Photosynthesis Flashcards
What is the role of thylakoids in chloroplasts?
- Site of the light dependent reactions
- Where photosynthetic pigments absorb light energy
- For synthesis of ATP, Reduce NADP and O2 to be produced
What is the role of grana in the chloroplast?
Provide a large surface area for the absorption of light energy
What is the role of the starch grain in chloroplasts?
- Excess carbohydrates produced stored as a startch grain
- Starch doesn’t affect water potential
What is the role of the double membrane in chloroplasts?
Controls movement of substances in and out of chlooplasts
Why are plants green?
Photosynthetic pigments absorb all wavelengths except green and reflect the green
What is an absorption spectrum?
A graph showing how much light energy is absorbed at different wavelengths by each photosythetic pigment
What are the two stages of photosynthesis?
- Light dependent reaction (on thylakoid membranes producing Reduced NADP and ATP from light energy)
- Light independent reaction (in stroma producing glucose from breaking down ATP and Reduced NADP)
What are the adaptations of leaves for photosynthesis?
- AIR SPACES in spongy mesophyll allowing CO2 to diffuse into photosynthesising cells
- LARGE SA to capture as much light as possible
- THIN to let light penetrate all the way through
- STOMATAL PORES to allow CO2 through from diffusion
What is an action spectrum?
A graph showing the ate of photosynthesis at different wavelengths
Where does photosynthesis occur?
In chloroplasts on the thylakoid membrane
What happened in the Engelmann’s experiment?
- As the spiral chloroplasts of the bacteia photosynthesise oxygen is produced as a waste product
- Mobile aerobic bacteria move towards the parts of the chloroplasts exposed to red and blue parts of the spectrum
Describe the structure of photosystems?
- Located in the thylakoid membranes
- Antenna complex where clusters of photsythetic pigments are held
- Reaction centre containing two molecules of chlorophyll a
What are the adaptations of chloroplasts of photosynthesis?
- More chloroplasts in palisade than spongy mesophyll so they are exposed to more light
- Large SA allows more CO2 and light absorption
- Thylakoid stacking maximises light catchment
- Chloroplasts can move within palisade cells allows or maximum absorvtion of light and protection from bleaching
What is the role of the stroma in the chloroplasts?
- SIte of the light independent reaction
- Holds reactants and products fo CO2 to boduuce glucose and ATP and Reduced NADP
- Contains starch grains that store the products of photosynthesis
What are the 2 types of photosystems?
Photosystem I has maximum absorption wavelength of 700nm and is used in both cyclic and non-cyclic photophosphorylation
Photosystem II has maximum absorption wavelength of 680nm and is used in only non-cyclic photophosphorylation
What is a photosystem?
A collection of accessory pigments in the antenna complex which absorb light at various wavelengths and transmit energy to the reaction centre
When and where does photophosphorylation occur?
In the light dependent stage on the thylakoic membrane
What happens in cyclic photophosphorylation?
- Photon hits PSI and is absorbed by accessory pigments in the antenna complex and transfered to the primary pigment
- Excites electrons to a higher energy level to an electron acceptor
- Moves down electron transport chain and loses energy which is used to convert ADP + Pi to ATP
- Electron returns to PSI
What is chemiosmosis?
- Energy released by the electron transport chain is used to pump protons from the stroma into the thylakoid space
- This creats a proton concentration gradient
Protons move back though ATP Synthetase - This energy released converts ADP + Pi to ATP
What happens in non-cyclic photophosphorylation?
- Photon hits PSII and excites electrons to a higher energy level to an electron acceptor
- Moves down electron transport chain and loses energy which is used to convert ADP + Pi to ATP
- Electron returns to PSI
- Simultaneously light energy hits PSI and excites electron from chlorophyll a and then travels down the ETC
- At the end joins to the terminal electron acceptor NADP to produce NADPH with H ions from photolysis
What happens in photolysis?
- Water splits into 1/2 O2 + 2e- + 2H+
- The electrons replace those lost in PSII
- Protons combine to make Reduced NADP
- Oxygen is a waste product
What does the electrochemical gradient produce?
A source of potential energy for the synthesis of ATP
Describe/Draw the Calvin Cycle
- Ribulose Bisphosphate and CO2 combine with RUBISCO making an unstable 6C Compound
- This splits for two Glycerate-3-Phosphate
- This becomes two Triose Phosphate with the breakdown of ATP and the oxidation of Reduced NADP
- One carbon becomes glucose (fructose bisphosphate) the rest is converted into Ribulose Phosphate for the cycle to continue with the breakdown of ATP
What stage of photosynthesis is the Calvin Cycle?
The light-independent stage
What is chromatography?
A seperation technique to separate pigments in leaves
What does an Rf value show?
How far a component has travelled compared to the solvent front
What are the limiting factors for plant metabolism?
Inorganic nutrients: Nitrogen and Magnesium
What happens with nitrogen defficiency?
- Limits metabolism
- Nitrogen is required to synthesise proteins and nucleic acids
- Usually transported as nitrates on the xylem
- Defficiency causes stunted growth of all organs, hinders cell division and chlorosis
What happens with magnesium defficiency?
- Limits metabolism
- Transported as Mg2+ in xylem
- Required in chlorophyll and for the activation of ATP Synthetase
- Defficiency causes chlorosis as unable to photosynthesise
What are the three limiting factors of photosynthesis?
Light intensity, carbon dioxide concentration, temperature
What happens to the rate of photosynthesis as light intensity is increased?
- As light increases so does the rate until it is no longer a limiting factor
- It will plateau as all photosystems are used and there is saturation at about 1000 lux
What happens to the rate of photosynthesis as carbon dioxide concentration is increased?
- As concentration increases so does the rate until it is no longer a limiting factor
- It will then plateau as something else is the limiting factor
What happens to the rate of photosynthesis as temperature is increased?
- Increase as temperatue increases as enzymes work best at warm temperature
- Optimum temperature at 45 degrees
- Then decrease as enzymes start to denature
What is the compensation point?
Where rate of photosynthesis and rate of respiration are equal and there is no net gas exchange
Why would the compensation point never be reached at night?
Light dependent reaction won’t take place at night so there is no photosynthesis
What happens in photosystems?
Photons hit photosystems and excite pigments in the antenna complex these transfer enegy until it reaches the primary pigment in the reaction centre. The electrons ae raised to a higher energy level to electron acceptor
What is the general formula for photosynthesis?
6CO2 + 6H2O –> C6H12O6 + 6O2
Why is there more than one photosynthetic pigment?
To maximise the wavelength of light that can be absorbed for photosynthesis
Name all the photsynthetic pigments
Chlorophyll a
Chlorophyll b
B-Carotene (carotenoid)
Xanthophyll (carotenoid)
