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Preparation of mitochondria from liver tissue. Substances added to the preparation and the amount of oxygen was monitored over a period of time. Suggest why the respiratory substrate added was a molecule from the Krebs cycle, not glucose

Glycolysis does not take place in the mitochondria (occurs in the cytoplasm)


What is the respiratory quotient (definition)?

The ratio of the volume of carbon dioxide evolved to that of oxygen consumed by an organism, tissue, or cell in a given time. (Vol of CO2 emitted/ vol of O2 consumed


Little carbon dioxide emitted after time C (little oxygen remaining). Explain why.

Insufficient oxygen left/ all respiratory substrate used / not enough oxygen to act as terminal electron acceptor


When the temperature is raised from 20 to 30 degrees, the cockroach becomes more active and its respiration rate and oxygen consumption increase. What causes the increase in respiration rate?

Respiration controlled by enzymes/ increased kinetic energy/ collision rate


The rate of carbon dioxide production by cockroaches is less 72 hours after they were last fed than it is 1 hour after they were fed. Explain why.

-Change of respiratory substrate
-Carbohydrate to fat


Potometer experiment set up with blowfly larvae- sodium hydroxide in experiment 1 to absorb co2. Experiment 2- water used instead of NaOH. Measuring oxygen uptake from how far the bubble moves. Give two reasons why the apparatus was left for ten minutes with the tap open when it was first placed in the water bath.

-Allow ANIMALS to equilibrate
-Allow for pressure changes in the air in the apparatus
-Reach respiration rate typical of that temperature


Explain why the bead of liquid moved along the scale in the first experiment when there was NaOH but didn't when the NaOH was replaced with water in the second experiment

-Exp 1- Oxygen CONSUMED by animals
-CO2 given out/ CO2 released but absorbed by NaOH
-Reduction in volume/ pressure
-Exp 2- O2 consumed= CO2 released/ because respiratory quotient =1


Scientists measured respiration in 3 parts of an ecosystem by measuring CO2 released by
-plants leaves
-plants roots and stems
-non photosynthetic organisms

A student concluded that the plants carry out more respiration than non photosynthetic organisms in the ecosystem. Suggest why the data do not support the conclusion.

-Data only includes heterotrophic soil organisms
-Doesn't include animals(above ground)/ non soil organisms
-Doesn't take into account anaerobic respiration


Suggest how the rise in the mean rate of photosynthesis could lead to the rise in the
mean rate of respiration in soil under trees.

-Photosynthesis produces sugars
-Sugars moved to the roots
-Sugars required for respiration


Suggest why there is a delay between the rise in the mean rate of photosynthesis and
the rise in the mean rate of respiration in the roots.

-Takes time to move the sugars to the roots


What are the products of
-Aerobic respiration
-Anaerobic respiration

>Carbon dioxide
>Much ATP

>Lactate (in animals)
>Ethanol (in bacteria)
>Carbon dioxide
>Only a little ATP in both cases


Briefly describe what happens in the 4 stages of respiration.

-GLYCOLYSIS- splitting of glucose 6C into two pyruvate molecules 3C
-LINK REACTION- conversion of pyruvate 3C into carbon dioxide and Acetyl Coenzyme A 2C
-KREBS CYCLE - introuction of Acetyl Coenzyme into a series of oxidation and reduction reactions that yields a small number of ATP and lots of electrons
-ELECTRON TRANSPORT CHAIN - synthesis of lots of ATP and water as a by product using electrons produced in the Krebs cycle


Where does glycolysis occur?

The cytoplasm of the cell


What are the 4 stages of glycolysis?

-Activation of glucose by phosphorylating it using 2 phosphates from ATP. This makes the glucose more reactive and lowers its activation energy

-Splitting of phosphorylated glucose- each glucose split into 2 triose phosphate molecules

-Oxidation of triose phosphate- hydrogen is removed from each triose phosphate and transferred to NAD to from NADH (reduced NAD)

-Production of ATP- enzymes convert the two molecules of triose phosphate into two molecules of pyruvate, in the process regenerating two molecules of ATP from ADP (2 ATP per molecule of pyruvate produced)


What is the net yield from glycolysis?

-2 molecules of reduced NAD
-2 ATP (2 from each conversion of TP to pyruvate - 2 ATP to start glycolysis)
-Two molecules of pyruvate


Is the process of glycolysis affected by the presence/ absence of oxygen?

No, it occurs regardless of whether there is oxygen- therefore it is the starting point for both aerobic and anaerobic respiration


Why is anaerobic necessary for glycolysis to continue?

Anaerobic respiration is necessary in order to re oxidise NAD so that glycolysis can continue


Describe how pyruvate is oxidised in the link reaction in order for it to enter the Krebs cycle so it can release its potential energy to form ATP. (Describe the processes in the link reaction)

-Pyruvate is oxidised by removing hydrogen
-This hydrogen is accepted by NAD to form reduced NAD (later used to produce ATP)
-Acetyl (2C) combines with Coenzyme A to form Acetylcoenzyme A
-A carbon dioxide is produced for each pyruvate


What is the overall equation for the processes in the link reaction?

Pyruvate + NAD + CoA --> CO2 + AcetylCoA + reduced NAD


Where does the Krebs cycle occur?

In the matrix of the mitochondria


Describe the sequence of events that take place in the Krebs cycle.

-Acetyl coenzymeA 2C combines with oxaloacetate (4C) to produce citric acid (6C)
-Citric acid loses carbon dioxide and hydrogens to form oxaloacetate and a single molecule of ATP is produced as a result of substrate level phosphorylation


What does the Krebs cycle produce per molecule of pyruvate?

-Reduced coenzymes NAD and FAD
-One molecule of ATP
-3 molecules of CO2

This yield is doubled per molecule of glucose as each glucose molecule produces 2 pyruvate molecules.


What are coenzymes and what do they do? Give examples of coenzymes in the Krebs cycle.

Molecules that some enzymes require in order to function. In photosyntehsis and respiration, they carry hydrogen atoms from one molecule to another. Examples include:
-NAD- important in respiration
-NADP- important in photosynthesis
-FAD- important in the Krebs cycle


What is the significance of the Krebs cycle? Why does it play an important role in the cells of organisms?

-Breaks down macromolecules into smaller ones eg pyruvate is broken down into carbon dioxide

-Produces hydrogen atoms that are carried by NAD to the electron transport chain for oxidative phosphorylation which produces ATP

-Regenerates oxaloacetate 4C which combines with AcetylCoA which would otherwise accumulate

-It is a source of intermediate compounds used by cells to manufacture substances such as amino acids, fatty acids and chlorophyll.


What is the function of NAD in respiration?

It works with dehydrogenase enzymes to catalyse the removal of hydrogen from substrates which are then carried by NAD to other molecules such as the hyrogen carriers in the electron transport chain


Where does the electron transport chain occur?



Describe the processes that cause ATP to be formed in the electron transport chain.

-Hydrogens from glycolysis and the Krebs cycle combine with NAD and FAD (coenzymes)

-Reduced NAD and FAD donate the electrons of the hydrogens that they are carrying to the first molecule in the electron transport chain

-This releases protons from the hydrogen atoms which are actively transported across the inner mitochondrial membrane

-Electrons pass down a chain of electron transport carrier molecules in a series of oxidation and reduction reactions

-As the electrons pass down the chain, they lose energy which is used to synthesise ATP by combining ADP with Pi (the remaining energy is released in the form of heat)

-Protons accumulate in the space between the two mitochondrial membranes and diffuse back into the mitochondrial matrix through ATPase which synthesises ATP

-At the end of the chain, the electrons combine with protons and oxygen (the terminal electron acceptor) to form water


Briefly describe the importance of oxygen in the electron transport chain

-It is the terminal electron acceptor and also accepts protons to form water.
-Without it accepting hydrogen atoms (formed from the combination of the protons and electrons) hydrogen ions and electrons would accumulate and 'back up' along the chain and the process of respiration would come to a halt.


What happens when oxygen is not available for respiration?

The Krebs cycle and the electron transport chain can no longer take place


Why can't the Krebs cycle take place under anaerobic conditions?

It requires products from the electron transport chain (which cannot occur in the absence of oxygen)