
Responder1
Adicionar samples y=0
remove a linha que conecta os pontos finais.
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot3 [
domain=0:10,
% ----------
% add `samples y=0' to remove the line connecting the endpoints
samples y=0,
% ----------
] (x, 25, {x^2});
\end{axis}
\end{tikzpicture}
\end{document}