Photosynthesis Flashcards
(26 cards)
What is catabolism?
breakdown of a substance releasing energy - respiration
What is anabolism?
synthesis of substances requiring energy - photosynthesis
Describe the structure of a chloroplast
double membrane, contains stroma (liquid inside) thylakoids stacking to form grana
What joins grana together?
intergranal lamellae
What makes up a photosystem?
pigment and proteins
What are thylakoids?
disc shaped fluid filled sacs made of thylakoid membrane
What is the stroma?
contains enzymes and starch granules (and chloroplast DNA and ribosomes)
How do thylakoids assist in photosynthesis?
-contain photosynthetic pigments to absorb light energy
-large SA as discs stacked to increase light absorption
-contains ATP synthase required to make ATP
What are the two reactions?
light dependent
light independent
What does the LDR produce?
ATP
NADPH
What is NADP?
a coenzyme
Why is it essential to break the bonds between the coenzyme and the product after a reaction?
to avoid drop in coenzyme concentration
Where does the LDR take place?
thylakoid membrane
What is the difference between PSII and PSI?
absorb different wavelengths of light
What happens in the LDR?
-light energy absorbed by PSII, exciting the electrons causing them to leave the chlorophyll to a higher energy level (photoionisation)
-the excited electrons pass from one carrier to the next along the electron transport chain, losing energy as they travel
-this energy is used to drive a protein pump that actively transports protons from the stroma to the inside of the thylakoid
-the electrons that left PSII are replaced due to photolysis of water- splitting water into oxygen, protons, and electrons
-electrons in PSI are also excited by light and passed along a second electron transport chain, where they react with protons and NADP to form NADPH. the electrons are replaced by the electrons from PSII
-protons in the thylakoid lumen build up and generate a concentration gradient- this causes chemiosmosis, where the protons diffuse down the gradient into the stroma using ATP synthase, which in turn causes photophosphorylation (ADP + Pi –> ATP)
Why is oxygen produced as a byproduct of the LDR?
product of photolysis of water, can be used in respiration or diffuse out of the leaf as a waste gas
What is the equation for photolysis of water?
2H2O –> 4H+ + 4e- + O2
Where does the LIR take place?
stroma
What can the LIR also be called?
Calvin Cycle
What happens in the LIR?
-CO2 reacts with Ribulose Bisphosphate, catalysed with the enzyme rubisco, forming an unstable 6C compound which breaks down quickly to form 2 molecules of Glycerate-3-phosphate
-both molecules of GP are reduced to Triose Phosphate, requiring H+ provided by the reduction of NADPH, which requires energy from the hydrolysis of ATP
-5/6 carbons are used from the Triose Phosphate to reform Ribulose Bisphosphate, requiring ATP, but 1 carbon is used to form organic products like glucose/amino acids/glycerol
How was the Calvin cycle discovered?
calvins lollipop experiments-
-made a suspension of algae, supplied with radioactive CO2
-use a flat sided flask to mimic the conditions of a leaf
-use a rapid action tap into hot alcohol/ethanol
-keep in a dark room, then switch light on for 5 second intervals, extract some algae, repeat every set time frame and analyse each sample
Why use hot ethanol?
to freeze metabolic reactions/kill algal cells
What indicator should you use to determine photosynthesis rate?
hydrogencarbonate-
red at normal CO2 levels (CO2 is acidic)
purple = decreased CO2 INCREASED PHOTOSYNTHESIS
yellow = increased CO2 DECREASED PHOTOSYNTHESIS
What are the limiting factors of photosynthesis?
-temp ]–tend to come together
-light intensity ]
-CO2 concentration
