Topic 5: Energy Transfers Flashcards
Describe the structure of a chloroplast and how its structure relates to its function. (4)
- Starch grains / lipid droplets : store products of
photosynthesis; - double membrane - provides large surface for light absorption.
- Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll.
- Intergranal lamellae: tubes attach thylakoids in adjacent grana.
- Stroma: fluid-filled matrix.- vesicular plastid
- Permeable membrane allows diffusion of gases /carbon dioxide;
- Stacking / arrangement of grana/thylakoids maximises
light catchment.
Define photolyis and photoisonisation.
- photolysis: Light energy is used to breakdown water producing hydrogen ions , electrons and oxygen.
- photoioinisation: excitation of electrons by the absorption of light energy.
Outline the equation for photolysis
H2O → 2H+ + 2e- + ½O2
Where do the light independent and light dependent reactions occur
LDR: Thylakoid membranes
LIR: the stroma
Name the 4 key stages in the light dependent reaction
- photoionisation of chlorophyll
- Photolysis
- Chemiosmosis
- Production of ATP and reduced NADP
Describe the photoionisation of chlorophyll
- light energy is absorbed by chlorophyll. This Excites electrons; to a higher energy level.
- The chlorophylll has been ionised by light.
LDR process
Describe photolysis
second stage of LDR
- light energy is absorbed by chlorophyll and splits water into oxygen, H+ and e-
- H2O → 2H+ + 2e- + ½O2
- Electrons move along carriers/electron transfer chain releasing energy;
- The oxygen is used for respiration or diffuses out of the leaf through the stomata.
Describe chemiosis
- The** excited** electrons move along a series of electron channel proteins embedded within the thylakoid membrane.
- As they move along the ETC, via a series of oxidation and reduction reactions they release energy.
- Light energy is absorbed again by PSI, re-exciting the electrons to a higher energy level.
- This energy is used to actively transport H+ ions from the stroma into the thylakoid lumen , creating an **elctrochemical gradient.
- Protons than flow back into the stroma through ATP synthase , which provides the needed for ATP synthesis
Describe the production of ATP and reduced NADP
- Energy from the electron transfer chain is used to join ADP and Pi to form ATP using ATP synthase through phosphorylation.
- At the end of the electron transport chain, electrons combine with H⁺ ions and are transferred to NADP⁺ (a coenzyme), reducing it to form NADPH.
- NADP reduced by the gain of electrons / electrons and protons / hydrogen;
- these are used in the Calvin Cycle.
D
Outline the difference between oxidation and reduction reactions
oxidation: loss of electrons, increases the oxidation state
reduction: gain of electron , decreases the oidation state
Describe what happens during photoionisation in the light-dependent reaction. (2)
- Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll; - Electron/s are lost
OR
Chlorophyll becomes positively charged
In photosynthesis, which chemicals are needed for the light-dependent reaction?
- NADP
- ADP
- Pi
- and water
The light absorbed by chlorophyll is used in the light-dependent reaction.
Name the two products of the light-dependent reaction that are required for the light-independent reaction. (2)
- ATP
- Reduced NADP
Accept NADPH
Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds. (4)
- Reduced transfer of protons across thylakoid membrane. OR Reduced chemiosomotic gradient / proton gradient across thylakoid
membrane. - (So) less ATP produced;
- (So) less reduced NADP produced;
- (So) light-independent reaction slows / stops;
OR Less reduction of GP to triose phosphate.
Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light-dependent reaction.
- Excites electrons / electrons removed (from chlorophyll); to a higher energy level
- Electrons move along carriers/electron transfer chain releasing energy through redox reactions
- Energy used to join ADP and Pi to form ATP;
Accept: energy used for phosphorylation of ADP to ATP - Photolysis of water produces protons, electrons and oxygen;
- NADP reduced by electrons / electrons and protons / hydrogen;
Accept: NADP to NADPH (or equivalent) by addition of
electrons/hydrogen.
Reject: ‘produces energy’ for either mark but not for both.
Do not accept NADP reduced by protons on its own.
What role do photosynthetic pigments play in chloroplasts?
- Photosynthetic pigments absorb different wavelengths of light within the thylakoids of chloroplasts, facilitating the process of photosynthesis.
How are pigment molecules arranged in a photosystem?
- pigment molecules are arranged in funnel-like structures within the thylakoid membrane.
- The funnel-like structure helps in passing energy from one pigment molecule to the next until it reaches the primary pigment reaction center, where it is collected and used in LDR.
Name the primary pigments in Photosystem I and Photosystem II
Photosystem I: Chlorophyll a
Photosystem II: Chlorophyll b
Explain the role of chlorophyll and carotenoids in photosynthesis.
- **Chlorophylls (a and b) **are primary pigments that absorb light in the blue-violet and red regions of the spectrum, reflecting green light.
- **Carotenoids **(β carotene and xanthophyll) are accessory pigments that absorb light in the blue-violet region.
https://cdn.savemyexams.com/cdn-cgi/image/w=960,f=auto/uploads/2021/03/Absorption-spectra-of-chlorophylls-and-carotenoids_1.png
Outline the required practical.
Where does the LIR occur?
- occurs in the stroma
What dooes the Calvin Cycle use?
uses:
- carbon dioxide
- reduced NADP and ATP to form a hexose sugar.
- The ATP is hydrolysed to provide energy for this reaction and the reduced NADP donates the hydrogen to reduce molecules GP in the cycle.