d Antimony-135 is radioactive with a half-life of 1.7s i State what is meant by
ID: 1044542 • Letter: D
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d Antimony-135 is radioactive with a half-life of 1.7s i State what is meant by 'half-life 121 131 ii Calculate what percentage of a sample of this isotope would remain after 68 s. State three problems associated with generaxing electricity using nuclear power 4 Biofuels such as ethanol and biodiesel are becoming increasingly important as fuelh for motor vehicles. The energy stored in biofuels and fuels derived from petroleum originally came from the Sun a Chlorophyll is the green pigment in plants.The structure of chlorophy'l is shown below Explain what feature of the chlorophyll molecule allows it to absorb visible light. CH2 ?? CH2 HyC ? ? 0 CHj Write a balanced b Light energy from the Sun is converted into chemical energy in equation for photosynthesis. c The structure of one of the triglycerides in sunflower oil is shown below can be converted to biodiesel in a transesterification reaction with ethanol in the presence of a base i Write an equation for the reaction. ii Explain why the biodiesel formed in c i is less viscous than sunflower oil. 121 12] d Explain one advantage and one disadvantage of uxsing liquid biofuels, such as ethanol and biodiesel, as opposed to liquid fuels derived from petroleum. 121Explanation / Answer
a)
Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light.
Chlorophyll molecules are arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts. In these complexes, chlorophyll serves three functions. The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light. Having done so, these same centers execute their second function: the transfer of that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. This pair effects the final function of chlorophylls, charge separation, leading to biosynthesis. The two currently accepted photosystem units are photosystem II and photosystem I, which have their own distinct reaction centres, named P680 and P700, respectively. These centres are named after the wavelength (in nanometers) of their red-peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them. Once extracted from the protein into a solvent (such as acetone or methanol), these chlorophyll pigments can be separated into chlorophyll a and chlorophyll b.
A Photon of Light Excites the Chlorophyll Molecule
When a chlorophyll molecule absorbs light, the process of photosynthesis, or the transfer of light into sugar, begins. Chlorophyll is a green liquid inside one part of a plant cell: the chloroplast.
When light hits the chlorophyll molecule, it becomes excited. This energy passes through other chlorophyll molecules, and into the reaction center of Photosystem II: this is the location of the first stage of photosynthesis, and the electron transport chain.
For each photon of light that enters and excites a chlorophyll molecule, one electron is released from the reaction center of Photosystem II. When two electrons are released, they are transferred to Plastoquinone Qb, a mobile carrier, which picks up two protons and starts moving towards the Cytochrome b6f complex. Cytochrome b6f, like Photosystem II, is a complex where photosynthesis processes occur.
Plastoquinone Qb on the Move with Two Electrons
While Plastoquinone Qb is moving, the two electrons that were lost in Photosystem II have to be replaced. This is done by splitting water molecules. Hydrogen ions and oxygen are released as a by-product of replacing the two electrons.
Passing through the Cytochrome b6f Complex
Finally, Plastoquinone Qb reaches its destination: Cytochrome b6f complex, which is another complex in the electron transport chain. Here, it releases the two protons into lumen space (open space between a plant cell's organelles and molecules) and releases the two electrons into the Cytochrome b6f complex. The electrons travel through the complex, two hydrogen ions are released, and the electrons arrive at Plastocyanin, a mobile carrier like Plastoquinone Qb, which takes the electrons over to Photosystem I.
Electron Transport in Photosystem I and the Production of ATP
In Photosystem I, a complex in the electron transport chain that works similarly to Photosystem II, the chlorophyll molecules are also stimulated by light, in turn resulting in the release of electrons. Two electrons are transferred to Ferrodoxin, then to an enzyme called FNR (Ferrodoxin NADP Reductase). The two electrons, and one hydrogen ion, are attached to NADP to produce NADPH. This entire process stimulates the production of ATP from ADP and Pi in ATP synthase.
b)
Photosynthesis is the process in plants and certain other organisms that uses the energy from the sun to convert carbon dioxide and water into glucose (a sugar) and oxygen.
The overall balanced chemical equation for the reaction is:
6 CO2 + 6 H2O ? C6H12O6 + 6 O2
Where:
CO2 = carbon dioxide
H2O = water
light is required
C6H12O6 = glucose
O2 = oxygen
The reaction requires energy in the form of light to overcome the activation energy needed for the reaction to proceed. Carbon dioxide and water don't spontaneously convert into glucose and oxygen.
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