Energy
Transfer
Unit 1
Sub-topic 3
Cell Function and Inheritance
Energy transfer
All living cells depend upon energy release to carry out their metabolic processes. Energy
enters biological systems in the form of light where it is converted into chemical energy in
the process called photosynthesis by plants. This chemical energy is then passed on from
organism to organism along a food chain and at each step some is used, some stored and
the rest lost (mainly as heat).
Part 1
The Role and Production of ATP
ATP
1 What compound is represented by the letters ATP?
2 a) Briefly describe the role of ATP in a cell.
b) Complete the diagram of a molecule of ATP and label where energy is stored.
c) How is energy released from a molecule of ATP?
d) Write a word equation to illustrate the break down and regeneration of ATP in a cell.
2
e) What is phosphorylation? Add where “phosphorylation” occurs to your word equation.
3 Give some examples of how the energy in ATP may be used in an organism.
4 The human body produces ATP at a rate of approximately 400g/hour, yet at any given
moment there are only about 50g present in the body. Explain why.
Oxidation and Reduction
1 a) What is (i) oxidation
(ii) reduction
b) Why are they described as a coupled reaction?
c) Draw a summary diagram of oxidation and reduction.
3
Mitochondria
Mitochondria are the organelles responsible for aerobic respiration.
a)(i) What is the fluid-filled inner cavity of this organelle called?
(ii) What is its function?
b)(i) What name is given to the folded extensions of this organelle’s inner membrane
which present a large surface area?
(ii) What is the function of these?
c) Label these 2 parts on the diagram of mitochondria
c) Which mitochondria would be more likely to be found in active muscle cells? Try to
explain why.
X
Y
4
Chemistry of Respiration
Respiration can be divided into THREE major stages that can be studied individually.
Stage 1 = glycolysis
Stage 2 = Krebs cycle
Stage 3 = hydrogen transfer system (electron transfer system)
(1) Glycolysis (breakdown of glucose)
1 a) Where does glycolysis occur?
b) (i) What substance results from the breakdown of a glucose molecule during
glycolysis?
(ii) How many molecules of ATP are gained by the cell as a result of glycolysis?
c) How many carbon atoms are present in a molecule of:
(i) glucose
(ii) pyruvic acid
d) (i) What other substance is released during glycolysis?
(ii) What is NAD and what is its purpose?
(iii) Complete the flow diagram for the reduction of NAD: ……………….
NAD
……………………
(iv) Why is this termed a reduction reaction?
5
d) Draw a detailed summary diagram of glycolysis.
Pyruvic acid then diffuses into a mitochondrion where it is converted into acetyl CoA.
2 a) How many carbon atoms are present in one molecule of acetyl CoA?
b) (i) Where in the mitochondria is acetyl CoA produced?
(ii) What TWO substances are released during the breakdown on pyruvic acid?
(iii) Which of these becomes bound to a coenzyme molecule?
(2) Krebs Cycle
The cycle of reactions by which citric acid is gradually converted back to a 4-carbon
compound is called the Krebs cycle.
3 a)(i) Explain how citric acid is formed, and state how many carbon atoms are present.
(ii) In which region of a mitochondrion is citric acid formed?
c) (i) Name 2 enzymes involved in the Krebs cycle and their roles.
(ii) What happens to the hydrogen released during the Krebs cycle?
(iii) What happens to the carbon dioxide formed during this cycle?
6
d) Draw a detailed summary diagram of Krebs cycle
7
(3) Hydrogen Transfer system
4 a) (i) What is the basic function of the cytochrome system?
(ii) Where is the cytochrome system located in a mitochondrion.
b) (i) Explain how ATP is synthesised as hydrogen passes along the cytochrome system.
(ii) Explain why the production of ATP on the cytochrome system is called oxidative
phosphorylation.
c) State the total number of ATP produced from the complete oxidation of ONE
molecule of glucose and explain where that total comes from.
d) (i) Identify the final hydrogen acceptor in the aerobic respiration.
(ii) Explain why it is termed the final hydrogen acceptor.
(iii) What is formed as a result?
e) Why is it more accurate to call the cytochrome system as an electron transfer
system?
8
f) Draw a detailed summary diagram of hydrogen transfer.
9
Summary diagram of aerobic respiration
10
Summary table of aerobic respiration
Reaction
Site of reaction
Net number of
ATP produced
Other Products
glycolysis
fate of pyruvic
acid
Krebs cycle
hydrogen
transfer system
Anaerobic respiration
3 a) Give THREE differences between aerobic and anaerobic respiration.
b) (i) State the number of ATP molecules formed from the breakdown of one glucose
molecule during anaerobic respiration.
(ii) What is the other product of anaerobic respiration?
(iii) What happens to this substance when oxygen is present?
c) Which type of respiration is most efficient? Explain why.
11
d) Draw a summary diagram of anaerobic respiration.
12
Part2
Sources of Energy
Many compounds are used as an energy source in a cell. Carbohydrates, fats and proteins
can all be oxidised to produce ATP in respiration.
Carbohydrates
1. a) What do all carbohydrates have in common?
2 a) Complete the table to summarise the three different types of carbohydrate.
Carbohydrate
Description
Examples
Monosaccharide
A double sugar consisting of 2
monosaccharide molecules joined together.
Soluble
Starch
Glycogen
b) Explain the meaning of the term reducing sugar.
c) (i) Name a disaccharide that is a non-reducing sugar.
(ii) By what means can this sugar be broken down into its components that do have
reducing properties?
13
d) (i) Draw a labelled diagram of part of a polysaccharide.
(ii) Why are polysaccharides ideal storage molecules?
3. Why are carbohydrates regarded as an important part of the human diet?
Testing Carbohydrates
1 Describe how you would test a carbohydrate to find is it is soluble or not.
2 Complete the following table to summarise the various tests used to identify
carbohydrates.
Test
Description of
test
Result when test
is positive
brick-red
precipitate
Benedict’s reagent
Acid hydrolysis +
Benedict’s reagent
Barfoed’s reagent
Carbohydrates that
cause this result
sucrose
heat
Clinistix
starch
Iodine solution
purple-red
14
3 a) Which test could be used to test for the presence of reducing monosaccharide sugar.
b) Describe the specific test for glucose.
Lipids
Lipids are a group of compounds that include fats, oils, phospholipids and steroids.
1 What do lipids have in common with, and how do they differ from, carbohydrates.
2 a) (i) Draw a labelled diagram of a molecule of a simple lipid.
(ii) Explain why this substance is also known as a triglyceride.
b) Draw a labelled diagram of a molecule of phospholipid to illustrate the ONE way in
which it differs from that of a simple lipid. Note the difference beside it.
15
2 a) Draw a labelled diagram of a basic steroid molecule.
b) Name TWO steroids that are formed from cholesterol.
The role of lipids
1 a) Complete the table to show the many roles of lipids.
Role
Brief description
insoluble adipose tissue stores energy that
can be used in respiration
Thermal insulation
Speeds up transmission of nerve impulses
b) Which releases more energy per unit mass, glucose or lipid?
16
c) Draw a flow diagram to illustrate how a triglyceride molecule can be used as a
respiratory substrate.
17
Proteins
Protein is not a major source of respiratory substrate but can be used in certain
situations.
1 a) Name an organic acid resulting from deamination of an amino acid that can act as a
respiratory substrate.
b) Why is a certain amount of energy always derived from dietary protein?
c) What is the difference between dietary and tissue protein?
d) When might tissue protein be used as a source of energy and why?
Marathon Running
Note the three main classes of food that act as the main source of fuel for a marathon
runner and indicate which part of the race each is most important in.
18