Energy Transfers In And Between Organisms Flashcards
Why is respiration important?
• Respiration produces ATP (to release energy)
• For active transport, protein synthesis etc.
Stages of aerobic respiration
1) glycolysis
2) link reaction
3) kreb cycle
4) oxidative phosphorylation
Glycolysis
- Substrate level phosphorylation
1.Glucose phosphorylated to glucose phosphate
• Using inorganic phosphates from 2 ATP
2. Hydrolysed to 2 x triose phosphate
3. Oxidised to 2 pyruvate
• 2 NAD reduced
• 4 ATP regenerated (net gain of 2)
Glycolysis in anaerobic respiration
- Pyruvate converted to lactate (animals &
some bacteria) or ethanol (plants & yeast) - Oxidising reduced NAD → NAD regenerated
- So glycolysis can continue (which needs
NAD) allowing continued production of ATP - 2 ATP produced
Suggest why anaerobic respiration produces less ATP per molecule of glucose than aerobic respiration
• Only glycolysis involved which produces little ATP (2 molecules)
• No oxidative phosphorylation which forms majority of ATP (around 34 molecules)
Link reaction
- mitochondrial matrix
- Reduced NAD and Pyruvate are actively transported into the matrix
- Pyruvate oxidised (and decarboxylated) to acetate
• Co, produced
• Reduced NAD produced (picks up H) - Acetate combines with coenzyme A, forming Acetyl Coenzyme A
- 2x Acetyl Coenzyme A, 2x CO2 and 2x reduced NAD
Kreb cycle
- mitochondrial matrix
- Acetyl coenzyme A (2C) reacts with a
4C molecule
• Releasing coenzyme A
• Producing a 6C molecule that enters the Krebs cycle - In a series of oxidation-reduction reactions, the 4C molecule is regenerated and:
• 2 x Co,lost
• Coenzymes NAD & FAD reduced
• Substrate level phosphorylation
(direct transfer of Pi from
intermediate compound to ADP)
→ ATP produced - 6 x reduced NAD, 2 x reduced FAD, 2 X ATP and 4 x COz
Oxidative phosphorylation
- Reduced NAD/FAD oxidised to release H atoms → split into protons (H*) and electrons (e)
- Electrons transferred down electron transfer chain (chain of carriers at decreasing energy levels)
• By redox reactions - Energy released by electrons used in the production of ATP from ADP + Pi (chemiosmotic theory):
• Energy used by electron carriers to actively pump protons from matrix → intermembrane space
• Protons diffuse into matrix down an electrochemical gradient, via ATP synthase (embedded)
• Releasing energy to synthesise ATP from ADP + Pi - In matrix at end of ETC, oxygen is final electron acceptor (electrons can’t pass along otherwise)
• So protons, electrons and oxygen combine to form water
How would lack of oxygen affect respiration?
• electrons can’t be passed along the electron transport chain
• the Kreb cycle and the link reaction stop because NAD and FAD cannot be produced
Describe how biomass is formed in plants
• During photosynthesis, plants make organic (carbon) compounds from atmospheric or aquatic CO2
• Most sugars synthesised are used by the plant as respiratory substrates
• Rest used to make other groups of biological molecules (eg. carbs, lipids & proteins) → form biomass
How can biomass be measured?
Mass of carbon or dry mass of tissue per given area
Describe how dry mass of tissue can be measured
- Sample dried in an oven eg. at 100°C (avoid combustion)
- Sample weighed and reheated at regular intervals until mass remains constant (all water evaporated)
Explain why dry mass is more representative than fresh (wet) mass
Water volume in wet samples will vary but will not affect dry mass.
Describe how the chemical energy stored in dry biomass can be estimated
Using calorimetry:
1. Known mass of dry biomass is fully combusted (burnt)
2. Heat energy released heats a known volume of water
3. Increase in temperature of water is used to calculate
chemical energy of biomass
Explain how features of a calorimeter enable
valid measurement of heat energy released
• Stirrer → evenly distributes heat energy (in water)
• Air / insulation → reduces heat loss & gain to & from surroundings
• Water → has a high specific heat capacity
