Aim for FiveBiology

Scientific investigation

Phosphate and algal growth

  • Unit 1
  • 4 points
  • About 10 minutes

You can use a calculator on this question, just like on exam day.

A short question about a described lab investigation. You describe a concept behind it, identify part of the method such as a control or a variable to hold constant, state a null hypothesis or predict a result, and justify a prediction. On the exam: Question 3 of 6 in Section II; about 10 minutes suggested.

The question and its sources

Phosphorus is an element that organisms must take in from their environment. Researchers investigated whether phosphate (PO₄³⁻) availability limits the growth of a freshwater green alga.

Investigation

Researchers prepared 15 flasks of a nutrient medium. Five flasks contained 0 μM phosphate, five contained 5 μM phosphate, and five contained 50 μM phosphate. All other nutrients were added in the same amounts to every flask. Each flask received the same number of algal cells and was kept under the same light at 20°C. After 7 days, the researchers measured the density of algal cells (cells/mL) in each flask.

Source: Hypothetical study

Suggested time: 10 minutes

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Part (a)

1 point

Describe ONE type of biological macromolecule that contains phosphorus and where the phosphorus is found in that molecule.

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Part (b)

1 point

Identify ONE variable that the researchers held constant in this investigation, other than the amounts of the other nutrients.

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Part (c)

1 point

State the null hypothesis for this investigation.

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Part (d)

1 point

The researchers predict that the algae in the 0 μM phosphate flasks will show little or no increase in cell density. Justify this prediction.

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