B9 Respiration

B.9.1 Compare aerobic and anaerobic respiration of glucose in terms of oxidation/reduction and energy released.
Redox equations should be used as appropriate.

Aerobic - uses oxygen as the terminal electron acceptor
Anaerobic - uses terminal electron acceptors other than oxygen

Aerobic respiration
- glucose is converted into pyruvate, which, in presence of oxygen, changes to carbon dioxide and water. Overall, glucose undergoes oxidation and oxygen undergoes reduction.
- breaks down glucose, amino acids and fatty acids to release energy
- oxygen is the terminal electron acceptor

Glucose + Oxygen à  Carbon dioxide + Water + Energy

- high energy yielding process
- up to 38 ATP molecules produced for every glucose
- occurs in almost all living organisms
- excess carbon dioxide and water is excreted (the removal of the toxic waste products of metabolism) and maximum energy is released from the glucose

Anaerobic respiration
- happens in the absence of air
- pyruvate is converted to lactate in human beings, whereas yeast converts pyruvate into ethanol and carbon dioxide.
- not so much energy and more toxic waste produced.
- If oxygen is unavailable this process also occurs in humans.
E.g. intense exercise - lactic acid in muscle tissue is built up, resulting in muscle pain and cramping.
E.g. bacteria in milk also produces lactic acid (the optical isomer of the one produced in muscle cramping)
E.g. yeast produces alcohol (also toxic). In the end there is too much alcohol that the yeast cannot survive.
- Respiration that occurs without oxygen to produce ATP

Glucose à Energy (ATP) + Ethanol + Carbon dioxide

or

Glucose à Energy (ATP) + Lactic acid

- relatively less energy yield than aerobic
- in alcoholic fermentation 2 molecules of ATP are produced for every glucose in the reaction. The same for lactate fermentation
- Hence, in anaerobic respiration one glucose is broken down into 2 ATP.




B.9.2 Outline the role of copper ions in electron transport and iron ions in oxygen transport.
(Cytochromes and hemoglobin are suitable examples)

HEMOGLOBIN AND OXYGEN
- iron is essential in this process, because of its ability to form complexes.

Hemoglobin
- a complex protein
- has porphyrin rings at certain sites.
- A Fe2+ ion at the center of the ring attracts and transports oxygen.
- At high oxygen concentrations (like the lungs) the hemoglobin binds to the oxygen which is then carried around through the bloodstream to cells for respiration.
- At high carbon dioxide concentrations (like in cells) the hemoglobin binds to the carbon dioxide which are then transported back to the lungs where the carbon dioxide is exhaled.
- Carbon monoxide and cyanide are poisonous for hemoglobin. They attach rather permanently to the Fe2+ ion so it is unable to bind to any oxygen molecules rendering it useless.

In the mitochondria food is oxidised at the cellular level involving redox reactions and electron transport.
Cytochromes - enzymes that catalyse the oxidation processes; it incorporates porphyrin rings with either a Cu2+ or Fe2+at the center,
- contain Cu2+ or Fe3+ ions
- porphyrin ligand contains 4 nitrogen atoms, each dontaes 2 electrons
For each step of the oxidation of glucose:

Fe3+à Fe2+ + e-

or 

Cu2+à Cu+ + e-

Cytochrome structure heme group is from cytochrome oxidase.

Oxidation stage of glucose:

C6H12O6 + 6H2O à 6CO2+ 24H+ +24e-

Fe3+ + e- à  Fe2+   (Metal ion is reduced)

Reduction stage:

O2 + 4H+ +4e- à  2H2O

Fe2+ à  Fe3+ + e-   (Metal ion is oxidized)

Cu+  à Cu2+  + e-

8.1 Theories of acids and bases

8.1.1 Define acids and bases according to the BrØnsted-Lowry and Lewis theories
BrØnsted - Lowry acid              H+/proton donor
BrØnsted - Lowry base              H+/ proton acceptor
Lewis acid                                 electron pair acceptor (dative bond)
Lewis base                                 electron pair donor (dative bond)

8.1.2 Deduce whether or not a species could act as a BrØnsted-Lowry and/or a Lewis acid or base.

All BrØnsted-Lowry acids are Lewis acids, but not all Lewis acids are BrØnsted-Lowry acids.

Some species can act as acids/bases (amphoteric/ amphiprotic substances)
Amphoteric:
- B-L acid must be able to disscociate + release H+
- B-L base must be able to accept H+, therefore must have a lone electron pair
According to B-L theory they must possess both a lone e- pair and hydrogen that can be released as H+.

8.1.3 Deduce the formula of the conjugate acid (or base) of any BrØnsted-Lowry base (or acid).
Conjugate pairs - there is always a donor and acceptor
B-L theory - if an acid donates a H+ there is also a base present to accept the proton

Conjugate base pairs

Acids react to form bases (vice versa), therefore it is easy to predict the formula, the conjugate acid-base pairs differs by ONE proton.

e.g. H2O and H3O+ (found in all acid-base reactions in aqueous solutions)

B1 Energy

B.1.1 Calculate the energy value of a food from enthalpy of combustion data.
Energy
Heat produced = mCΔT
Energy comes from respiration.
Calorific value - the amount of energy available
Carbohydrates are the most readily available source of energy
Fats that are non-oxidised provide the the most energy per mass.
Food is (not burned but) converted into carbon dioxide and water through oxidation.


The bomb calorimeter
Used to measure the energy content of food.
The sample of food is heated and ignited electrically. The heat given out from the combustion is transferred to a water system and the energy is calculated by the change in temperature and mass of water.

Heat produced = heat absorbed by water + heat absorbed by calorimeter
= (m x C x ΔT)water + (m x C x ΔT)calorimeter

Stirrer: to keep the water at a uniform temperature
Bomb: sealed unit where the combustion reaction occurs
Thermometer: measures the rise in temperature of water
Water: absorbs the heat of the reaction
Electric coil: heats the device to start the reaction



Cellular respiration
A set of metabolic processes that occur in the cell to convert biochemical energy from nutrients into adenosine triphosphate (ATP)
Involves catabolic redox reactions, one molecule is reduced the other is oxidised.

Adenosine Triphosphate (ATP)
- adenine group
- ribose sugar
- 3 phosphate groups
Energy that is released from combustion of carbon molecules is stored in ATP.

ATP to ADP (Adenosine Diphosphate)
- Energy released when phosphate group is released (to form ADP)
- Reversible reaction, the cell can store or release energy.
- ATP to ADP releases ~30.5 kj/mol

A1 Analytical Techniques

A.1.1 State the reasons for using analytical techniques.
Qualitative analysis - detects the presence not quantity of a substance in a mixture. e.g substances in an athlete's blood
Quantitative analysis - measure the quantity of a substance in a mixture. e.g. alcohol in a driver's breath
Structural analysis - how the atoms are arranged in molecular structures. e.g. to determine the structure of a naturally occurring or artificial product.

A1.2 State that the structure of a compound can be determined by using information from a variety of analytical techniques singularly or in combination.
The techniques analyses the effect of different forms of energy on the substance.
Infrared spectroscopy - identifies the bonds in a molecule.
Mass spectroscopy - determines relative atomic and molecular masses. The fragmentation pattern is like a fingerprint, it identifies unknown substances or evidence for the arrangement of atoms in a molecule.
Nuclear magnetic resonance spectroscopy - shows the chemical environment of certain isotopes (hydrogen, carbon, phosphorus and fluorine) in a molecule, giving vital structural information.

**However, information from only one technique is usually insufficient to determine or confirm a structure.**