3.5 Energy Transfer In and Between Organisms Flashcards
Describe the process of photoionisation.
This is where light is absorbed by pigments in the thylakoid membrane which causes two electrons in the chlorophyll molecule to be excited to a higher energy level. This causes the electrons to emitted from the chlorophyll molecule.
Describe what happens to electrons after photoionisation and their involvement in the electron transport chain.
The excited electrons travel down the electron transport chain where chemiosmosis occurs. This is the process in which the energy from the electrons are given to channel proteins which enable the movement of protons/H+ ions from the low concentration in the stroma to the high concentration in the thylakoid lumen.
What is the process of photolysis?
Within the thylakoid, there is a water-splitting enzyme which is called the oxygen-evolving complex which catalyses the breakdown of water (photolysis). The electrons lost by the pigments in photoionisation are replaced by the electrons produced in this process.
How does the proton gradient created in the electron transport chain enable the production of ATP?
The high concentration of protons in the thylakoid membrane allows the diffusion of protons through the protein ATP synthase via facilitated diffusion. This gives kinetic energy to the enzyme which enable it to phosphorylate a molecule of ADP to make ATP.
What is produced in the light-dependent reaction that is significant to the light-independent reactions and why is it?
NADP and ATP are produced which are used to provide the extra energy needed in the light-independent reaction to produce simple sugars.
How does the light-dependent reaction reduce NADP?
The electrons from the electron tranpsort chain and the hydrogen ions from photolysis are combined with regular NADP to form reduced NADP/NADPH.
Briefly describe the structure of a photosystem.
Funnel-like structures that are found in the thylakoid membrane which are made from accessory pigments that absorb light energy and transfer it to the primary pigment reaction centre.
Describe the carbon fixation part of the light-independent reaction.
Carbon dioxide combines with ribulose bisphosphate (RuBP (5C)) which is catalysed by the enzyme rubisco (ribulose bisphosphate carboxylase). The 6C compound produced is unstable and therefore splits in half, producing two 3C compounds called GP (glycerate 3-phosphate).
What is meant by the term ‘fixed’ in the context of photosynthesis?
It describes the idea that carbon dioxide from the atmosphere has been converted into a solid compound and therefore is removed from the atmosphere.
Describe the process of the reduction of GP (glycerate 3-phosphate) and how its turned into more useful biological molecules.
The energy from ATP produced in the light-dependent reaction and the hydrogen from the reduced NADP are used to reduce the GP therefore producing another 3C sugar called triose phosphate (TP). 1/6 of the TP molecules are used to produce useful organic molecules. TP can condense to become 6C hexose phosphates which can be turned into starch, sucrose or cellulose. It could also be converted into glycerol and GP into fatty acids therefore allowing the production of lipids. Finally, could also be used in the production of amino acids for protein synthesis.
Briefly describe how RuBP is regenerated and what the process needs.
5/6ths of the TP made in the Calvin cycle are used to regenerate RuBP. This process requires ATP.
Name factors that could limit the rate of photosynthesis.
Carbon dioxide supply.
Light energy.
Temperature.
Could also limit:
Availability of photosynthetic pigments.
Water supply.
