🧮 Survival Curves:

1) In your Science Notebook take notes on Scatter Plots.
2) After taking notes, complete Practice CAST Question below.
3) Then click Continue to complete the next section of notes.
4) Turn In: I will be stamping completed notes!

Survival Curves

Survival curves show how many individuals in a group are still alive over time. On the CAST, you compare different curves and explain what might cause drops in survival.

Populations Over Time

Bacteria Surviving Under Different Temperatures

Question: "How does temperature affect the survival of bacteria over 48 hours?"

• Independent variable (x-axis): Time (hours)
• Dependent variable (y-axis): Percent of bacteria still alive
• Groups: 25 °C (room), 37 °C (body temp), 45 °C (hot)

To read survival curves:

• Look at which line is highest at a certain time (greatest survival).
• Notice any sudden drops (something harmful happened).
• Use evidence language: “According to the survival curve...”

Survival of Bacteria at Different Temperatures

According to the data, bacteria survive best at 37 °C and worst at 45 °C after 48 hours.

37 °C (body temp) 25 °C (room) 45 °C (hot)

Notice how the 45 °C line drops quickly. This could mean high temperature is killing the bacteria faster.

Notebook Task – Survival Curve Notes

• Draw a smaller version of the three survival curves with a clear legend.
• At 48 hours, mark which group has the highest survival and which has the lowest.
• Answer these questions in complete sentences:
  1. Which group shows the highest survival rate after 48 hours?
  2. Describe how survival changes over time for each group.
  3. What might explain the sudden drops in survival for the 45 °C group?
• Begin one answer with “According to the survival curve...”.

Practice – CAST-Style Survival Curve Questions

Use the survival curves above and the simplified data table.

Temperature	Time (h)	% Surviving
25 °C	48	40
37 °C	48	55
45 °C	48	10

1. Which group shows the highest survival rate after 48 hours?

25 °C 37 °C 45 °C All have the same survival.

2. A student writes: “According to the survival curves, very high temperature (45 °C) causes a rapid drop in survival after 12 hours.”
Why is this a good scientific explanation?

It ignores the graph and only uses background knowledge. It talks about survival but does not mention any specific time. It uses evidence from the curve (the steep drop after 12 hours) and connects it to the idea that heat can damage cells. It is incorrect because all groups have the same shape.

Check Answers

Continue to page 7

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