sugar, CO2, and alcohol.

For the second question, the evidence supports the conclusion that the alcohol produced has inhibited the growth of the yeast cells. So the answer is option 4 - the alcohol produced has inhibited the growth of the yeast cells.

For the first question, the biologist assumed that only aerobic respiration was occurring in the corn plant. To determine where the radioactivity would be found, we need to understand the process of aerobic respiration in plants.

During aerobic respiration, glucose is broken down in the presence of oxygen to produce energy in the form of ATP. One of the byproducts of this process is carbon dioxide (CO2), which is released into the atmosphere. Another byproduct is water.

Based on this understanding, the radioactivity would be present in compounds that are directly involved in aerobic respiration. The options given are sugar extracted from the plant, CO2 produced by the plant, and alcohol, if produced by the plant.

Since aerobic respiration involves the breakdown of glucose, which is a sugar, radioactivity would be expected in sugar. Additionally, CO2 is produced as a byproduct of aerobic respiration, so radioactivity would also be expected in CO2. Alcohol, on the other hand, is not directly involved in the aerobic respiration process and therefore would not have radioactivity.

Therefore, the biologist would predict that radioactivity would be found in sugar and CO2 only. The correct answer would be option 4: sugar and CO2 only.

For the second question, the student observed an experiment where yeast cells were used to produce alcohol. The experiment was kept in constant darkness and excluded oxygen, suggesting that anaerobic respiration was occurring.

Based on the given information, the student noticed an increase in yeast biomass and CO2 production for the first 2 weeks. After 4 weeks, there was a decrease in biomass, very little CO2 production, and glucose was still present.

From this evidence, we can deduce that the yeast cells have likely depleted their energy source, which is glucose. This is the strongest conclusion supported by the evidence. Option 1: "The yeast cells have totally depleted their energy source" would be the correct conclusion.

For the first question, if the biologist assumed that only aerobic respiration was occurring, she would predict that radioactivity would be found in option 4: sugar and CO2 only. This is because during aerobic respiration, glucose is broken down in the presence of oxygen to produce carbon dioxide and water. Since the corn plant had previously incorporated radioactive carbon into starch stored in its cells, the radioactivity would be expected to appear in the carbon dioxide produced during respiration.

For the second question, based on the evidence provided, the strongest conclusion would be option 4: The alcohol produced has inhibited the growth of the yeast cells. This conclusion is supported by the observation of a decrease in yeast biomass and very little production of CO2 after 4 weeks, despite glucose still being present. The presence of alcohol can inhibit the growth of yeast cells and affect their ability to carry out fermentation, leading to a decrease in biomass and reduced CO2 production.