Photosynthesis Flashcards
Where does the light dependent reaction occur?
Thylakoid membrane
Where does the light independent reaction occur?
The stroma
Draw and describe the structure of a chloroplast [7]
Diagram must contain
1. Inner membrane
2. Outer membrane
3. Stroma
4. Thylakoid
5. Thylakoid membrane
6. Granum
7. Intergranum lamellae
What is the photolysis equation?
H2O -> 2H+ + 2e- + 1/2O2
What is photolysis?
The splitting of water due to light
What are the hydrogen ions from photolysis used for?
Reducing coenzyme NADP to reduced NADP
What are the electrons from photolysis used for?
Used in the photo systems in the light dependent stage of photosynthesis
What happens when sunlight hits the first photosystem in the light dependent reaction?
In photosystem 2 the electrons are excited and move into the electron transfer carriers
What happens as electrons move across the electron transfer carriers in the light dependent stage of photosynthesis?
Each transfer releases energy allowing H+ ions to be pumped into membrane to make ATP
What is cyclic phosphorylation?
When electrons leaving photosystem 1 return to the photosystem after passing through the electron transfer carrier chain
What is the other name for the light independent stage of photosynthesis?
The Calvin cycle
In stage 1 of the Calvin cycle what reaction occurs using carbon dioxide?
What is the catalyst for this reaction?
CO2 + RuBP = 6 carbon unstable molecule
The enzyme RuBisCo catalyses this reaction
What inhibits the RuBisCo enzyme used in the Calvin cycle?
OXYGEN
What does the unstable 6 carbon molecule, made from the reaction between CO2 AND RuBisCo, break up into?
2 x 3 carbon molecules called GP
What does GP get converted into during the Colvin cycle, and using what molecules?
GP get converted into TP
It does this using the products of the light dependent reaction in photosynthesis - ATP & reduced NADP
What two things does TP go on to make in the Calvin cycle
- Lipids, glucose, amino acids and carbohydrates
- Regenerated RuBP (used in stage 1 of the Calvin cycle)
To produce 1 glucose molecule, the Calvin cycle needs to happen 6 times - this resulting in 10 spare TP molecules, which can be shuffled to make 6 RuBP molecules
What are the 4 limiting factors of photosynthesis?
- Light intensity
- CO2 concentration
- Temperature
- Water stress
How does light intensity impact rate of photosynthesis?
Low levels of light intensity impact rate of photosynthesis as there will be fewer of the products (Reduced NADP & ATP) of the light dependent reaction, which will slow down the light independent reaction
How does CO2 concentration impact rate of photosynthesis?
If there is less CO2 the reaction between carbon dioxide and RuBP will occur at a slower rate, slowing down the Calvin cycle
How does temperature impact the rate of photosynthesis?
In the light independent reaction the enzyme RuBisCo may be affected by temperature change impacting the rate of reaction between CO2 and RuBP
How does water stress affect rate of photosynthesis?
In an attempt to lose less water plants will close their stomata, however this prevents carbon dioxide form entering stopping the light independent reaction occurring
What is the impact of low light intensity on the Calvin cycle?
The amount of GP will increase as there is no ATP or reduced NADP to convert it to TP and then RuBP, meaning concentration of TP and RuBP will decrease
What is the impact of low carbon dioxide concentration on the Calvin cycle?
Both GP and TP will decrease as there is no carbon dioxide to react with RuBP to make these products, however RuBP concentration will increase
What is a light harvesting system?
A light harvesting system is a combination of accessory pigments and their proteins
What is the reaction centre of a photosystem?
The primary pigment (chlorophyll a) and its proteins
The reaction centre is surrounded by accessory pigments
Why is it important the the primary pigment and different accessory pigments absorb different wavelengths of light?
So that the maximum amount of light energy can be absorbed
What does a photosystem consist of?
The light harvesting system and the reaction centre
