photosynthesis Flashcards
what is metabolism?
processing of carbohydrates to give us energy, via glycolysis and krebs cycle. glucose and oxygen into carbohydrates and water
how is light harvested?
the reaction of pigments with light. radioactive decay and radiation absorbed then re-emitted as light. Light is harvested in ATP generation, with the aid of trans-membrane electrochemical gradients. ATP is produced by the gradients of the membrane.
where do the actions of light harvesting take place?
Actions take place in the chloroplast, within the chloroplast thylakoids are stacked like mini-power cells.
what are thylakoids and what do they do?
Thylakoids membrane is the site of photosynthesis and chemiosmosis. These thylakoids are in the chloroplast, and has a light harvesting complex in the membrane. All abut generating proton gradients.
what happens to the electrons in energy transfer?
Also gets non-radiative decay. The excited electron can excite the next electron in the next molecule. Energy transferred to an adjacent molecule. Resonance energy transfer.
what is a pigment antenna and what does it do?
A pigment antenna complex harvests the light energy, light energy moved to reaction centre by resonance energy transfer. All of this happens very fast- picoseconds
do pigment antennas need energy?
Each of the pigment complexes are absorbing the energy, as the energy is being progressively lost. Need enough energy left, that when it gets to chlorophyll A, it can kick an electron out.
how do you convert light to electricity?
Converting light to electricity: this is what happens in the reaction centre. Decay by successive electron transfers. Needs to be energetically favourable. Requires adjacent molecule to have an available excited state at a lower energy level.
how is light energy absorbed?
Light energy absorbed by a special pair of chlorophylls. Initiates electron transfer chain across the membrane. A cascade that also acts as gearing.
what is oxidised?
Water, in the oxygen evolving complex. What is the mechanism of water oxidation? Involves a manganese cluster. Mn- transition metal, as multiple valences.
what is the role of the manganese cluster?
chlorophyll replaces lost electron, steals one from 3, which steals one from 4, etc. electron from chlorophyll is transferred to the exchangeable 5, and picks up H ion to stay neutral. When this happens 2 times, the reduced quinone is released and replaced with a fresh one.
After 4 cycles, 2 reduced quinones generated and Mn cluster is completely depleted of electrons. Replenished its electrons by stripping a water molecule thus liberating O2.
what happens after PSII?
Follow the plastoquinone. PSII helps generate H+ ion gradient for ATP generation. But also need reducing power t catalyse reaction NADH. But it hasn’t got enough energy to produced NADH, electros have lost too much energy to help produce NADH; electrons need another boost. this therefore shows the N complex of PSI and PSII.
Combination of PSIi and Psi allows sufficient generation of H+ ion gradient for TP generation for energy. NADPH generation for reducing power.
what is the light independent step?
Carbon fixation: first and crucial step. Combines 1 molecules CO2 with a 5-carbon sugar, to generate 2 3 carbon sugars.
Catalysed by the enzyme RuBisCo.
what happens in the calvin cycle?
Rubisco: ribulose-1,5-bisphosphate carboxylase/oxygenase. Cannot distinguish between carbon an oxygen. When it reacts with O2, it produces 2 carbon unit. When cyanobacteria first started generating O2, water product, they were poisoning themselves, so many plants, algae and bacteria have evolved CO2 concentration mechanisms. Within the cells and chloroplasts, they have a whole mechanism for the concentration of CO”, so they get the maximum out of biosynthesis.
when was the first form of life?
This happened 3.5 Ga years ago
