Question

which experiments led to changes to the original cell theory?
○ experiments that showed that blood cells transport gases, waste, and nutrients throughout the body
○ experiments that showed that all cells are similar in how they metabolize and in their composition
○ experiments that transplanted synthetic chromosomes into bacterial cells to create a new species
○ experiments that established the existence of single-celled organisms and microbes

Explanation:

1. Analyze Option A: Experiments showing blood cell transport don't change the original cell theory (which focuses on cell as basic unit, origin, etc.), so A is incorrect.
2. Analyze Option B: Showing all cells similar in metabolism/composition doesn't alter the core cell theory ideas, so B is incorrect.
3. Analyze Option C: Transplanting synthetic chromosomes to create new species is related to modern genetic engineering, not changing the original cell theory (original cell theory was about basic unit, all cells from pre - existing cells, all living things have cells). So C is incorrect.
4. Analyze Option D: The original cell theory was developed with the knowledge of larger organisms' cells. Experiments establishing single - celled organisms and microbes (like those by Leeuwenhoek) expanded the understanding that not just multicellular organisms are made of cells, but also unicellular ones, which led to changes in the original cell theory (e.g., recognizing that single - celled organisms exist as complete living entities made of one cell).

Answer:

D. experiments that established the existence of single - celled organisms and microbes