This experiment involves using a photosynthometer to investigate how temperature affects the rate of photosynthesis in the elodea. Using this apparatus makes it possible to measure the rate of oxygen production by the elodea specimen, while varying the temperature. Bubbles of oxygen molecules are collected in a capillary tube of the apparatus. When a suitable volume of gas has been collected in five minutes, it can be drawn (by a syringe) as bubbles along side the scale and the length of the bubbles measured.
The volume of oxygen produced is calculated by multiplying the length of the bubble(s) by pie, which is then multiplied by 0.82 (radius of the tube). The results from this experiment have revealed that an increase in temperature correlates to an increase in the rate of photosynthesis up to 45o C. Beyond this temperature, the rate of photosynthesis starts to decrease in a non uniform manner. Aim: To investigate how temperature affects the rate of photosynthesis in the elodea specimen. Introduction: Photosynthesis is trapping or fixation of carbon dioxide followed by its reduction to carbohydrate (triose phosphate), using hydrogen from water.
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The necessary energy comes from the absorbed light energy. Light nCo2 + nH2O ======> (CH2O)n + O2 At high light intensities the rate of photosynthesis increases as the temperature is increased over a limited range. At low light intensities, increasing the temperature has a little effect in increasing the rate of photosynthesis1. Research has suggested that photochemical reactions (reactions dependant on light) are generally not affected by temperature. Having said this, research had also stressed that temperature can have a significant impact on the rate of photosynthesis.
Thus a firm conclusion can be made that photosynthesis compromises two processes known as the ‘light dependant photochemical stage’ & the ‘light-independent temperature dependant stage’. From this we can see that light independent stages are primarily influenced by temperature. In the chloroplast lamellae, light is trapped by pigments which can either be Chlorophyll’s (a and b) or Carotenoids (B carotene and xanthophyll). Different pigments absorb different wavelength of light. An absorption spectrum for a particular pigment describes the wavelengths at which it can absorb light.
The effectiveness of different wavelengths in promoting photosynthesis can be plotted an action spectrum: Fig 1- Obtained from http://users. rcn. com/jkimball. ma. ultranet/BiologyPages/A/AbsorptionSpectrum. gif Pigments such as the ones listed above are arranged in a photosytem within the chloroplast lamellae. A photosystem is a light harvesting cluster of pigments, each which consist of a central primary pigment, which can be one of the two forms of chlorophyll a, with an absorption peak of 700 nm (P700) in photosystem 1 and 680 nm (P680) in photosystem 2.
Surrounding accessory pigments can be either chlorophyll’s a, b or carotenoids. These pigments trap light and pass the energy on to photosytem 1. Fig 2 – www. sirinet. net/~jgjohnso /Ithylakoidmem. jpg The process of reduction of carbon dioxide into carbohydrate is dependant upon a hydrogen carrier molecule nicotinamide adenine dinucleotide phosphate reduced (or NADP red), which provides the necessary hydrogen atoms for the reduction to take place. In the light dependant stages NADP becomes NADP red , which is then used in the light independent (temperature dependant stage) for the formation of a carbohydrate.
The light independent stages involve cyclic phosphorylation and non-cyclic phosphorylation. As the name suggests, the first type of phosphorylation occurs in a cycle and other does not. During cyclic phosphorylation, a photon of light is trapped by photosystem 1, and an electron from the primary pigment (P700) is excited to a higher energy level. The electron is then trapped by an electron acceptor and passed via an electron chain. The energy released by the motion of the electron is used to synthesis ATP.
Followed by cyclic phosphorylation comes non-cyclic phosphorylation, in which both of photosystems 1 and 2 are involved. Light is trapped by both photosystems and electrons emitted by both primary pigments (P700 and P600). The electrons are absorbed by electron acceptors and passed along a chain of electron acceptor in a ‘Z- scheme’. In this the P700 in photosystem 1 absorbs electrons emitted by photosystems 2, and the P680 absorbs electrons emitted by the splitting of water during the process of photolysis. This is aided by an enzyme Ribulase bisphosphate carboxylase in photosytem 22.
The resultant reactions are shown below: 2H2O ====> 4H+ + 4e- + 1O2 2 2NADP ====> 2NADP red Two molecules on NADP red are formed (when NADP accepts two electrons from cyclic phosphorylation and a hydrogen ion) which are used in the light independent (temperature dependant) reactions to form triose phosphate. Oxygen is simply a waste product photolysis. The Z scheme is illustrated below: Fig 3 – obtained from: http://www. scool. co. uk/topic_quicklearn. asp? loc=ql&topic_id=15&quicklearn_id=2&subject_id=3&ebt=83&ebn=&ebs=&ebl=&elc=13.