A-LevelBiologyTransport in plants9700/51 · May/June 2024 · Q110 Marks

A student investigated the effect of wind speed on the rate of transpiration. The student used the flowering plant Japanese spiraea, Spiraea japonica. The student used the apparatus shown in Fig. 1.1 to measure the rate of transpiration. [Figure 1.1] To set up the apparatus the student: • obtained a Japanese spiraea plant growing in a container of soil • added 200 cm³ of water to the soil • placed a plastic bag around the container of soil to prevent water loss from the soil • placed the plant and container on the balance • switched on the fan to a low setting. The roots of the Japanese spiraea plant absorbed water from the soil. Water was carried in the xylem and water vapour was lost by transpiration from the leaves of the plant. This caused the reading on the balance to decrease during the investigation.

(a)(i)Identify the independent variable in this investigation.[1]
(a)(ii)The student carried out the investigation in a laboratory with standard laboratory apparatus. Describe a method, using the apparatus shown in Fig. 1.1, that the student could use to investigate the effect of wind speed on the rate of transpiration by Japanese spiraea. Your method should be set out in a logical order and be detailed enough to allow another person to follow it. Details of how to set up the apparatus shown in Fig. 1.1 should not be included.[6]
(a)(iii)Predict the effect of wind speed on the results of the investigation using the method you have given in (a)(ii).[1]
(b)(i)Using the information given in Table 1.1 and Fig. 1.3, calculate the rate of transpiration for leaf 2 of the Japanese spiraea plant. Give your answer to three significant figures.[1]
(b)(ii)To improve the validity of the results, the student decided to measure the time taken for blue cobalt chloride paper to change colour on a greater number of leaves of the Japanese spiraea plant. State one other change the student could make to the method to improve the validity of the results.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] wind speed;
[1] method to use fan(s), to obtain a minimum of five different wind speeds ;
[1] ref. to standardised variable for using the fan;
[1] use a method to maintain, same / stated, temperature ;
[1] use a method to maintain, same / stated, light intensity;
[1] at each wind speed, measure / note / record / AW, the initial mass and final mass, in a fixed time ;
[1] idea of equilibration / acclimatisation, of, plant / Japanese spiraea / apparatus ;
[1] use at least three measurements for each wind speed and calculate a mean;
[1] safety comment with hazard and precaution ; hazard: Japanese spiraea / plant; risk: irritant/allergy; precaution: gloves / mask / PPE; hazard: soil; risk: biohazard / pathogens / allergy / irritant; precaution: gloves / mask / PPE; hazard: fan; risk: hair / clothing / AW, trapped in fan; precaution: method to, control loose, hair/clothing / AW
[1] method for measuring wind speed ;
[1] idea of replacing water lost from plant (before each new measurement) ;
[1] as wind speed, increases: rate of transpiration - increases; or decrease in mass, in fixed / stated time - increases; or rate of decrease in mass - increases; or time taken, for a fixed decrease in mass - decreases ; ora
[1] 263;
[1] any one from: use, same / stated, size of (blue) cobalt chloride paper; idea of use a (pink) colour standard (to determine end point); idea of measure different positions on (lower) surface of leaf ; idea of unbiased selection of, leaves / leaf position ;

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