For bacterial growth in a cell culture, growth law is very similar to the law of radioactive decay. Which of the following graphs is most suitable to represent bacterial colony growth? Where N - Number of bacteria at any time, N0 - Initial number of bacteria.
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Answer
(3) [figure]
Solution
Radioactive decay: dNdt = -kN. Bacterial growth follows the same first-order law, but the number increases:
dNdt = +kN
N0N dNN = k 0t dt
NN0 = kt
NN0 = ekt
At t = 0, NN0 = 1 (a non-zero intercept on the y-axis), and NN0 then rises exponentially (ever more steeply) with time.
Graph (1) is exponential decay, graph (2) is a linear fall and graph (4) rises from zero and levels off; only graph (3) starts above zero and increases exponentially.
Answer: (3)