Who proposed the theory that "Cells arise only from the pre-existing cells"?

If $\overrightarrow{a}, \overrightarrow{b}, \overrightarrow{c}$ are three vectors such that $\overrightarrow{a}=\overrightarrow{b}+\overrightarrow{c}$ and the angle between $\overrightarrow{b}$ and $\overrightarrow{c}$ is $\frac{\pi}{2}$,then:

If $z = \sec^{-1}\left(\frac{x^4+y^4-8x^2y^2}{x^2+y^2}\right)$,then $x \frac{\partial z}{\partial x} + y \frac{\partial z}{\partial y}$ is equal to

$A$ $4 \mu F$ capacitor is charged by a $200 \ V$ battery. It is then disconnected from the supply and connected to another uncharged $2 \mu F$ capacitor. During the process,the loss of energy (in $J$) is:

What is the percentage of Photosynthetically Active Radiation $(PAR)$ in the incident solar radiation?

When a weight of $10\, kg$ is suspended from a copper wire of length $3\, m$ and diameter $0.4\, mm$,its length increases by $2.4\, cm$. If the diameter of the wire is doubled,then the extension in its length will be ........ $cm$.