Answer:
Active uptake (which I think you mean active transport) is important when the concentration gradient is against that of a certain substance, so it doesn't cross the membrane through diffusion or passive transport. It is sometimes necessary if a substance needs to move across a membrane but can't do so due to electrical charge or that there is a substance on the other side of the membrane preventing diffusion.
Explanation:
Has varied greatly over time
<span>Bio-indicators are macro-invertebrates that detect Water Quality based on how tolerant they are to pollution. The number of species of each type of Bio-indicator (pollution tolerant, intolerant, and semi-tolerant) will calculate the index of the water.</span>
