Photosynthesis Flashcards
Describe the LDR
- Photons collide with the chlorophyll, causing a pair of electrons to excite (gain energy)
- When the electrons move across transport chain, energy is lost as carriers are in decreasing energy levels.
- Passage involves redox and it occurs in thylakoid membrane
- This is used to covert ADP to ATP by the addition of Pi.
- Photolysis of water means H+, e- and O2 are formed.
- H+ and e-‘s from the transport chain combine with NADP, forming NADPH
- e-‘s go to the chlorophyll to replace the lost e-‘s
Explain the advantage of having other photosynthetic pigments rather than just chlorophyll a
- More wavelengths of light can be absorbed
- Different pigments may have high absorption when other pigments has low absorption
- Photosynthesis is more efficient as it can still occur with a range of wavelength
Why does the pH increase during photosynthesis
- Less CO2 present as it’s used up
- Less carbonic acid formed
Explain the link between % light absorbed and the rate of photosynthesis.
- More light absorbed leads to a greater rate of photosynthesis.
- Light provides the energy for photolysis in the LDR
- More NADPH can be formed.
Methods to measure the rate of photosynthesis
- Volume of O2 produced
- CO2 removed
- Change in pH
Ways in which CO2 could be added in a greenhouse
- manure
- decaying organic material
Photolysis
- Water is split up. H+, e- and O2 are made.
- The protons are taken up by NADP, forming NADPH.
- Oxygen used in respiration.
Calvin cycle
- CO2 diffuses in through the stomata and then goes into the stroma.
- Here the CO2 combines with RuBP (5C) using the enzyme rubisco.
- This makes 2 GP (3C)
- Using the ENERGY from ATP, NADPH reduce the activated GP to 2 TP (3C) molecules.
- NADP is reformed and goes back to the LDR to be reduced again
- Some TP are converted to useful organic substances like glucose
- Most TP are used to regenerate RuBP using ATP from the LDR
Why ATP is a better IMMEDIATE energy source than glucose
- Each ATP molecule releases less energy than each glucose molecule. So the release is in smaller, more suitable chunks
- The hydrolysis of ATP to ADP is a single reaction whereas the breakdown of glucose is a long series of reactions
- Rapidly made during glycolysis
Adaptations of leaves for photosynthesis
- Large surface area to collect more light energy;
- Transparent cuticle to allow light penetration;
- stomata to allow exchange of gases;
- thin to reduce diffusion pathway
- air spaces in lower mesophyll to allow CO2 and O2 diffusion
- xylem brings water;
- phloem for removal of sugar
When the electron transport is inhibited why is there less in triose phosphate made
- Less ATP produced as the electrons aren’t releasing energy due to moving along the transport (LDR)
- Less NADPH produced
- Less GP is reduced to triose phosphate using NADPH and ATP
Why is the rate of photosynthesis very low between 525nm and 575nm (low absorption)
- Green light is reflected in those wavelenghts
- Light provides energy for photolysis in LDR
- Less ATP and NADPH is formed
How does the CO2 conc in change through day/night and at different heights above the ground?
Time
- High conc in the night (dark) as no photosynthesis but plants respire
- Photosynthesis absorbs CO2
- CO2 released during respiration
- In light, the rate of photosynthesis> respiration
- In dark , the rate of respiration> photosynthesis
- Photosynthesis only occurs in light (day)
- Respiration occurs constantly throughout the day
Height
- CO2 decreases as the height increases
- At ground levels, less photosynthesising tissue and more micro-organisms produce carbon dioxide;
Describe how NADP is reduced in the light-dependent reaction.
- Electrons excite and pass along ETC
- Then they combine with NADP and H+
- Hydrogen ions come from the photolysis of water
Role of water in photosynthesis
- provides hydrogen and electrons by photolysis
- H+ reduces NADP;
- the electron reduce the oxidised chlorophyll
