Describe two ways to measure o2 consumption

Question

Problem:

Question 1: Describe two ways to measure O2 consumption and two ways to measure CO2 production in living cells.

Question 2: A post-translational modification that occurs in the ER is

(a) Removal of mannose

(b) Addition of N-acetylglucosamine

(c) N-linked glycosylation

(d) Addition of mannose-6-phosphate

Please Explain don't just write the answer.