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IB biology: Cell respiration and photosynthesis

HL additional material (mandatory) and option C for SL (only section C.3 and C.4). If you like these notes then please become a fan of IB notes on facebook for more similar styled notes.

IB Notes

on 19 May 2011

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Transcript of IB biology: Cell respiration and photosynthesis

Cell respiration and photosynthesis Cell respiration State that oxidation involves the
loss of electrons from an element, This can easier be represented this way (learning outcome in pink): Oxidation Electrons Reduction Oxygen Hydrogen Results in many Results in a compound Loss Gain Loss C-O bonds with lower potential energy Gain Loss Gain C-H bonds with higher potential energy Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation. Phosphorylation: Starting product: End product: 2 ATP's
6-carbon sugar Process: ATP's phosphorylate the glucose 2 ADP's
fructose-1, 6-bisphosphate Lysis: 2 ADP's
fructose-1, 6-bisphosphate Splitting (lysing) of fructose Glyceraldehyde-3-phosphate (G3P) Glyceraldehyde-3-phosphate (G3P) produces the reduced form of NAD . Released energy used to add inorganic phosphate to the remaining 3-carbon compound, thus resulting in a compound with 2 phosphate groups. Enzymes remove the phosphate groups and add them to ADPs. 2 NADH
4 ATP's
2 pyruvates Oxidation of G3P Oxidation: + Summary: Net gain: Starting product: Process: 2 ATP's
6-carbon sugar Phosphorylation
Oxidation 2 NADH
2 ATP's
2 pyruvates Cytoplasm For pictures, please look it up in the book (page 219-220 in HL Pearson). But I mostly found them to complicate everything. Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs. Explain aerobic respiration: the link reaction, the Krebs cycle, the role of NADH + H , the electron transport chain and the role of oxygen. + The link reaction: Pyruvate enters mitochondrial matrix Pyruvate is decarboxylated removal of a carbon atom 2-carbon acetyl group is the product Removed carbon is release as CO (waste gas) 2 Acetyl group oxidized with the formation of reduced NAD Acetyl group combines with coenzyme A to form acetyl CoA + The Krebs cycle: Acetyl CoA combines with 4-carbon compound: 6-carbon compound oxaloacetate Citrate 5-carbon compound Oxidation CO 2 NADH 4-carbon compound Oxidation Decarboxylation NADH 2 CO Various changes NAD + NAD + + NADH NAD FAD FADH 2 ATP While learning about the Krebs cycle, there are some things you should know about how to read the diagram:
You do NOT need to memorize the text in
The name of the process is inside the circle
The end products of the single processes are listed OUTSIDE the circle (only the products the arrows point TO)
The products which the arrows point away from are the products that are used to turn into the end products white The electron transport chain (ETC) Note: For every glucose that enters cellular respiration, the cycle will run twice.
The starting product (oxaloacetate) is the same as the end product; hence the Krebs 'cycle'
The cycle takes place in the mitochondrial matrix Net gain: 2 ATP's
6 NADH's
2 FADH 's
4 CO (released as waste) 2 2 Proteins with haem groups (carriers) are referred to as cytochrommes. Their characteristics are:
Being easily reduced and oxidized
Carrying electrons (energy)
Being close to each other
Having differing eletronegativity One carrier is a protein.
It is called coenzyme Q. NOT Electrons are passed from a carrier with lower electronegativity to a carrier with higher electronegativity. Everytime, small amounts of energy are released. The sources of the electrons are the coenzyms FADH and NADH from previous stages of cellular respiration. Reduction-oxidation reactions Free energy relative to O /k cal mol 2 -1 1
2 O _ 2 NADH FADH Notice how FADH enter the ETC at a lower free energy level than NADH Diagram not to scale nor complete.
It is only for the sake of getting a visual idea of what the ETC looks like. The ETC takes place on the inner membrane and on the membranes of cristae At the very end of the chain, the de-energized electrons combine with available oxygen. Other points to note: Since FADH enters at lower free energy level than NADH, it only allows for the production of 2 ATP's (NADH allows for 3 ATP's) 2 It is not until here oxygen really needed; it is the final carrier because it has the highest electronegativity (and thus the strongest attraction for electrons) Two hydrogen ions from the aqueous surrounding combine with the oxygen+electron and this results in water (called water of metabolism) There are many carriers so that the difference in electronegativity won't be so great. Thus only small amounts of energy are lost at each exchange. The energy released is harnessed by the cell to carry out phosphorylation (see later in slideshow). Big amount of lost energy might harm the cell. Explain oxidative phosphorylation in terms og chemiosmosis. Explain the relationship between the structure of the mitochondrion and its function. whereas reduction
involves a gain of electrons; and that oxidation fre-quently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen. Go through the slideshow or read around the assessment statements. Information is based on the Pearson HL biology book to which page numbers also refer to. Good luck studying! 2 2 Hydrogen ions are pumped from the matrix into the intermembrane space by the energy released in the electron transport chain (the proton pump in the picture).
This creates a concentration gradient and so the hydrogen ions start passively moving back into the matrix through the ATP synthase. As they do so, the ATP synthase harnesses the available energy, allowing the phosphorylation of ADP (turning ADP to ATP). H = protons (hydrogen ions)

ATP synthase = enzyme on the inner membrane of the mitochondria + Chemiosmosis Oxidative phosphorylation: Eletron transport chain + chemiosmosis Outer mitrochondrial membrane

Inner mitochondrial membrane

Mitochondrial intermembrane space


Cristae Separates the contents of the mitochondrion from the rest of the cell Contains carriers for the electron transport chain and ATP synthase for chemiosmosis Reservoir for hydrogen ions, high concentration of it it necessary for chemiosmosis to occur The cytosol-like area contains enzymes for the link reaction and Krebs cycle Increases surface area for oxidative phosphorylation Photosynthesis Draw and label a diagram showing the structure of a chloroplast as seen in electron micrographs. State that photosynthesis consists of light-dependent and light-independent reactions. Explain the light-dependent reactions. Organized Chlorophyll
Carotenoids Membrane of thylakoid Further details > Photosystems: Chlorophyll a molecules Protein matrix pigments: Organized pigments: Pigments: Reaction centre: Accessory
pigments The light dependent reaction: A pigment in photosystem II absorbs a photon of light and transfers it to other pigments until it reaches chlorophyll a in the reaction centre. The photon energy excites a chlorophyll a electron to a higher energy state.
The chlorophyll a electron is captured by the primary acceptor of the reaction centre.
An enzyme splits water into electrons, hydrogen ions and an oxygen atom. This is called photolysis and is achieved by light energy. One by one the electrons move to the chlorophyll a molecules of the reaction centre.
The excited chlorophyll a electrons pass from the primary electron acceptor down an electron transport chain that drives chemiosmosis (much like in cellular respiration). One carrier is called PQ and the another cytochrome complex.
Energy lost from the ETC is used to drive chemiosmosis which brings about phosphorylation of ADP to produce ATP. A photon of light is absorbed by photosystem I and transfers it to other pigments until it reaches chlorophyll a in the rection centre. The photon energy excites a chlorophyll a electron to a higher state.
The chlorophyll a electron is captured by the primary acceptor of the reaction centre.
The excited electrons pass down a second ETC which involves the carrier ferredoxin.
An enzyme (NADP reductase) catalyzes the transfer of the electron from ferredoxin to the energy carrier NADP . 2 electrons are required to fully reduce NADP to NADPH. + +
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