What is the technique of obtaining a large number of plantlets by tissue culture called?

Which of the following is a polyamide?

If $Q$ denotes the set of all rational numbers and $f\left(\frac{p}{q}\right)=\sqrt{p^2-q^2}$ for any $\frac{p}{q} \in Q$,then observe the following statements.
$I$. $f\left(\frac{p}{q}\right)$ is real for each $\frac{p}{q} \in Q$
$II$. $f\left(\frac{p}{q}\right)$ is a complex number for each $\frac{p}{q} \in Q$.
Which of the following is correct?

The equation of the parabola with the focus $(3,0)$ and the directrix $x+3=0$ is:

What is the cause of embryo formation from pollen grains in tissue culture medium?

During which phase of meiosis does crossing over occur?