Photosynthesis C1.3 Flashcards
What are phototrophs?
organisms that use sunlight to make carbon compounds from water and O2.
What are heterotrophes?
organisms that obtain food from other organisms.
What light does photosynthesis use?
visible range of the electromagnetic spectrum
What is the wavelength of visible light?
400-700mm
What is dispersion?
the separation of visible light into different colors” red, orange, yellow, green, blue, violet
What affects the bend of the light wave?
frequency and wavelength upon passage through a prism.
What is pigment?
chemical molecules that absorb visible light and reflect light which includes the colors that we see.
Which colors are absorbed and which are reflected?
red/blue absorbed
green reflected
What are photosynthetic pigments responsible for?
the absorption of light in plant leaves
Where are photosynthetic pigments?
embedded in the thylakoid
What is the porphyrin ring?
light absorbing head with magnesium center of a chlorophyll
What is the hydrocarbon tail of
tail of the chlorophyll that interact with hydrophobic regions of proteins inside the thykaloid membranes
What is the photosynthesis equation?
6CO2 + 6H2O –> C6H12O6 + 6O2
What are three limiting factors of photosynthesis?
temperature, CO2, light
How does temperature limit photosynthesis?
as temperature rises, the rate of collision also increases. an optimum is reached and begins decreasing when the temperature starts to denature enzymes
How does CO2 limit photosynthesis?
When CO2 is low, there isn’t enough CO2 for plants to use for photosynthesis, but when there is too much CO2, the plants can not use all of it, so they reach a plateau/another factor has become limiting.
How does light limit photosynthesis?
When light is low, there isn’t enough light (energy) for plants to use for photosynthesis, but when there is too much light, the plants can not use all of it, so they reach a plateau/another factor has become limiting.
Why are factors affecting rate of photosynthesis considered limiting factors?
each factor can limit the rate if they are below the optimal level. HOWEVER, in combination, only one factor will limit the rate. the factor furthest from its optimum.
Absorbtion spectrum
a graph showing the relative amount of light absorbed at each wavelength by each pigment of a plant
Action spectrum
a graph showing relative effectiveness of photosynthesis at different wavelengths.
What is the photosystem?
a protein complex found in the thylakoid membrane inside chloroplasts. they harvest light by passing on energy from photons until it reaches the reaction center chlorophyll.
What is the photosystem composed of?
reaction center which are two special chlorophyll a molecules and light harvesting antenna pigments which are pigments bound to proteins.
What happens when electrons drop down to ground state?
heat and energy is released.
Explain the process of light hitting photosystem II?
- accessory pigments in photosystem II absorb light causing the electrons to get excited.
- this energy is absorbed by adjacent pigment molecules to become excited too
- this process of excitation energy transfer is repeated across the antenna pigments
- the energy is transferred until the reaction center chlorophyll is reached.
- at the reaction center chlorophyll, the electrons are transferred to an electron acceptor
What are the advantages of the structured array of different types of pigment molecules in a photosystem?
- different pigment molecules can absorb light in different ranges of wavelengths thus maximizing ability to use light
- antenna pigment molecules are in close and precise orientation which is crucial for efficient energy transfer
- more pigments to intercept randomly scattered photons which means a higher chance of absorption
- pigment molecules in the photosystem are interdependent which means they cannot perform photosynthesis individually
What is the light dependent reaction?
conversion of light energy into chemical energy in the form of ATP and NADPH and waste product of O2. carried out in the thylakoid membrane
What are outcomes of light dependent reaction in photosystem II?
- generation of oxygen
- production of ATP
- reduction of NADP
What are the steps of oxygen generation by photosystem II?
- photolysis
- photo-activation
- redox reaction
- Explain the 3 steps of oxygen generation in PSII
- H2O is split by the energy of light and enzymes to produce electrons, protons, and oxygen.
- the electrons replenish the chlorophyll a pigment to return it to its ground state by filling the “holes” - a photon of light is absorbed by a pigment in PSII and transferred to other pigments until it reaches chlorophyll a at the reaction center.
- the energy excited an electron to a higher energy - chlorophyll a is oxidized when the electron leaves to the acceptor and the primary electron acceptor is reduced when the electron attached.
- Explain the steps of ATP production by chemiosmosis
- the excited electron pass from the primary electron acceptor down to an electron transport chain.
- energy is lost at each transfer - with energy from the electron transport chain, H+ ions from the stoma are pumped into the thylakoid space.
- generating a concentration gradient of H+ - chemiosmosis - accumulating H+ causes the pH to drop and the establishment of a proton gradient.
- the flow of protons through ATP synthase allows phosphorylation of ADP +Pi –> ATP - electrons keep moving down to the next electron carrier
- Explain the steps of reduction of NADP by photosystem I
- at the same time, a photon of light is absorbed by a pigment in photosystem I, resulting in displacement of a electron from P700 and transfer of an electron with a higher energy state to lower.
- the denergized electron from PSII fills the vacancy - electron with higher energy is passed down an electron transport chain to carrier ferrodoxin
- enzyme NADP reductase catalyzes transfer if electrons from ferrodoxin to carrier NADP+.
- two electrons required to fully reduce NADP+ –> NADPH
REPEAT 2X
What is the cyclic photosynthesis?
instead of excited electrons going to ferrodoxin then NADP+ reductase, it goes back to the cytochrome complex to become cyclic.
- electrons move down remaining ETC from the cytochrome complex to allow ATP production via chemiosmosis
What is special about cyclic photosynthesis?
- only occurs in bacteria
- ATP generated more rapidly
What is the great oxidation event?
a period in earth’s history, roughly 2.4 billion years ago, when the atmosphere experienced a significant rise in oxygen levels
What are some outcomes of the great oxidation event?
- first glaciation event due to a reduction in green house effect
- a drop in temperature as a result of decrease in CO2 and methane
- oxidation of dissolved iron in water, resulting in precipitation of it, resulting in formation of bonded iron structures seen in many iron ores today
Light independent reaction
aka the calvin cycle, is when CO2 is foxed by combining it with a molecule called ribulose bisphosphate to produce an intermiediate product. it follows the light dependent reaction and require ATP and NADPH to produce sugars like glucose.
What are the stages of the calvin cycle?
- carbon fixation
- triosephosphate synthesis
- rubisco regeneration
What happens during carbon fixation of the calvin cycle?
3 CO2 molecules combine with 3 RuBP (that has 5 carbons) to form 3 short lived unstable 6 carbon compound… which immediately splits into 6 separate 3 carbon molecule (PGA)
What is rubisco?
an enzyme which catalyzes the binding of CO2 to RuBP. it is the most abundant enzyme. a high concentration of it is needed in the stoma because it works relatively slowly and are not effective in low concentrations when doing carbon fixation
What happens during synthesis of triosephosphate of the calvin cycle?
6 PGA molecules are reduced by 6 NADPH, donating its electrons. those 6 PGA also become phosphorylated by 6 ATP into 6 ADP. then, 6 triosephosphates are created, 1/6 going to make carbohydrates, amino acids, carbon compounds
What happens during the rubisco regeneration of the calvin cycle?
5/6 of the triosephosphate used for regeneration ribulose bisphosphate, 3 ATP phosphorylates into 3 ADP
Synthesis of starch using products of calvin cycle and where they are stored?
many glucose monomers joined together through condensation reactions. temporarily stored in chloroplasts, they look like white blobs.
What is the connection between LDR and LIR?
- lack of light stops LIR because it needs the ATP and electron carriers produced by LDR, which requires light
- lack of CO2 prevents PSII from functioning because CO2 is an electron acceptor in PSII, no CO2 means the electrons have no where to go in the ETC to create energy.
