2019 Year 12 IB Extended Essays

Dependent Variable: Variable

How it is measured

Height of Wheatgrass Sprouts

The wheat grass is a straight plant, making it easier for its height to be measured using a 15cm ruler. The seed must not be disturbed when taking the reading so therefore, the ruler will be placed inside the cup to measure its height rather than taking the seed out as this will cause the roots to get damaged and will also prevent them from setting their roots deep within the cotton bed and absorb nutrients.

Controlled Variable: Variable

How it is controlled

Why its controlled

Temperature of water

The temperature of the water being used to water the plants will be controlled by using a thermometer to measure the temperature of the water before watering the plants, ensuring that it remains constant at 20˚C.

Colder water serves to slow the enzymatic activity of the plant, warm water ensures that the plant functions most effectively while hot water dehydrates the plant, damaging its cells and eventually kills it. Therefore, if the temperature of the water used isn’t constant for all the plants used, then the rate at which the plant takes in and immobilises the contaminants will also not be constant.

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