BIO U2 SUMMARY

• ATP

  Intracellular energy currency in all organisms
• ATP

  • Contains a nitrogenous base (adenine), a ribose sugar and three inorganic phosphate groups
  • When the bonds between these groups are broken, energy is released
• ADP


  • Only has two inorganic phosphate groups
  • If another phosphate group is added, it will become ATP
• Phosphorylation


  Adding a phosphate group
• Photosynthesis


  1. Producers take in inorganic molecules and produce organic substances, such as glucose

  2. Occurs in chloroplasts, which contain the pigment, chlorophyll

  3. Has a light-dependent and light-independent stage

  4. Carbon dioxide and water are the main reactants

  5. Glucose is the main product

  6. Oxygen is a by-product
• Photosynthesis


  • Within the chloroplast, the light-dependent reaction occurs in the thylakoid membranes
  • The light-independent (Calvin Cycle) occurs in the stroma
• Light-dependent stage of photosynthesis


  1. Light energy is used to break the bonds of water molecules (photolysis)

  2. Oxygen diffuses out of stomata

  3. Hydrogen molecules combine with carbon dioxide molecules, which eventually form glucose
• Dicot leaf


  • Upper epidermis - Transparent layer of cells, coated with watertight, waxy cuticle
  • Lower epidermis - Thin layer of cells, including guard cells with stomata. Allows diffusion and transpiration
  • Spongy mesophyll - Loosely, irregularly packed layer of cells with air spaces. Facilitates gaseous exchange between palisade mesophyll and stomata
• Palisade mesophyll cells


  • Contain a large number of chloroplasts for light absorption
  • Contain a very large vacuole to keep chloroplasts on outer edges on cells to maximize light exposure
  • Are adjacent to vascular bundles, which supply water via the xylem
  • Have very thin cell walls for rapid diffusion of gases
• Photophosphorylation


  A process that uses light to attach a phosphate group to an organic compound
• Photophosphorylation


  1. Light is absorbed by photosystems

  2. This stimulates electrons

  3. Electrons 'bounce' from carrier to carrier

  4. This drives H+ ions to power an enzyme, ATP synthase, to attach a phosphate to ADP to turn it into ATP

  5. Occurs in the thylakoid membranes
• NAD and NADP


  • Reducing agents
  • NAD for respiration, NADP for photosynthesis
• NADH and NADPH


  • The reduced forms of NAD and NADP
  • They 'release' the H+ ion and 2 electrons and become NAD and NADP
• Cyclic photophosphorylation


  1. Light stimulates electrons in PSI

  2. Involves a 'cyclic' movement of electrons to and from PSI

  3. Excited electrons drive the formation of ATP
• Non-cyclic photophosphorylation


  1. Excited electron moves from PSII to PSI

  2. Light also splits water molecules (photolysis) into H+ ions, electrons and oxygen

  3. Electrons are accepted by NADP to turn it into NADPH

  4. H+ ions then flow through ATP synthase, an enzyme that turns ADP to ATP
• Calvin cycle


  1. Catalysed by the enzyme Rubisco, which combines carbon dioxide (1C) with RuBP (5C)

  2. This forms a 6C sugar, which breaks down into two 3C compounds, PGA

  3. PGA is converted into G3P (triose phosphate)

  4. G3P is used to make glucose, but excess G3P is recycled to regenerate RuBP
• Limiting factor


  A factor that, when increased or decreased, influences the rate of a reaction
• Limiting factors for photosynthesis

  • Energy from sunlight
  • Carbon dioxide and water
  • Reasonable temperature (25 – 35°C)
  • Chlorophyll
• CO2 concentration


  • If limited, the Calvin Cycle process is slowed down and photosynthesis decreases
  • At high levels, it reaches a saturation point where all of the Rubisco enzymes are working at optimum efficiency
• Temperature


  Too much heat can denature the enzyme Rubisco, causing the photosynthesis rate to drop to zero
• Applications of photosynthesis knowledge

  • Greenhouses - Artificial light levels can be adjusted to maximize photosynthesis
  • Growth chambers - Temperature and CO2 levels can be regulated for sensitive crops such as groundnuts
• Glycolysis


  • Translates to 'breaking apart of glucose'
  • Energy is released as a result
• Glycolysis


  1. STEP 1: Glucose has two phosphate groups added to it, becoming glucose-6-phosphate, then fructose-6-phosphate, then fructose biphosphate

  2. STEP 2: Fructose biphosphate splits into two 3C sugar molecules, G3P

  3. STEP 3: G3P is converted to pyruvate, with 2 ATP and 2 NADH produced
• Glycolysis


  • 2 ATP are needed to start the process
  • 4 ATP are made in total, but 2 net ATP are gained (substrate-level phosphorylation)
  • 2 NADH are also gained
• Mitochondrion


  • Pyruvate from glycolysis enters the mitochondria
  • ATP is made in the mitochondrial matrix due to the energy from the flow of H+ ions
  • The inner membrane contains the ATP synthase enzyme and an electron transport chain
  • Cristae are inward folds of this membrane, the more present the more active the mitochondrion
• Aerobic respiration


  1. Glycolysis - turns 6C glucose into 3C pyruvate

  2. Link reaction - turns 3C pyruvate into 2C acetyl CoA, carbon dioxide exits

  3. Krebs cycle - combines 2C acetyl CoA with 4C oxaloacetate to become 6C citrate, builds up NADH and FADH2

  4. Oxidative phosphorylation - NADH becomes NAD, releasing energy to drive ATP production along electron transport chain
• Link reaction


  1. Pyruvate (3C) loses a carbon due to the removal of CO2, becoming a 2C compound

  2. NAD accepts hydrogen to become NADH

  3. An enzyme, CoA, converts the 2C compound to Acetyl CoA, which powers the Krebs cycle
• Krebs cycle


  1. Citrate (6C) is gradually turning into Oxaloacetate (4C)

  2. Acetyl CoA (2C) combines with Oxaloacetate (4C) to become citrate (6C)

  3. Two CO2's leave as the cycle continues, causing the 6C to become 5C, then 4C

  4. Hydrogens are taken up by NAD to become NADH, and FAD to become FADH2

  5. One ATP is formed per cycle
• Krebs cycle


  • 32 net ATP is made from one glucose molecule
  • The cycle restarts as oxaloacetate binds with more Acetyl CoA to become citrate
• Oxidative phosphorylation


  1. STEP 1: NADH and FADH2 release hydrogens and become NAD and FAD again, electrons are shuttled along the electron transport chain

  2. STEP 2: The energy from the electrons is used to pump H+ ions across channels into the intermembrane space

  3. STEP 3: H+ ions diffuse from a higher to lower 'concentration' (chemiosmosis) back down to the mitochondrion matrix, powering ATP synthases to phosphorylate ADP to ATP
• Anaerobic respiration


  1. Pyruvate is converted into lactate, as NAD converts to NADH during glycolysis and converts back to NAD as lactate is produced

  2. This allows glycolysis to occur continuously, but only produces 2 ATP per glucose, as opposed to 32 ATP during aerobic respiration
• Anaerobic respiration (yeast)


  1. Pyruvate releases carbon dioxide to form ethanal before forming ethanol

  2. Ethanol is a major constituent of commercial alcohol, such as beer

  3. The carbon dioxide is used in breadmaking
• Comparison of aerobic and anaerobic respiration

  • Aerobic - Uses oxygen, 32-36 ATP produced
  • Anaerobic - Does not use oxygen, 2 ATP produced
• Energy transfer in food chains

  1. Food chain depicts feeding relationships in an ecosystem

  2. Grass is the producer, transforming electromagnetic energy from the Sun into chemical energy

  3. This chemical energy is transferred from consumer to consumer as feeding occurs

  4. An average of 10% of energy is transferred from one trophic level to another, as 90% is lost to the atmosphere as heat
• Organisms higher up in the food chain receive very little energy from feeding on trophic levels directly below them, so they may have to feed on multiple lower trophic levels to have enough energy to sustain their biomass
• • Only 10% of energy is stored in cells, available for transfer if the organism is eaten
  • Not all parts of the organism may be consumed during feeding
  • Not all molecules consumed would be digested and assimilated, e.g. humans eating cellulose
• Producer


  Autotroph that can transform electromagnetic energy from the Sun into stored chemical energy (such as sugars)
• Energy transfer


  Transferred from consumer to consumer as feeding occurs
• Energy flow


  Transfer of energy that cannot be returned to its source (the Sun)
• An average of 10% of energy is transferred from one successive trophic level to another