Energy Transfers In And Between Organisms Flashcards
Where do light dependent and light independent reactions occur in plants?
Light dependent- Thylakoid membrane
Light independent- Stroma
Explain the role of light in photolysis
Light energy is absorbed which splits water molecules into O2, H+ and e-
Name the two main stages involved in ATP production in light dependent reactions
Photoionisation
Chemiosmosis
What are the three key reactions that take place in light dependant reactions?
Photolysis
Photoionisation
Chemiosmosis
Define photolysis of water
Using light to split water into oxygen,hydrogen and electrons
Explain Photoionisation
Light energy is absorbed by photosynthetic pigments in PSII, electrons become excited and move to a higher energy level and leave the Chlorophyll
Electrons move across the electron transport chain via electron carriers and move into PSI
Explain chemiosmosis
Energy released during the electron transfer pumps H+ ions from stroma to thylakoid
There is an increase concentration of H+ ions on the than the stroma which causes a proton gradient
Protons move into the ATP synthases which causes it to rotate and hydrolyse ADP and Pi into ATP
Why can photolysis only occur in PSII?
Has the correct enzyme complexes for the reaction to take place
What happens to the electrons produced by photolysis?
Move back into the chlorophyll to replace the electrons lost so photoionisation can happen again
What happens to the oxygen produced during photolysis?
Diffuses out the leave via stroma and is used in respiration
What happens to the H+ produced by photolysis?
Reduce the coenzyme NADP to form NADPH
What is name of the process that produces ATP in chemiosmosis?
Photophosphorylation
What are the two types of photophosphorylation?
Cyclic
Non-cyclic
Explain non-cyclic photophosphorylation
The flow of electrons in a linear motion
Route: PSII,Electron carriers, PSI to NADPH
Products: ATP
NADPH
Oxygen
Explain cyclic photophosphorylation
Flow of electrons is a cyclic motion
Route: PSII,Electron carriers, PSI back to electron carriers and repeats
Products: ATP
State three differences between cyclic and non-cyclic photophosphorylation
Cylcic:
Produces only ATP
Uses only PSI
electrons move in a cycle
Non-cyclic:
Produces ATP, NADPH and Oxygen
Uses both PSII and PSI
electrons move in a linear motion
Why is no oxygen produced in cyclic photophosphorylation?
Electrons move back into the electron carries and not the PSII so photolysis does not occur during this cycle
What is the advantage of cyclic photophosphorylation?
The electrons move back into the electron carries and as they move along the transport chain energy is released
This is an advantage as the repetition of this cycle means more energy is being released causing more ATP production
Where does the light- independent reaction take place?
Stroma
What two products from the light dependant reaction are needed for the light- independent reaction?
ATP
NADPH
Why does the light-independent reaction take place in the stroma?
CO2 diffuses into the leaf via the stomata and is stored in the stroma
The light-independent stage is an enzyme driven reaction. What enzyme is used and what does it do?
Rubisco and it catalyses the reaction
Explain the Calvin cylce
Carbon dioxide is absorbed into the leaf via stomata and diffuses into stroma and combines with RuBP which forms an unstable 6c molecule
This is broken down into 2-3c molecules of GP
GP is then reduced to TP using ATP and NADPH from the LDR
TP can now either produce a hexose sugar
or
then go on to further regenerate more RuBP with the help of another ATP molecule in order to carry the cycle on
What two molecules are used to produce glycerate phosphate (GP)?
Carbon dioxide and ribulose Biphosphate
What is the product from the LDR that reduces GP to TP, and how does it do this?
ATP——> ADP + Pi
This releases energy so GP can be reduced to form TP
How does NADPH allows GP to form TP?
NADPH loses the hydrogen which is then accepted by GP and causes it to be reduced to TP
Why does GP need to be converted to TP in order to produce an organic substance?
GP does not contain hydrogen so it needs to be reduced to TP which can then form the organic (oxygen,hydrogen and carbon containing substance) molecule
How many times does the Calvin cycle occur for every glucose molecule?
6
How many of each molecule is there in one cycle of the light- independent stage?
1 carbon dioxide
1 RuBP
2 GP
2 TP
3 ATP
2 NADPH
What are the 4 stages of respiration?
Glycolysis
Link reaction
Kreb cycle
Oxidative phosphorylation
Where does glycolysis occur and why?
In the cytoplasm and glucose is too big to leave
Describe the process of glycolysis
ATP is hydrolysed to ADP + Pi
Glucose is phosphorylated into glucose phosphate
Glucose phosphate is now converted into 2 molecules of TP (3c molecule)
A co-enzyme NAD is reduced to NADH
TP molecules are hydrolysed with the use of NADH into 2 molecules of pyruvate
What are the products of glycolysis?
2 ATP
2 NADH
2 Pyruvate
Where does the link reaction occur?
Matrix of the mitochondria
How is Acytelcoenzyme A formed from pyruvate?
Pyruvate gets oxidised to acetate (2c molecule)
3c to 2c as carbon dioxide is released
Coenzyme NAD gets reduced to NADH
Acetate now reacts with another coenzyme called ‘Coenzyme A’ which then forms acetylecoenzyme A
How many times does the link reaction occur for every glucose molecule?
Twice as glycolysis produces 2 pyruvate a from one glucose molecule
Where does the Kreb cycle occur?
Matrix of the mitochondria
What enzyme is specific to the kerb cycle?
FAD—> FADH
Explain what happens in the kerb cycle
Oxaloacetate (4c compound) combines with acetylecoenzyme A to form citrate
Citrate releases co2 which reduces NAD to NADH
A 5c compound is formed which then also releases co2 which reduces NAD to NADH and FAD to FADH
ADP + Pi then is phosphorylated into ATP
What is the net gain per kreb cycle?
2x co2—> citrate releases 1 and 5c compound releases 1
1x ATP
1x FADH
3x NADH
What is the net gain for the kreb cycle per glucose molecule ?
4x co2
2x ATP
2x FADH
6x NADH
Where does oxidative phosphorylation occur?
Cristae of the mitochondria
Explain the process of oxidative phosphorylation
Reduced coenzymes release the hydrogens in the matrix which splits into protons and electrons
The electrons move across electron transfer chain which releases energy
Energy is used to actively transport protons from matrix to inter-membrane space
An electrochemical gradient is formed which causes protons to move by facilitated diffusion through ATP synthase which produces ATP
At the end of electron transfer chain the electrons are picked up by O2 and then O2 picks up the protons which pass through which ultimately produces water
How many ATP molecules are finally produced at the end of oxidative phosphorylation?
34 ATP molecules
What are the factors that limit photosynthesis?
Light intensity
Carbon dioxide concentration
Temperature
What are the four optimum growing conditions for photosynthesis?
Light intensity and wavelength
Temperature
Carbon dioxide levels
Availability of water
How is light intensity an optimum condition for photosynthesis?
More light means more energy
However too high will damage chlorophyll
Pigments in plants mostly absorb blue and red (reflect green)
How is the temperature an optimum growing conditions for photosynthesis?
Photosynthesis relies on enzymes:
(ATP=LDR)(Rubisco=LIR)
<10 degrees means enzymes for work too slowly
> 45 degrees means enzymes or denature
How is carbon dioxide level in optimum current condition for photosynthesis?
How is the availability of water an optimum growing condition for photosynthesis?
