Photosynthesis

• What are the 2 stages of photosynthesis?

  Light-dependent reaction

  Light-independent reaction
• Why do plants need energy?

  Photosynthesis, active transport, DNA replication, cell division, protein synthesis
• What is the site of the light-dependent reaction?

  Thylakoid membrane
• Why is this site beneficial for the light-dependent reaction?

  Provide a large surface area for attachment of chlorophyll, electron carriers and enzymes.

  Network of proteins in grana hold chlorophyll in precise manner allow maximum absorption.

  Have ATP synthase channels within them, catalyse production of ATP.

  Selectively permeable allows establishment of proton gradient.

  Contain DNA and ribosomes can quickly and easily manufacture proteins

  
  
• What is the structure of the chloroplast?

  Outer and inner membrane enclose chloroplast, stroke is fluid-filled space where light independent-reaction occurs, thylakoids are flattened membrane-bound sacs stacked in a structure called grana for larger surface area, connected by lamellae. Contains its own DNA similar to prokaryotic DNA.
• What is the energy from light used for in the light-dependent reaction?

  To add an inorganic phosphate molecule to ADP, making ATP.

  To split water into H+ ions and OH- ions, photolysis.
• What are the pigments found in chloroplasts and what do they do?

  They are photosynthetic pigments that absorb the light energy: chlorophyll, chlorophyll b and carotene. They are found in the thylakoid membrane and are attached to proteins.

  
  
• What is a photosystem?

  The protein and a pigment combined, two photo streams used by plants to absorb light are PS1 and PS2.
• What is the definition of photophosphorylation?

  The process of producing ATP using light energy in photosynthesis.
• Explain the capture of light in non-cyclic photophosphorylation?

  Light energy is absorbed by PS2, the light energy excites electrons in chlorophyll, the electrons move to a higher energy level. These high energy electrons move along the electron transport chain to PS1.
• What is the electron transport chain?

  A series of protein complexes embedded in the thylakoid membrane that use energy from excited electrons to pump protons from the into the thylakoid lumen, creating a proton gradient.
• What is photolysis?

  Light energy splits water into H+ ions, electrons and oxygen.

  2H2O -> 4H+ + 4e- + O2
• Why does photolysis occur during the light dependent reaction?

  As the excited electrons from chlorophyll leave PS2 to move along the electron transport chain, they must be replaced to carry on the series of redox reactions that provides the energy that maintains the proton gradient. The splitting of water provides electrons to PS2 as excited electrons leave.
• When do PS2 and water absorb light?

  They all absorb light simultaneously
• What is the process of chemiosmosis in the light dependent reaction?

  Excited electrons lose energy as the move in a series of redox reactions down the ETC. This energy is used to transport protons into the thylakoid lumen so that there is a higher concentration of protons in the thylakoid than the stroma. This forms a proton gradient across the membrane.

  Protons move down their conc. gradient, into the stroma via an enzyme ATP synthase, the energy from the movement of the protons combines ADP and inorganic phosphate to form ATP.
• What is the definition of chemiosmosis?

  The name of the process where the movement of H+ ions across a membrane generates ATP.
• What is the process of generation of reduced NADP in light dependent reaction?

  Light energy is absorbed by PS1 which excites electrons again to an even higher energy level. The electrons are transferred to NADP along with a proton(H+ ion) from the stroma to form reduced NADP.
• What is cyclic photophosphorylation?

  Only uses PS1, cyclic because the electrons used aren’t passed to NADP, but passed back to PS1 via electron carriers. Electrons recycled and used repeatedly to flow through PS1. Produces small amounts of ATP and only occurs when there is enough reduced NADP.
• What are the products of the light dependent reaction?

  ATP, reduced NADP, Oxygen
• Why does the light independent reaction still need light to be present?

  Light independent reaction requires the products from the light dependent reaction which are only produced due to light being present, therefore light must be present for the light independent reaction to take place.
• What and why is the site light independent reaction?

  The light independent reaction takes place in the stroma as it contains a high concentration of enzymes that are required. There is a short diffusion pathway from granum to site of light dependent reaction to stroma for the products of the light dependent reaction. It contains ribosomes and DNA to synthesize the proteins needed for LIR.
• Describe the first stage of the calvin cycle.

  CO2 from the atmosphere diffuses into the leaf through the stomata and dissolves in water around the walls of the mesophyll cells. It then diffuses through the cell-surface membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast.
• Describe the 2nd and 3rd stage of the calvin cycle.

  In the stroma, the CO2 reacts with 5-carbon compound ribulose biphosphate(RuBP) a reaction catalysed by an enzyme called ribulose biphosphate carboxylase(rubisco).

  Reaction between CO2 and ribulose bisphosphate produces two molecules of the 3-carbon glycerate 3-phosphate.
• What is the forth stage of the calvin cycle?

  Reduced NADP from the light dependent reaction is used to reduce glycerate 3-phosphate to triose phosphate using energy supplied by ATP. 2 ATP molecules used to reduce and 2 reduced NADP molecules are oxidised to NADP.
• What are the fifth and sixth stage of the calvin cycle?

  NADP is reformed and goes back to the light dependent reaction to be reduced again(H+ ions come from reduced NADP) , some triose phosphate used to make starch, cellulose, lipids, glucose, amino acids, nucleotides, goes to respiration or reforms ribulose biphosphate, which requires one molecule of ATP.
• What are some products of calvin cycle used for?

  Glucose - 2 triose phosphate

  Lipids- glycerol - made from triose phosphate

  Fatty acids - glycerate 3-phosphate

  Amino acids - glycerate 3-phosphate
• How is glucose formed?

  Calvin cycle needs to turn 6 times to make glucose, 18 ATP used and 12 reduced ATP.
• What is the definition of compensation point?

  The particular light intensity at which the rate of photosynthesis is the exact same to the rate of respiration.
• What are the factors that affect photosynthesis ?

  Light, carbon dioxide, temperature
• How does light affect the rate of photosynthesis?

  Rate of photosynthesis is directly proportional to light intensity, as light intensity increases the volume of oxygen produced and CO2 absorbed due to photosynthesis increases until the compensation point, when O2 absorbed and CO2 by respiration is balanced. Further increases will have no affect on the rate
• How does carbon dioxide affect the rate of photosynthesis?

  The optimum concentration of CO2 is 0.1% it is present in atmosphere at 0.04%. It affects enzyme activity when Conc is too high enzyme denatures as bonds in rubisco break changing the tertiary structure. Meaning combination of ribulose biphosphate and CO2 cannot combine decreasing the rate of reaction. If CO2 too low not enough for combination so rate decreases. Farmers enrich greenhouse with CO2 for higher yield.
• What is the affect of temperature on photosynthesis?

  The rate of photosynthesis is directly proportional to temperature, between 0-24 rate of photosynthesis is approximately doubled for each 10 rise in temp. Rate decreases at very high temperatures as bonds in enzyme rubisco are broken tertiary structure altered cannot catalyse the combination of ribulose biphosphate and CO2.
• How do you measure the rate of photosynthesis?

  Measure the volume of oxygen produced by using a photosynthometer.
• Describe the method of measuring the rate of photosynthesis.

  Set up apparatus introduce no bubbles into it.Water bath maintains constant temp.Potassium hydrogen carbonate solution used to provide CO2

  Source of light close to apparatus or dark room. Apparatus kept in dark room for 2 hours before. Light source switched on plant left for 30 mins, O2 released by plant and collects in funnel end or capillary tube. After 30 mins O2 drawn up capillary tube by gently withdrawing syringe until volume can be measured. Gas drawn up and depressed again.
• How can you ensure the results are reliable?

  Repeat at same light intensity 5 times, mean volume of O2 per hour is calculated. Apparatus left in dark for 2 hours before procedure is repeated with different light intensity
• How do farmers enable maximum yield?

  CO2 added to air by burning small amounts of propane in CO2 generator.

  Light can get though glass in a greenhouse, lamps provide light at night.

  Greenhouses trap heat energy from sunlight increasing temp, heaters and cooler can be used to maintain optimum temp, air circulation systems ensure temp is constant throughout.