Plants

• Cellular respiration


  The mechanism of breakdown of food materials within the cell to release energy and trapping of energy for the synthesis of ATP
• Respiration

  The process by which breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy
• Respiratory substrates

  The compounds that are oxidised during the process of respiration
• Usually carbohydrates are oxidised to release energy, but proteins, fats and even organic acids can be used as respiratory substrates in some plants under certain conditions
• For the process of respiration, plants take O2 and release CO2. The plants have stomata and lenticels for gaseous exchange instead of specialised organs
• Glycolysis


  1. A stepwise process by which one molecule of glucose (6C) breaks down into two molecules of pyruvic acid (3C) without the help of oxygen

  2. Occurs in the cytoplasm of the cell

  3. A chain of 10 reactions occurs under the control of different enzymes

  4. A net gain of 8 ATP molecules occurs during glycolysis
• Anaerobic respiration


  The process which involves the incomplete breakdown of organic substrate without using oxygen as oxidant. Its common products are CO2, ethyl alcohol and lactic acid
• In yeast, incomplete oxidation of glucose is achieved under anaerobic conditions. In this, pyruvic acid is converted to CO2 and ethanol
• Types of fermentation

  • Alcoholic fermentation (occurs in many fungi like yeast, Rhizopus)
  • Lactic acid fermentation (occurs in muscle cells or certain bacteria when oxygen is inadequate for cellular respiration)
• Aerobic respiration


  1. The final product of glycolysis, i.e. pyruvate, is transported from the cytoplasm into the mitochondria

  2. Pyruvate Oxidation occurs in the mitochondrial matrix when pyruvate of cytoplasm from glycolysis enters with the help of a specific transport protein

  3. Involves the conversion of glycolysis product, pyruvate into acetyl Co-A that enters the next step i.e. Krebs cycle

  4. Krebs Cycle (Tricarboxylic Acid Cycle) occurs in the mitochondrial matrix, it is a cyclic process that involves the conversion of acetyl Co-A to oxaloacetate
• The summary equation for this phase of respiration may be written as follows: Pyruvic acid +4NAD+FAD+2H2O -> 3CO2+4NADH+4H+FADH2 + ATP
• Electron Transport Chain (ETC) or mitochondrial respiration or Electron Transport System (ETS)


  A series of coenzymes and cytochromes that take part in the passage of electrons through a series of activated chemical compounds to its ultimate acceptor, i.e. oxygen
• Oxidative Phosphorylation

  The synthesis of energy rich ATP molecules with the help of energy liberated during oxidation or reduction of coenzymes (NADH, FADH) produced in respiration
• The enzyme required for this is ATP synthase which is the complex-V of ETS. ATP synthase is located in F1 or head piece - elementary particles. This particle is present in inner mitochondrial membrane
• Chemiosmotic ATP synthesis

  The method of ATP formation where the energy liberated during oxidation or reduction of coenzymes (NADH, FADH) produced in respiration is used to synthesize ATP
• Complete oxidation of a glucose molecule to CO2 and H2O takes just in a second and produces 38 ATP molecules
• Amphibolic pathway

  The respiratory pathway involves both anabolism and catabolism, therefore it is known as amphibolic pathway
• Respiratory Quotient (RQ) or respiratory ratio


  The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration
• For carbohydrates, fats and proteins, the RQ will be 1, less than 1 and 0.9 (approximately), respectively
• Citric acid cycle is the major pathway for the formation of ATP molecules
• Photosynthesis is the process by which green plants convert solar energy into chemical energy to form carbohydrates
• Photosynthesis purifies atmospheric air by consuming carbon dioxide and liberating oxygen
• Chloroplasts

  • Double membrane bound organelle
  • Contains stroma and thylakoid lamellae
  • Thylakoids contain photosynthetic pigments
• Photosynthetic pigments

  • Chlorophyll
  • Carotenoids
  • Phycobilins
• Chlorophyll

  Major photosynthetic pigment
• Carotenoids and phycobilins

  Accessory photosynthetic pigments
• Photochemical phase

  1. Utilises light energy

  2. Occurs in thylakoids of chloroplasts

  3. Called light reaction
• Biosynthetic phase

  1. Uses assimilatory power of light reaction

  2. Occurs in stroma of chloroplast

  3. Called dark reaction
• Light reaction

  • Involves participation of pigment molecules in two separate photosystems (PS-I and PS-II)
  • Photosystems contain reaction centre, core complex and light harvesting antenna complex
  • Reaction centre of PS-I is P700 (chlorophyll a)
  • Reaction centre of PS-II is P680 (chlorophyll a)
  • Generates strong reductant NADPH and strong oxidant that forms oxygen from water
• Photolysis of water

  1. Releases electrons used for production of ATP through photophosphorylation

  2. May be non-cyclic or cyclic
• Non-cyclic photophosphorylation

  • Electrons from PS-II transferred to PS-I, reducing NADP
  • Responsible for reduction of NADP, production of ATP and evolution of oxygen
• Cyclic photophosphorylation

  • Electrons from PS-I returned to PS-I without reducing NADP
  • Serves to generate extra ATP only
• Assimilatory power

  • ATP and NADPH produced in light reaction
  • Used to fix CO2 into carbohydrates in dark reaction
• Calvin cycle (C3 cycle)

  1. CO2 combines with RuBP and produces glucose via many intermediate steps

  2. Consists of Carboxylation, Reversal of glycolysis and Regeneration of RuBP
• C4 plants

  • Fix atmospheric CO2 into phosphoenolpyruvic acid to produce oxaloacetic acid
  • CO2 fixation occurs in mesophyll cells, Calvin cycle in bundle sheath cells
  • Avoids disadvantage of photorespiration
• Photorespiration

  Harmful process where up to half the photosynthetically fixed CO2 is lost to the atmosphere
• Factors affecting photosynthesis

  • External: Light quality and quantity, CO2, water, temperature
  • Internal: Age of leaf, chlorophyll content, leaf histology