Investigating the effect of temperature on the rate of photosynthesis

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Investigating the effect of temperature on the rate of photosynthesis

Contents                                                                         Page

Abstract:…………………………………………………………………….

Aim:…………………………………………………………………………

Introduction:………………………………………………………………..        

                Light dependent reactions in photosynthesis-

                        Cyclic photophosphorylation……………………….

                        Non-cyclic photophosphorylation………………….

                Light independent reactions of photosynthesis……………..

                Factors affecting the rate of photosynthesis………………...

                Limiting factors……………………………………………..

Prediction:……………………………………………………………………

Preliminary experiment:

                Method………………………………………………………

                Results        ………………………………………………………

        Evaluation……………………………………………………

Apparatus:…………………………………………………………………...

Method:………………………………………………………………………

Diagram:…………………………………………………………………….

Safety:………………………………………………………………………..

Key variables:………………………………………………………………..

Results:……………………………………………………………………….

Graphs:………………………………………………………………………..

Conclusion:

                T-test for 0oC and 35oC………………………………………

                T-test for 0oC and 65oC………………………………………

                T-test for 35oC and 65oC……………………………………..

        Discussion…………………………………………………….

Evaluation:

                Anomalous results……………………………………………

                Limitations……………………………………………………

                Significant limitation…………………………………………

                Accuracy……………………………………………………..

                Reliability…………………………………………………….

                Errors and their effects……………………………………….

                Improvements………………………………………………..

Abstract:

Before starting my investigation on how temperature affects the rate of photosynthesis I carried out some research into photosynthesis. From this initial research I made a prediction based on the evidence that I found about the enzyme rubisco that is used in the dark stages of photosynthesis, and also on the limiting factors of light intensity, carbon dioxide concentration and temperature. I then went on to carrying out a preliminary experiment from which I learnt the factors that made the investigation inaccurate, therefore improving on them for my actual experiment. During my actual experiment I used 7 different temperatures ranging from 0oC- 65oC. The elodea was placed in these temperatures and a light shone on them for 5 minutes. The elodea was attached to a scale and syringe that was used to pull through oxygen bubbles so we could measure the rate of oxygen released and relate this to the rate of photosynthesis. I found that the rate of photosynthesis increased with temperature. The temperature peaked at 42oC, after this point the rate started to decrease. We collected a class average and did 3 T tests to compare 2 sets of results. The T test allows us to see whether the means of the sets of data differ significantly. I am 95% sure that there is a significant difference in my results between 0oC and 35oC, 0oC and 65oC, and 35oC and 65oC.

Aim: The aim of this experiment is to evaluate the effect of varying the temperature on the rate of photosynthesis. This will be done by measuring the rate of oxygen released from the olodea.

Introduction:

In my experiment I will be measuring the volume of oxygen released from the elodea by shining a lamp to give the elodea light energy needed for photosynthesis to occur. I will repeat the experiment with the elodea in different temperatures to see the affect of this on photosynthesis. From the volume of oxygen released we will use this to predict the rate of photosynthesis.

Photosynthesis is the process by which plants that contain chlorophyll use sunlight to convert carbon dioxide and water into carbohydrates and oxygen. (http://www.chemsoc.org/networks/learnnet/cfb/Photosynthesis.htm). The trapped carbon dioxide is using the hydrogen from water to form the carbohydrate (commonly hexose sugars and starch). Here light energy is converted to chemical energy. The overall equation is written as:

 

There are two sets of reactions involved in photosynthesis. These are the light-dependant reactions, where light energy is needed, and light-independent reactions, where light energy is not needed. In our experiment the light energy source will be a lamp shining directly on the elodea. The light dependant reactions take place in the presence of suitable pigments that absorb certain wavelengths of light. Light energy is used to split water into hydrogen and oxygen. Oxygen is a waste product of the reaction. In our experiment we will measure the amount of oxygen released by pulling the oxygen bubbles released with a syringe and measure this using a scale. Light energy is also needed to provide chemical energy (ATP) for the reaction of carbon dioxide to carbohydrate in the light-independent reaction.

Photosynthetic pigments trap light energy. Different pigments absorb different wavelengths of light. The photosynthetic pigments of higher plants form two groups: chlorophylls and the carotenoids, each absorb different wavelengths of light so that the total amount of light absorbed is greater than if a single pigment were involved.

Chlorophyll absorbs light from the visible part of the electromagnetic spectrum. Chlorophyll is made up of different pigments: chlorophyll a, chlorophyll b, and chlorophyll c etc. mainly in the red (650- 700nm) and blue (400- 450nm) regions of the light spectrum as shown by the absorption spectrum graph and also the action spectrum. It absorbs least in the green region (550nm), which means it is mostly reflected, and why plants appear green.

The carotenoids absorb mainly in the blue-violet region of the spectrum.

The light energy that is absorbed excites electrons in the pigment molecules. When a solution of chlorophyll a or b is illuminated with ultraviolet light, a red fluorescence will appear. This is because the ultraviolet light absorbed excited the electrons. In a solution that contains only extracted pigment, the absorbed energy cannot usefully be passed on to do work and electrons return to their unexcited state and the absorbed energy is transferred to the surroundings as thermal energy and as light at a longer and less energetic wavelength than that which was absorbed, this is the red fluorescence. This is the energy that drives the process of photosynthesis in the system.

The light-dependant reactions of photosynthesis

These reactions occur in the grana, and include the synthesis of ATP in photophosphorylation and the splitting of water by photolysis to give hydrogen ions. The hydrogen ions combine with a carrier molecule NADP to make reduced NADP. ATP and reduced NADP are passed from the light-dependant to the light- independent reactions. The water in our experiment will be contained in the test tube the elodea is placed in, therefore it will be taken from here to be used in photosynthesis.  

Photophosphorylation of ADP to ATP can be cyclic or non-cyclic depending on the pattern of electron flow in one or both photosystems.

Cyclic photophosphorylation:

This type of photophosphorylation involves only photosystem I. Light is absorbed by chlorophyll molecules in photosystem I and is passed to chlorophyll a (P700). An electron in the chlorophyll a molecule is excited to a higher energy level and is emitted from the chlorophyll molecule. Instead of falling back into the photosystem and losing its energy as fluorescence, it is captured by an electron acceptor and passed back to a chlorophyll a (P700) molecule via a chain of electron carriers. During this process enough energy is released to synthesise ATP from ADP and an inorganic phosphate group. The ATP then passes to the light-independent reactions. The electron is then returned to the photosystem to become stable

Non-cyclic photophosphorylation:

Non-cyclic photophosphorylation involves both photosystems involves both photosystems in the electron flow. Light is absorbed by both photosystems and excited electrons are emitted from the primary pigments of both reaction centres (P680 and P700). These electrons are absorbed by electrons acceptors and pass along chains of electron carriers leaving the photosystems positively charged. The P700 of photosystem I absorbs electrons from photosystem II. P680 receives replacement electrons from the splitting of water. As in cyclic photophosphorylation, ATP is synthesised by the ADP getting added to a phosphate group, as the electrons lose energy whilst passing along the carrier chain.

Photosystem II includes a water-splitting enzyme which catalyses the breakdown of water (photolysis):

Oxygen is a waste product of this process. The hydrogen ions combine with electrons from photosystem I and the carrier molecule NADP to give reduced NADP.

This passes to the light-independent reactions and is used in the synthesis of carbohydrate.

The light-independent reactions of photosynthesis

These series of reactions occur in the stroma. The fixation of carbon dioxide is a light-independent process in which carbon dioxide combines with a five-carbon sugar, ribulose bisphosphate  (RuBP), to give two molecules of a three-carbon compound, glycerate 3-phosphate (GP). When carbon dioxide concentration is low less GP can be produced. The carbon dioxide in our experiment will come from the H20 from which it is dissolved. We will add sodium bicarbonate to increase the amount of carbon dioxide the elodea is exposed to, therefore will increase the rate of photosynthesis.

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In the presence of ATP and reduced NADP, GP is reduced to triose phosphate (3-carbon sugar).

The enzyme ribulose bisphosphate carboxylase (rubisco) catalyses the combination of carbon dioxide and RuBP.

Some of these triose phosphates condense to form hexose phosphates, sucrose, starch and cellulose or are converted to acetylcoenzyme A to make amino acids and lipids. Others regenerate RuBP. This cycle is the Calvin cycle.

http://www.bio.umass.edu/biology/conn.river/calvin.html

Factors affecting the rate of photosynthesis:

The main factors affecting the rate of photosynthesis are light intensity, temperature and carbon dioxide concentration.

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