Hansatech Instruments Ltd Oxygen Electrode Measurement Systems are based around the S1 Clark type oxygen electrode disc. The oxygen electrode systems featured on this website are configured to allow studies within a wide range of applications in cellular respiration and photosynthesis research.
Feb 6, 2017. Find out what the products of photosynthesis are and view the overall chemical reaction and equation. In the Light-Independent Process the Dark reaction. comes from the first phase of the photosynthetic process. This lesson will go over the basics of photosynthesis and its chemical reaction, explaining how the chemical equation is formed and how it can be.
Photophosphorylation is the production of ATP using the energy of sunlight. Photophosphorylation is made possible as a result of chemiosmosis. Chemiosmosis is the movement of ions across a selectively permeable membrane, down their concentration gradient. During photosynthesis, light is absorbed by chlorophyll molecules. Electrons within these molecules are then raised to a higher energy state. These electrons then travel through Photosystem II, a chain of electron carriers and Photosystem I. As the electrons travel through the chain of electron carriers, they release energy. This energy is used to pump hydrogen ions across the thylakoid membrane and into the space within the thylakoid. A concentration gradient of hydrogen ions forms within this space. These then move back across the thylakoid membrane, down their concentration gradient through ATP synthase. ATP synthase uses the energy released from the movement of hydrogen ions down their concentration gradient to synthesise ATP from ADP and inorganic phosphate.
The light-independant reactions of photosynthesis occur in the stroma of the chloroplast and involve the conversion of carbon dioxide and other compounds into glucose. The light-independent reactions can be split into three stages, these are carbon fixation, the reduction reactions and finally the regeneration of ribulose bisphosphate. Collectively these stages are known as the Calvin Cycle.
In addition to producing NADPH, the light dependent reactions also produce oxygen as a waste product. When the special chlorophyll molecule at the reaction centre passes on the electrons to the chain of electron carriers, it becomes positively charged. With the aid of an enzyme at the reaction centre, water molecules within the thylakoid space are split. Oxygen and H+ ions are formed as a result and the electrons from the splitting of these water molecules are given to chlorophyll. The oxygen is then excreted as a waste product. This splitting of water molecules is called photolysis as it only occurs in the presence of light.
A limiting factor is a factor that controls a process. Light intensity, temperature and carbon dioxide concentration are all factors which can control the rate of photosynthesis. Usually, only one of these factors will be the limiting factor in a plant at a certain time. This is the factor which is the furthest from its optimum level at a particular point in time. If we change the limiting factor the rate of photosynthesis will change but changes to the other factors will have no effect on the rate. If the levels of the limiting factor increase so that this factor is no longer the furthest from its optimum level, the limiting factor will change to the factor which is at that point in time, the furthest from its optimum level. For example, at night the limiting factor is likely to be the light intensity as this will be the furthest from its optimum level. During the day, the limiting factor is likely to switch to the temperature or the carbon dioxide concentration as the light intensity increases.
Glycerate 3-phosphate is reduced during the reduction reactions to a three-carbon sugar called triose phosphate. Energy and hydrogen is needed for the reduction and these are supplied by ATP and NADPH + H+ (both produced during light-dependent reactions) respectively. Two triose phosphate molecules can then react together to form glucose phosphate. The condensation of many molecules of glucose phosphate forms starch which is the form of carbohydrate stored in plants. However, out of six triose phosphates produced during the reduction reactions, only one will be used to synthesise glucose phosphate. The five remaining triose phosphates will be used to regenerate RuBP.
As we can see, there is a close relationship between the action spectrum and absorption spectrum of photosynthesis. There are many different types of photosynthetic pigments which will absorb light best at different wavelengths. However the most abundant photosynthetic pigment in plants is chlorophyll and therefore the rate of photosynthesis will be the greatest at wavelengths of light best absorbed by chlorophyll (400nm-525nm corresponding to violet-blue light). Very little light is absorbed by chlorophyll at wavelengths of light between 525nm and 625 (green-yellow light) so the rate of photosynthesis will be the least within this range. However, there are other pigments that are able to absorb green-yellow light such as carotene. Even though these are present in small amounts they allow a low rate of photosynthesis to occur at wavelengths of light that chlorophyll cannot absorb.
If the light intensity is not a limiting factor, there will usually be a shortage of NADP+ as NADPH accumulates within the stroma (see light independent reaction). NADP+ is needed for the normal flow of electrons in the thylakoid membranes as it is the final electron acceptor. If NADP+ is not available then the normal flow of electrons is inhibited. However, there is an alternative pathway for ATP production in this case and it is called cyclic photophosphorylation. It begins with Photosystem I absorbing light and becoming photoactivated. The excited electrons from Photosystem I are then passed on to a chain of electron carriers between Photosystem I and II. These electrons travel along the chain of carriers back to Photosystem I and as they do so they cause the pumping of protons across the thylakoid membrane and therefore create a proton gradient. As explained previously, the protons move back across the thylakoid membrane through ATP synthase and as they do so, ATP is produced. Therefore, ATP can be produced even when there is a shortage of NADP+.
Antarctica is involved in the carbon cycle in the ways that other ecosystems in the world are, notably in the absorption of carbon dioxide by plants (in Antarctica, these are overwhelmingly phytoplankton in the oceans), the production of carbon dioxide by the respiration of plants and animals and also the decay of dead plants and animals.
In between the early atmosphere and the present day, atmospheric carbon dioxide has fluctuated considerably and so has the temperature of the earth. At times the equator has been almost uninhabitable for most plants and animals on land due to to high temperatures while the poles have been very productive. At other times, the equator has been tropical and lush as it is now, while the poles are ice-bound and barren. It is not just carbon dioxide that has had this effect on the climate, though it has a significant part to play. and the position of the earth in space relative to the sun (the Milankovitch cycles) occur in cycles and affect the amount of solar radiation reaching the earth and so the temperature and climate. Other factors such as volcanic activity and the reflectivity of the surface due to snow/ice cover have their effects too so making the understanding of why the temperature at any particular time in the past not straightforward, particularly in estimating the point in the various cycles.