IB Biology Unit 14 (HL): Photosynthesis
Describe the shape of the curve for an absorption spectrum
- Both absorption and action displays peak at the blue (~450nm) and red (~670nm) - Both displays a drop at green/yellow region (~550nm)
Describe the shape of the curve for an action spectrum
- Both absorption and action displays peak at the blue (~450nm) and red (~670nm) - Both displays a drop at green/yellow region (~550nm)
Explain the role of ATP and NADPH to produce triose phosphate
- GP is converted to TP, which is a 3-carbon carbohydrate that can be used to make a range of carbohydrates by other pathways. - NADPH transfer hydrogen atom(s) to GP (reducing H) while the hydrolysis of ATP provides the energy.
Outline the process of carbon fixation in the stroma
- The CC begins with a 5-carbon compound called ribulose biphosphate (RuBP) - An enzyme called RuBP carboxylase (Rubisco) catalyzes the attachment of a CO2 molecule to RUBP (carbon fixation). - The resulting 6-carbon molecule is broken down into two 3-carbon compounds called glycerate-3-phosphate (GP)
State the three phases of light-independent reactions.
1) Carbon fixation — CO2 is covalently linked to a carbon skeleton (RuBP) by an enzyme called Rubisco. 2) Reduction — a carbohydrate is formed at the expense of ATP and NADPH. 3) Regeneration — RuBP reforms at the expense of ATP.
Outline the process of separating pigments using chromatography
1) Place a line of pigment extract from leaf tissue on one end of the filter paper and dip it in an inorganic substance. 2) As the solvent moves up the semi-polar paper, the pigments get moved as well. The components that adhere more strongly to the other paper travels more slowly compared to those which are less adhesive.
Write the chemical equation for photolysis
2H20 --light--> 4H+ +O2 + 4E-
Outline the importance of photolysis in the light-dependent reaction
4H+ contribute to the proton gradient used to make ATP. 4E- replace the electrons the reaction center chlorophyll lost during photoactivation of PSII.
State evidence that suggests chloroplasts were once free living prokaryotes
70s ribosomes, binary fissions, size, double membrane, own circular naked DNA.
Distinguish between an action spectrum and an absorption spectrum
Action: Overall rate of photosynthesis acting at each wavelength Absorption: wavelength of light absorbed by each pigment.
Define photosystem and reaction center
Are membrane proteins that contains many chlorophyll and other light harvesting pigments. There are two special chlorophyll molecules located at the reaction center.
Explain how movement of electrons through the electron transport chain leads to a proton gradient between the thylakoid space and the stroma
As electrons are passed from one carrier to the next through the chain, they lose/release energy. This is used to pump H+ ions from the stroma into the thylakoid space. This creates a H+ gradient , called a proton gradient, with a higher concentration of protons inside the thylakoid, a store of potential energy.
Define "limiting factor"
Chemicals depend on more than one essential condition, the rate of reaction will be limited by the factor nearest its minimum value. If the factor is changed to make it closer to the optimum, the reaction rate increases, but changing other factors will have no effect as they're not the limiting factor.
Outline process of photoactivation of the reaction center chlorophyll
Chlorophyll at the reaction center in PSII and PSI absorb energy from light, which triggers the release of high energy electrons (photoactivation).
Outline how electrons from photosystem I are used to reduce NADP
Chlorophyll molecules without PSI absorb light energy and pass it to the reaction center where de-energized electrons are re-energized. The excited electron pass along a chain of carriers which ultimately pass the electron to NADP+ and reduce it to NADPH. The pair of electron it carries can be used for redox reactions in the light-independent reactions.
State the location of the light dependent reactions of photosynthesis
Chloroplast, specifically thylakoids.
Draw and label a diagram of the chloroplast State the function of the following chloroplast structures: double membrane, thylakoids, pigment molecules, thylakoid lumen, and stroma
Double Membrane: normal membrane functions, evidence of endosynbiotic theory. Granum: A flat membrane stack of thylakoids so that it increases the SA:V (increase function). Thylakoid: contains pigment to carry light absorption, internal lumen is smal so proton gradient develops quickly, membrane contains of electron transport chain. Stroma: has the appropriate enzymes and pH for the Calvin Cycle.
State that the light dependent reactions of photosynthesis begin at Photosystem II
PSII is the first photosystem that ultimately generates a proton gradient used for the production of ATP. PSI is the second photosystem that ultimately reduce NADP.
Define visible light
Electromagnetic radiation in the range of 400-7000nm, which can be detected by the eye and used by plants.
State the energy conversion that occurs during photosynthesis
Energy can't be created/destroyed. The energy in the form of light is converted into chemical energy in the bonds of carbohydrates.
Define independent variable, controlled variable, and responding variable
IV: What you purposely change in an experiment. DV: What you measure during the experiment to see if the IV affect it. CV: Make sure only is affecting DV — all other limiting factors are kept constant.
Define photolysis State that the oxygen produced in photolysis is a waste product of photosynthesis
In photosynthesis light dependent reaction, light is converted to chemical energy in the molecules of ATP. Light is not only absorbed by the chlorophyll but water as well. Then there's the presence of light, water *splits* due to PHOTOLYSIS. Oxygen comes out as waste product.
State that the discovery of radioactive 14C isotope allowed Calvin to determine the pathway
Kamen and Ruben discovered the 14-carbon. Calvin replaced the 12-carbon dioxide supply to algae with 14-carbon dioxide. Samples are taken at short time intervals.
State that in the Calvin Cycle, triose phosphate is used to regenerate RuBP and create glucose
Of the six molecules of TP produced per three cycles, five TP are needed to regenerate three more RuBP, this leaves only 1 TP to form glucose.
State that to replace the electrons lost during photoactivation, the reaction center chlorophyll takes electrons by splitting it.
Once the plastoquinone becomes reduced, the chlorophyll in the reaction center is then powerful oxidizing agent, causing the water molecules nearest to split and give up its electrons.
State that (some) prokaryotes, algae and plants carry out photosynthesis
Prokaryotes were the first to perform photosynthesis around 3.5 billion years ago, they became a part of the algae and plants million of years later.
Calculate the Rf value for pigments using pigment chromatography
Rf value: (distance of pigment traveled)/(distance solvent traveled).
Name the enzyme that catalyzes carbon fixation (carboxylation) of RuBP
Rubisco AKA ribulose biphosphate carboxylase
State that six turns of the Calvin Cycle are needs to produce one molecule of glucose
Since glucose is a 6-carbon molecule, it takes 6 turns of the cycle to produce 1 glucose
Define pigment
Substances, often proteins, which absorbs light and therefore color appears to us the ones that the pigment doesn't absorb.
Explain why plants are green
Sunlight contains all the wavelengths of visible light. The main photosynthetic pigment in plants is the chlorophyll, which appears *green* because it reflects light most strongly in the green portion of the spectrum. Chlorophyll absorbs light most strongly in the *blue* portion followed by the *red* portion of the spectrum.
Outline chemiosmosis and the production of ATP in photosynthesis
The H+ ions (protons) will passively (with gradient, from high to low) move back across the thylakoid membrane through ATP synthase, an enzyme embedded in the membrane. The movement of protons is coupled to the phosphorylation by ATP synthase of ADP to yield ATP. (The addition of phosphate group to make ATP creates a more unstable and active molecule that can be used as energy in the Calvin Cycle).
State that electrons pass through a chain of electron carrier molecules
The electrons excited from chlorophylls in photoactivation are transferred to carrier molecules in the thylakoid membrane called the electron transport chain.
State that photosystem I and photosystem II are linked
The electrons lost from the special chlorophylls in the reaction center during photoactivation of PSI are continually replaced by the de-energized electrons from PSII that finished the ETC.
State the location of the light independent reactions of photosynthesis
The light-independent reactions takes place in the stroma, a protein rich fluid containing enzymes (Rubisco).
State the primary and accessory pigments found in chloroplasts
The primary pigment in the chloroplast is the chlorophyll (green). - Chlorophyll-A is the most abundant and has a darker green. - Chlorophyll-B is the less abundant and has a lighter green. - Carotenes are orange. - Protective pigments (red, violet, blue) attracts pollinators and protects DNA from UV light.
Define photosynthesis State the chemical equation for photosynthesis
The process in which cells synthesize organic compounds (eg. glucose) from inorganic compounds (H2O + CO2) in the presence of sun light.
State the use of ATP and NADPH for the light dependent reactions
The products of the light-independent reaction — NADPH and ATP — are to serve as energy sources for the light independent reactions of photosynthesis. - Light energy is converted to chemical energy in the form of ATP. - NADPH now carries two elections which can be used to carry out reduction reactions.
Define and state evidence for the "Great Oxidation Event."
The rise in oxygen concentration to 2% about 2.4 billion years ago is known as the Great Oxidation Event. * Banded ion formation in rocks dated between 2.4-2.2 BYO. * Only when iron dissolved in ancient oceans where it was exposed to oxygen resulted in rusting. Due to no other significant sources of oxygen are known, scientists attribute the rise in atmosphere O2 to biological synthesis.
State the relationship between wavelength and energy
The shorter the wavelengths, the more energy there is. The longer the wavelengths, the less energy there is.
List mechanisms for measuring the rate of photosynthesis
• Measuring CO2 uptake • H2O + CO2 -> H+ +HCO3- • Measuring O2 production: • Water displacement • # of bubbles • Measuring biomass: glucose production can be indirectly measure by a change in the plant's weight. After plant tissue has been dehydrated. Iodine staining will detect starch and can be qualified using a colorimeter.
