Mitochondria are the site of aerobic respiration in animal cells. A theory of the evolution of animal cells states that these mitochondria may once have been aerobic bacteria that were taken into the cytoplasm of a cell in an early ancestor of the animals, allowing the cells to gain the ability to respire using oxygen. Assuming this theory is correct, which of the following statements are true of these aerobic bacteria and human white blood cells?
1 The structure of their DNA is a double helix.
2 They would both possess a cell wall.
3 They would both possess a nucleus.
4 They would both possess a cell membrane.

Answer:

21) A

1 – All DNA has a double-helix structure meaning mitochondria and human white blood cell contain double-helix DNA. So 1 is correct.

2 – Human cells do not contain a cell wall. Therefore, we can conclude that 2 is wrong.

3 – A mitochondria does not have a nucleus since the passage states that mitochondria may once have been an aerobic bacteria. We know bacteria do not have a nucleus. 3 is wrong

4 – Both must have a cell membrane since all cells have a cell membrane.

Statements 1 and 4 are correct.
So A is answer.