Module 5- Photosynthesis Flashcards
(16 cards)
Explain LDR
- Light excites an electron- chlorophyll has been photoionized (chlorophyll absorbs light energy)
- Electrons have been raised to a higher energy level
- The electrons are gained by an electron carrier molecule (reduction of electron carrier molecule, oxidation of chlorophyll- loss of electrons)
- ETC- series of redox reactions- electrons release energy
- Energy used to pump protons from stoma–> thylakoid lumen
- High concentration of H+ in the lumen of thylakoid- established H+ gradient
- H+ diffuses through ATP synthase back to stroma (chemiosmotic theory)
- Energy is used to join ADP+Pi–> ATP
- NADP is reduced by electrons and protons
- Photolysis of water produces protons, electrons, and oxygen using light energy. H₂O → 2H⁺ + 2e⁻ + ½O₂
6 marks
Describe the light- independent reaction of photosynthesis
- Carbon dioxide reacts with RuBP
- Produces two GP using Rubisco
- GP reduced to TP
- Using reduced NADP
- Using energy from ATP
- TP converted to useful organic substances like glucose
- RuBP is regenerated
6 marks
Desribe the role of electron transport chains in the light-dependent reactions of photosynthesis
1 electron transport chain accepts excited electrons
2 from chlorophyll
3 electrons lose energy along chain
4 ATP produced
5 from ADP and Pi
6 reduced NADP formed
7 when electrons and H+ combine with NADP
8 H+ from photolysis
6 marks
Explain the absorption of light energy and electron transfer chain
- Chlorophyll molecule absorbs light energy
- Pair of electrons become excited and move to higher energy level
- Electrons leave, chlorophyll molecule = oxidised
- Taken up by electron carrier molecule = reduced
- Move down chain in series of oxidation-reduction reactions
- Losing energy at each stage - used to combine ADP+Pi = ATP
3 marks
What structural features of the thylakoids increase rate of photosynthesis
- Contain photosynthetic pigments to absorb light energy
- Large SA as discs stacked into grana to increase light absorption
- Contain ATP synthase enzymes required to make ATP in LIR
5 marks
Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP
Excitation of electrons raised to higher energy level
Electrons emimted from chlorophyll molecule
Electrons to electron transport chain
Loss of energy by electrons along electron transport chain
Energy lost by electrons is used to synthesise ATP; From ADP + Pi
5 marks
The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur.
- High concentration of carbon dioxide at night
- No photosynthesis in the dark as light is required for LDR
- In dark plants respire
- In light, plants use more carbon dioxide than they produce / rate of photosynthesis greater than rate of respiration
- Decrease in carbon dioxide concentration with height
- At ground level fewer leaves/ less photosynthesising
2 marks
The scientists measured the rate of photosynthesis of the seaweeds in this investigation in terms of oxygen produced. Suggest the units they should use.
- Unit of volume (cm3) and unit of time (min)
- Unit of mass (g)
5 marks
Large areas of tropical forest are still found on some Caribbean islands. The concentration of carbon dioxide in the air of these forests changes over a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the concentration of carbon dioxide in the air changes:
* over a period of 24 hours
* at different heights above ground.
- Higher concentration of carbon dioxide in the dark linked with respiration
- No photosynthesis in dark, photosynthesis only in light
- Rate of photosynthesis greater than rate of respiration
- Decrease in carbon dioxide concentration with height
- At ground level, less photosynthesis - cannot recieve sunlight
2 marks
Mature leaves from slow-growing, shade-tolerant plants produce poisonous chemicals that are a defence against being eaten by herbivores. Suggest how this benefits slow-growing, shade-tolerant plants.
- In the shade, so slower rate of photosynthesis
- Slow-growing, so would take a long time to replace mature leaves
Leaves take a long time to mature - Plants can grow more- increase surface area for light absorption
2 marks
Explain why the LIR slows down at low temperatures unlike LDR
- LIR is an enzyme controlled reachtion (unlike LDR)- rubisco
- Lower temp–> lower kinetic energy so fewer ES complexes
3 marks
Describe what occurs at photosytem 2 during the LDR
- Chlorophyll absorbs light energy- photoionisation of chlorophyll
- Loss of electrons- chlorophyll molecule becomes oxidised
- Photolysis of water produces oxygen, protons and electrons
2 marks
Why is there little photosynthesis between 530–630 nm?
- 530–630 nm is the green wavelength
- Green light is reflected, not absorbed, so cannot be used in photosynthesis
2 marks
Why is ADP considered a limiting factor in the light-dependent reaction of photosynthesis?
ATP is produced from ADP and Pi during the LDR
If ADP is in short supply, ATP production slows down, even if light and Pi are available.
This limits the rate of the LDR
Therefore, ADP is a limiting factor because its availability affects the rate of ATP formation.
4 marks
Explain Link reaction
- Pyruvate enters mitochondrial matrix by active transport
- Pyruvate oxidised to acetate
- Acetate + coenzyme A produce acetylcoenzyme A
- CO₂ is released and NAD is reduced (to reduced NAD)
Products: 1 CO₂, 1 reduced NAD,1 acetyl-CoA
4 marks
Explain glycolysis
- Glucose is phosphorylated using Pi from ATP
- NAD is reduced
- As triose phosphate is oxidised to form pyruvate
- Net gain of 2 ATP
