What would happen to oxygen, carbon dioxide, and food supply on Earth if plants and chlorophyll were absent?

Let's look at Q8. If there were no plants or other organisms with the green pigment 'chlorophyll' on Earth:

a) The amount of oxygen on Earth would:
Plants produce oxygen through photosynthesis. Without them, oxygen levels would fall.
Your answer: decrease ✅ Correct

b) The amount of carbon dioxide on Earth would:
Plants absorb carbon dioxide for photosynthesis. Without them, carbon dioxide levels would rise.
Your answer: increase ✅ Correct

c) The supply of food on Earth would:
Plants are the base of most food chains, producing food through photosynthesis. Without them, the food supply would diminish.
Your answer: decrease ✅ Correct