General
What is the equation of photosynthesis?
Carbon Dioxide + Water --> Oxygen + Glucose
Where in the chloroplast does the calvin cycle occur?
In the storm
What is the wavelength is absorbed by photosystem 2?
680 nm
What is the Action Spectrum?
A graph showing the relative amount of light absorbed at each wavelength by each pigment of a plant.
What is chemiosmosis?
The movement of protons (H⁺) across a membrane, down their electrochemical gradient, to generate ATP via ATP synthase.
why is photosynthesis important?
1. produces oxygen- essential for living organisms to breathe and respire
2. maintains CO2 level- helps reduce CO2 in atmosphere, reducing global warming
3. makes glucose and releases energy- which fuels plant growth, respiration and transport (active transport)
What is used to produce 1 glucose molecule?
6CO2
12 ATP
12 NADPH
What are photosystems?
Photosystems are pigment–protein complexes located in the thylakoid membranes in chloroplasts.
Which regions of the light spectrum are most effective for photosynthesis?
Blue (around 450 nm) and red (around 680 nm) regions.
Where does chemiosmosis occur in the chloroplast?
Across the thylakoid membrane—from the thylakoid lumen into the stroma.
What are the factors affecting photosynthesis?
Light, Humidity, Temperature, Wind speed and Surface area
The Calvin cycle is described as a "light-independent" process, yet it slows in the dark. Explain why.
Though it doesn’t directly require light, the Calvin cycle depends on ATP and NADPH from light-dependent reactions. In darkness, these are not produced, and enzymes like RuBisCO also become inactive.
how is energy transferred from pigment to pigment?
occurs in light harvesting complex. when excited electron in pigment molecule drops back to its original level, energy emitted is absorbed by an electron in adjacent pigment molecule, causing it to become excited. process called excitation energy transfer. process repeated across light harvesting complex until it reaches core complex.
How is the produced the absorption spectrum?
It is produced by shining different wavelengths of light (produced by diffraction of white light through a glass prism) through a solution of chlorophyll. The amount of light transmitted through the chlorophyll sample can be detected and measured.
How does chemiosmosis link the light-dependent and light-independent reactions?
It produces ATP (and also helps produce NADPH) needed to power the Calvin cycle in the light-independent reactions.
What is the most abundant enzyme on earth?
Rubisco
How many molecules of triose phosphate are used to produce sugars?
1/6th triose phospate molecules
What are the differences between photosystem 1 and 2?
Photosystem 1:
- location: thylakoid membranes between the grana, called stroma lamellae
- primary electron donor in the reaction centre: P700, a pair of chlorophyll with peak absorbance at 700nm
- transfer of excited electrons from the primary electron donor: to the enzyme NADP reductase, which uses the electrons to reduce NADP
- source of replacement electrons: two electrons from plastocyanin
Photosystem 2:
- location: in the thylakoid membranes in grana
- primary electron donor in the reaction centre: p680, containing pair of chlorophyll with 680nm peak absorbance
- transfer of excited electrons from the primary electron donor: to plastoquinone, which transfers the electron chain of electron carriers
- source of replacement electrons: photolysis of water
What would be the effect on photosynthesis if a plant lacked accessory pigments?
The action spectrum would be narrower and photosynthesis less efficient under a range of light wavelengths, especially in green light.
Explain how the structure of the inner mitochondrial membrane is adapted to maximize ATP production via chemiosmosis.
Inner membrane is folded into cristae, increasing surface area for electron transport chains and ATP synthase. Contains embedded protein complexes for electron transport and ATP synthase for ATP production. Impermeable to protons, allowing a steep electrochemical gradient to form for efficient chemiosmosis.
why do leaves appear green?
Chlorophyll absorbs red and blue light, but reflect green light. The reflected green light is what we see.
Describe and explain the stages of the calvin cycle
1. Carbon fixation using Rubisco: CO2 combines with RuBP to form a 6C molecule. Which is split into two 3C molecules (Glycerate-3-phosphate) by using the Rubisco enzyme
2.Synthesis of triose phosphate using NADPH and ATP: 3C reduced by NADPH. It gets phosphorylated by ATP form triose phospate. The oxidised NADP+ and ADP go back to the thylakoid for LDR.
3. Regeneration of Rubisco using ATP: Ribulose 5 phosphate is phosphorylated using ATP. To make RuBP
How is oxygen generated in photosystem 2?
by PHOTOLYSIS OF WATER.
Absorbing photons of light causes chlorophyll (P680) in reaction centre to become oxidised by emitting electrons. The chlorophyll regains electrons from water. this occurs in OEC. OEC binds to 2 water molecules and splits them, releasing 4 electrons and 4 protons. remaining 2 oxygen bond to form 1 molecule of oxygen.
electrons are transferred to reaction centre to replace the emitted electrons by P680 chlorophyll. protons are released into thylakoid space to maintain the proton gradient across the thylakoid membrane.
oxygen (waste product) diffuse out of the stomata.
Explain why the action spectrum of photosynthesis does not exactly match the absorption spectrum of chlorophyll a.
The action spectrum includes the contribution of accessory pigments (e.g., chlorophyll b, carotenoids). These pigments absorb light at different wavelengths and transfer energy to chlorophyll a, enhancing photosynthesis where chlorophyll a absorption is low.
How would the inhibition of ATP synthase affect chemiosmosis and overall ATP production?
Inhibiting ATP synthase would block the flow of protons back into the matrix, preventing ATP synthesis. The proton gradient would remain but not be used for ATP production, significantly reducing overall ATP yield.