Section 5 - Unit 11: Photosynthesis Flashcards
Describe how in the light-dependent reaction of photosynthesis, light energy generates ATP (5 marks)
- Light (energy) excites / raises energy level of electrons in chlorophyll
- Electrons pass down electron transfer chain
- (Electrons) reduce carriers / passage involves redox reactions
- Electron transfer chain associated with chloroplast membranes / in thylakoids / grana
- Energy released / carriers at decreasing energy levels
- ATP generated from ADP and phosphate / Pi / phosphorylation of ATP
Describe how in the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate (5 marks)
- Carbon dioxide combines with ribulose bisphosphate / RuBP
- To produce two molecules of glycerate 3-phosphate / GP
- Reduced to triose phosphate / TP
- Requires reduced NADP
- Energy from ATP
Describe how crop plants use light energy during the light-dependent reaction (5 marks)
- Excites electrons/electrons removed from chlorophyll
- Electrons move along carriers/electron transfer chain releasing
energy - Energy used to join ADP and Pi to form ATP
- Photolysis of water produces protons, electrons and oxygen
- NADP reduced by electrons/electrons and protons/hydrogen
Describe how during the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances (6 marks)
- Carbon dioxide combines with ribulose bisphosphate / RuBP
- Produces two glycerate (3-)phosphate/GP
- GP reduced to triose phosphate/TP
- Using reduced NADP
- Using energy from ATP
- Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate
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 linked with night
- No photosynthesis in dark
- In dark, plants respire
- In light net uptake of carbon dioxide by plants
- Decrease in carbon dioxide concentration with height
- At ground level fewer leaves/less photosynthesising tissue
Explain why in the presence of oxygen, respiration yields more ATP per molecule of glucose than it does in the absence of oxygen (3 marks)
- Oxygen as terminal hydrogen/electron acceptor allowing operation of electron transport chain/ oxidative phosphorylation
- Fate of pyruvate
- Significance of ATP formed in glycolysis
Where precisely in a cell does the Calvin cycle take place (1 mark)
Stroma
Explain the advantage to the plant of the stomata closing when there is no sunlight (2 marks)
- Water is usually lost through stomata
- Closure reduces water loss
- Maintain water content of cells
Explain why in leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for photosynthesis (2 marks)
- Light not limiting
- So light-dependent reaction not limiting / fast;
OR - Temperature not limiting
- Fast reactions of enzymes in light-independent reaction
OR - High use of CO2
- Light-independent reaction is limiting
Suggest why decreasing the carbon dioxide concentration in a plant decreases the amount of GP produced (1 mark)
(Less) RuBP combines with carbon dioxide
Where exactly in a cell is the enzyme Rubisco found? (1 mark)
Stroma
Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars (6 marks)
- 5C / RuBP combines with CO2
- To form 3C compound / TP / GP
- Using ATP
- And reduced NADP
- 2 molecules of 3C compound / TP / GP form hexose
- All RuBP is regenerated
- 10 molecules of 3C / TP / GP form 6 molecules of 5C / RuBP
Describe the role of electron transport chains in the light-dependent reactions of photosynthesis (6 marks)
- Electron transport chain accepts excited electrons
- From chlorophyll / photosystem
- Electrons lose energy along chain
- ATP produced
- From ADP and Pi
- Reduced NADP formed
- When electrons (from transport chain) and H combine with NADP
- H from photolysis
Describe and explain the effect of increasing carbon dioxide concentration on the rate of photosynthesis (3 marks)
- Carbon dioxide increases rate of photosynthesis
- Up to max
- Until something else / correct suggestion is a limiting factor
Describe the part played by chlorophyll in photosynthesis (3 marks)
- Light (energy) absorbed by chlorophyll
- Raises energy level of electrons / electrons are excited / emitted
- ATP formed
Describe the effect of light energy in the light-dependent reaction of photosynthesis (2 marks)
- Excites chlorophyll / electrons
- Releases electrons
State the number of carbon atoms in the following molecules:
- RuBP
- GP
- TP
- Glucose
- RuBP: 5
- GP: 3
- TP: 3
- Glucose: 6
What proportion of triose phosphate molecules is converted to ribulose bisphosphate (1 mark)
5/6 (83.33%)
Explain why the light-independent reaction slows down at low temperatures (2 marks)
- Enzymes involved
- Slow rate of enzyme / less kinetic energy / fewer collisions
A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent is blue when oxidised and is colourless when reduced. The suspension of chloroplasts in blue reagent was exposed to sunlight. Use your knowledge of the light-dependent reactions of photosynthesis to explain why the blue colour disappeared (2 marks)
- Chlorophyll excited / reduced NADP formed
- Electrons from chlorophyll / reduced NADP changes the dye colour
Explain how maintaining a high temperature in a glasshouse of plants in winter, when the light intensity is low, may reduce the yield of the plants (2 marks)
- Increases rate of respiration
- Rate of photosynthesis too low to replace respiratory loss
Explain why the uptake of carbon dioxide falls to zero when there is no light (2 marks)
- No use of carbon dioxide in photosynthesis in the dark
- No diffusion gradient for CO₂ into leaves
Explain how increasing the temperature could either increase or have no effect on the amount of oxygen produced by a plant (3 marks)
No effect:
- Because photolysis during photosynthesis does not use up any enzymes
Increase:
- Because rate of respiration is faster
- So more oxygen used
Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period (3 marks)
- Some hexose / biomass / used in respiration
- CO2 produced (is lost to air)
- Some parts of the plant are eaten / some parts lost to decomposers / in leaf fall
Describe what happens during photoionisation (2 marks)
- Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll - Electron/s are lost OR Chlorophyll becomes positively charged
