Photosynthesis Flashcards
what is the importance of photosynthesis
- for plants to make their own food to gain energy
- energy for metabolic reactions
what is the equation of photosynthesis
Carbon Dioxide + Water = Glucose + oxygen
what is the need for energy
- metabolic reactions
what is a metabolic pathway
series of small reactions controlled by enzymes
what is phosphorylation
- adding a phosphate to a molecule
- ADP is phosphorylase to ATP
what is photophosphorylation
- using light to add a phosphate to a molecule
what is photolysis
splitting of a molecule using light energy
what is hydrolysis
splitting of a molecule using water
what is decarboxylation
removal of carbon dioxide
what is dehydrogenation
removal of hydrogn
what is chemiosmosis
- diffusion of protons from high to low concentration
- movement of protons down the gradient releases energy that is used in the attachment of and inorganic phosphate to ADP to create ATP
- energy to do this comes from excited electrons
what are excited electrons
- excited in pigment molecules when absorbing light energy
- high energy electrons released when chemical bonds are broken in respiratory substrate molecules
- excited electrons pass into electron transport chain and used to generate a proton gradient
what is the electron transport chain
- made of electron carriers
- electrons move down the gradient from one carrier to another and release energy
- pumps protons across creating a concentration difference and a gradient
what is the structure of a chloroplast
Chloroplast envelope = double membrane
Thylakoids = stacked up into grana and linked by thylakoid membranes called lamellae
Photosynthetic pigments = coloured substances that absorb light energy, in thylakoid membranes attached to a protein
Stroma = fluid-filled membrane, contains starch grains, oil droplets, DNA + Ribosomes, light-independent stage
what are photosystems
- contains primary and secondary pigments
- photosystem 1 and 2
what is chlorophyll what colours do each pigment represent
Chlorophyll A = yellow/green (Primary)
Chlorophyll B = blue/green
Carotene = yellow/ orange
Xanthophyll = yellow
what is the light dependent stage
- needs light energy
- in thylakoid membranes
- energy absorbed by photosynthetic pigments and converted to chemical energy
what are the 4 stages of non-cyclic phosphorylation
- light energy excites electrons
- photolysis of water
- energy makes ATP
- energy generates reduced NADP
how does light energy excite electrons
- light energy absorbed by PSII
- light energy excites electrons in chlorophyll
- electrons move to a higher energy level
- high energy electron move along the electron transport chain to PSI
what happens in the photolysis of water
- as excited electrons leave PSII to move along the ECT they must be replaces
- light energy splits water into protons, electrons and oxygen
how does energy from excited electrons create ATP
- excited electrons lose energy as they move along the ETC
- energy used to transport protons into the thylakoid via proton pumps
- thylakoid has a higher concentration of protons than the stroma
- proton gradient formed across membrane
- protons move down the concentration gradient into the stroma via ATP synthase
- energy combined ADP and Pi to form ATP
how does energy from the excited electrons generate reduced NADP
- light energy absorbed by PSI
- excites electrons to a even higher level
- electrons are transferred to NADP with a proton (H+ ion) from the stroma
- reduced NADP formed (NADPH)
What is cyclic photophosphorylation
- only uses PSI
- electrons from the chlorophyll aren’t passed onto NADP
- passed back to PSI via electron carriers
- electrons are recycled and repeatedly flow through PSI
- doesn’t produce NADPH or oxygen only small amounts of ATP
what is the light independent reaction
- calvin cycle
- doesn’t use light energy directly
- relies on the products from the light independent reaction
- takes place in the stroma
what is the first stage of the calvin cycle
- carbon dioxide enters the leaf through the stomata and diffuses into the stroma
- CO2 combined with RuBP (5 carbon compound)
- unstable 6 carbon compounds which break down into 2 molecules of 3 carbon compounds called GP
- RuBisCO catalyses the reaction between CO2 and RuBP
what is the second stage of the Calvin cycle
- ATP from light dependent reaction provides energy to turn 3GP to 3 TP
- reaction requires H+ ions from reduced NADP in LDR
- reduced NADP recycled to NADP
- TP converted to several organic compounds
what is the third stage of the Calvin cycle
- 5 out of every 6 molecules of TP produced used to regenerate RuBP which used the rest of the ATP produced by LDR
what organic substances are made from the Calvin cycle
Carbohydrates
- hexose sugars made by joining 2 TP molecules together
Lipids
- made using glycerol synthesised from TP and fatty which are synthesised from GP
Amino acids
- made from GP
how many times does the calvin cycle need to turn to make a hexose sugar
- three turns produce 6 TP molecules
- 5/6 TP molecules are used to regenerate RuBP
- three turns produces 1 TP to make a hexose so two TP molecules needed
- 6 turns are needed
- 6 turns need 18 ATP and 12 NADH from LDR
What are limiting factors of photosynthesis
- light
- temperature
- carbon dioxide
how can light be a limiting factor
high light intensity = high energy to excite electrons
Very high light intensity = photosynthetic pigments are damaged
low = products of LDR are in short supply
- conversion of GP to TP and RuBP is slow
- level of GP rises and levels of TP and RuBP fall
how can temperature be a limiting factor
- too high (above 45)
- too low (below 10)
- denaturing of enzymes
- all reactions in the Calvin cycle are catalysed by enzymes
- levels of RuBP, TP, GP fall + denature
how can carbon dioxide levels be a limiting factor
- low concentrations conversion of RuBP to GP is slow
- level of RuBP rises and GP and TP fall
