Final answer:
To analyze cell growth, review the graph for time durations corresponding to population milestones and the slope for the rate of growth. For a visual representation of exponential growth, the graph's curve will steepen over time. Logistic growth, in contrast, will result in an S-shaped curve, with the growth rate eventually decreasing.
Step-by-step explanation:
To determine the rate of cell growth, one would analyze the provided graph of bacterial population growth over time. Without specific numerical values or a graph image, we will discuss the conceptual approach:
A) To gauge how long it took to grow the first 20 cells, you would locate the point on the graph where the population reaches 20 cells and then trace down to the time axis to find the corresponding time duration.
B) Similarly, to find the duration for the last 20 cells, locate where the population increases by 20 cells towards the end of the graph, then trace down to identify the time taken for this increase.
C) To decide if the rate of cell division is increasing or decreasing, examine the slope of the graph. In the phase where the slope is steepest, the rate of growth is increasing. If the slope becomes less steep over time or flattens, the rate is decreasing. If a segment of the graph has a horizontal line, then the growth rate during that interval is zero.
The exponential growth model is characterized by a growth rate that increases as the population grows, which manifests as a progressively steeper curve on the graph. Conversely, logistic growth reflects a situation where the growth rate eventually decreases as resources become limited, producing an S-shaped curve.
Using the graph, annotations can be added to mark intervals with different growth patterns. One would be the exponential phase (log phase), which shows increasing growth rate. Another would be the stationary phase, where the rate of growth decreases to zero, often due to resource limitation or environmental factors. Lastly, the death phase would show a decrease in the number of cells.