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Question

A flask containing nutrient-rich media is seeded with 100 isogenic bacteria. Assuming that no bacteria die in the flask, after approximately how many generations will the population reach a size of $10^5$?

The correct answer is
10

Bacterial Growth Calculation: Generations to Reach Target Population

This problem involves calculating the number of generations for a bacterial population to grow exponentially from an initial size to a target size.

Understanding Exponential Growth

Bacteria reproduce through binary fission, where one cell divides into two. This results in exponential growth. The formula relating the final population ($N_t$), initial population ($N_0$), and the number of generations ($n$) is:

$ N_t = N_0 \times 2^n $

Solving for Number of Generations

We are given:

  • Initial population, $N_0 = 100$
  • Target population, $N_t = 10^5$

We need to find the number of generations, $n$. Substitute the values into the formula:

$ 10^5 = 100 \times 2^n $

Step 1: Isolate the Growth Factor

Divide both sides by the initial population ($N_0 = 100$):

$ \frac{10^5}{100} = 2^n $

$ 1000 = 2^n $

Step 2: Solve for 'n' using Logarithms

To find $n$, we can take the logarithm base 2 of both sides:

$ n = \log_2(1000) $

Step 3: Approximate the Result

We know that $2^{10} = 1024$. Since 1024 is very close to 1000, the number of generations ($n$) is approximately 10.

Therefore, after approximately 10 generations, the population will reach $10^5$.

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Important Questions from Population growth curves

  1. Population growth of a species can be modelled as $$ \frac{dN(t)}{dt} = rN(t)\left(1 - \frac{N(t)}{K}\right) $$ where $N(t)$ is the population size at time $t$; $r$ is the growth rate; and $K$ is the carrying capacity of the environment. 

    For $K = 9000$, $\frac{dN(t)}{dt}$ is maximized at $N =$ _____ 

    (Answer in integer)

  2. The population size at which net recruitment is the highest is also when the greatest amount can be harvested, while ensuring the long-term survival of the population. The amount harvested at this population size is known as
  3. The graphs shown represent the relationship between population size ($N$) and population growth rate ($\frac{dN}{dt}$). Which one of the following growth curves represents a density-dependent population that experiences a strong Allee effect?

  4. Overfishing reduced food availability for sea lions in California, causing a decline in their population size. In 1972, under the US Endangered Species Act, fishing was banned from sea lion foraging areas. Subsequently, the population of sea lions increased in a logistic form as shown in the figure.

    The per capita growth rate is highest in the interval __________ and the population growth rate is highest in the interval __________

  5. A population grows as per the equation $dn/dt = rn (1-n/1000)$ where $n$ is the population density, $r$ is the intrinsic growth rate and 1000 is the carrying capacity. The growth rate of the population is maximum at a population density of ________
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