📈  LINE GRAPH INSTRUCTIONS:

1) In your Science Notebook take notes on Line Graphs.
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!

Line Graphs

Line graphs show how something changes over time or as one variable changes smoothly. On the CAST, you will often explain the trend and connect it to science ideas.

Start With Context

What Question Does This Graph Answer?

Our graph asks: "How does temperature affect the rate of an enzyme reaction?"

• Independent variable (x-axis): Temperature (°C)
• Dependent variable (y-axis): Reaction rate (arbitrary units)
• Units: °C on x, rate units on y

Before reading data, say the question out loud. This focuses your brain on what the line is showing.

Describe the Trend First
Choose the best trend statement for the graph on the right. -- pick a description -- The reaction rate stays constant at all temperatures. The reaction rate increases as temperature rises up to about 40 °C, then decreases at higher temperatures. The reaction rate is highest at the lowest temperature. Check Trend

Enzyme Reaction Rate vs. Temperature

According to the data, there is an optimal temperature where the reaction rate is highest.

Enzyme reaction rate

Science idea: At higher temperatures, enzymes can denature (change shape), so the reaction rate drops.

Notebook Task – Line Graph Notes

• Copy the question and the axis labels from this graph into your notebook.
• Draw a smaller version of the graph and label the optimal point.
• Write 3 sentences using evidence language:
  1) The graph shows that...
  2) According to the data...
  3) Based on the trend...

Use the graph to predict what might happen at 70 °C. This is called extrapolation.

Practice – CAST-Style Line Graph Questions

Use the graph above and the data table below to answer the questions.

Temperature (°C)	20	30	40	50	60
Reaction Rate (units)	2	4	7	5	3

1. A student says, “According to the data, the reaction rate increases between 20 °C and 40 °C, then decreases from 40 °C to 60 °C.”
Which statement best explains this pattern using science ideas?

Enzymes do not depend on temperature, so this pattern is random. The graph is wrong because line graphs cannot show reaction rates. Enzymes work faster as temperature increases up to their optimal temperature, but very high temperatures can denature the enzymes and lower the rate. The reaction rate decreases only because the units change after 40 °C.

2. Based on the trend, what is the best prediction for the reaction rate at 70 °C?

Higher than the rate at 40 °C, because temperature always speeds up reactions. Lower than the rate at 60 °C, because the graph shows the line continues to drop after 40 °C. Exactly the same as at 40 °C, because 70 °C is also warm. It cannot be predicted at all from the graph.

Check Answers

Continue to page 3

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