Core M - Photosynthesis Flashcards
Describe the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra. (8)
- Chlorophyll a is primary pigment
- Carotenoids / chlorophyll b is accessory pigment
- Arranged in light harvesting clusters / photosystems
- On grana / thylakoids
- PI and PII (P700 and P680)
- Primary pigment / chlorophyll a in reaction centre
- Accessory pigment / carotenoids / chlorophyll b surround primary pigment
- Light energy absorbed by accessory pigments
- Energy passed on to primary pigment
- Chlorophyll a and b absorb light in red and blue violet region
- Carotenoids absorb light in blue violet region
- Absorption spectrum peaks at red and blue violet regions
- Different combinations of pigments in different plants to give different spectra
Outline the process of the photolysis of water and describe what happens to the products of photolysis. (10)
- PII absorbs light
- Enzyme in PII involved
- To break down water
- 2H2O –> 4H+ + 4e- + O2
- Oxygen is produced
- Used by cells for aerobic respiration
- Or released out of plant through stomata
- Protons used to reduce NADP
- With electrons from PI
- Reduced NADP used in Calvin Cycle
- To convert GP to TP
- Electrons also used in ETC
- To release energy for photophosphorylation
- To produce ATP
- Electrons from PII go to PI
- Re-stabilise PI
Explain how the palisade mesophyll cells of a leaf are adapted for photosynthesis. (7)
- Closely packed to absorb maximum light
- Vertical (at right angles) to surface of leaf to reduce number of cross walls
- Large vacuole pushes chloroplast to edge of cell
- Chloroplasts at edge, short diffusion path for carbon dioxide
- Chloroplasts at edge to absorb maximum light
- Large number of chloroplasts to absorb maximum light
- Cylindrical cells (air spaces) to circulate gases / provide a reservoir of carbon dioxide
- Moist cell surfaces for diffusion of gases
- Cell walls thin for maximum light penetration / diffusion of gases
- Chloroplasts can move towards light to absorb maximum light
- Chloroplasts can move away from high light intensity to avoid damage
Describe the structure of photosystems and explain how are photosystem functions cyclic photophosphorylation. (8)
- Arranged in light harvesting clusters
- Primary pigments
- At reaction centre
- P700 absorbs at 700 nm
- P680 absorbs at 680 nm
- Accessory pigments (chlorophyll b and carotenoids) surround primary pigment (chlorophyll a)
- Pass energy to primary pigment
- P700 involved in cyclic photophosphorylation
- Light absorbed results in electron excited
- Emitted from chlorophyll
- Flows along chain of electron carriers (ETC)
- ATP synthesis
- Electron returns to P700
Describe how the structure of a chloroplast is related to its functions. (9)
- Stroma
- For light independent stage (Calvin cycle)
- Contains enzymes eg rubisco
- Also sugars, lipids, starch, ribosomes, DNA
- Internal membrane system
- For light dependent stage
- Fluid filled sacs (thylakoids)
- Grana are stacks of thylakoids
- Grana hold photosynthetic pigments
- Grana have large surface area for maximum light absorption
- Pigments are arranged in light harvesting clusters
- Primary pigment surrounded by accessory pigments
- Accessory pigments pass energy to primary pigment
- Different photosystems absorb light at different wavelengths
- Membranes hold ATP synthase and electron carriers
- For photophosphorylation and chemiosmosis
Describe how you would separate chloroplast pigments using chromatography. (6)
- Grind leaf with solvent
- With propanone
- Leaf extract contains mixture of pigments
- Concentrate extract
- Pencil line drawn, extract placed on chromatography paper, repetitive spotting, drying between spots
- Paper placed vertically in jar of different solvent
- Solvent rises up paper
- Each pigment travels at different speed
- Pigments separated as they ascend
- Distance moved by each pigment is unique
- Rf value
- Two dimensional chromatography
- Better separation of pigments
Describe and explain the effects of different wavelengths of light on the rate of photosynthesis. (4)
- High rate at photosynthesis at 430-435 nm and 655 nm
- High absorption of light at these wavelengths
- Highest rate at 430-435 nm
- Shorter wavelengths have more energy
- Lower rate in middle range of wavelengths (500-600 nm)
- Low light absorption here
- Absorbed light used for photosynthesis
- In light-dependent stage
Name two products of the light-dependent stage of photosynthesis that are used in the light-independent stages (2)
- ATP
* Reduced NADP
Describe how ATP and reduced NADP are used in the light-independent stage of photosynthesis. (3)
- ATP provides energy
- Reduced NADP is reducing agent, providing hydrogen
- For converting GP to TP
- ATP used to regenerate RuBP
Explain what is meant by the term limiting factor. (2)
- Process is affected by more than one factor
* Rate is limited by the factor nearest its minimum value
Describe how carbon dioxide reaches the photosynthetic cells in a leaf. (4)
- Enters leaf through open stomata
- By diffusion
- Substomatal air space
- Many air spaces in spongy mesophyll
- Spaces between palisade cells
- Dissolves in moisture on cell walls
- Enters through cell walls
