Photosyntheseis Flashcards
What organisms use photosynthesis?
Plants
Algae
Some types of bacteria
What are organisms that carry out photosynthesis called?
Photoautotrophs
What number balances the photosynthesis equation?
6 infront of everything except glucose
What is a photon?
A particle of light
Each photon contains a quantum of energy
Describe carbon fixation?
Process by which Carbon dioxide is converted into sugars. Eg- photosynthesis
Why does carbon fixation require energy?
As it is endothermic
What was one of the early organisms to carry out photosynthesis?
2 billion years ago
Cyanobacteria
What is the relationship between oxygen and carbon dioxide?
The products of one are the raw materials for the others
When do plants respire?
All of the time
When do plants photosynthesise?
During daylight
What is the plants compensation point?
When photosynthesis and respiration proceed at the same rate so the is no loss or gain of carbohydrates
What is the name for the time taken for a plant to reach its compensation point?
Compensation period
What kind of plants reach there compensation point quicker?
Shade plants
How many many membranes do a chloroplast have?
3
Inner
Outer
Thylakoid membrane
Describe chloroplasts?
Disc shaped
2-10 micrometers long
Surrounded by a double membrane- outer membrane highly permeable
Granum?
Made of stacks of thylakoid membrane
Stroma?
Fluid filled matrix of chloroplasts
Thylakoid?
Flattened membrane bound sac
Contains photosynthetic pigments
Where does the light dependent stage occur?
Thylakoid
Where does the light independent stage occur?
Stroma
What is the intergranal lamellae
Connects the thylakoids within a granum
What is found in the stroma?
Enzymes
Starch grains
Oil droplets
Smaller ribosomes
What do you find in the thylakoid membrane?
Embedded proteins to hold the photosystems in place
Photosystems
Describe photosystems?
Funnel shaped
System of photosynthetic pigments
What are photosynthetic pigments?
Pigments that absorb a specific wavelength of light and traps the energy associated with the light
Examples of photosynthetic pigment?
Chlorophyll A and B
Carotene
Xanthophyll
What happens to the light captured?
It is funnelled down to the primary pigment reaction centre
What colour do both types of chlorophyll a appear?
Blue-green
What colour do both types a chlorophyll a absorb?
Red
What are the different absorption peaks of chlorophyll a?
P680- PSii
P700- PSi
What colour does chlorophyll b appear? What wavelength does it absorb?
Yellow green
400-500nm and 640nm
What colour does carotenoids absorb? What wavelength does it absorb? What colour does it reflect?
Blue light
400-500nm
Reflect yellow and orange light
What colour does Xanthophylls absorb? What wavelength does it absorb? What colour does it reflect?
Blue and green light
375-550nm
Yellow light
What are the stages of the light dependent stage?
Light harvesting
Photolysis
Photophosphorylation
Formation of reduced NADP
What is phosphosphorylation?
The generation of ATP from ADP and inorganic phosphate in the presence of light
What is the first step of non-cyclic phosphosphorylation?
A photon of light excites a pair of electrons in the chlorophyll molecule
What is the second step of non-cyclic phosphosphorylation?
The energised electrons enter an electron carrier
What is the third step of non-cyclic phosphosphorylation?
As the electrons are passed down the election carrier chain they loose energy
What is the fourth step of non-cyclic phosphosphorylation?
This energy is used to pump h+ into the thylakoid space
What is the fifth step of non-cyclic phosphosphorylation?
Ferredoxin accepts the elections from PSi and passes them to NADP in the stroma. This reduces the NADP
What is the sixth step of non-cyclic phosphosphorylation?
As h+ accumulate a proton gradient is created across the membrane
What is the seventh step of non-cyclic phosphosphorylation?
H+ diffuse through channels associated with ATP synthase enzymes. This flow of protons causes ADP and and inorganic phosphate to join producing ATP
What enzyme catalyses the reduction of NADP?
NADP Reductase
What happens to the oxygen from photolysis?
Some for aerobic respiration
The rest diffuses out
What energy conversion has taken place?
Light to chemical
Describe cyclic photophosphorylation?
Only uses PSi Light excites electrons Enter electron carrier system Pass back to PSi Small amount of ATP generated
Which cells only contain PSi
Guard cells
To generate ATP to pump potassium into cells lowering the water potential for osmosis.
What is the journey for carbon dioxide?
Through stomata Spongy mesophyll Palisade cells- cell wall Chloroplast envelope Stroma
First step of Calvin cycle?
Carbon dioxide combines with Ribulose biphosphate
This is catalysed by rubisco
Second step of Calvin cycle?
This combination is an unstable 6-carbon-compound which immediately breaks down.
Third step of Calvin cycle?
The product is 2 molecules of a 3 carbon compound Glycerate-3-phosphate (GP)
Fourth step of Calvin cycle?
GP is then reduced (using the hydrogens from the reduced NADP) to triose phosphate (TP)
Last step of Calvin cycle?
5/6 TP molecules are reused in the cycle to regenerate Rubp
What is RuBp
Ribulose biphosphate
A 5 carbon compound present in the chloroplasts
What is TP
Triose phosphate
A three carbon compound
What happens in the stroma when protons are pumped into the thylakoid space?
The ph in the stroma increases to 8
What do you know about rubisco?
Optimum at pH 8
Is activated by the presence of ATP in the stroma
Uses magnesium ions as a cofactor
What role does ferredoxin play in PSi?
Activates enzymes involved in the Calvin cycle
Why does the Calvin cycle only run in daylight?
Required products of LDS
- ATP and reduced NADP
For Rubisco to work
For the concentration of magnesium ions to increase in the stroma
Roles of TP?
Glucose can be converted to starch, sucrose or cellulose
Some TP synthesises amino acids, fatty acids and glycerol
