4Location: chloroplast or prokaryotic equivalent. Reaction: Traps light energy (photons) and converts it into chemical energy.Organisms: Prokaryotic and EukaryoticSubstrate: Inorganic CO2 and H2OProducts: Organic compounds (sugars) and O2
5Environments: Aquatic environments with light Terrestrial environments with lightExtremophiles can do photosynthesis at some extreme latitudes and altitudes. At extreme high temperatures we see photosynthesis in geothermal active regions.
63.8.2 State that light from the Sun is composed of a range of wavelengths (colours). State means to give a specific name, value or other brief answer without explanation or calculation.
7Light from the sun is composed of a range of wavelengths (colours). The visible spectrum illustrates the wavelengths and associated colour of light.Combined together these wavelengths give the 'white' light we associate with full sunlight.The shortest wavelengths are the 'blues' which have more energy.The longer wavelengths are the 'reds' which have less energy.
83.8.3 State that chlorophyll is the main photosynthetic pigment. State means to give a specific name, value or other brief answer without explanation or calculation.
9Chlorophyll is the main photosynthetic pigment Chlorophyll is the main photosynthetic pigment. This is where light energy is trapped and turned into chemical energy.The head of the molecule is polar and composed of a ring structure. At the heart of this ring structure is the inorganic ion magnesium. This is the light trapping region of the chlorophyll molecule.The tail of the molecule is non polar and embeds itself in membranes in the chloroplast.There are other pigments, reds, yellows and browns but these are only usually seen in the experimental chromatography or the autumnal colours of deciduous trees in a temperate climate.
10Outline means to give a brief account or summary 3.8.4 Outline the differences in absorption of red, blue and green light by chlorophyll.Outline means to give a brief account or summary
11The 'peaks' show which wavelength of light are being absorbed. Look at the x-axis for colours of light absorbed at the 'peaks'.The main colour of light absorbed by chlorophyll is red and blue.The main colour reflected (not absorbed) is green.Hence why so many plants are seen as green, the light is reflected from the chlorophyll to your eye.
133.8.5 State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.State means to give a specific name, value or other brief answer without explanation or calculation.
14(a) Light is absorbed by chlorophyll molecules (green) on membranes inside the chloroplast. This is the light trapping stage in which photons of light are absorbed by the chlorophyll and turned into chemical energy (electrons).(b) The chemical energy (electrons) is trapped in making ATP.Photolysis(c):Water used in photosynthesis is split which provides:Hydrogen for the formation of organic molecules. (C6H12O6)Oxygen gas is given off.
153.8.6 State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.State means to give a specific name, value or other brief answer without explanation or calculation.
16H+ from the splitting of water are combined with carbon dioxide to form organic compounds like sugar.Bonds are formed between the carbon, hydrogen and oxygen using the energy from ATP (which came form the sun).C, H, O are enough to form lipids and carbohydrates.With a Nitrogen source amino acids and therefore proteins can be made.Plants have this remarkable ability to manufactory all their own organic molecules and by definition all the basic organic molecules required by all life forms.
183.8.7 Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.Explain means to give a detailed account of causes, reasons or mechanisms.
19Processes like photosynthesis and respiration can be measured by either: Depletion of substrate.Accumulation of productsInvestigation: Photosynthesis:Carbon dioxide + water ---> Organic molecule + OxygenThe rate of photosynthesis can therefore be measured by:Depletion of substrate which includes measuring how much carbon dioxide has been used or how much water is used.Accumulation of product which might include measuring how much oxygen is produced or organic molecules (biomass) produced.
20In this simple experiment the accumulation of oxygen is measure of rate of reaction. Independent variable: Light Intensity or wavelength of light.Dependent variable O2 vol. against timeMethod the collection of gas over water.Specimen: Pond weed Elodea
21Outline means to give a brief account or summary. 3.8.8 Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesisOutline means to give a brief account or summary.
22The effect of temperature on the rate of photosynthesis: Photosynthesis is a biological reaction and like all other such reactions there are steps that require the presence of enzymes.Temperature as we have already met is a change in the average kinetic energy of the particle.The graph the left should look familiar as this is the same one covered in the section on the effect of temperature on the rate of an enzyme catalysed reaction.(a) Increasing rate of photosynthesis as the kinetic energy of reactants increases.(b) Maximum rate of reaction of photosynthesis at the 'optimal' temperature.(c) Decrease in rate of photosynthesis as the enzymes become unstable and denature.
24The effect of carbon dioxide concentration on the rate of photosynthesis Carbon dioxide is one of the reactants of the reaction so this graph is very much like the effect of substrate on the rate of reaction.(a) O2 is used up as the plant is not photosynthesizing but only respiring.(b) As the concentration of the carbon dioxide (substrate) increases the rate of reaction increases.(c) The atmospheric levels of carbon dioxide and the associate rate photosynthesis.(d) Maximum rate of photosynthesis (see section e).(e) The is a range of values for different plants reaching their saturation level with carbon dioxide. One the saturation level has been reached there is no further increase in the rate of photosynthesis
26The effect of light concentration on the rate of photosynthesis The effect of light intensity on the rate of reaction.Light energy absorbed by chlorophyll is converted to ATP and H+ see sectionAt very low light levels (a) the plant will be respiring only not photosynthesizing.As the light intensity increases then the rate of photosynthesis increases.At high light intensities the rate becomes constant, even with further increases in light intensity there are no increases in the rate.The plant is unable to harvest the light at these high intensities and indeed the chlorophyll system can be damaged by very intense light levels.
28Draw means to represent by means of pencil lines 8.2.1 Draw and label a diagram showing the structure of a chloroplast as seen in electron micrographs.Draw means to represent by means of pencil lines
30Internal membranes called thylakoids which is the location of the light dependent reaction Stroma surrounding the thylakoids and inside the double membrane. This is the location of the light independent reaction that includes the Calvin cycle.The stroma often contains starch grains and oil droplets both products of photosynthesis
318.2.2 State that photosynthesis consists of light-dependent and light-independent reactions. State means to give a specific name, value or other brief answer without explanation or calculation.
34Light Dependent Reaction Energy of sun is trapped by chlorophyll molecules (oxidation)Photon energy is used to raise the energy of electrons which escape the chlorophyll (oxidation)This energy is coupled to the reduction of ADP to ATP and the coenzyme NADP+ is reduced to NADPH + H+ .The reaction must have light to take place.This reaction takes place on the thylakoid membranes.
35Light Independent Reaction Uses the chemical energy from the LDR to fix atmospheric carbon into organic molecules such as glucose.The process does not require light and can occur in both the light and dark periods.This reaction takes place in the stroma
368.2.3 Explain the light-dependent reactions. Explain means give a detailed account of causes, reasons or mechanisms.
37Light energy is converted into chemical energy. Chlorophyll molecules are attached to the thylakoid membranes.They are often associated with accessory pigments and other proteins to form Photosystem.At the centre of all photosystem are forms of chlorophyll a each of which is specialised to absorb a particular wavelength of light.Electrons within the chlorophyll absorb the energy from photons and this raises them to higher 'excited' states.Excited electrons are more easily lost from the chlorophyll which is a form of oxidation
38Summary of Non-Cyclic Photophosphorylation: 1. Light energy is trapped in two Photosystem.2. ATP is produced.3. The co-enzyme NADP+is reduced
39Cyclic Photophosphorylation 1) PS II absorbs light at a peak of 680 nm2) Electrons in chlorophyll are 'excited' and raised to the next energy level.3) Electrons are lost (oxidation) from PS II and picked up by acceptors like cytochrome4) The electrons transfer to other membrane proteins releases free energy in pumping H+into the thylakoid space which in turn birng about the synthesis of ATP5) The electron is taken up by PS I reducing this back to ground state.6) PS I has already absorbed lower energy electrons 700nm and released electrons at the more 'excited' higher energy level.7) The electron is passed in a series of redox reactions along membrane proteins.8) Free energy released is coupled to the reduction of co-enzyme NADP+Cyclic Photophosphorylation
40Cyclic Photophosphorylation When the ratio of NADPH + H+: NADP+ is high then only ATP is produced in a cyclic process.PS I does not generate NADPH + H+ but sends its 'excited' electron to a proton pump.
411. PS I is oxidised releasing an 'excited' electron. 2. The electron reduces the membrane proton pump. Protons are pumped into the thylakoid space. This generates ATP.3. The electrons are cycled back to PS I for its own reduction.
428.2.4 Explain photophosphorylation in terms of chemiosmosis State that photosynthesis involves the conversion of light energy into chemical energy.State means to give a specific name, value or other brief answer without explanation or calculation.
43Chemiosmosis theory is based on: Accumulation of a high concentration of H+ which is due to proton pumping.There being a concentration difference between two places which is the high concentration of H+in the thylakoid space and a lower concentration in the stroma.The protons diffuse through the core of the ATP synthetase.This drives the motor mechanism of the structure resulting the in the reduction of ADP to ATP.Note how the same mechanism was seen on the cristae membranes in respiration.
443.8.1 State that photosynthesis involves the conversion of light energy into chemical energy. State means to give a specific name, value or other brief answer without explanation or calculation.
458.2.5 Light-Independent Reaction The energy trapped from sunlight in the light dependent reaction (ATP and NADPH) is used to fix carbon from carbon dioxide into organic molecules.The reaction called the Calvin Cycle takes place in the stroma and is controlled by enzymes.Ribulose Bisphosphate Carboxylase (Rubisco) allows carbon (carbon dioxide) to be fixed into an initial organic molecule