In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

Question: Which of the following structures is not present in animal cells? Answer: cell wall
A cell wall is not present in animal cells.

Question: The structure of mitochondrion plays an important role in what? Answer: aerobic respiration
The structure of mitochondrion plays an important role in aerobic respiration.

Question: What property of warm air causes it to rise above cold air? Answer: lower density

The lower density of warm air causes it to rise above cold air.