EFFECT OF Light wave Length on Photosynthisis

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Introduction

Plants are vital for the life of humans, animals and the ecosystem. They add beauty to the places that we live in and play a major role in the air purification process. Many of the medications we use to cure the diseases are made from plants. Plants and plant communities also provide the necessary habitat for wildlife and fish populations, which is very important to humans as particular wildlife and fish make up a significant portion of our diet. Most of all, the oxygen in the air we breathe comes from the photosynthesis of plants, and as a result, the quality of the air can be greatly influenced by plants. (Environment Explorers, 2008).

 Photosynthesis is one of nature's greatest miracles. Through this process, green plants absorb sunlight in their leaves and convert the photonic energy into chemical energy that is stored as sugars in the plants' biomass.

Photosynthesis is the source of the oxygen, which we breathe. Before plants appeared, the earth's atmosphere was high in carbon dioxide but contained no oxygen. The present atmosphere, by comparison, is about 0.035% carbon dioxide and 21% oxygen - thanks to photosynthesis (Calvin M., 1962).

Each year, 105 billion ton of biomass is produced by photosynthesis energy conversion (Quantum-mechanical) Optimization of Light-Harvesting in Photosynthesis, a biomass that is equal to two great pyramids of Giza is produced every single hour.

If we can learn from nature and develop an artificial version of photosynthesis we would have an energy source that is absolutely clean and virtually inexhaustible.

  Photosynthesis requires sunlight, carbon dioxide and chlorophyll, the reaction that occurs through the combination of these ingredients causes the release of oxygen as a gas and glucose, which is the form of sugar that plants need.

Chemically, cellular respiration is the exact opposite of photosynthesis. While photosynthesis occurs only in some cells, respiration occurs in all cells. (Jolliffe and Tregunna,2007)

Fig. 1 The photosynthesis equation

Six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.

In most plants, the primary organ in which photosynthesis occurs is the leaf. This is why, we are able to identify which plants photosynthesise by looking at their colour. If it is green, then it photosynthesises (Workman, 2000).

Factors that affect photosynthesis:

Photosynthesis is controlled by several determining factors.

  • Light intensity and wavelength (colour)
  • Temperature (needs to be at an optimum for the plant enzymes)
  • CO2 
  • H2O
  • O2
  • Chlorophyll

The light dependent reaction In the light dependent phase, the photosynthetic organism converts the light energy into energy carried by electrons. In photosynthesis the electrons are picked up by electron transport system, which uses the energy in the electrons to make energy carrying compounds called ATP. It also makes another compound called NADPH. The ATP and the NADPH are then used in the next step, which is called the light independent stage.

The light independent phase also known as the dark phase, takes place in the stromal, within the chloroplast. The result of the process is the conversion of carbon dioxide into sugar. This reaction does not depend on light, however it depends on the products of the light dependent phase. With the assistance of ATP (product of light reaction) and another chemical called NADPH, the carbon dioxide is turned into sugar.( CALVIN, M. 1962 ).

Aim:

The aim of this experiment is to determine whether changing the light colour /intensity can affect photosynthesis. This was done by fixing all the variables influencing this process and changing the colour of light source then measuring the concentration of Co2 and O2 gases.

Hypothesis:

It was hypothesised that as the light intensity increase, so will the rate of photosynthesis.  However, it was also predicted that once the light intensity reached a certain level, it would cease affecting the photosynthesis as the plants are receiving the maximum amount of light that they can use.

Materials

1.        Seedlings

2.        10 cm diameter pot

3.        Eco-chamber.

4.        Soil

5.        Water

6.        Light intensity sensor probes

7.        Oxygen sensor probes

8.        Carbon dioxide sensor probes

9.        Temperature probes

10.        Fluorescent light

11.        Timer

12.      Cellophane  (green, blue and red colour)

Methodology:

        The experiment was conducted between March 19th and March 29th 2012 at The Rockhampton Grammar School. Basil seedlings were obtained from Bunnings Warehouse, Rockhampton. Seedlings were transferred to 10cm diameter pots. 365g of soil was weighed and added. (The seedling had 40mL of water added to the soil and placed in the Eco-chamber. The oxygen, carbon dioxide, temperature and light probes were placed in to the eco-chamber. The fluorescent light was turned on with the timer set to have the light come on at 6am and turn off at 6pm. The Eco-chamber was placed under the light and the data logger was turned on. The data logger was set to read and record oxygen, carbon dioxide, light and temperate levels in the Eco-chamber. The readings were taken every 30 minutes for 48 hours. After 48 hours) Process1, the data was saved and collected. The plant was removed from the chamber and the chamber was wiped dry. A new basil seeding was potted into a 10cm pot with approximately 365g soil. The seeding had 40mL of water added and was placed into the Eco-chamber. The oxygen, carbon dioxide, light and temperature probes were placed in the Eco-chamber and a sheet of red cellophane was wrapped around the outside. The data logger was set to record the oxygen, carbon dioxide, light and temperature every 30 minutes for 48hrs. Process 1 was repeated at 48-hour intervals, using different coloured cellophane (green, and blue) wrapped around the outside of the Eco-chamber. After all the coloured cellophane was used the final seedling was not placed under the light but in a dark cupboard. (No results were provided for this part). Again the carbon dioxide, oxygen, temperature and light probes were all placed in the Eco-chamber. The readings were recorded at 30 minutes intervals for 48 hours. The zero hour was 02:00pm for the experiments. Once the analysis was complete the results were recorded.

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Results

Table and diagram (1) showing the readings over 48 hours of the effect of a change in the intensity of blue light on the CO2 AND O2 CONCENTRATION

Blue Light Table 1

  We can notice that the changes in light intensity has a minor influence on the O2 production, while Co2 concentration shows dramatic variation

When light intensity was zero, the process of photosynthesis continued and the concentration of ...

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