Question

another function of the kidney is to aid in regulating the number of red blood cells. the kidneys produce a protein known as erythropoietin (epo) that stimulates the increased production of red blood cells.
the graph below shows the results of a study. participants were exposed to different conditions prior to time zero, then epo levels were measured over a 4.5 - hour time period.
effect of oxygen exposure on epo production
key

• normal oxygen exposure
• eight 4 - minute cycles of low oxygen
• 120 minutes of continuous low oxygen

1. using the information provided, describe the evidence to support the claim that exposure to low oxygen levels results in a feedback mechanism that allows the body to maintain homeostasis. 1

Explanation:

To support the claim, we analyze the graph:

• Normal oxygen (black dot line): EPO levels stay relatively low (around 10 - 11 mU/ml) over time.
• Low oxygen conditions (open circle and black square lines):
• For "eight 4 - minute cycles of low oxygen" (open circles), EPO levels increase from ~12 to ~14 mU/ml.
• For "120 minutes of continuous low oxygen" (black squares), EPO levels rise more steeply, from ~11 to ~20 mU/ml.
• EPO stimulates red blood cell production, which carries oxygen. When oxygen is low, the body increases EPO (a feedback response) to boost red blood cells and restore oxygen levels, maintaining homeostasis. The graph shows that low oxygen exposure leads to higher EPO production compared to normal oxygen, providing evidence for this feedback mechanism.

Answer:

In the graph, conditions with low oxygen (eight 4 - minute cycles of low oxygen and 120 minutes of continuous low oxygen) result in higher EPO levels over time compared to normal oxygen exposure. EPO stimulates red blood cell production (which transports oxygen). When oxygen is low, increased EPO production (a feedback response) helps boost red blood cells to restore oxygen levels, thus maintaining homeostasis. For example, continuous low oxygen leads to a steep rise in EPO (from ~11 to ~20 mU/ml), and cyclic low oxygen also increases EPO (from ~12 to ~14 mU/ml), while normal oxygen has low, stable EPO levels (around 10 - 11 mU/ml). This shows low oxygen triggers a feedback mechanism (increased EPO) to maintain homeostasis.