8.2 Cell Respiration

The Krebs cycle takes place in the mitochondrial matrix. The process releases hydrogen ions which provide a source of energy for the synthesis of ATP, using co-enzymes and carrier proteins.

Describe the role of co-enzymes and carrier proteins in the production of ATP. 

The following reaction takes place in the Krebs cycle.

A student investigated the effect of the enzyme inhibitor malonate on this reaction. The structure of malonate is similar to the structure of succinate.

In the investigation, the student added malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria. She also bubbled oxygen through the suspension.

Explain why the student used pyruvate and not glucose as a respiratory substrate.  

Explain how malonate inhibits the formation of fumarate from succinate. 

The student measured the uptake of oxygen by the mitochondria during the investigation. The uptake of oxygen decreased when malonate was added.

Explain why.

A group of scientists measured the mean rate of respiration in soil found under trees and soil that was not from under trees within the same woodland. The mean rate of photosynthesis in leaves was also measured. The measurements were taken throughout a 24 hour period during the summer.  

The diagram below shows the scientists' results. 

Suggest an explanation for the mean rate of respiration in soil not under the trees between midday and sunset. 

The mean rate of respiration is higher in soil under the trees throughout the 24hours. The scientists suggested the mean rate of photosynthesis was the cause of this. 

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.

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

State the measurements needed for the scientists to calculate the rate of carbon dioxide production. 

The diagram below shows the main stages of aerobic respiration.

 Name substances A, B and C

Annotate on the diagram,

[1]

State precisely where in the cell Process 2 is occurring. 

Compare the roles of NAD+ and NADH in Process 1 and Process 3.

One mark is available for clarity of communication throughout this question.

A large number of disorders are being linked to mitochondrial disease, MD. MD can affect the skeletal muscles, causing fatigue and weakness. Some mitochondrial diseases are caused by mutations of mitochondrial genes inside the mitochondria. Most mitochondrial diseases are caused by mutations of genes in the cell nucleus that are involved in the functioning of mitochondria. 

One form of MD is caused by a mutation of a mitochondrial gene that codes for a tRNA. which changes the anticodon on the tRNA.  This results in the formation of a non-functional protein in the mitochondrion.

Suggest how a  change in anticodon on the tRNA can lead to muscle weakness and fatigue.

A person with MD often has a decreased uptake of oxygen in their respiring cells. This has been attributed to an inhibitory compound of the Krebs cycle.

Explain why an inhibitor of the Krebs cycle would decrease the rate of oxygen uptake by cells.

Explain the role of chemiosmosis in the process of oxidative phosphorylation 

The Krebs cycle, which takes place in the mitochondrial matrix, releases hydrogen ions.

These hydrogen ions provide a source of energy for the synthesis of ATP, using coenzyme.

Describe the role of the coenzymes in the synthesis of ATP.

Explain why the link reaction is described as an oxidative decarboxylation reaction.

The diagram below shows the Krebs cycle.

Identify the number of carbon atoms (e.g. 1C) at each stage of the Krebs cycle.

NAD and FAD are important electron carriers produced throughout the stages of respiration.

Complete the table below to show how many molecules of NAD and FAD are produced at each stage per molecule of glucose.

Describe the role of oxygen in respiration.

Outline the events of the electron transport chain.

The diagram below shows part of a mitochondrion.

Suggest, with a reason, which part of the mitochondrion is shown in the diagram.

Label parts A, B and C in the diagram in part c).

Draw an annotated diagram of a mitochondrion as seen through an electron microscope.

Your drawing should be a longitudinal cross-section; it should show the mitochondrion as if it has been cut open end-to-end.

Electron tomography has been used to make new discoveries about mitochondria.

Describe features of the mitochondria that have been identified by the use of electron tomography.

The diagram below shows the cristae of a mitochondrion viewed with a magnification of x7000.

Use the information from the diagram and above to calculate the actual size space between A and B. You may assume that the line AB, when printed on paper, has a length of 3.5 cm. 

Phosphorylation occurs on the cristae membrane.

1. Describe the process of phosphorylation of ATP.   
2. State the stage(s) of respiration in which substrate level phosphorylation occurs.

One mark is available for clarity of communication throughout this question.

Describe the mechanism by which ATP is formed in the mitochondria.

In the 1960s Peter Mitchell developed the theory of chemiosmosis which was a novel idea from the current theories.

Outline the key principles of his hypothesis that made it a paradigm shift.

Explain the relationship between the structure of the mitochondria and how it is related to its function.