Using Two-way ANOVA may make sense if the explanatory variables (i.e., different organisms and stress levels) are categorical. However, if one of the variables is continuous numeric, you can use covariance analysis (ANCOVA). If the two explanatory variables are continuous, you can perform multiple regression.

Considering that the model residues have normal distribution and homoscedasticity.

Hello Ahmed,

If your research question concerns whether the two organisms have comparable responses to specific stress levels, then yes. A two-way anova could be an appropriate way to analyze the data. Note that you could also use multiple regression to answer the same questions (same hypotheses can be tested), but some folks are more comfortable with the anova set-up and interpretation.

The basic assumptions are normality (of "errors" or residuals), homogeneity of variance (across cells), and independence of observations.

Good luck with your work.

Ahmed Ali, do you mean that you have two different types of organisms with multiple (independent) organisms of each type? Or do you have two organisms in total, one of each type?

Yes, it does make sense