Edexcel IAL Biology 7.8 Respirometer and respiratory quotient

Average capillary distance, use radius in the cylinder-volume equation and divide by time, then remove carbon-dioxide absorbent when both gases must be measured.

Exam points

Calculate oxygen uptake rate from capillary distance, tube radius and elapsed time.
Explain why removing soda lime allows carbon dioxide production and RQ measurement.

[Maximum number: 4]

The diagram shows some maggots in a respirometer.

Figure for Question 7.8—Core Practical 16 - respirometer, respiration rate and RQ question 1 — Edexcel A-Level Biology A2

This respirometer can be used to investigate the uptake of oxygen during the respiration of maggots.

A student used this respirometer with soda lime to measure the movement of the coloured liquid.

The table shows the results.

Table for Question 7.8—Core Practical 16 - respirometer, respiration rate and RQ question 1 — Edexcel A-Level Biology A2

(a)

Calculate the mean rate of oxygen uptake in $\mathrm{mm}^{3} \mathrm{~min}^{-1}$ .

The internal diameter of the capillary tube was 0.2 mm .
The volume of a cylinder (V) is calculated using the formula

\pi r^{2} l

Give your answer to two significant figures. $\mathrm{mm}^{3} \min ^{-1}$

[ 3 ]

ai

- calculation of mean distance (1)

- correct use of $r^{2}(1)$

- correct answer (1)

Allow ECF for MP2 and MP3 L = $4.4(\mathrm{~mm})$ $\mathrm{r}^{2}=0.01\left(\mathrm{~mm}^{2}\right)$ $0.14\left(\mathrm{~mm}^{3} \mathrm{~min}^{-1}\right)$ 0.138 gets 2 marks

correct answer with no working gains (3) marks

(b)

The soda lime was removed and replaced with glass beads in order to calculate the RQ .

Suggest why this allows the student to calculate the RQ.

[ 1 ]

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7.8—Core Practical 16 - respirometer, respiration rate and RQ question 1

Question (a)

Question (b)