The krebs cycle will not take place if
oxygen is not present
water levels are normal
carbon dioxide levels are high
light intensity is high

a.oxygen is not present

Explanation:  The citric acid cycle is also known as the Kreb cycle. It doesn't directly need oxygen, it will solely occur once oxygen is present as a result of it depends on by-products from the electron transport chain, which needs oxygen. The citric acid cycle is thus an aerobic process. Hence , it cannot take place without oxygen.

step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.