Photosynthesis

• What are thylakoids?

  Fluid-filled sacs.
• What are grana?

  multiple thylakoids stacked up.
• What is a stroma?

  Gel-like substance that surrounds the thylakoids.
• What is a lamellae?

  Connects granums together.
• What do grana’s provide?

  Provides a large surface area for attachment of chlorophyll, electrons and enzymes.
• What does the granal membrane have in it?

  ATP synthase channels which allows ATP to be synthesised and be selectively permeable allowing a protein gradient.
• Why do chloroplasts have a network of proteins?

  Holds the chlorophyll in a specific way to absorb the maximum amount of light.
• What are the three pigments?

  Chlorophyll a

  Chlorophyll b

  Carotenoids
• Why are pigments photosynthetic?

  So they can absorb light energy needed for photosynthesis.
• What is a photosystem?

  A pigment and a protein.
• What is the purpose of photosystems?

  Absorbs light and transfers energy and electrons.
• What are the 2 photo systems used by plants to absorb light?

  Photosystem 1 - 700nm wavelength

  Photosystem 2 - 680nm wavelength
• Where does the light dependent reaction occur?

  Thylakoid membrane.
• What is the equation of photolysis?


  H20 -> 2H+ + 2e- + 0.5O2
• Where does the hydrogen from photolysis go?

  Picked up by NADP to reduce it to form NADPH
• Where do the electrons from photolysis go?

  Passes along a chain of electron carrier proteins.
• Where does the oxygen in photolysis go?

  Used in respiration or diffuses out of leaf via stomata.
• Describe non-cyclic phosphorylisation.

  Light energy is absorbed by PSII and electrons are excited.

  Excited electrons pass through ETC.

  Whilst they move the energy is used to produce ATP by chemosmosis.

  Light energy is absorbed by PSI and electrons are excited again.

  They pass through ETC.

  Whilst they move the energy is used to produce ATP by chemosmosis.

  Electrons used to reduce NADP in stroma.
• What happens in cyclic phosphorylisation?

  Electron is excited from PSI and then returned instead of being used to reduce NADP.
• Cyclic vs non-cyclic phosphorylation.


  PSI vs PSI and PSII

  ATP vs ATP and NADPH

  Electron reabsorbed vs not reabsorbed

  Water doesn’t under go photolysis vs water undergoes photolysis.

  No oxygen released vs oxygen released
• Describe the electron transport chain?


  Electrons move to a higher energy level when excited.

  As it moves it reduces and oxidises proteins.

  Energy is used to actively transport H+ ions from stroma to lumen creating a protein gradient.
• Describe chemosmosis in LDR.

  Hydrogen ions move across chloroplast membrane.

  Uses energy from electrons moving along ETC to move ions from a low to a high concentration.

  Electrochemical gradient created.

  Hydrogen ions pass through ATP synthase producing ATP.

  NADP picks up electrons and protons to reduce it into NADPH.
• Where does the light-independent reaction occur?

  Stroma.

  Contains enzyme Rubisco
• Describe the carbon fixation stage of LIR.

  Carbon dioxide is fixed by adding ribulose bisphosphate (RuBP).​

  Forms a 6-carbon molecule.​

  Reaction is catalysed by enzyme Rubisco.​

  The molecule is unstable and immediately breaks down to form 2 compounds called glycerate-3-phosphate (GP)
• Describe the reduction stage of LIR.

  Isomerisation reaction occurs converting GP into triose phosphate (TP).​

  This requires energy so ATP is hydrolysed into ADP.​

  Also requires electrons so reduced NAPD transfers electrons to GP.​

  Some TP is converted into organic molecules 1/6: sugars, lipids and amino acids.​

  The other 5 molecules of TP will be used for RuBP regeneration.
• Describe the regeneration stage of LIR.

  TP is converted back into RuBP.​

  Requires energy from ATP hydrolysis.​

  Cycle is completed and another round of carbon fixation can occur.​
• How can light be a limiting factor of photosynthesis?

  A high light intensity means that the light-dependent reaction can work faster.​

  Needs to be the right wavelength to have maximum absorbed.
• How can people ensure light isn’t a limiting factor?

  Gardens grown plants in transparent greenhouses or polytunnels which let in light and also use lamps.
• How can low temperatures become a limiting factor?

  At low temperatures, enzymes become inactive and photosynthesis slows.
• How can high temperatures become a limiting factor for photosynthesis?


  At high temperatures, enzymes denature and their active sites change shape so no ES complexes form.​

  Also the stomata close at high temperatures to conserve water so gas exchange stops and reduces rate of photosynthesis.​

  An increase in temperature also increases fluidity in membrane so it reduces the hydrogen concentration gradient.
• What temperature is the best for photosynthesis?

  25 degrees
• How can people ensure temperature doesn’t become a limiting factor?

  Greenhouses trap heat from sunlight, some have heaters and cooling systems to ensure an optimum temperature is maintained.​
• What is the atmospheric carbon dioxide percentage?

  0.04%
• How can be carbon dioxide be a limiting factor in photosynthesis?

  Concentrations above 0.4% causes stomatal closure and a reduction in photosynthesis.​
• How can people prevent carbon dioxide from becoming a limiting factor?

  Gardeners can add carbon dioxide to a greenhouse by burning propane.