Question

Glucose is broken down in different ways both in the presence and in the absence of oxygen.

Answer 1

For the given reaction set:

Glycolysis (A) 
Krebs cycle (B) 
ETS (C) 
lactic acid fermentation (D)

Each of the elements of the reaction set is preceded by corresponding elements of set D which consists of:

A. photosynthesis in plants
B. glycolysis
C. Krebs cycle
D. glycolysis

To summarize the order of the reactions:

photosynthesis in plants > glycolysis > Kreb's cycle (aerobic respiration) or lactic acid fermentation (anaerobic respiration) > Electron Transport Chain (ETC)

Aerobic respiration: 
Photosynthesis produces glucose, which is used in glycolysis. Glycolysis produces ATP, NADH, and pyruvate. Pyruvate is then used in the Kreb's cycle to produce NADH, FADH2, ATP, and CO2. The ETC then uses the NADH and FADH2 to produce energy.

Anaerobic respiration:
The same process is followed until glycolysis. The pyruvate produced from glycolysis is used in the lactic acid fermentation process to produce lactic acid.

Answer 2

Correct answer is

A. NAD+

B. ATP

C. Pyruvic Acid, ATP, NADH

D. ATP, FADH2, NADH