A-Level Edexcel Biology Tangents and Instantaneous Rates

Review A-Level Edexcel Biology tangents and instantaneous rates through reaction curves, initial gradients, oxygen production and rate-unit calculations.

Exam points

draw tangents to reaction curves and calculate instantaneous rates at stated times
plot mass or product against time and use the starting gradient for initial rate
round tangent-gradient rates to required precision with biological rate units

[Maximum number: 3]

In an investigation, scientists attached a molecule called PBF to the cell surface of a species of green algae, C. pyrenoidosa.

These algae are photosynthetic organisms and PBF absorbs green light.
The scientists measured the production of oxygen by C.pyrenoidosa, C. pyrenoidosa with PBF attached and PBF only.

The graph shows the results of this investigation.

Figure for Question A.3.6—Tangents and instantaneous rates question 1 — Edexcel A-Level Biology A2

Calculate the rate of production of oxygen at 1200 seconds for C. pyrenoidosa with PBF attached. nmol secs ${ }^{-1}$

tangent correctly drawn (1)

- rate calculated (1)

- rate value between 0.060 and 0.090 expressed to 3 dps max (1)

line touches the outside of the curve at 1200 seconds

e.g. $65 \div 880=0.073863636363$ $50 \div 720=0.069444444$

ECFs:
$\begin{aligned} & 147 \div 1120=0.1386792 & 147.5 \div 1120=0.131696428571 & 148 \div 1120=0.13962 & 147 \div 1130=0.13725490 & 147.5 \div 1130=0.13053097 & 148 \div 1130=0.1383177 \end{aligned}$

Ecf values from mp 2 correctly rounded to a max of 3 dps

Ecf value of 0.1225 / 0.122916 / 0.12333 correctly rounded to max 3 dps but do not accept recurring numbers

(3)

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A.3.6—Tangents and instantaneous rates question 1