AQA A Level Biology - Photosynthesis

• What are the two stages of photosynthesis called>

  The Light Dependent reaction

  The Light Independent reaction (The calvin cycle)
• What is the purpose of photosynthesis?

  To energy from light is used to make glucose
• What is the general equation for photosynthesis ?

  6H2O + 6CO2 + energy --> C6H12O6 + 6O2
• What are the x stages of the light dependent reaction ?

  1. Photoionisation of PSII

  2. Photolysis of water

  3. Photoionisation of PSI

  4. Active transport of H+ ions

  5. Oxidative phosphorylation

  6. Reducing NADP
• Describe what happens during photoionisation of PSII

  Chlorophyll absorbs light

  Electrons excited and move to higher energy level

  Electrons move down electron transport chain to PSI
• Describe what happens during photolysis of water

  Light energy splits water molecules into H+, e- and oxygen

  The electrons replace those lost from PSII during photoionisation
• Explain how H+ ions are moved across the thylakoid membrane

  The excited electrons from photoionisation lose energy as they move down the electron transport chain

  The energy is used to actively transport H+ into the chloroplast
• Explain how H+ are involved in the synthesis of ATP in chloroplasts

  H+ move down their concentration gradient into the stroma

  This is via ATP synthase in the thylakoid membrane

  The energy synthesises ATP from ADP and Pi
• Explain why the photoionisation of PSI is important

  The excited eletrons are transferred to NADP with H+ to form reduced NADP

  This is needed for the light-independent reaction
• What is chemiosmosis ?

  Electrons move down the electron transport chain and creating a proton gradient

  This drived ATP synthesis
• Which molecules from the light-dependent reaction are needed in the light-independent reaction?

  ATP

  reduced NADP
• Where does the light dependent reaction take place?

  (acrodd) thylakoid membranes of chloroplasts
• Where does the light-independent reaction take place?

  Stroma of chloroplasts
• What are the 3 stages of the light-independent reaction?

  1. Formation of glycerate 3-phosphate

  2. Formation of triose phosphate

  3. Regeneration of ribulose bisphosphate
• Explain how glycerate 3-phosphate (GP) is formed

  Ribulose bisphosphate (RuBP) combines with CO2

  Forms unstable 6 carbon compound which breaks down to give 2 molecules of glycerate 3-phosphate

  Catalysed by Rubisco
• How does CO2 enter the stroma from the atmosphere?

  Diffusion through the stomata

  Difussion into the stroma
• Which enzyme catalyses the reaction of CO2 with ribulose bisphosphate (RuBP) ?

  Rubisco
• How many molecules of glycerate 3-phosphate (GP) are produced from 1 molecule of CO2 and 1 molecule of ribulose bisphosphate (RuBP) ?

  2
• How many carbon atoms are in ribulose bisphosphate ?

  5
• How many carbon atoms are in glycerate 3-phosphate (GP) ?

  3
• Explain how triose phosphate (TP) is formed from glycerate 3-phosphate (GP)

  Glycerate 3-phosphate (GP) is reduced to triose phosphate (TP) using H+ ions
• How is glycerate 3-phosphate (GP) reduced to triose phosphate (TP) ?

  Hydrolysis ATP from the light dependent reaction provide energy

  reduced NADP releases H+ to form NADP
• What two things can triose phosphate (TP) be used for?

  1. regenerating ribulose bisphosphate (RuBP)

  2. Converted to useful organic substances
• How many of the carbon atoms in 2 molecules of triose phosphate (TP) are used to regenerate ribulose bisphosphate (RuBP) ?

  5/6 carbon atoms
• How many of the carbon atoms in 2 molecules of triose phosphate (TP) are converted to useful organic substances?

  1/6
• Which two stages in the light independent reaction is ATP hydrolysed ?

  Reduction of glycerate 3-phosphate (GP) to triose phosphate (TP)

  Regeneration of ribulose bisphosphate (RuBP)
• Which 3 factors can limit the rate of photosynthesis?

  1. Light Intensity

  2. Temperature

  3. CO2 concentration
• Why is it important that ribulose bisphosphate (RuBP) is regenerated?

  So that glycerate 3-phosphate (GP) is formed and the light-independent reaction can continue

  Photosynthesis can continnue
• What are the 4 optimum conditions for photosythesis ?

  1. High light intensity of a certain wavelength (red and blue for chlorophyll a/b )

  2. 25 C

  3. 0.4% CO2

  4. Water of the right volume
• What 5 things will happen at a higher light intensity to cause faster growth of the plant?

  Faster production of ATP and NADP in LDR

  Faster light independent reaction

  More sugars produced/synthesis of new materials

  Sugars used for respiration

  More energy for growth
• Why is chlorophyll green?

  Chlorophyll does not absorb green light well
• What is the saturation point on a limiting factor/rate of photosynthesis graph ?

  The point where increasing the limiting factor has no effect on the rate of photosynthesis
• What does the saturation point indicate ?

  That another factor is limiting the rate of photosynthesis
• How do growers of plants create optimum conditions ?

  Using glasshouses
• How might plant growers control the CO2 concentration?

  Burning propane
• How might plant growers control the light intensity ?

  Use lamps
• How might plant growers control the temperature ? (3 ways)

  Glasshouses trap heat energy

  Heating/cooling systems

  Air circulation systems
• REQUIRED PRACTICALS
• What is a photosynthetic pigment?

  Coloured substances which absorb the light energy needed for photosynthesis
• What does the stroma contain?

  Enzymes, sugars, organic acids , starch grains