Photosynthesis and Cellular Respiration

• ATP stands for adenosine triphosphate and is a molecule that all cells use to supply energy to cellular processes.
• ATP is like a charged battery because it stores chemical energy in the bonds between the second and third phosphate groups, therefore can power something in the cell.
• The ATP-ADP cycle is when ATP releases energy for cellular processes when the third phosphate is removed. This creates ADP and a free phosphate. ADP can be converted back into ATP with an input of energy and rejoining of a phosphate group.
• The equation for photosynthesis is 6CO2 + 12H2O = C6H12O6 + 6O2 + 6H2O.
• Photosynthesis is important because it:

  • releases free oxygen gas
  • absorbs carbon dioxide
  • transforms sunlight energy into chemical energy
• Plant cells and some algae contain chloroplasts. They allow plants to harvest energy from sunlight to carry out photosynthesis.
• Pigments like chlorophyll absorb sunlight and use this energy to combine carbon dioxide and water to make glucose and oxygen.
• Chloroplast:

  A) inner membrane

  B) outer membrane

  C) lumen

  D) stroma lamellae

  E) thylakoid

  F) intermembrane space

  G) stroma

  H) granum

  
• The light-dependent phase:

  1. chlorophyll absorbs sunlight
  2. light splits H2O into O2 gas and H+ ions
  3. O2 is released from chloroplast to diffuse out of stomata or be used in cellular respiration
  4. ATP and NADPH (electron donor) is produced using H+
  5. ATP and NADPH coenzymes move to the light independent stage in the stroma
• The light-independent phase:

  1. ATP + NADPH fixes CO2 into triose phosphate that is exported from the chloroplast
  2. low energy molecules ADP + NADP+
• Mitochondria:

  A) matrix

  B) DNA

  C) inner membrane

  D) outer membrane

  E) ribosome

  F) cristae

  
• Mitochondria are the powerhouses of the cell because they burn or break the chemical bonds of glucose to release energy.
• The equation for cellular respiration is C6H12O6 + 6O2 = 6CO2 + 6H2O.
• Cellular respiration:

  A) glycolysis

  B) glucose

  C) pyruvate

  D) acetyl CoA

  E) kreb cycle

  F) cytoplasm

  G) ATP

  H) 2 ATP

  I) mitochondria

  J) electron transfer

  K) NADH

  L) FADH2 + NADH

  M) 26 or 28 ATP

  
• A) H2O

  B) granum

  C) outer membrane

  D) inner membrane

  E) O2

  F) thylakoid

  G) CO2

  H) stroma

  I) NADPH

  J) NADP+

  K) ADP+P

  
• Photosynthesis

  • The process using energy from the sun to convert water and carbon dioxide into glucose and oxygen.
  • Organisms that can photosynthesize are called autotrophs and include plants, algae, and photosynthetic bacteria
  • To photosynthesize the cell must contain chlorophyll to capture light energy.
  • The organelles within these organisms that contain this pigment are called chloroplasts and are present in both plants and algae.
• Light INDEPENDENT Stage:

  
  

  INPUTS:

  • 6 CO2
  • 12 NADPH
  • 12 ATP

  OUTPUTS:

  • glucose (C6H12O6)
  • 6 H2O
  • 12 NADP+
  • 12 ADP+Pi
• Light DEPENDENT Stage:

  INPUTS:

  • 12 H2O
  • 12 NADP+
  • 12 ADP + Pi

  OUTPUTS:

  • 6 O2
  • 12 NADPH
  • 12 ATP
• Carbon fixation:

  When inorganic carbon dioxide is turned into organic molecules (carbohydrates) which are of more use to cells.
• RuBisCO

  The enzyme Rubisco catalyses the first step of the light independent reaction.

  Rubisco binds carbon dioxide and attaches it to another molecule (a sugar - ribulose diphosphate). 

  Once this is done the other steps of the light independent reaction follow.
• The 3 stages of RuBisCO's role in photosynthesis:

  1. Carbon fixation

  inorganic C from CO2 is incorporated into an organic molecule (3-PGA). A molecule called RuBP is used as well as the CO2 to produce 3-PGA

  1. Reduction

  NADPH donates electrons (reduces) an intermediate 3-C molecule to produce G3P (a different 3C molecule)

  1. Regeneration

  the RUBP molecules needed to begin the cycle are reproduced
• RuBisCO can also use oxygen (O2) as an alternative substrate to undergo a series of reactions known as photorespiration.

  Photorespiration creates a product that cannot be used to make sugars and hence reduces the efficiency of the Calvin Cycle.

  Photorespiration reduces levels of photosynthesis by up to -25% in C3 plants, reducing energy yield.
• In C4 plants, the initial stage of photosynthesis takes place in mesophyll cells where CO2 is converted into malate or aspartate. This process is similar to the Calvin cycle but uses phosphoenolpyruvate instead of RuBP. The resulting compounds then move to bundle sheath cells where they release their CO2 through decarboxylation. Here, the CO2 enters the Calvin cycle and is fixed into glucose.
• C4 plants have evolved to reduce photorespiration because they live in hot dry environments with high temperatures and low humidity. These conditions increase the rate of photorespiration so C4 plants have adapted to avoid it.
• Crassulacean acid metabolism (CAM) plants open stomata at night when water loss is minimal. During the day, stomata close to prevent further water loss. At night, CO2 diffuses into leaf cells and combines with bicarbonate ions to form carbonic acid. Carbonic acid dissociates into hydrogen ions and bicarbonate ions. Bicarbonate ions combine with PEP to form malate. Malate is stored until daytime when it breaks down to release CO2 for the Calvin cycle.
• Products of anaerobic fermentation

  A) animals

  B) yeast

  C) 2

  D) 2

  
• Anaerobic fermentation takes place in the cell cytosol in the absence of oxygen and involves glycolysis followed by extra steps to regenerate NAD+ to allow glycolysis to continue producing ATP.
• In animal cells, glucose is converted to lactic acid via lactic acid fermentation.
• In yeasts, glucose is converted to ethanol and carbon dioxide via ethanol fermentation.
• Differences between aerobic cellular respiration and anaerobic fermentation

  A) lactic acid

  B) ethanol

  C) cytosol

  D) oxygen

  E) carbon dioxide and water

  F) slow

  G) fast

  H) toxic

  
• NADH and FADH2 are electron carriers that carry electrons from one reaction to another. They donate their electrons to the electron transport chain which generates ATP through oxidative phosphorylation.
• Krebs Cycles: occurs in the mitochondrial matrix

  Inputs:

  • 2 pyruvate/acetyl CoA
  • 2 ADP +2Pi
  • 6 NAD+ + 6 H+
  • 2 FAD + 4 H+

  Outputs:

  • 4 CO2
  • 2 ATP
  • 6 NADH
  • 2 FADH2
• Electron transport chain: Occurs in the mitochondrial cristae

  Inputs:

  • 6 O2
  • 10 NADH
  • 2 FADH2
  • 26-28 ADP + Pi

  Outputs:

  • 6 H2O
  • 10 NAD+ + 10 H+
  • 2 FAD + 4 H+
  • 26 or 28 ATP
• alcohol fermentation

  A) atp

  B) pyruvate

  C) co2

  D) ethanol

  E) nadh

  
• lactic acid fermentation

  A) atp

  B) pyruvate

  C) lactate

  
• ATP synthase: an enzyme that coupes the diffusion of hydrogen ions through the thylakoid membrane with the synthesis of ATP. 

  • This enzyme takes up the substrates ADP and phosphate to make ATP.
  • Occurs in the light-dependent reaction
• Carbon Fixation: RuBisCO catalyzes the first step of the Calvin cycle, called carbon fixation. In this step, RuBisCO combines a molecule of CO2 with a five-carbon sugar molecule called ribulose-1,5-bisphosphate (RuBP) to form an unstable six-carbon molecule. This molecule then splits into two molecules of 3-phosphoglycerate (3-PGA), which are used to synthesize glucose and other organic compounds.
• RuBisCO is not a perfect enzyme. It can also catalyze a competing reaction called photorespiration, where it binds with oxygen instead of CO2. This process can be wasteful, as it consumes energy and reduces the efficiency of photosynthesis. However, plants have evolved various adaptations to mitigate this inefficiency, such as the C4 and CAM pathways, which optimize carbon fixation in environments with high temperatures and low CO2 levels.
• As light intensity increases, so does the rate of photosynthesis.

  At very low light intensities, the rate of photosynthesis is lower than the rate of cellular respiration, and the plant may be using more oxygen than it is producing.
• Plants absorb short (blue) and long (red) wavelength ends.

  Chlorophyll A converts the light energy to chemical energy. Chlorophyll B and carotenoids are accessory pigments, absorbing light and passing the energy to Chlorophyll A.