During a practical lesson, a student compares oxygen uptake by soaked, germinating pea seeds with that of boiled seeds. Each flask is kept in a water bath a...
Question 1 Report
During a practical lesson, a student compares oxygen uptake by soaked, germinating pea seeds with that of boiled seeds. Each flask is kept in a water bath at 25 degrees C. Fig. 1 shows the sealed apparatus used for the flask containing living seeds. The capillary has an internal cross-sectional area of 0.50 mm2. After 15 minutes, the coloured drop labelled P has moved 24 mm towards the flask.
(a) Name the parts labelled P and Q. [2]
(b) Use the movement of P and the cross-sectional area of the capillary to calculate the volume of oxygen taken up each minute. Give your answer in mm3 per minute. [3]
(c) Explain why the coloured drop moves towards the flask when the pea seed cells respire. [3]
(d) Suggest two features that would make the boiled-seed flask a valid control for this investigation. [2]
(e) State the type of respiration occurring in the germinating pea cells. [1]
Answer Details
(a) P is the coloured liquid drop, or marker drop. Q is soda lime, which absorbs carbon dioxide. [2]
(b) The volume of oxygen taken up in 15 minutes is:
\[\text{volume}=\text{distance moved}\times\text{cross-sectional area}\]
\[24\text{ mm}\times0.50\text{ mm}^2=12\text{ mm}^3\]
\[\text{rate}=\frac{12\text{ mm}^3}{15\text{ min}}=0.80\text{ mm}^3\text{ min}^{-1}\]
The oxygen uptake rate is 0.80 mm3 per minute. [3]
(c) Pea cells use oxygen in aerobic respiration. Carbon dioxide produced by respiration is absorbed by soda lime. Therefore the total gas volume and pressure in the flask fall, drawing the coloured drop towards the flask. [3]
(d) Use the same apparatus and the same mass or number of seeds in the boiled-seed flask. Keeping it at the same temperature, using the same time period and using the same amount of soda lime are also valid controls. Any two are required. [2]
(e) The germinating pea cells carry out aerobic respiration. [1]
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