L17. The chloroplast and the photosynthesis

Introduction:

We're going to investigate the photosynthesis in an algae. During the photosynthesis, plants and algae produce oxygen.

In this experiment we want to observe how light intensity affects the rate at which photosynthesis occurs and the rate of oxygen production.

Objetives: 

- Relate the light intensity with the photosynthesis process.
- Measure the rate of photosyntesis.
- Identify the products of the process and the variables that can affect it.

Materials: 

- Algae (Elodea)
- 600 ml beaker
- Test tube
- Funnel
- Tap water 
- Light source
- Metric ruler

Procedure: 

1. First we assigned the different distances to do the experiment and compare the results to each group.
2. We took the 600 ml beaker and placed 7 g of an algae under a clear funnel inside the beaker. The funnel was raised off the bottom on pieces of blue-tack to allow unhampered diffusion of CO2 to Elodea. 
3. We didn't have sodium bicarbonate so we filled the beaker with tap water, the algae and the funnel should be completely under the water.
4. Then we filled a test tube with tap water and placed the thumb over the end of the test tube. We turned the test tube upside down taking care that no air enters and no water comes out and we put this test tube over the end of the funnel (the skinny part)
5. We marked the level of the water on the surface of the test tube with a marker pen.
6. Each group placed the preapartion close to a light source, each group placed the preparation in a different distance 5, 10, 20 and 25 cm, and one with no light source.
7. We also measured the temperature.
8. Finally we left this preparation for and hour and a half. After this time we measured the difference of gas accumulation on the top of the test tube. 

Distance: 5cm

Questions: 

1- Identify the dependent and the independent variable of this experiment.
Dependent: gas production, Independent: distance (intensity of the light)
  
2-Using the data from your results prepare a graph and describe what happened to the amount of gas in the test tube.

Names	Distance	Gas Production	Temperature
Laura i Andrea	25 cm	0,5 cm	22,7 º C
Edu i Ignacio	0 cm	0 cm	21,5º C
Inés i Maria	20 cm	0,3 cm	22,5º C
Myriam i Paula	5 cm	0,5 cm	26,5º C
Liza i Anna	10 cm	0,4 cm	24º C

Myriam and I had 5 cm distance and our water level decreased 0,5 mm in an hour and a half. 

If you have a little distance, the light intensity is higher and the phtoshyntethic rate will be higher too.

We controled the temperature and the algae quantity because this could have and influence on the result. Also, we think that Laura's and Andrea's result is incorrect because the distance is higher so the water level decrease should be lower than the other. Maybe they measured it incorrectly.

3-How much gas was producted in the test tube after one hour? And an hour and a half?
Results in the graphic 

4- Write the photosynthesis equation. Explain each part of the equation. Which subtances are produced by photosynthesis. Which gas is produced that we need in order to live? 

From Laura's blog

Substances produce by photosyntesis; 

Gas is produced that we need in order to live: Oxygen