How are the terms 'critical concentration' and 'deficient' different from each other in terms of the concentration of an essential element in plants? Can you find the values of 'critical concentration' and 'deficient' for minerals $Fe$ and $Zn$?

(N/A)

Term	Definition
Critical Concentration	The concentration of an essential element in plant tissues below which plant growth is retarded.
Deficient	The concentration of an essential element which is lower than the critical concentration, resulting in specific morphological symptoms and reduced growth.

Regarding the values for $Fe$ and $Zn$ (as per standard plant physiology data):
$1$. Critical concentration for $Zn$ is approximately $20 \text{ } \mu g \text{ } g^{-1}$ of dry weight. Below this, the plant is considered deficient.
$2$. Critical concentration for $Fe$ is approximately $100 \text{ } \mu g \text{ } g^{-1}$ of dry weight. Below this, the plant is considered deficient.
Note: The values provided in the original prompt were incorrect; standard physiological values are measured in $\mu g \text{ } g^{-1}$ (ppm), not percentages.