Photosynthesis of Elodea

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Abstract: An experiment was carried out to determine how certain factors such as light intensity and availability of carbon dioxide, affected the rate of photosynthesis. The rate of photosynthesis was measure by the amount of oxygen produce (cm3/min).

A valid conclusion was made and most of the results were in accordance with the prediction, although there were some anomalies present. The errors and limitations were evaluated and some improvements were suggested.

Photosynthesis is an essential importance to organisms. It is the process by which green plants and a few organisms convert sunlight energy into chemical energy which is stored in molecules. Photosynthesis in green plants generally involves the green pigment chlorophyll and produces oxygen as a byproduct. This can be shown in the equation:

The rate of photosynthesis is dependent on environmental factors such as light intensity, availability of carbon dioxide, availability of water, nutrients and temperature. The most important factors are the availability of light and carbon dioxide, which are limiting factors. Temperature is of some importance, however its influence is less clear because it is dependent on the other two limiting factors (light and CO2) and the temperature tolerance of the plant.

The peak rate of photosynthesis is constrained by a limiting factor. This factor will prevent photosynthesis from rising above a certain level even though other factors essential for photosynthesis are improved. This liming factor will control the maximum rate of the photosynthetic reaction.

Photosynthesis takes place in two major parts:  ATP and NADPH production (light reactions) and carbon fixation (“dark” reactions). – (Photosynthesis and the Environment , 1) Both processes are dependent upon each other – the relative concentrations of NADPH and ATP due to their consumption in the Calvin cycle influences photosystem mechanisms, and the amount of ATP and NADPH produced in the light reactions dictates how fast CO2 is fixed in the Calvin cycle. The Calvin cycle can be defined as a cyclical series of biochemical reactions that occur in the stroma of chloroplasts during photosynthesis. It includes the light-independent reactions such as carbon fixation, reduction reactions and ribulose 1,5-diphosphate (RuDP) whereby sugars and starch are ultimately produced – (2)

Water is required in photosynthesis. However, only 1% of water passing up the xylem is actually used in photosynthesis. The rest is used in other chemical reactions, to hydrate cells, or is lost in transpiration. If there is not enough water to hydrate the cells and keep them turgid, the stomata close. This prevents CO2 entering the leaves, so photosynthesis decreases.

Water enters the root and is transported up to the leaves through the xylem. Land plants must guard against drying out and so have evolved specialised structures known as stomata to allow gas to enter and leave the leaf. Carbon dioxide cannot pass through the protective waxy layer covering the leaf, but it can enter the leaf through an opening edged by two guard cells. Similarly, oxygen produced during photosynthesis can only pass out of the leaf through the opened stomata. Unfortunately for the plant, while these gases are moving between the inside and outside of the leaf, a great deal water is also lost.

An investigation was carried out to determine how limiting factors can change the rate of photosynthesis.

Aim: To determine whether factors such as light intensity and concentration of sodium hydrogen carbonate (NaHCO3) will affect the rate of photosynthesis in the water plant, elodea.

Hypothesis: The higher the light intensity the faster the rate of photosynthesis as this provides more energy available for plants photosynthesis to take place. In addition, the higher the concentration of NaHCO3, the faster the rate of photosynthesis will become. This is due to the NaHCO3 providing more...
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