5.6 photosynthesis Flashcards
(31 cards)
What do you call organisms that are able to self synthesise their own organic compounds?
Autotrophs
What is a compensation point?
Where the rate of photosynthesis and respiration is the same
What is a compensation period?
The time taken to reach the compensation point
Do shade or sun tolerant plants have shorter compensation periods?
Shade tolerant
Is chlorophyll a p680 found in PS one or two?
Photosystem two
What is a photosystem?
A cluster of photosynthetic pigments that absorb sunlight and excite electrons within the pigment molecules
Where in the chloroplast does the light dependant reaction occur?
Stroma
Describe the steps of the light dependent reaction
- PS II absorbs sunlight
- Oxidises PS II, exciting electrons into the electron transport chain (photoionisation)
- Water is hydrolysed to reduce PS II again (photolysis) O2 diffuses out, H+ join the others
- Electrons excited from PS II provide energy to H+ ion channels on thylakoid membrane, H+ diffuse into stroma
- H+ diffuses down the concentration gradient back to the stroma
- H+ ions diffuse through ATP synthase, phosphorylating ADP to ATP in a process called chemiosmosis
- Chlorophyll harvests light in PS I
- Electrons excited into electron transport chain, oxidising PS I
- Electrons from E.T.C and H+ ions used to reduce NADP, forming reduced NADP in the stroma
Describe the movement of electrons in non-cyclic phosphorylation
- From water
- Into PS II
- To H+ ion channels
- To PS I
- To NADP
Describe the movement of electrons in cyclic phosphorylation.
The electrons get stuck in a circle.
Electrons excited from PS I are recycled to power H+ ion channels rather than going to NADP
reduced NADP is not produced
What is chemiosmosis?
Production of ATP by the diffusion of H+ down the electrochemical gradient through ATP Synthase
What is photoionisation?
When electrons are excited from their current energy level via sunlight
In photosynthesis, sunlight excites electrons, oxidising PS I and II
What is Photolysis?
The splitting of water molecules into H+ and O2 to release electrons (reducing PS II)
What is the series of redox reactions called in photosynthesis?
The electron transport chain
Describe the light independent reaction
- RuBP is reacted with CO2 to form 2x GP catalysed by RuBisCo
- 2x GP are reduced to form 3x TP. During this reduction, ATP is hydrolysed to ADP + Pi and reduced NADP is oxidised to NADP
- One carbon is lost from the 2x TP to form carbohydrates, amino acids, or lipids, while the rest is converted back to RuBP with ATP
How many turns of light-independent reaction would it take to form one glucose molecule?
6
How many carbons does each intermediate of the light independent reaction have?
RuBP = 5
CO2 = 1
TP = 3
GP = 3
What is the other name for the light-independent reaction?
The Calvin cycle
How would you describe the interrelationship between photosynthesis and respiration?
The products of photosynthesis are used for respiration
Where in the chloroplast does the light independant reaction occur?
Stroma
What are the factors affecting photosynthesis?
- CO2 concentration
- Light intensity
- Temperature
- Water stress
What is a limiting factor?
A variable that will affect the rate of reaction if restricted
What happens when light intensity is the limiting factor in the Calvin cycle?
GP builds up
GP cannot be reduced to TP as no rescued NADP or ATP
TP cannot be converted to RuBP as no ATP
What happens when CO2 is restricted in the Calvin cycle?
RuBP buildup as it cannot be converted to GP to convert to TP
