Unit 3 - Photosynthesis Flashcards
what are the 4 different types of organisms
determined by where the organism gets its carbon
1. autotrophs - able to convert an inorganic form of carbon into an organic form of carbon
2. photo autotrophs - get energy from sunlight, eg. plants and algae
3. chemo autotrophs - get energy from chemical compounds, eg. sulfur oxidising bacteria, nitrogen fixing bacteria and iron oxidising bacteria
4. heterotrophs - organisms that obtain their carbon from organic molecules synthesized by other organisms, eg. animals. fungi, protists, most bacteria
what are the equations of photosynthesis and respiration
Photosynthesis -
Energy + 6CO₂ + 12H₂O = C ₆H₁₂O₆ + 6O₂ +6H₂O
or Energy + Carbon dioxide + water = Glucose + Oxygen +water
(CO₂ undergoes reduction to glucose, while water undergoes oxidation to oxygen)
Respiration -
C₆H₁₂O₆ + 6O₂ = 6CO₂ +6H₂O + Energy
(glucose undergoes oxidation to carbon dioxide, while Oxygen undergoes reduction to water)
What are the two stages of photosynthesis
- Light dependent/Light capture
- needs sunlight to occur
- energy from sun is captured into usable chemical forms - Light independent/Carbon fixation
- independent of light
- energy is used to synthesize carbohydrates from CO₂
why do cells need light energy
light energy is required for the production of NADPH and ATP, in order to further power the calvin cycle
what is visible light
the portion of electromagnetic spectrum that we can see with our eyes, which includes the range in wavelengths used in photosynthesis
what are pigments
they are molecules that absorb some wavelength of visible light - they look coloured because they reflect light enriched in the wavelengths that they don’t absorb
why do leaves appear green
because chlorophyll, the major photosynthetic pigment is poor at absorbing green wavelengths
What allows chlorophyll to absorb visible light
chlorophyll consists of a light absorbing region that contains magnesium atom at its center and a long hydrocarbon side chain. The large number of alternating double and single bonds surrounding the magnesium atom creates the overlapping electron orbitals that allow for the absorption of visible light
where in the chloroplast is chlorophyll found
it is precisely positioned with intergral membrane proteins
what are photosystems
a protein-pigment complex that absorbs light energy to drive redox reactions and thereby sets the photosynthetic electron transport chain in motion
what are the different forms of chlorophyll and what causes these differences
small differences in the chemical structure between the different types results in differences in their light absorbing properties
1. Chlorophyll a - found in all photosynthetic eukaryotes
2. Chlorophyll b - green algae and land plants
what are accessory pigments
all the light absorbing pigment other than chlorophyll in the photosynthetic membrane
give an eg. of a notable accessory pigment
carotenoids (an orange-yellow pigment) which can absorb wavelengths of visible light that are poorly absorbed by the chlorophyll
why are accessory pigments necessary
allow photosynthetic cells to absorb a broader range of wavelengths than would not be possible with chlorophyll alone
what is antenna chlorophyll
a chlorophyll molecule that absorbs energy from the sunlight and passes it to another chlorophyll molecule during photosynthesis
what does the antenna chlorophyll do
- captures sunlight energy
- electron in energized state
- transfer energy to next antenna chlorophyll
when does this passing of energy between chlorophyll molecules stop
once it reaches a specially configured pair of chlorophyll molecules known as the reaction centre
what happens at the reaction centre
light energy is converted into electron transport
what does the reaction centre do with the electron
- receives energy from the antenna chlorophyll
- transfers electron itself
-centre becomes oxidized - electron acceptor is reduced
- triggers a chain of redox reactions that ultimately leads to the formation of NADPH
what is wrong with having an oxidized reaction centre
the oxidized reaction centre is unable to absorb light and cannot contribute an electron because it is missing an electron
where does the replacement electron come from usually
water
what would happen without antenna chlorophyll
reaction centres would sit idle much of the time, therefore working much less efficiently
what makes water a challenging electron donor
it takes a great deal of energy to pull electrons from water
what is the order in which electrons flow in the photosystems
from photosystem II to photosystem I
what does the energy captured by photosystem II allow
allows electrons to be pulled from water, thus the energy captured by photosystem I allows electrons to be transferred to NADP+ to form NADPH
why do electrons move in one direction between photosystems
the decrease in energy as they move between photosystems, running the reactions in opposite directions would require an input energy
what are the main protein complexes of the photosynthetic electron transport chain
photosystem II, photosystem I, cytochrome-b6f complex (Cyt-b6f)
how do the electrons convey between these protein complexes
- plastoquinone (Pq) diffuses through the membrane from photosystem II to Cyt-b6f
- Plastocyanin (Pc) diffuses through the thylakoid lumen from Cyt-b6f to Photosystem I
where is the enzyme that pulls e- from water, and what is it released
located on the lumen side of the thylakoid at photosystem II
releases H+ and O2
what does water and NADP+ do in the reaction
Water donates electrons to one end of the photosynthetic electron transport chain and NADP+ accepts electrons at the other end
when is NADPH formed and where. explain the formation
when electrons are passed from photosystem I to ferredoxin on the stroma side of the thylakoid membrane. Ferredoxin-NADP+ reductase catalyses the formation of NADPH by transferring 2 electrons from 2 molecules of reduced Ferredoxin to NADP+ as well as a proton from the surrounding solution
what causes protons to accumulate in the thylakoid lumen
the light driven movement of electrons through the photosynthetic electron transport chain
what is photophosphorylation
the process by which the energy of sunlight is harnessed to move electrons, leading to the accumulation of protons and the synthesis of ATP
what two features of the photosynthetic electron transport chain are responsible for the buildup of protons in the thylakoid lumen
- the oxidation of water, which releases protons and O2 in the thylakoid lumen
- Pq and Cyt-b6f, which produce a proton pump that moves protons from the stroma to the lumen
what are three phases of the calvin cycle
- carboxylation - CO2 enters the calvin cycle and is added to RuBP, catalysed by Rubisco
- reduction - 3-PGA in reduced, ATP donates a phosphate group to 3-PGA and NADPH transfers two electrons plus one H+ which releases 1 phosphate group (Pi) (ATP to ADP, and NADPH to NADP+)
this produces triose phosphates used to provide energy to cells or synthesize larger molecules - regeneration - triose phosphate molecules are used to regenerate RuBP through reactions that require ATP
Write down the calvin cycle equation
6CO₂ + 18ATP +12NADPH +H₂O = 16Pi + 18ADP +12 NADP+
what compound is CO2 added to in the first phase of the calvin cycle
(a 5-carbon compound) ribulose 1,5-biphosphate (RuBP)w
what catalyses phase 1 of the calvin cycle
Ribulose biphosphate carboxylase oxygenase (Rubisco)
name and explain 3 photosynthetic challenges
- excess light energy can damage cells - increases chance of creating reactive molecules known as reactive oxygen species
- formed either by the transfer of absorbed light energy from antenna chlorophyll to O2
- or by the transfer of an electron to O2 - Photorespiration leads to loss of energy and carbon - Rubisco can use both CO2 and O2 as substrates
- if O2 diffuses into the active site of rubisco instead of CO2 the reaction can still proceed, O2 is added to rubisco rather than CO2
- results in the release of CO2 and requires light - photosynthesis captures just a small % of incoming solar energy - photosynthetic electron transport chain captures about 24% of the suns energy arriving on the surface of a lea
- the incorporation into carbohydrates results in considerable energy loss; about 20%
- maximum energy efficiency of photosynthesis is about 4%
Name and explain the four stages of thylakoid reaction
- Light capture -
- Energy transfer -
- Electron transport -
- ATP synthesis -
Explain the different components of chloroplasts and their functions
- Lumen - third highly folded membrane that encloses a fluid filled space (photosynthetic electron transport chain is located here)
- Thylakoid - entire structure plus the lumen
- Grana - the thylakoid is folded into grana, enhances light capture due to the increased surface area
- Stroma - region between the inner membrane and the thylakoid membrane (carbon fixation takes place here)
Describe the Ruben et al experiment and what it proved
proved that O2 released during photosynthesis was released from H2O and CO2
they found that when photosynthesizing chlorella cells were supplied with C18O₂, they did not observe heavy 18O₂ as a byproduct of photosynthesis
what is the difference between anabolic and endergonic
anabolic - promotion of the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy
endergonic - reactions that require a sustained input of energy
difference between anabolism and catabolism
anabolism = building of complex organic molecules
catabolism = breaking of complex organic molecules
