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Characteristics and Classification of Living Organisms: Question 6

Syllabus 1.1

Multiple choice Core 1 mark

A gardener plants a bean seedling in a pot of soil. Each week, for four weeks, the gardener measures the height of the seedling with a ruler. At the end of the experiment, a similar seedling grown under the same conditions is dried in an oven until its mass no longer changes, and this dry mass is compared with the dry mass of a seedling of the same age measured in week 1.

Both the height and the dry mass are found to have permanently increased over the four weeks, and neither measurement decreases again afterwards.

Which life process is being shown by the bean seedling?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall the definition of growth

Growth is defined as a permanent increase in size and dry mass. Both parts of this definition matter: the increase must be lasting, not a temporary change, and it must apply to dry mass, not just fresh mass.

Step 2: Apply the definition to the seedling

The bean seedling’s height increases week by week and does not decrease again, showing a permanent increase in size. Its dry mass, measured by drying a seedling until its mass stops changing, is also found to be greater after four weeks than in week 1. Using dry mass rather than fresh mass rules out the possibility that the increase is simply due to the plant temporarily taking up more water. Together, a permanent increase in both height (size) and dry mass is exactly what defines growth.

Step 3: Rule out the other life processes

  • Nutrition is the taking in of materials for energy, growth and development. The seedling does take in materials from the soil, but the process being described and measured here is the resulting increase in size and dry mass, which is growth, not the uptake itself.
  • Movement is an action by an organism, or part of an organism, causing a change of position or place. Becoming taller is not a change of position or place, so this is not movement.
  • Reproduction is the process that makes more of the same kind of organism. No new bean plants are described as being produced, so this is not reproduction.

Final answer

  • A permanent increase in height and dry mass over time is an example of growth, option A.