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12.112 · Energy and Respiration

Energy — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

15 min read 25 parts Lesson 1 of 18 4 quizzes

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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12.1 Energy — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain why organisms need energy, how ATP is made and used, and how respiratory substrates, RQ and respiration stages are linked.Anabolic reactions — for example protein synthesis and DNA synthesis from nu…

  • Active transport
  • Body temperature
  • Autotrophs
  • Heterotrophs
  • Source of energy
  • Hydrolysis

Part 1 of 9The need for energy

Anabolic reactions
  • Anabolic reactions for example protein synthesis and DNA synthesis from nucleotides.
Active transport
  • Active transport such as the sodium-potassium pump, and exocytosis.
Movement
  • Movement muscle contraction and movement of chromosomes on the spindle.
Body temperature
  • Body temperature maintaining it, in mammals and birds only.
Autotrophs
  • Autotrophs plants and algae make organic compounds from CO2 using light energy in photosynthesis.
Heterotrophs
  • Heterotrophs they obtain ready-made organic molecules from food.
Source of energy
  • Source of energy almost all energy in organisms comes originally from the Sun and is released by respiration in every cell.

Part 2 of 9ATP as the energy currency

ATP as the energy currency
Hydrolysis
  • ATP → ADP + Pi releases about 30.5 kJ per mol.
Regeneration
  • ATP is regenerated from ADP + Pi by ATP synthase.
Good currency
  • Good currency it is small, soluble, easily hydrolysed in one step, releases energy in small amounts and cannot leave cells.
Continuous synthesis
  • Continuous synthesis cells hold only a tiny amount of ATP and it does not cross the surface membrane, so it is resynthesised constantly.
  • The synthesis is a condensation reaction (water released) needing energy from respiration or photosynthesis.
Phosphorylated intermediates
  • ATP can transfer a phosphate group, for example to glucose in glycolysis.
  • The phosphorylated molecule is more reactive, lowering the activation energy for the next step.

Part 3 of 9Two ways of making ATP

1Substrate-linked phosphorylation
  • Substrate-linked phosphorylation a phosphate is transferred directly from a substrate to ADP.
  • It occurs in the cytoplasm and mitochondrial matrix.
  • It yields few ATP per glucose.
2Chemiosmosis
  • Chemiosmosis a proton gradient across a membrane drives ATP synthase.
  • It occurs in the inner mitochondrial membrane and thylakoid membranes.
  • It yields most of the ATP.

Part 4 of 9Glycolysis and the mitochondrion

1Glycolysis
  • Glycolysis glucose is phosphorylated using 2 ATP and split into hexose bisphosphate and then two triose phosphates.
  • They are oxidised to 2 pyruvate, making 4 ATP (net 2) and 2 reduced NAD.
2Pyruvate
  • Pyruvate it is actively transported into the mitochondrial matrix.
3Link reaction
  • Link reaction pyruvate is decarboxylated and dehydrogenated and combined with coenzyme A to form acetyl CoA.
4Krebs cycle
  • Krebs cycle acetyl (2C) joins oxaloacetate (4C) to make citrate (6C).
  • Decarboxylation and dehydrogenation regenerate oxaloacetate.
  • Each turn releases 2 CO2, 3 reduced NAD, 1 reduced FAD and 1 ATP.
5Mitochondrion adaptations
  • Mitochondrion adaptations folded cristae give a large surface area for the electron transport chain and ATP synthase.
  • The matrix contains Krebs enzymes.
  • The impermeable inner membrane maintains the gradient.

Part 5 of 9Oxidative phosphorylation

Reduced NAD and FAD release H at the inner membrane.
H splits into H+ and electrons.
Electrons pass along carriers in the electron transport chain, releasing energy.
The energy pumps H+ from the matrix into the intermembrane space, forming a gradient.
H+ diffuse back through ATP synthase (chemiosmosis), making ATP from ADP + Pi.
Oxygen accepts electrons and H+, forming water.
Role of oxygen
  • Role of oxygen without O2 the chain stops.

Part 6 of 9Respiratory substrates and RQ

Respiratory substrates and RQ
Energy values
  • Energy values lipids have a higher energy value than carbohydrates because they contain more H atoms per unit mass.
Protein
  • Protein it is used mainly when other stores are low.
Respiratory quotient (RQ)
Respiratory quotient (RQ) volume CO2 produced ÷ volume O2 consumed (no units).
  • Typical valuescarbohydrate 1.0, lipid 0.7, protein 0.9.
Interpreting RQ.
  • About 0.85 suggests a mixture of carbohydrate and lipid.
  • Above 1 suggests carbohydrate is being converted to fat (overfeeding).
  • Below 0.7 suggests underfeeding, with unusual substrates in use.
Anaerobic RQ
  • Anaerobic RQ in mammalian muscle no O2 is used and no CO2 made, so RQ cannot be calculated.
    • (glucose → lactate)
  • In yeast, CO2 is released with no O2 uptake, so RQ tends to infinity.

Part 7 of 9Respirometer measurements

1
Set up a respirometer with the organisms and soda lime or KOH in one tube, and a control tube with glass beads of equal volume.
2
Equilibrate in a water bath at constant temperature for 10 minutes with taps open.
3
Close the taps, start timing and measure movement of the coloured liquid in the capillary over a set time.
4Calculate O2 uptake
πr2 × distance moved (mm3).
5
Repeat with water instead of soda lime to find CO2 produced − O2 used.
6
Reading x is gas volume change with soda lime (O2 used); reading y is change without it (O2 used − CO2 made).
7CO2 produced
CO2 produced x − y, so RQ = (x − y) ÷ x. If the fluid does not move without soda lime, RQ = 1.
8
Repeat and average.
9Rate of respiration
Rate of respiration volume O2 used ÷ (time × mass), for example mm3 min-1 g-1.
10Redox indicators
  • Redox indicators methylene blue, DCPIP and TTC can measure respiration rate in yeast.

Part 8 of 9Anaerobic respiration and rice

Mammals
  • Mammals pyruvate is reduced to lactate by lactate dehydrogenase.
Yeast and plants
  • Yeast and plants pyruvate is decarboxylated to ethanal, then reduced to ethanol.
Purpose
  • Purpose both regenerate NAD so glycolysis continues.
Yield
  • Yield only 2 ATP per glucose, because most energy remains in lactate or ethanol.
Lactate
  • Lactate it is taken to the liver and converted back to pyruvate or glucose (oxygen debt).
Rice
  • Rice it survives flooding.
  • Aerenchyma (air spaces) supply O2 to roots.
  • High alcohol dehydrogenase gives ethanol tolerance.
  • Fast stem growth lifts leaves above water.

Part 9 of 9More from the specification

More from the specification
Respiratory oxidation of dietary amino acids
  • Respiratory oxidation of dietary amino acids deaminating surplus amino acids yields keto acids metabolized through Krebs cycles, providing a means of ATP generation.
Respiratory Quotient Formula
  • The respiratory quotient is calculated using the equation RQ = / (volume of oxygen consumed), identifying the respiratory substrate metabolized by living tissue.
    • (volume of carbon dioxide produced)
Respirometer and Manometer Setup
  • In a respirometer, an experimental chamber connects to a fluid manometer;
  • as organisms consume oxygen and released carbon dioxide is absorbed by potassium hydroxide, the manometer fluid moves.
Proton Concentration Gradient Across Membranes
  • During aerobic respiration, electron transport chains pump hydrogen ions across the inner mitochondrial membrane, establishing a steep electrochemical concentration gradient.
ATP Synthesis via Chemiosmosis
  • Protons diffuse down their concentration gradient back into the mitochondrial matrix through ATP synthase, driving phosphorylation of ADP into ATP.
Carbon
  • Element with four valence electrons that forms the backbone of organic molecules.
Manometer
  • U-tube whose fluid moves as gas volume changes.
Concentration gradient
  • The difference in concentration of a substance between two regions.
Amino acid
  • The unit from which proteins are made; the sequence decides the protein's shape and function.

Key terms

TermMeaning
ATPAdenosine triphosphate, the universal energy currency.
ChemiosmosisATP synthesis driven by a proton gradient across a membrane.
Substrate-linked phosphorylationDirect transfer of a phosphate from a substrate to ADP.
Respiratory quotientCO_{2} produced divided by O_{2} consumed.
GlycolysisSplitting of glucose to pyruvate in the cytoplasm.
AerenchymaAir spaces in plant tissue that carry oxygen to roots.

Avoid these mistakes

1
Saying respiration produces energy — it produces ATP, which stores and carries energy.
2
Saying oxygen is used in glycolysis — its role is as the final electron acceptor.
3
Saying anaerobic respiration makes as much ATP as aerobic — it makes only 2 ATP per glucose.
4
Saying a cell stores large amounts of ATP — it makes it as needed.

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