Nitrate Fertilisers and Algal Growth

Aim: To investigate the effect of increasing nitrate concentration on algal growth.

Underlying Biology: Nitrogen is a requirement for all living things. It is also required for making

proteins. Proteins are a necessity as they make hormones, enzymes and cell membranes. Nitrogen is

a part of fertilisers which increase plant growth as the plants take up nitrogen in the form of nitrates.

Although nitrogen is not the only element present in fertilisers as they also contain phosphorus and

potassium. Algal blooms are a big issue in the environment as they decrease oxygen supply in

freshwater. They do this by blocking out sunlight which means plants underneath cannot

photosynthesise, lowering the oxygen supply. They can cause a widespread death of organisms, due

to a low oxygen supply. The dead organisms sink to the bottom of their habitat and begin to

decompose. Decomposers use oxygen to breakdown the dead organisms, leading to a further lack of

oxygen. Algal blooms can naturally grow but they more commonly grow due to nutrient pollution,

which is caused by fertilisers.

Experiment: I put 5 different concentrations of nitrates into beakers with algae and after 5 days measured the absorbance of light in each beaker. Results table

Nitrate concentration (%)

Absorbance

Experiment

1 2 3 Average

0 0.09 0.00 0.00 0.03

0.25 0.12 0.00 0.02 0.05

0.5 0.15 0.06 0.07 0.09

1 0.24 0.10 0.13 0.16

1.5 0.23 0.16 0.15 0.18

National 5 Biology Assignment | Session 2017-18 Candidate 1 evidence

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The graph shows that as the nitrate concentration increases the absorbance also increases. This is because more algae has grown. Internet/literature research

- New Higher Biology with Answers by James Torrance, Page 266, ISBN: 0-340-74320-4 Analysis: My experimental data and the data from the book both show that as the concentration of nitrate increases the algal growth increases but the data from the book shows that it doesn’t keep rising it levels off. Conclusion: In conclusion increasing the nitrate concentration increases the rate of algal growth. Evaluation: The first sets of results are higher than the other 2. I think this might be because I didn’t stir the beakers the same each time. I should have made sure that I stirred each beaker for the same length of time.

National 5 Biology Assignment | Session 2017-18 Candidate 1 evidence

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