Astudent mixes some heat-killed type iis streptococcus pneumoniae bacteria with live type iir bacteria and injects the mixture into a mouse. the mouse develops pneumonia and dies. the student recovers some type iis bacteria from the dead mouse. if this is the only experiment conducted by the student, has the student demonstrated that transformation has taken place? what other explanations might explain the presence of the type iis bacteria in the dead mouse?

No, only this experiment is not enough to prove that transformation has taken place.

In the original experiment by Griffith, IIR and IIIS bacteria were used. Here the student has used IIS and IIR bacteria. There might have been a mutation in IIR strain due to which it got converted to IIS strain and killed the mice. So first he needs to set up a control of only injecting IIR bacteria into mice and prove that it alone can not kill the mice.

Also, he did not demonstrate that the heat killed all the IIS bacteria. Some might have survived and killed the mice. To check this, he needs to inject the mice with heat killed IIS bacteria and check if it is still able to kill them or not.