12. Energy and Respiration Flashcards
Outline the need for energy in living organisms [5]
- active transport
- movement within a cell
- synthesising large molecules from smaller ones through anabolic reactions (which are energy-consuming)
- muscle contraction
- production of heat (in maintaining a constant body temperature, for mammals and birds)
Describe the features of ATP that makes it suitable as the universal energy currency [7]
- loss of phosphate / hydrolysis leads to energy release
- small packets of energy
- small / water-soluble, so can move around cell
- immediate energy donor
- link between energy-yielding and energy-requiring reactions
- high turnover
- stable molecule in the range of pH (doesn’t break down unless ATPase is present)
State the 2 ways that ATP is synthesised [2+3]
- transfer of phosphate in substrate-linked reactions
- physical addition of a phosphate group to ADP from a phosphorylated compound (a substrate) by an enzyme - chemiosmosis in membranes of mitochondria and chloroplasts
- an H+ ion (proton) gradient is generated in the electron transport chain (ETC)
- H+ ions pass through ATP synthase by facilitated diffusion, providing energy to phosphorylate ADP into ATP in aerobic organisms
Explain the relative energy values of carbohydrates, lipids and proteins as respiratory substances [3+2]
- Carbohydrates release 15.8kJ per gram
- Lipids release 39.4kJ per gram
- Proteins release 17.0kJ per gram
- Brain cells only use glucose
- Heart muscle cells preferentially use fatty acids
State what the respiratory quotient (RQ) is [3]
- The respiratory quotient is the ratio of the number of molecules of carbon dioxide produced to the number of molecules of oxygen taken in, as a result of respiration
- Respiratory Quotient = (Volume of Carbon Dioxide given out in unit time) / (Volume of Oxygen taken in in unit time)
- RQ is expressed as a single number, rather than as a ratio
Calculate RQ values of different respiratory substrates from equations for respiration [4]
- Use the formula Vol. CO2 / Vol. O2 to calculate RQ
- Respiratory Substrate: Respiratory Quotient
Carbohydrate: 1.0
Lipid: 0.7
Protein: 0.9
Describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae) [5]
- use a manometer (U-shaped tube) connected between 2 boiling tubes with KOH(aq) or soda lime to absorb CO2, with respiring organisms in one and glass beads or dead/boiled organisms in the other (this will act as a control) - make sure they are not in the KOH solution
- close the system and allow a set period of time to elapse, before measuring the shift in the liquid in the manometer
- the distance shifted x π x r² will give the volume of O2 used by the respiring organisms
- repeat the experiment, but with water instead of KOH solution, after allowing some time for equilibriation, in order to find the volume of CO2 produced (subtract shift due to oxygen to find shift due to carbon dioxide)
- calculate RQ value using formula
State where each of the four stages in aerobic respiration occurs in eukaryotic cells [4]
- glycolysis occurs in the cytoplasm
- link reaction occurs in the mitochondrial matrix
- Kreb’s cycle occurs in the mitochondrial matrix
- oxidative phosphorylation occurs on the inner membrane of mitochondria
Outline the process of glycolysis [6]
- glucose undergoes a first phosphorylation reaction (requiring 1 ATP) to produce glucose-6-phosphate
- glucose-6-phosphate undergoes an isomerisation reaction to produce fructose-6-phosphate
- fructose-6-phosphate undergoes a second phosphorylation reaction (requiring 1 ATP) to produce fructose-1,6-bisphosphate
- fructose-1,6-bisphosphate undergoes lysis to produce two triose phosphates
- each triose phosphate undergoes oxidation to produce a pyruvate (2 ATP and 1 NADH are formed in the process)
- After the glycolysis of one glucose molecule, there are: 2 ATP, 2 NADH and 2 pyruvates
When ______ is available, ________ enters ____________ to take part in the ____ reaction.
oxygen, pyruvate, mitochondria, link
Describe the link reaction [5]
- the pyruvate undergoes a decarboxylation reaction (a single carbon is lost as carbon dioxide)
- the pyruvate undergoes a dehydrogenation reaction (two hydrogens are lost, reducing NAD)
- the pyruvate combines with Coenzyme A to produce Acetyl CoA
- these three steps all happen simultaneously
- once the 2-carbon fragment enters the Krebs cycle, Coenzyme A is recycled back into the link reaction
Outline the Krebs cycle [5]
- oxaloacetate (4C) acts as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate (6C)
- citrate (6C) undergoes decarboxylation (CO2 released) and oxidation (NADH formed) to produce a 5C compound
- the 5C compound undergoes decarboxylation (CO2 released) and oxidation (NADH formed) to produce a 4C compound, in the process energy is released and used to synthesise ATP
- the 4C compound undergoes oxidation (FADH formed) to produce another 4C compound
- this 4C compound undergoes oxidation (NADH formed) to produce oxaloacetate (4C) once again
- Decarboxylation
- Dehydrogenation
- the removal of carbon from a molecule, lost as CO2
- the removal of hydrogen from a molecule, which is then oxidised in the process
Describe the role of NAD and FAD [5]
- coenzymes NAD and FAD are reduced by accepting the removed hydrogens in dehydrogenation steps
- reduced NAD/FAD is split by a dehydrogenase enzyme into NAD/FAD and H+ and e-
- the electrons are then carried along an electron trasnport chain (ETC) in the inner mitochondrial membrane
- the protons are pumped into the intermembrane space (between the two mitochondrial membranes)
- NAD is reduced in glycolysis, the link reaction and the Krebs cycle, but is oxidised at the ETC; FAF is reduced in the Krebs cycle and oxidised at the ETC
Explain what happens during oxidative phosphorylation [5]
- a dehydrogenase enzymes splits hydrogen atoms from NADH and FADH from the Krebs cycle into protons and energetic electrons
- negatively charged, energetic electrons release energy as they pass through the electron transport chain
- the released energy is used by pump proteins to actively transport protons across the inner mitochondrial membrane against their concentration gradient
- protons return to the mitochondrial matrix by facilitated diffusion down their concentration gradient through the channel protein specific to H+, ATP synthase, providing energy for ATP synthesis
- oxygen acts as the final electron acceptor to form water, so oxidative phosphorylation only occurs if oxygen is present
Describe the relationship between the structure and function of mitochondria [5]
- external doubble membrane - permeable to pyruvate, CO2, O2, NAD and NADH
- matrix - site of the enzymes of the link reaction and the Krebs cycle
- inner membrane - large surface area due to cristae, for increased number of electron transport chain and ATP synthase systems for ATP synthesis
- inner membrane - impermeable to hydrogen ions (protons), allowing the formation of a potential difference between the intermembrane space and the matrix
- inter-membrane space - relatively tiny space, allowing the accumulation of hydrogen ions (protons) there to generate a large potential difference with the matrix, making phosphorylation possible
Outline respiration in anaerobic conditions in mammals [6]
- called lactate fermentation
- single step
- reversible
- pyruvate is reduced by NADH from glycolysis
- lactate is produced
- lactate dehydrogenase catalyses the reaction
Outline respiration in anaerobic conditions in yeast cells [7]
- called ethanol fermentation
- two steps
- irreversible
- decarboxylation occurs
- ethanal is reduced by NADH from glycolysis
- ethanol is produced
- ethanol dehydrogenase catalyses the reaction
Explain why the energy yield from respiration in aerobic conditions is much greater than the energy yield from respiration in anaerobic conditions [4]
anaerobic conditions:
- only glycolysis occurs
- 2 ATP produced per glucose molecule
aerobic conditions:
- glycolysis and oxidative phosphorylation occur
- 38 ATP produced per glucose molecule
Explain how rice is adapted to grow with its roots submerged in water [3]
- aerenchyma tissue in the stems and roots contain large air spaces
- ethanol fermentation occurs in roots, whose cells are tolerant of high concentrations of ethanol
- stems grow faster and are elongated to keep the plants’ leaves above the water level (important for gas exchange)
Describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast [4]
- place a suspension of yeast in glucose solution into two boiling tubes
- add indicator (which accepts hydrogens like NAD to one tube)
- note the time taken for the indicator to change colour from blue (oxidised) to colourless (reduced)
- use the other tube as a reference colour as the yeast suspension isn’t colourless
Describe and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration
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