3.5 Energy transfers in and between organisms Flashcards
Give 3 ways a plant is adpated for photosynthesis.
- Large flat leaves for a large SA for light absorption, spread out so that they can access as much ligth as possible
- Transparent cuticle layer on leaves, allowing sunlight to pass through and photoionisation/photlysis to occur
- Xylem and phloem for transport of water to leaves and tranport of dissolved sugars to sinks
Where is chlorophyll found in a plant?
Photosystems in the thylakoid membrane
- accessory pigments = chlorophyll b, carotenoids
- primary pigment = chlorophyll a
What energy stores are found in a chloroplast?
Lipid droplet, starch grains
What are the main structures of chloroplasts?
Stroma, double membrane, grana, thylakoids and thylakoid membrane, lamella, lipid droplet, starch grain
What are the different photosynthetic pigments and what colours do they absorb/reflect?
Chlorophyll- absorb blue and red, reflect green
Carotenoids - absorb blue, reflect orange/red
Why is it important that a plant has several pigmenets present?
- Different pigments absorb different wavelengths of light
- More light is able to absorbed during different conditions
- More photosynthesis and more growth from the production of more organic substances
What happens during the LDR?
- Photoionisation: light energy absorbed by chlorophyll, electrons excited and chlorophyll is oxidised
- Electrons transferred down ETC, releasing energy which is used to pump protons into the thylakoid lumen
- Final electron acceptor is NADP, which is reduced using electrons and protons to produce NADPH
- Chemiosmosis: proton gradient created, protons move down electrochemical gradient back into stroma through ATP synthase, catalysing the production of ATP
- Photolysis: water molecules split into oxygen, hydrogen and elctrons (used in chlorophyll)
Describe what happens in the LIR?
Calvin cycle
- Carbon fixation: RuBP + carbon dioxide (substrate to RuBisCo) producing GP
- GP reduced using energy from ATP and NADPH to form triose phosphate
- Some molecules of TP are converted into organic substances, the majority however are used to regenerate RuBP using energy from ATP
1/6 = glucose, 5/6 = RuBP regeneration
Why is the LIR not techincally the ‘dark’ reaction or light independent reaction?
Relies on products ATP and NADPH from the LDR
What are the 3 factors affecting photosynthesis?
- Temperature
- Light intensity
- Carbon dioxide concentration
How would a gardener control temperature and carbon dioxide concentration in his greenhouse?
Burn a fuel, releases heat and carbon dioxide
What do the following terms mean:
a) light compensation point
b) saturation point
a) Rate of respiration = rate of photsynthesis, so there is no net production of carbon dioxide
b) New limiting factor
How does increased light intensity affect the rate of photosynthesis?
- More light energy absorbed by chlorophyll, more elctrons excited and chlorophyll oxidised
- More elctrons transferred down ETC, more protons pumped into thylakoid lumen, steeper conc. gradient
- More NADP reduced at final elcetron acceptor
- More ATP synthesised as protons pass through ATP synthase back into the stroma
- Increased rate of LDR, more ATP and NADPH for LIR
- Increased reduction of GP and increased rate of Calvin cycle
How does increased carbon dioxide concentration affect the rate of photosynthesis?
- More carbon dioxide so more substrate for RuBisCo
- More GP produced from RUBP so more available to be reduced to triose phosphate using energy from ATP and NADPH
- Increased rate of Calvin cycle
How does increased temperature affect the rate of photosynthesis?
- Increase in kinetic energy, more successful collisions over time
- More E-S complexes form (RuBisCo)
- If temperature is too high proteins/enzymes denature
Explain 3 ways you can measure the rate of photosynthesis.
- Photosynthometer- measures volume of oxygen produced
- Density of leaves- remove air, air spaces fill up with gas as plants photosynthesise, less dense, float to the top
- Hydrogencarbonate indicator- monitors carbon dioxide uptake, use colorimetry to quantify
What are the 2 limitations of measuring the volume of oxygen produced overtime whilst measuring the rate of photosynthesis?
- Other gases (nitrogen, carbon dioxide) could be present in the sample
- Some oxygen that is produced is used up in respiration
Describe and explain the Hill Reaction as a technique to measure the rate of photosynthesis?
- Measuring the activity of dehydrogenase enzymes in the reduction of DCPIP, acts as final electron accpetor (instead of NADPH)
- DCPIP is reduced and there is a colour change from blue to colourless (with chloroplasts, this is a colour change from blue-green to green)
In the Hill reaction, describe and explain the results for the green filter and the blue/purple/orange filter.
Green filter: Infinite time for colour change
- Only green light allowed through filter
- DCPIP was not reduced as no light was absorbed so no photoionisation and no electrons transferred down ETC and therefore no colour change
Blue/purple/orange: Shorter time for colour change
- DCPIP was reduced quicker
- There is more photoionisation and more elctrons transferred down ETC and increased rate of photosynthesis
- This is because blue/purple/orange light is more strongly absorbed by chlorophyll
Describe glycolysis.
think: location, products, reactions
- Occurs in cytoplasm
- Glucose phosphorylated using 2 molecules of ATP
- Forms hexose bisphospahte (6C) which is highly unstable and splits into 2 molecules of triose phosphate (3C)
- Triose phosphate oxidised using 2 NAD molecules (NAD is reduced)
- Produces 2 x pyruvate and 4 x ATP
- Net production of 2 pyruvate, 2 ATP and 2 NADH
Describe the link reaction.
think: location, products, reactions
- Occurs in matrix of mitochondria
- Decarboxylation and oxidation of pyruvate (3C) using NAD to produce acetate (2C)
- Acetate reacts with conenzyme A to produce acetylcoenzyme A
- Reaction occurs twice, producing 2 NADH, 2 carbon dioxide and 2 acetycoenzyme A
Describe the Krebs cycle.
think: location, products, reactions
- Occurs in the matrix
- Acetycoenzyme A reacts with a 4C molecule to produce a 6C molecule
- Series of oxidation (NAD reduced) and decarboxylation (carbon dioxide produced) reactions produce a 5C then a 4C molecule
- The 4C molecule is rearranged, releasing energy for ATP synthesis, and then oxidised using FAD and NAD to regenerate the original 4C molecule
- Cycle happens twice, once for each molecule of acetylcoenzyme A
- Overall 6 NADH, 2 FADH2, 2 ATP and 4 carbon dioxide are produced
Describe oxidative phosphorylation.
think: location, products, reactions
- Occurs in the inner membrane of mitochondria
- Oxidation of NADH and FADH2 releases protons and electrons
- Electrons transferred down ETC, releasing energy to pump protons into the intermembrane space through the inner mitochondrial membrane
- Protein gradient forms, protons move back into matrix through ATP synthase (chemiosmosis), synthesesising ATP
- Oxygen is the final electron acceptor and produces water molecules from oxyegen, protons and electrons
What happens to the aerobic pathway when no oxygen is present?
- No final electron acceptor on ETC
- Electrons not transferred down so coenzymes are not oxidised
- Less NAD and FAD avalable for oxidation in glycolysis, Kreb’s cycle and link reaction
- Can’t get reduced coenzymes from Kreb’s cycle, can’t synthesise ATP
