What is the primary reason why the experiment with seeds is invalid?

The experiment with seeds is considered invalid primarily because it has no control. A control is essential in any scientific experiment as it serves as a baseline to compare the effects of the independent variable. Without a control group, it's difficult to determine if the observed results are due to the treatment being tested or if they are influenced by other factors. The absence of a control means the experiment lacks a point of reference to validate the reliability of the findings.

In experiments, control groups allow scientists to see what happens in the absence of the experimental treatment, providing context for understanding the results. This setup helps ensure that any changes observed in the experimental group can be attributed to the variable being tested rather than external influences. Hence, having a control is a fundamental component to establish credibility and validity in scientific research.