Unit 3 Photosynthesis Flashcards
What part of the plant is responsible for the intake of solar energy?
Leaves (maximize surface area)
What part of the plant is responsible for the intake of water?
Roots (uptake) and stomata (transpiration)
What part of the plant is responsible for the intake of nutrients?
Roots (uptake via capillary action)
What part of the plant is responsible for the intake of CO2?
Stomata
Where do light reactions occur?
Light reactions occur in the thylakoid.
What do light reactions do?
Light reactions convert solar energy (photons) to chemical energy (ATP and NADPH).
What do light reactions lead to?
Light reactions lead to photophosphorylation.
What is photophosphorylation?
Photophosphorylation is the light-dependent formation of ATP by chemiosmosis in photosynthesis.
How many photosystems are present in light dependent reactions?
Two
Where are the photosystems located?
Photosystems are located in the thylakoid membranes.
What do the photosystems contain?
Photosystems contain pigments.
What is the purpose of accessory pigments?
Accessory pigments absorb and pas energy to chlorophyll a (the reaction site).
What happens when 2 electrons become excited in chlorophyll A?
The electrons are transferred to the Electron Transport Chain.
What do the electrons falling from PSII replace?
The electrons falling from PSII replace electrons lost to the ETC.
What does the Energy produced by the transfer of fallen PSII electrons to chlorophyll a produce?
The energy produced by the transfer reduces NADP+ to NADPH.
Which occurs first, PSI or PSII?
PSII occurs first.
What is the purpose of PSII?
PSII generates ATP via chemiosmosis as electrons pass down its transport chain.
What is the purpose of PSI?
PSI generates NADPH when electrons reach the end of its electron transport chain?
Photolysis of water occur?
Photolysis occurs when chlorophyll a (the reaction center) lacks an electron.
Which enzyme catalyzes the splitting of water in photolysis?
Enzyme Z catalyzes the splitting of water into photolysis.
What does water split into?
Water becomes O, H ions, and a pair of electrons for replacement of the ones missing from chlorophyll a.
How is O released?
O is released as O2.
What are the four steps of cyclic photophosphorylation?
- PSI electrons go to the first electron carrier.
- The electrons pass to the PSII chain.
- Their energy is used to generate ATP.
- The electrons are returned to PSI.
What is the equation of photosynthesis?
6CO2 + 6H2O + Light energy → C6H12O6 + 6O2
How does water move out of the plant?
Transpiration: the loss of water vapour from plant tissues, primarily through stomata.
What does evaporation of water create?
Evaporation of water from leaves creates a transpirational pull which helps move water, minerals and other substances from the roots to the leaves and other parts of the plant. Also provides cooling effect.
What happens in terms of CO2 and O2 movement, and the rate of photosynthesis when the stomata are open?
CO2 can diffuse into the leaf quickly (less CO2 in plant because it is used up in photosynthesis. O2 can diffuse quickly out of the leaf (more in the plant because it is a product of photosynthesis).
The rate of photosynthesis is high.
What controls stomatal action?
The concentration gradient created by the active pumping of K+ ions into the guard cells controls stomatal action.
What happens when water diffuses into the guard cells?
When water diffuses in, the turgor pressure increases and the guard cells swell and subsequently buckle, opening the stomata.
What happens when the water diffuses out of the guard cells?
There is a loss of turgor pressure, causing the guard cells to become flaccid, and they close.
How does water affect stomatal action?
In dry conditions, the stomata are closed, so that transpiration is limited to conserve water.
How does CO2 affect stomatal action?
Stomata are closed during low CO2 concentration, there is no photosynthesis. Stomata are opened during high CO2 concentration resulting in photosynthesis.
How does light affect stomatal action?
When there is light, stomata are opened, when there is no light the stomata is closed.
What powers photosynthesis?
Light/electromagnetic radiation.
What wavelengths does photosynthesis use?
Photosynthesis uses the visible spectrum (wavelengths from 400 to 750 nm).
What pigments do chloroplasts contain?
Chlorophyll a, chlorophyll b, carotene, xanthophyll.
What do pigments do?
Pigments absorb specific photons (wavelengths) of light and reflect others.
Which produces more photon energy, high wavelengths or low wavelengths?
Low wavelengths produce the highest amount of electromagnetic radiation.
How many membranes to chloroplasts have?
Chloroplasts have three membranes.
Where is the inter membrane space located?
The IMS is located between the outer membrane and the inner membrane.
What is the innermost membrane called?
The thylakoid membrane.
What is inside the thylakoid space?
Protein rich fluid (stroma) is in the thylakoid space.
What is the makeup of chlorophyll?
Chlorophyll has a porphyrin ring (polar) and a long tale (nonpolar).
What are the reactants and products of light reactions?
H20, and photons produce ATP, NADH, and O2.
Why is the calvin cycle endergonic?
The Calvin Cycle is endergonic because it requires ATP (which becomes ADP) and NADPH to begin the process.
Describe the calvin cycle.
The enzyme RUBISCO (ribulose bisphosphate carboxylease) causes CO2 to combine with RuBP forming an unstable 6-C compound, which spontaneously splits into 2 3-Carbon molecules of 3PG
What is the formula of the Calvin Cycle?
CO2 + RuBP → 6C compound → 2 3PG
What three things prove that rubisco is inefficient?
Competition between CO2 and O2 (O2 does not create energy, wasteful for plant)
(Existence of C4 cycle and CAM).
Requires 3 turns of Calvin Cycle to produce 1 glucose.
Photorespiration reduces photosynthetic output by as much as 50% via O2 outcompeting CO2 for the C3 cycle (depending on environmental conditions).
What is the C4 pathway? (5 steps)
CO2 fixed to mesophyll cells to form oxaloacetate (4C acid). This is carried out by PEP carboxylase.
Oxaloacetate is converted to malate.
Malate is transported into the bundle-sheath-cells.
Malate breaks down, releasing a CO2 molecule.
The molecule is fixed by rubisco and made into sugars via the Calvin Cycle.
What is the Crassulacean Acid Metabolism? (4 steps)
At night the stomata is open, CO2 diffuses in.
The CO2 is fixed into oxaloacetate by PEP carboxylase.
The oxaloacetate is converted to malate.
The organic acid is stored inside the vacuoles until the day. The stomata are not open in the day. The acids are broken down and release CO2 which then enters the Calvin Cycle.
What is the light compensation point?
The light-compensation point is the point on a light-response curve at which the rate of photosynthetic CO2 uptake exactly equals the rate of respiratory CO2 evolution.
What is a light saturation point?
The light-saturation point is the irradiance level at which the carbon fixation reactions reach a maximum overall rate.
How is photosynthesis limited by light intensity?
In a light-response curve, the rate of photosynthesis is light limited between the light-compensation point and the light-saturation point. In this range, providing more light causes the rate of photosynthesis to increase.
How does high O2 concentration affect photosynthesis and photorespiration?
Low photosynthetic rate, high photorespiration rate.
How does high CO2 affect photosynthesis and photorespiration?
High photosynthetic rate, low photorespiration rate.
What are Grana?
Stacked coins within the thylakoid space.
What are Lamella?
Lamella connect the different grana.
What is the purpose of the absorption spectra?
The purpose of the absorption spectra is to show the wavelengths of light best absorbed by photosynthetic pigments.
What colours does chlorophyll absorb well?
Chlorophyll absorbs violet, blue and red light well, and appears green since it is reflected.
What colours do carotenoids absorb well?
Carotenoids absorb blue and green light and therefore appear red, orange and yellow.
What colours to Xanthophylls (another type of carotenoid) absorb well?
Xanthophylls absorb green and yellow light appearing blue and purple.
Why are plants green?
Least absorption occurs for green wavelengths.
What is the purpose of an action spectrum?
The action spectrum indicates the rate of photosynthesis for each wavelength of light.
What is noncyclic electron flow?
Noncyclic electron flow occurs when photoenergized electrons flow from water to NADP+ through ETC into the thylakoid membranes, which produces NADPH via reduction, and ATP via chemiosmosis.
Where does the calvin cycle occur?
The calvin cycle occurs in the stroma.
What are the three steps of the calvin cycle?
- Carbon fixation.
- Reduction to G3P.
- Regeneration of RUBP
What is the formula of carbon fixation?
CO2 + RuBP → 6C compound → 2 3PG
What is the formula of reduction to G3P?
3PG + ATP → 1 3BPG + 2e- → G3P
How does Regeneration of RuBP work?
5 molecules of G3P (3C) are used to regenerate 3 molecules of RuBP (5C)
What does regeneration of RuBP require?
ATP
How many turns of the calvin cycle to produce 1G3P?
3 turns
How many molecules of CO2 to produce 1G3P?
3CO2
How many turns of the calvin cycle to produce a glucose?
6 turns
How many ATP and how many NADPH are needed to produce a glucose?
18 ATP and 12 NADPH
