Before a dry seed can germinate it takes up water. A student investigated this by weighing a group of 20 dry bean seeds and then soaking them in water. Fig....
Question 1 Report
Before a dry seed can germinate it takes up water. A student investigated this by weighing a group of 20 dry bean seeds and then soaking them in water. Fig. 7.1 shows how she placed the beaker of seeds on a balance to find their mass. Every two hours she removed the seeds, blotted them dry, measured their total mass, and then returned them to the water. Her results are shown in Table 7.1. She wanted to find out how the mass of the seeds changed as they soaked up water.
| Time / hours | 0 | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|---|
| Mass of 20 seeds / g | 8.0 | 10.5 | 12.8 | 14.2 | 14.9 | 15.0 |
(a) Name the apparatus used to measure the mass of the seeds. [1]
(b) Describe how the student found the increase in mass of the seeds over the ten hours. [3]
(c) Use Table 7.1 to state the mass of the seeds after 4 hours of soaking. [1]
(d) Calculate the percentage increase in mass of the seeds between 0 hours and 10 hours. Show your working. [2]
(e) Explain why the mass of the seeds increased during soaking. [2]
(f) Explain why the mass stopped increasing after about 8 hours. [2]
(g) State the independent variable and the dependent variable. [2]
(h) State two variables that should be kept constant. [2]
(i) Explain why the student blotted the seeds dry before weighing them each time. [2]
(j) Suggest how taking up water in this way helps a seed to begin germinating. [3]
Answer Details
(a) The mass of the seeds was measured with a (top-pan / electronic) balance. [1]
(b) To find the increase in mass she would record the starting mass of the dry seeds [1], record the mass again after soaking [1], and subtract the starting mass from the later mass [1].
(c) From Table 7.1 the mass after 4 hours is 12.8 g. [1]
(d) Percentage increase \(=\dfrac{15.0-8.0}{8.0}\times100=\dfrac{7.0}{8.0}\times100=87.5\,\%\). Working [1]; answer 87.5 % [1].
(e) The mass increased because the seeds absorbed water through the micropyle and seed coat [1], and this water was held in the seed tissues, so their mass rose [1].
(f) After about 8 hours the seed tissues had become fully swollen and could take up no more water [1], so the mass stayed the same (reached a plateau at 15.0 g) [1].
(g) The independent variable is time [1]; the dependent variable is the mass of the seeds [1].
(h) Any two kept constant: the number of seeds; the temperature; the volume of water; the type of seed. [2]
(i) The seeds were blotted dry to remove surface water [1], so that only the water actually taken up by the seeds is measured and the mass is not falsely high [1].
(j) Taking up water helps germination because the water activates the enzymes in the seed [1]; the enzymes then digest the stored food (such as starch) into soluble substances [1], which are used for respiration and for the growth of the embryo [1].
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