5.2.1 - Photosynthesis Flashcards
What is photosynthesis?
a process that converts light energy into chemical energy
-energy is used to synthesise large organic molecules from inorganic substances
What is the equation for photosynthesis?
carbon dioxide + water -> glucose + oxygen
6CO2 + 6H20 -> C6H12O6 + 6O2
What is an autotroph?
an organism that uses energy and inorganic molecules to synthesise organic molecules
What is a chemoautotroph?
an organism that synthesises complex organic molecules using energy from exergonic reactions
What is a photoautotroph?
an organism that can photosynthesise
Describe the structure of a chloroplast
- double membrane
- stacks of thylakoids (granum) -LDS on thylakoid membrane
- intergranal lamella join grana together
- stroma (fluid filled matrix containing enzymes, DNA, ribosomes, starch, etc) -LIS
What are photosynthetic pigments?
pigments that absorb light energy
-different pigments absorb different wavelengths
What are the two main types of photosynthetic pigments?
chlorophylls -chlorophyll a -chlorophyll b carotenoids -xanthophyll -carotene
What is a photosystem?
a funnel found in thylakoid membrane which light is reflected down (by accessory pigments) to the reaction centre (primary pigment)
What are the accessory pigments?
- xanthophylls
- carotenes
- chlorophyll b
What is the primary pigment?
chlorophyll a
What is an absorption spectrum?
a graph of different wavelengths of light by a pigment
(-chlorophylls absorb red + blue regions and reflect green
-carotenoids absorbs blue/purple region)
What is an action spectrum?
a graph of the rate of photosynthesis at different wavelengths of light
What are the two stages of photosynthesis?
- light dependant stage
- light independent stage
Where does the light dependant stage occur?
thylakoid membrane
What does the electron transport chain do?
makes ATP (needed as energy for the rest of the reactions in photosynthesis)
What is the role of water in the light dependent stage?
in PSII, an enzyme splits a molecule of water into H+ ions, electrons and oxygen (photolysis)
- electrons replace the ones previously lost in PSII
- H+ ions combine with the electrons in PSI and are accepted by NADP to become redNADP
What is cyclic photophosphorylation?
when some of the electrons lost from PSI return back to PSI
-on the way, these electrons loose energy, which is used to convert ADP into ATP
What is the roles of electron carriers in the light dependent stage?
transport excited electrons down an electron transport chain
What happens in the light dependent stage?
- photon of light reflected down PSII and absorbed by chlorophyll
- excites 2 e- which then move down an electron transport chain to PSI
- photon of light hits PSI where e- get excited and move down an electron transport chain
- electrons lost from PSI are replaced with electrons from PSII
- some e- lost from PSI return back to PSI (cyclic phosphorylation)
- these e- loose energy on the way, which is used to convert ADP to ATP
- in PSII, a molecule of water is split into H+ ions, electrons and oxygen (photolysis)
- these e- replace the ones lost from PSII
- H+ ions (from H2O molecule) combine with e- from PSI and are accepted by NADP to form redNADP (aka NADPH)
- H+ ion gradient is formed across the thylakoid membrane and H+ ions flow down the gradient through channel proteins (chemiosmosis)
- as they do so, they switch on ATP synthase and ATP is made from ADP (photophosphorlyation)
What is the Calvin Cycle?
the light independent stage of photosynthesis
Where does the the light independent stage occur?
stroma of chloroplasts
What products of the light dependent stage are used in the light independent stage?
ATP
redNADP
What happens in the light independent stage?
- CO2 combines with RuBP which is catalysed by Rubisco (CO2 is fixed and RuBP is carboxylated)
- this forms an unstable 6C intermediate
- this intermediate splits into 2 GP compounds
- GP is reduced and phosphorlyated (uses redNADP and ATP from LDS)
- this forms 2 TP compounds
- 10 out of every 12 TP produced are used to regenerate RuBP (using ATP from LDS)
- 2 out of every 12 TP produced are used to make biological molecules
What is produced in the light independent stage of photosynthesis?
- GP
- TP
How are the products from the light independent stage used?
- GP is used to make amino acids and fatty acids (used to make proteins and lipids)
- TP is used to make hexose sugars and glycerol (used to make carbohydrates and lipids)
What is the role of ribulose bisphosphate carboxylase (Rubisco)?
catalyses carbon fixation (RuBP and CO2 combining)
What are the limiting factors of photosynthesis?
- light intensity
- temperature
- carbon dioxide concentration
Why is light intensity a limiting factor?
- needed for stomata to open
- needed to excite e- in LDS
- needed for photolysis in LDS
- e- and H+ are needed in photophosphorylation in LIS
Why is temperature a limiting factor of photosynthesis?
- enzymes needed (eg. Rubisco in LIS)
- when too high, water is lost and stomata close
- increased oxygen production causes O2 molecules to compete for Rubisco’s active site, preventing Rubisco from accepting CO2 (photorespiration)
Why is carbon dioxide a limiting factor of photosynthesis?
-needed for LIS
What is photorespiration?
when oxygen molecules bind to Rubisco’s active site (instead of carbon dioxide) which doesn’t release any ATP
What effect does darkness have on the levels of GP, TP and RuBP in the Calvin Cycle?
- GP increases and TP decreases (redNAD and ATP from LDS are needed to convert GP into TP)
- RuBP decreases (RuBP continues being converted into GP, increasing GP, but less TP is regenerated into RuBP)
