5.6 Photosynthesis Flashcards
What is Photosynthesis?
Physiological process used by plants algae and some bacteria to convert light energy(from sun) to chemical energy
What is an Autotroph(primary producer)?
organism that produces complex organic compounds from simple substances
What is Autotrophic nutrition?
organisms producing food from inorganic raw materials like CO2 and H2O present in the surroundings
Organisms that photosynthesise are…..
PLANTS, Photoautotrophs
How are Photosynthesis and Respiration related?
Respirations products are photosynthesis reactants
Vice-versa
Plants constantly respire, but photosynthesise only when sunlight’s present. The compensation point is…
when photosynthesis and respiration occur at the same rate and oxygen used and released is equal
Where does photosynthesis take place in a plant?
Chloroplast
Describe the structure of a chloroplast.
- Usually disc-shaped.
- Double membrane (Inner & outer )(envelope)
- Intermembrane space
- Stroma: fluid-filled matrix with high enzyme & substrate concentration & own loop of DNA.
- Thylakoids: flattened discs stack to form grana.
- Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana.
Where do the light-dependent & light-independent reactions occur in plants?
- Light-dependent: in the Thylakoids
* Light-independent: in the Stroma
What are ‘Photosynthetic Pigments’?
pigments embedded within thylakoid membrane that Absorb different wavelengths of light to maximise rate of photosynthesis.
What are the 2 types of Photosynthetic Pigment ?
- Primary pigment: chlorophyll (made of chlorophyll a & chlorophyll b) found in photosystems.
- Accessory pigments: carotenoids (carotene & xanthophylls) found in light-harvesting systems.
What are the 2 forms of chlorophyll A what light wavelengths do they absorb?
P680 in photosystem 2 (peak light absorption 680nm)
P700 in photosystem 1(peak light absorption 7000nm)
What wavelength does chlorophyll b absorb?
400-500nm
What wavelength do Accessory pigments absorb?
550 and below
What is Photolysis?
breakdown of water in the presence of light
What is Photophosphorylation?
The generation of ATP from ADP and an inorganic phosphate in the presence of light
Name the processes in the light-dependent reaction
- photolysis
- non-cyclic photophosphorylation
- electron transfer chain
- cyclic photophosphorylation
How is water relevant in Photosynthesis?
• Reactant for Photolysis
Protons for oxidativephosphorylation
Electrons for photosystem 2
• keep plant turgid & functional
2 types of Photophosphorylation?
(Photosystems used)
cyclic (PSI only)
non-cyclic (PSI& PSII)
What is PSI & PSII?
Photosystems 1 AND 2
PSI (P700)
PSII (P680)
Explain the role of light in Non-cyclic Photophosphorylation
PSII absorb energy from photons of light. ‘excites’ 2 electrons , causing them to be released from the chlorophyll.
What happens to excited electrons?
escapes PSI, captured by an electron carrier to enter the electron transfer chain, replaced by one from photolysis
What happens in the Electron Transfer Chain (ETC)?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo redox reaction (Fe3+ —> Fe2+ back to Fe3+), which releases energy & passes on the electrons .
What happens to the electrons after the Electron Transfer Chain?
Enter PSI and either
• cyclic photophosphorylation •carried of to NADP in the stroma by ferredoxin, forms NADPH
What is done with the energy from the Electron Transfer Chain?
used to pump protons across the thylakoid membrane into the thylakoid space
What happens as protons (H+ ions) accumulate in the Thylakoid space?
Protons move down concentration gradient from thylakoid space into stroma via transmembrane channel protein ATP synthase.
ATP synthase catalyses ADP + Pi → ATP
Summarise Non-cyclic Photophosphorylation
Uses Photosystems Ⅰ & Ⅱ. Excited electrons enter ETC to produce ATP. NADP acts as final electron acceptor & is reduced. Water is photolysed to release electrons to replace those lost from PS Ⅱ.
Purpose is to produce ATP & reduced NADP Light independent stage of photosynthesis
Summarise cyclic photophosphorylation
Uses only Photosystem Ⅰ. Excited electrons enter ETC to produce ATP then return directly to photosystem (so no reduction of NADP & no water needed to replace lost electrons).
Purpose is to produce additional ATP to meet surplus energy demands of cell.
What happens in Photolysis of water?
accompanying equation and what the products do
Light energy splits molecules of water
2H2O → 4H + 4e- + O2
e- replace electrons lost by chlorophyll
H+ ions move into thylakoid space, help ATP form
O2 used in respiration or diffuses away
How and where is reduced NADP produced in the light-dependent reaction?
Happens in the Stoma
NADP + 2H+ (from photolysis of water) + 2e- (from acting as final electron acceptor in ETC) → NADPH
Name the 3 main stages in the light-independent reaction (Calvin cycle)
- Carbon fixation
- Reduction (GP to TP)
- Regeneration (TP to RUBP)
What is RuBP(Ribulose bisphosphate)?
a 5 carbon compound, accepts CO2
*catalysed by RuBisCO
(ribulose bisphosphate carboxylase )
What is GP(Glycerate-3-phosphate)?
a 3 carbon compound product of carbon fixing,
RuBP + CO2 -› unstable inter -› GP
What is TP(Triose phosphate)?
a 3 carbon compound and the final product of the Calvin cycle, formed from GPs reduction
2GP+ 2ATP+2NADPH -›
2TP +2(ADP+i) +2NADP
What happens during carbon fixation?
stage 1
Reaction between CO2 & RuBP catalysed by RuBisCO.
Forms unstable 6C intermediate that breaks down into 2 x glycerate 3-phosphate (GP).
What happens during reduction in the light-independent reaction?
(stage 2)
2 GP are reduced to 2 TP Requires 2 (reduced NADP & ATP) Forms 2 (NADP & ADP)
Outline the roles of TP from the light-independent reaction
Involved in regeneration of RuBP:(12TP -› 5RUBP + 2TP)
unit to make biological molecules
Sugars, starch,amino acids & fats.
Summarise the Calvin cycles needed for 1 mol of glucose(6 turns needed, use equations)
6CO2+ 6RuBP→ 12GP
12GP + 12ATP +12NADPH→ 12TP + 12ADP+ 12NADP
12TP→2TP(product) +10TP
10TP + 5 ATP→ 6RuBp +5ADP
Define ‘Limiting factor’
Factor that determines maximum rate of a reaction, even if other factors change
Name factors that can limit the rate of Photosynthesis
- Light intensity
- Temperature
- CO2 levels & Water
- Minerals
How does Light intensity affect the rate of Photosynthesis?
Low light intensity = slower light- dependent reaction = less ATP & NADPH produced to convert GP to TP in light-independent reaction
*vice versa
How does Temperature affect the rate of Photosynthesis?
Calvin cycle involves many enzyme controlled reactions so to high temp and they denature, too low the too slow
How does CO2 levels affect the rate of Photosynthesis?
CO2 needed to react with RuBP and form Gp to form Tp. Need good levels otherwise Calvin cycle cant run
Describe the implications of water stress (not enough water)
- cells plasmolyse
- tissues become flaccid, leaves wilt
- roots cant replace water lost from transpiration
- Rate of photosynthesis reduced
- roots make abscisic acid which if transpired cause stomatal closure
State the purpose and principle of Paper Chromatography
Separate mixtures depending on solubility of components, identifies compounds with RF values
Outline a method for extracting Photosynthetic Pigments.
Use a pestle and mortar to grind a leaf with an extraction solvent
Outline how TLC can be used to separate Photosynthetic pigments.
- Use a capillary tube to spot pigment extract onto pencil ‘start line’ (origin) 1 cm above bottom of plate.
- Place chromatography paper in solvent (origin should be above solvent level).
- Allow solvent to run until it almost touches the other end of the paper.
- Different pigments move different distances
