Question 1
Paper 1A style
What is the source of the oxygen released in photosynthesis by plants, algae and cyanobacteria?
- Carbon dioxide
- Glucose
- Water
- Chlorophyll
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Answer: C [1]
Question 2
Paper 1A style
Which statement explains why the action spectrum of photosynthesis is not zero in the green part of the spectrum?
- Chlorophyll absorbs green light more strongly than red light.
- Accessory pigments absorb some light in this region.
- Green light has the highest energy per photon.
- Green light is reflected and then used by the stroma.
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Answer: B [1]
Question 3
Paper 1B style
Pigments from a spinach leaf were separated by paper chromatography. The solvent front moved 9.0 cm from the origin. Reference Rf values for this method are: carotene 0.93, xanthophyll 0.70, chlorophyll a 0.50, chlorophyll b 0.40. The data are for practice. (a) Calculate the Rf value of spot 2. [1] (b) Using colour and Rf values, identify spots 1 and 3. [2] (c) Suggest why the pigments separate. [1]
| Spot | Colour | Distance from origin / cm |
|---|---|---|
| 1 | Orange-yellow | 8.4 |
| 2 | Yellow | 6.3 |
| 3 | Blue-green | 4.5 |
| 4 | Yellow-green | 3.6 |
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- (a) 6.3 ÷ 9.0 = 0.70 [1]
- (b) spot 1: Rf 0.93 / 8.4 ÷ 9.0, orange-yellow, so carotene [1]
- (b) spot 3: Rf 0.50 / 4.5 ÷ 9.0, blue-green, so chlorophyll a [1]
- (c) pigments differ in solubility in the solvent / attraction to the stationary phase, so travel different distances OWTTE [1]
Question 4
Paper 1B style
An aquatic plant was placed 10 cm from a lamp behind filters that let through light of one colour. The volume of oxygen released in 10 minutes was measured. The data are for practice. (a) Calculate the rate of oxygen production in blue light, in cm³ min⁻¹. [1] (b) Compare the rates in the different colours of light. [2] (c) State two variables that should be controlled. [2]
| Colour of light | Approximate wavelength / nm | Volume of oxygen / cm³ |
|---|---|---|
| Blue | 450 | 1.8 |
| Green | 550 | 0.4 |
| Red | 680 | 1.5 |
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- (a) 1.8 ÷ 10 = 0.18 cm³ min⁻¹ [1]
- (b) highest rate in blue light, then red [1]
- (b) lowest rate in green light, but not zero [1]
- (b) blue rate is 4.5 times green / use of values from the table [1]
- (b) [max 2]
- (c) light intensity / distance from lamp [1]
- (c) temperature [1]
- (c) CO₂ concentration / concentration of hydrogencarbonate [1]
- (c) same plant / mass of plant / time allowed to adjust [1]
- (c) [max 2]
Question 5
Paper 2A style
Compare enclosed greenhouse experiments with free-air carbon dioxide enrichment (FACE) experiments as ways of predicting future rates of photosynthesis and plant growth.
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- both: grow plants at raised CO₂ concentration to predict effects of future CO₂ levels [1]
- greenhouse: variables (temperature, water, light) easier to control [1]
- FACE: plants in field / natural ecosystem conditions so results more realistic [1]
- FACE: other variables (weather, soil, pests) harder to control / vary [1]
- [max 3]