partial pressure of oxygen and hemoglobin

Question

Which of the following statements about the partial pressure of oxygen and hemoglobin is true?

1. As the partial pressure of oxygen decreases, a proportionately greater number of oxygen molecules are bound by heme

2. The higher the partial pressure of oxygen, the fewer oxygen molecules are bound to heme

The option:

a) Both statements 1 and 2 are correct.

b) Statement 2.

c) Statement 1.

d) Neither statement 1 or 2 is correct.

I know statement 1 is incorrect, i'm not sure if statement 2 is correct

Answer 1

The easiest way to answer this question is by referring to oxygen dissociation curve:

https://d16qt3wv6xm098.cloudfront.net/Mzs1SRMqTxiwEoc2Ja1dsXLXR0CsMeUS/_.jpg

The higher the partial pressure of oxygen (going right on the x axis), the greater number of oxygen molecules are bound to hemoglobin (going up on y axis). Notice the shape of the curve is sigmoidal, which indicates that oxygen-hemoglobin binding is cooperative. In other words, the binding of one oxygen molecule to hemoglobin subunit increases the affinity of other subunits to O₂.

So you are right, statement 1 is incorrect, and so is statement 2. The answer is D.