9.1.1     Outline that oxidation involves the loss of electrons from an element whereas reduction involves gain in electrons, and that oxidation frequently involves gaining oxygen or losing hydrogen; whereas reduction frequently involves loss of oxygen or gain in hydrogen.

Oxidation is Loss (of electrons), Reduction is Gain (in electrons)

9.1.2     Outline what is achieved by the process of glycolysis including phosphorylation, lysis, oxidation and ATP formation.

In the cytoplasm, one hexose sugar is converted into two three-carbon atom compounds 2-oxopropanoate (pyruvate) with a net gain of two ATP and two NADH + H⁺

Phosphorylation is a process in which ATP is made in vivo (in glycolysis the process is "substrate level phosphorylation")

 

 

9.1.3     Outline aerobic respiration including oxidative decarboxylation of 2-oxopropanoate (pyruvate), Krebs cycle, NADH + H⁺ and electron transport chain.

In aerobic respiration (in mitochondria in eukaryotes) each 2-oxopropanoate (pyruvate) is decarboxylated (CO₂ removed), the remaining two carbon molecule (ethanoyl or acetyl group) reacts with reduced Coenzyme A, and at the same time one NADH + H⁺ is formed. This is known as the link reaction.

CH₃.CO.COOH + CoAs-H + NAD⁺ -> CO₂ + NADH + H⁺ + CH3CO-S-CoA

In Krebs cycle each ethanoyl (acetyl) group (CH₃ CO) formed in the link reaction yields two CO₂ . The names of the intermediate compounds in the cycle are not required. Thus it would be acceptable to note : C₂ + C₄ = C₆ -> C₅ -> etc. Students should also note that the hydrogen atoms removed are collected by "hydrogen-carrying co-enzymes". (Cross reference 9.1.1). The names of the intermediate carriers in the respiratory chain, the structures of FAD and NAD⁺ , the role of GTP or the involvement of another CoA in the cycle is not required; nor is knowledge of experimental procedures used to elucidate Krebs cycle or the electrons transport chain (ETC).

In summary – the ETC transports two hydrogens (and two electrons) from either FADH₂ or NADH eventually to molecular oxygen forming water and, in so doing, makes ATP. Students should know that aerobic respiration occurs only if there is sufficient oxygen available.

9.1.4     Describe oxidative phosphorylation in terms chemiosmosis including proton pumps, a proton gradient and ATP synthetase (cross reference 9.2.4).

The synthesis of ATP is coupled to electron transport and the movement of protons (H⁺ ions) – the chemiosmotic theory. Briefly, the ET carriers are strategically arranged over the inner membrane of the mitochondrion and as they progressively oxidise NADH + H⁺ and FADH ₂ , energy from this process forces protons to move, against the concentration gradient, from the mitochondrial matrix to the space between the two membranes (a proton pump). The pH therefore drops between the membranes (pH8 -> pH7, a 10* increase) and a potential difference is created.

Eventually the H⁺ ions flow back into the matrix through special gates in the ATP synthetase molecules in the membrane ("Structure and Function" – the enzymes are the stalked particles seen in electronmicrographs). As the ions are flowing down the gradient, energy is released and ATP is made.

 

 

 

 

 

9.1.5     Draw the structure of a mitochondrion as seen in electronmicrographs.

9.1.6     Explain the relationship between the structure of the mitochondrion and its function.

9.1.7     Describe the central role of ethanoyl (acetyl) CoA in carbohydrate and fat metabolism.

Ethanoyl (Acetyl) CoA as an intermediate in carbohydrate (glucose) metabolism as described above. In lipid metabolism the oxidation of the fatty acid chains results in the formation of two-carbon atom ethanoyl (acetyl) fragments which then pass through Krebs cycle. "Equilibrium within Systems" here. Cross reference 9.1.3.

9.1.8     Outline fermentation to 2-hydroxypropanoate (lactate) and to ethanol, and the circumstances in which they occur in cells.

Anaerobic respiration in yeast is known as fermentation and in the absence of oxygen the 2-oxopropanoate (pyruvate) is converted to ethanol with the release of carbon dioxide and a greatly reduced yield of ATPs (about 5% compared to aerobic respiration). In animal cells the 2-oxopropanoate is usually converted to lactate in the absence of oxygen with no loss of carbon dioxide so the reaction is reversible.

 

ALCOHOLIC FERMENTATION

  

 

LACTATE FERMENTATION

 

 9.2.1     Draw the structure of a chloroplast as seen in electron-micrographs.

9.2.2     State that photosynthesis consists of light-dependent and light-independent reactions.

* Not "light" and "dark" reactions.

   

 

 

9.2.3     Explain the light-dependent reactions including the photoactivation of Photosystem II, photolysis of water, electron transport, cyclic and non-cyclic photophosphorylation, photoactivation of Photosystem I and reduction of NADP⁺.

THE LIGHT-DEPENDENT REACTION

9.2.4     Explain photophosphorylation in terms of chemiosmosis (cross reference 9.1.4).

9.2.3- Chlorophylll a molecules in PsII (mainly in the grana)

9.2.4 absorb tlight 9.2.4 mainly at 680 nm, electrons are excited and (therefore more easily) removed by a chain of electron carriers 9oxidising agents – names not required). This process is couples (aided by the no, Chl a ⁺ molecules) with the photolysis (splitting) of water so thata oxygen, protons and electrons are released. (The latter reduce Chl a ⁺ back to Chl a ). The protons (H⁺ ions) are pumped to the inside of the thylakoids, they accumulate (pH drops) and eventually move out to the stroma through protein channels in the ATP synthetase enzymes providing energy for ATP synthesis (non-cyclic photophosphorylation). Some of the protons release are converted to NADPH which acts later as a reducing agent. Chlorophyll a molecules in PS I (in intergranal lamellae) absorb light mainly at 700 nm and can control a cycling of electrons via carriers so that ATP is formed (chemiosmosis) but not NADPH (and this is called cyclic photophosphorylation).

 

 

CYCLIC PHOSPHORYLATION

 

CHEMIOSMOSIS

 

 

 

9.2.5     Explain the light-inependent reactions including the roles of ribulose bisphosphate (RuBP) carboxylase, reduction of glycerate 3-phosphate (GP) to triose phosphate (TP or GALP), NADPH + H ⁺, ATP, regenration of RuBP and synthesis of carbohydrate and other products.

In the stroma of the chloroplasts the ATP provides energy, and the NADPH energy and reducing power for biosynthesis using carbon dioxide. The Calvin cycle in which the five-carbon molecule RuBP acts as the CO₂ acceptor (catalysed by RuBP carboxylase) is important, (then forming two 3 carbon molecules – GP) but the intermediates can be given the initials GP and TP or (GALP). Note that the reduction of GP (removal of O) to TP requires H and most of the energy from NADPH (and some from ATP). TP can be converted to glucose, sucrose, starch, fatty acids, amino acids and other products. (It could be noted that GP and TP are also intermediates in glycolysis). Some of the TP is used, via intermediates, to regenerate more RuBP, a process that involves some more ATP. Details of experimental procedures to elucidate the stages are not required.

9.2.6     Outline the differences in carbon dioxide fixation between C₃, C₄ and CAM plants, noting their adaptive significance.

C4 pathway

9.2.5 describes the C₃ pathway since a three carbon compound (GP) is the first recognisable product after the fixation of CO₂ . C₄ pathway uses propenoate 2-phosphate (PEP – a 3C compound) to manufacture a four carbon compound (2-oxobutanedioate-oxaloacetate). The enzyme that carries out this process (PEP carboxylase) has a greater affinity for CO₂ that RuBP carboxylase so that it can be fixed at much lower concentrations. 

 

CAM (Crassulacean Acid Metabolism) is an adaptation where some plants living in dry areas keep their stomata closed during the day (to conserve water). They open them at night and fix the CO₂ using PEP carboxylase to eventually form various organic acids which are later decarboxylated releasing the CO₂ for synthesis. These are particularly adapted to high light, high temperature and drought. Histological details are not required nor details of photorespiration.

 

9.2.7     State one crop plant example for each of the following: a C₃, C₄ and CAM plant.

C₃: rice and most temperate region crops, wheat, potatoes.

C₄: sugar cane, maize.

CAM: pineapple, prickly pear, vanilla orchid.

9.2.8     Describe how photosynthetic pigments can be separated and identified by means or chromatography.

9.2.9     Draw the action spectrum of photosynthesis.

9.2.10     Explain the relationship between the action spectrum and the absorption spectra of photosynthetic pigments.

9.2.11     Explain the concept of limiting factors with reference to light intensity, temperature and concentration of carbon dioxide.