Photosynthesis 3.5.1 ( Energy transfers in and between organisms 3.5) Flashcards
Explain why most light falling on producers is not used in photosynthesis
- Light is reflected or wrong wavelength
-Light misses chlorophyll - CO2 concentration or temperature is a limiting factor
What are the stages of photosynthesis
1) light dependent reaction
2) light independent reaction
where does the first stage of photosynthesis take place
Thylakoid membrane of chloroplast
where does the second stage of photosynthesis take place
Stroma of chloroplast
Describe photoionisation in the light dependent reaction
•Chlorophyll absorbs light energy which excites its electrons
• So electrons are released from chlorophyll ( chlorophyll becomes positively charged )
Describe what happens after photoionisation in light dependent reaction
Some energy from electrons released in photoionisation is conserved in the production of ATP / NADPH ( chemiosmotic theory) :
1) electrons move along electron transfer chain , releasing energy
2) this energy is used to actively pump protons from stroma into thylakoid
3) protons move by facilitated diffusion down electrochemical gradient into stroma via ATP synthase
4) Energy used to join ADP and Pi to form ATP ( photophosphorylation)
5) NADP accepts a proton and an electron to become NADPH
Describe photolysis of water in the LDR
- water splits to produce protons , electrons and oxygen
( H20 => 1/2 O2 + 2e- + 2H+ )
• electrons replace those lost from chlorophyll
Describe the light independent reaction of photosynthesis ( calvin cycle )
1) CO2 reacts with RuBP
• catalysed by enzyme rubisco
2) Forming GP molecules
3) GP is reduced to triosephosphate
• using products from light dependent reaction - NADPH and energy from ATP
4) Some triosephosphate converted to useful organic substances
5) Some triosephosphate used to regenerate RuBP in the Calvin Cycle ( using energy from ATP)
Describe and explain how temperature affects rate of photosynthesis
1) as temperature increases , rate increases
• enzymes gain kinetic energy
• so more enzyme substrate complexes form
2) Above an optimum temperature , rate decreases
• enzymes denature as H bonds in tertiary structure break.
• So fewer enzyme substrate complexes form
Describe and explain how light intensity affects rate of photosynthesis
1) as light intensity increases , rate increases
• Light dependent reaction increases so more ATP and NADPH produced
• So light independent reaction increases as more GP reduced to triose phosphate and more triose phosphate regenerates RuBP
2) Above a certain light intensity, rate stops increasing
• Another factor is limiting e.g temperature / CO2 concentration
Describe and explain how CO2 concentration affects rate of photosynthesis
1) As CO2 conc increases , rate increases
• light independent reaction increases
• as more co2 combines with RuBP to form GP
• so more GP reduced to TP
• so more TP converted to organic substances and more RuBP regenerated
2) Above a certain CO2 concentration, rate stops increasing
• another factor is limiting e.g. temperature / light intensity
Explain the key considerations when evaluating data relating to agricultural practices used to overcome the effect of limiting factors
- Agricultural practice should increase rate of photosynthesis, leading to increased yield .
• As more glucose production for faster respiration
• So more ATP to release energy for growth e.g. cell division , protein synthesis
• But profit from extra yield should be greater than costs ( money and environmental costs)
EQ : The pigments in leaves are different colours . Suggest and explain the advantage of having different coloured pigments in leaves . (1)
Absorb more wavelengths of light for photosynthesis
EQ : The student did not use a buffer to maintain the pH of the solution . Explain what would happen to the pH of the solution during this investigation
pH would increase
As more carbon dioxide is removed for photosynthesis
