Biology by Bradford
C1.3.4Reading the strip
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Rf = distance moved by the pigment ÷ distance moved by the solvent, so the pigment that moved 36 mm here has an Rf of . Pigments are identified by their Rf values and their .
C1.3 Photosynthesis: revision map
The subtopic in the middle and twelve tasks round it: label six diagrams, complete a table, put a process in order and fill 63 gaps. Every standard level statement has a box; the six boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Photosynthesis
Molecules · Interaction and interdependenceHover over a box to see it. Untick it to leave it off this sheet and its printout.
NameC1.3.5, C1.3.6Two spectra
An action spectrum shows the rate of at each wavelength; an absorption spectrum shows how much light a pigment absorbs. Here the action spectrum is the line. A pigment absorbs a photon only if its energy is just right to one of its electrons, so chlorophyll absorbs blue and red light but most green.
C1.3.11, C1.3.12, C1.3.13Electrons and oxygenHL
Photosystem II replaces the electrons it loses by splitting water: . The protons and electrons are used, but the oxygen is a . Its release changed Earth for ever: it oxidised iron dissolved in the oceans, which settled as banded rock, then built up in the air. Photosystem I passes two electrons to NADP, which also takes an H⁺ from the stroma and so is . In photophosphorylation, electrons from photosystem I return to the carrier chain instead, so only ATP is made.
C1.3.15, C1.3.16, C1.3.17Fixing carbonHL
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The carbon-fixing enzyme is the most enzyme on Earth: it is slow and works poorly when CO₂ is low, so the stroma is packed with it. The 3C product of fixation is reduced using ATP and . Five 3C sugars are rearranged into 5C molecules, using more ATP, so to make glucose of the 3C sugar made is recycled.
C1.3.1, C1.3.2, C1.3.3Capturing light
Photosynthesis transforms light energy into energy in carbon compounds, the source of most of the energy that flows through ecosystems. In words: carbon dioxide + water → + oxygen. Splitting water supplies the needed to reduce the carbon dioxide, and the oxygen is given off as a . Plants, algae and all release oxygen this way.
C1.3.4Running a chromatogram
Number the steps in order.
- Stand the strip in solvent, with the origin line just above the surface.
- Take the strip out before the solvent reaches the top, and mark how far it went.
- Put small drops of extract on one spot of the origin line, letting each dry.
- Grind leaves with a little propanone to extract their pigments.
- Measure how far each pigment moved and work out its Rf value.
The origin line is drawn in , as ink would dissolve and run.
C1.3Photosynthesis
C1.3.7Testing a limiting factor
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Here light intensity is the variable and the rate of photosynthesis is the variable. A hypothesis is a provisional explanation, so it needs testing.
C1.3.8Enriching the air
| Enclosed greenhouse | Free-air CO₂ enrichment (FACE) | |
|---|---|---|
| Setting | a closed glasshouse or chamber | open |
| Control of other variables | harder, as weather and soil vary | |
| How realistic the results are |
Both predict how photosynthesis and plant growth will respond as atmospheric CO₂ . A variable kept the same in the enriched and control plots, such as the plant species, is a variable.
C1.3.9, C1.3.10Inside a photosystemHL
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Energy from light absorbed anywhere in the array is passed inwards, pigment to pigment, until it an electron that is then emitted to an acceptor. A single pigment molecule could do no part of photosynthesis on its own: the array absorbs a wider range of and funnels the energy to one point.
C1.3.12, C1.3.14A thylakoid at workHL
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Water is split on the side facing the , where pumped protons also build up, and NADP is reduced on the side facing the . Protons flow back down their gradient through a channel enzyme, making ATP by .
C1.3.18, C1.3.19Two stages, one systemHL
Every carbon atom in a plant's compounds was fixed in the : sugars, fatty acids and amino acids are made by pathways that start from its intermediates, and amino acids also need , taken up as a mineral nutrient. The two stages depend on each other. Without light, no ATP or reduced NADP is made, so GP is not converted to triose phosphate and runs out. Without CO₂, reduced NADP is not used, NADP runs out, electrons back up along the chain, and the stop.
C1.3 examA simplified model of a photosystem in a chloroplastHL
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Word bank 0.45abundantaccessory pigmentATP synthasebubblesby-productCalvin cyclecarotenechemicalchemiosmosischlorophyllchlorophyll bcolourcontrolledcyanobacteriacyclicdasheddependenteasierelectron carrierexciteexcitesfieldsfive-sixthsglucoseglycerate 3-phosphatehydrogenindependentlamplesslight-dependent reactionsmorenitrogenoriginpencilphotolysisphotosynthesisphotosystem Iphotosystem IIpondweedproteinreaction centrereducedreduced NADPreflectsrepeatedrisesRubiscoRuBPsodium hydrogencarbonate solutionsolvent frontstromathreethylakoid membranethylakoid spacetriose phosphatewaste productwater bathwavelengths
Answer key
Every box on the sheet with its gaps filled in, as the subtopic reads in full.
GapsCapturing light
Photosynthesis transforms light energy into chemical energy in carbon compounds, the source of most of the energy that flows through ecosystems. In words: carbon dioxide + water → glucose + oxygen. Splitting water supplies the hydrogen needed to reduce the carbon dioxide, and the oxygen is given off as a by-product. Plants, algae and cyanobacteria all release oxygen this way.
OrderRunning a chromatogram
- Grind leaves with a little propanone to extract their pigments.
- Put small drops of extract on one spot of the origin line, letting each dry.
- Stand the strip in solvent, with the origin line just above the surface.
- Take the strip out before the solvent reaches the top, and mark how far it went.
- Measure how far each pigment moved and work out its Rf value.
The origin line is drawn in pencil, as ink would dissolve and run.
LabelReading the strip
- solvent front
- origin
- carotene
- chlorophyll b
Rf = distance moved by the pigment ÷ distance moved by the solvent, so the pigment that moved 36 mm here has an Rf of 0.45. Pigments are identified by their Rf values and their colour.
GapsTwo spectra
An action spectrum shows the rate of photosynthesis at each wavelength; an absorption spectrum shows how much light a pigment absorbs. Here the action spectrum is the dashed line. A pigment absorbs a photon only if its energy is just right to excite one of its electrons, so chlorophyll absorbs blue and red light but reflects most green.
LabelTesting a limiting factor
- lamp
- pondweed
- bubbles
- sodium hydrogencarbonate solution
- water bath
Here light intensity is the independent variable and the rate of photosynthesis is the dependent variable. A hypothesis is a provisional explanation, so it needs repeated testing.
TableEnriching the air
Enclosed greenhouse Free-air CO₂ enrichment (FACE) Setting a closed glasshouse or chamber open fields Control of other variables easier harder, as weather and soil vary How realistic the results are less more Both predict how photosynthesis and plant growth will respond as atmospheric CO₂ rises. A variable kept the same in the enriched and control plots, such as the plant species, is a controlled variable.
LabelInside a photosystem HL
- reaction centre
- chlorophyll
- accessory pigment
- thylakoid membrane
Energy from light absorbed anywhere in the array is passed inwards, pigment to pigment, until it excites an electron that is then emitted to an acceptor. A single pigment molecule could do no part of photosynthesis on its own: the array absorbs a wider range of wavelengths and funnels the energy to one point.
LabelA thylakoid at work HL
- photosystem II
- photosystem I
- ATP synthase
- electron carrier
Water is split on the side facing the thylakoid space, where pumped protons also build up, and NADP is reduced on the side facing the stroma. Protons flow back down their gradient through a channel enzyme, making ATP by chemiosmosis.
GapsElectrons and oxygen HL
Photosystem II replaces the electrons it loses by splitting water: photolysis. The protons and electrons are used, but the oxygen is a waste product. Its release changed Earth for ever: it oxidised iron dissolved in the oceans, which settled as banded rock, then built up in the air. Photosystem I passes two electrons to NADP, which also takes an H⁺ from the stroma and so is reduced. In cyclic photophosphorylation, electrons from photosystem I return to the carrier chain instead, so only ATP is made.
LabelFixing carbon HL
- RuBP
- glycerate 3-phosphate
- triose phosphate
- Rubisco
The carbon-fixing enzyme is the most abundant enzyme on Earth: it is slow and works poorly when CO₂ is low, so the stroma is packed with it. The 3C product of fixation is reduced using ATP and reduced NADP. Five 3C sugars are rearranged into three 5C molecules, using more ATP, so to make glucose five-sixths of the 3C sugar made is recycled.
GapsTwo stages, one system HL
Every carbon atom in a plant's compounds was fixed in the Calvin cycle: sugars, fatty acids and amino acids are made by pathways that start from its intermediates, and amino acids also need nitrogen, taken up as a mineral nutrient. The two stages depend on each other. Without light, no ATP or reduced NADP is made, so GP is not converted to triose phosphate and RuBP runs out. Without CO₂, reduced NADP is not used, NADP runs out, electrons back up along the chain, and the light-dependent reactions stop.
Exam diagramA simplified model of a photosystem in a chloroplast HL
- accessory pigment
- reaction centre
- protein
- thylakoid membrane