Biology SME

Key unit competence
Describe the structure and importance of ATP, and outline the roles of the
coenzymes NAD, FAD and coenzyme A during cellular respiration and the
process of cellular respiration.

Introductory activity 2.1

Living organisms perform different tasks like running, moving and pumping
substances across cell membranes as shown on the figures below:

a) What is the requirement to perform such activities and others that seem
like these?
b) By which mechanism do you think is taking place in organism cells to
obtain such requirement? In which form this requirement would appear?

2.1 Energy of living organisms

Activity 2.1

Observe the figures below and answer to the following questions

a) The figures A represents the activity that requires energy, based on
     figure A above identify other more activities that requires energy.
b) What could be the name of figure B, its main chemical parts and its
    roles for living organisms?

2.1.1 Need for energy by organisms
Without some input of energy, natural processes tend to break down in
randomness and disorder. Living organisms have high ordered systems that
require a constant input of energy to prevent them becoming disordered which
would lead to their death. This energy comes from the breakdown of organic
molecules to make adenosine triphosphate (ATP) which is a source of energy
needed to carry out processes that are essential to life.

More precisely energy is needed for:
• Metabolism which involves specifically the anabolism process in which
simple substances are build up into complex ones e.g. monosaccharides
are built up into polysaccharides and amino acids are built up into
polypeptides

• Active transport of ions and different molecules against a concentration
gradient across cell membranes. The transport of sodium (Na+), potassium
(K+) magnesium (Mg+), calcium (Ca+) and chloride (Cl-) across the plasma
membrane cannot be possible without the use of energy. The transport
proteins that move solutes against their concentration gradients are all
carrier proteins rather than channel proteins. Active transport enables a
cell to maintain internal concentrations of small solutes that differ from
concentrations in its environment. Some transport proteins act as pumps,

moving substances across a membrane against their concentration
or electrochemical gradients. Energy is usually supplied by adenosine
triphosphate (ATP) hydrolysis.

• Movement within an organism when substances move in the body e.g.
circulation of blood and of the orgasm it’s self during locomotion due to
muscular contraction or movement of cilia and flagella.
• Maintenance, repair and division of cell and organelles within
them.
• Maintenance of body temperature in endothermic organisms e.g.
birds and mammals that need energy to replace that lost as heat to the
surrounding environment.
• Production of substances used within organism e.g. enzymes and
hormones.

2.1.2 Structure of adenosine triphosphate (ATP)
The special carrier of energy is the molecule of adenosine triphosphate (ATP).
The ATP molecule is a phosphorylated nucleotide and it has three parts:
• Adenine: is a nitrogen containing organic base belongs to the group
   called purines
• Ribose: is a pentose sugar molecule means it has 5-carbon ring structure
  that act as the backbone where the other parts are attached.
• Phosphates: that are chain of three phosphate groups.

ATP has the following biological functions in the cell:

a) Active transport
ATP plays a critical role in the transport of macromolecules such as proteins
and lipids into and out of the cell membrane. It provides the required energy for
active transport mechanisms to carry such molecules against a concentration
gradient.

b) Cell signaling
ATP has key functions of both intracellular and extracellular signaling. In nervous
system, adenosine triphosphate modulates the neural development, the control
of immune systems, and of neuron signaling.

c) Structural maintenance
ATP plays a very important role in preserving the structure of the cell by helping
the assembly of the cytoskeletal elements. It also supplies energy to the flagella
and chromosomes to maintain their appropriate functioning.

d) Muscle contraction
ATP is critical for the contraction of muscles. It binds to myosin to provide
energy and facilitate its binding to actin to form a cross-bridge. Adenosine
diphosphate (ADP) and phosphate group (Pi) are then released and a new ATP
molecule binds to myosin. This breaks the cross-bridge between myosin and
actin filaments, thereby releasing myosin for the next contraction.

e) Synthesis of DNA and RNA
The adenosine from ATP is a building block of RNA and is directly added to
RNA molecules during RNA synthesis by RNA polymerases. The removal
of pyrophosphate provides the energy required for this reaction. It is also a
component of DNA.

Application activity 2.1

1) Energy is contained within ATP, draw and label its structure. On
     diagram show the names that result from the combination of different
     parts of ATP.
2) The person faints on playground as a result of doing vigorous physical
      exercise for long time. What can you do to save the life of that person?

2.2 Adenosine triphosphate (ATP) and coenzyme in
       respiration

Activity 2.2

Based on the structure of ATP molecule, explain how the synthesis and
breakdown of ATP is done.

2.2.1 Synthesis and breakdown of ATP

a) Breakdown of ATP

Adenosine triphosphate (ATP) is the energy currency for cellular processes. It
provides the energy for both energy-consuming endergonic reactions and
energy-releasing exergonic reactions. The three phosphate groups in ATP
structure are the main key to how ATP stores energy. Each phosphate group
is very negatively charged so they repel one another which makes the covalent
bonds that link to be unstable. These unstable covalent bonds are broken easily
because they have low activation energy. When the first two phosphates are
removed 30.5Kjmol-1 are released for each phosphate group and 14.2 KJ mol-1
are released for the removal of the final phosphate group. In living cells, usually
only the terminal phosphate group is removed as follow:

These reactions are all reversible. It is the interconversion of ATP and ADP that
is all-important in providing energy for the cell:

The calculated ∆G for the hydrolysis of one mole of ATP into ADP and P_i is
estimated at −7.3 kcal/mole equivalent to −30.5 kJ/mol. However, this is only
true under standard conditions, and the ∆G for the hydrolysis of one mole of
ATP in a living cell is almost double the value at standard conditions and equals
-14 kcal/mol or −57 kJ/mol. ATP is a highly unstable molecule. Unless quickly
used to perform work, ATP spontaneously dissociates into ADP + P_i, and the
free energy released during this process is lost as heat. To harness the energy
within the bounds of ATP, cells use a strategy called energy coupling.

The hydrolysis of ATP to ADP and P_i is a reversible reaction, where the reverse
reaction combines ADP + P_i to regenerate ATP from ADP as it is shown in the
equation above.

b) Synthesis of ATP
Energy for ATP synthesis can become available in two ways. In respiration, energy
released by reorganizing chemical bonds (chemical potential energy) during
making some ATP. However, most ATP in cells is generated using electrical
potential energy. This energy is from the transfer of electrons by electron carriers
in mitochondria and chloroplasts. It is stored as a difference in proton (hydrogen
ion) concentration across some phospholipid membranes in mitochondria and
chloroplasts, which are essentially impermeable to protons. Protons are then
allowed to flow down their concentration gradient (by facilitated diffusion)
through a protein that spans the phospholipid bilayer. Part of this protein acts
as an enzyme that synthesizes ATP and is called ATP synthase. The transfer
of three protons allows the production of one ATP molecule, provided that ADP
and an inorganic phosphate group (Pi) are available inside the organelle. This
process occurs in both mitochondria and chloroplasts and it was first proposed
by Peter Mitchell in 1961 and is called chemiosmosis.

Since the hydrolysis of ATP releases energy, ATP synthesis must require an
input of free energy. Recall that free energy is the portion of system’s energy
that can perform work when temperature and pressure are uniform throughout
the system. The synthesis of ATP from ADP involves the addition of a phosphate
molecule, which is called phosphorylation reaction. This Phosphorylation is
catalyzed by the enzyme ATP synthase (sometimes called ATP synthetase or
ATPase).

2.2.2 Roles of coenzymes in respiration
The transformation of succinate to fumarate, the sub-products of the breakdown
of glucose during glycolysis process, two hydrogens are transferred to flavin
adenine dinucleotide (FAD), forming FADH₂. The reduced coenzymes NADH
and FADH₂ transfer higher energy electrons to the electron transport chain.
Finally, another coenzyme called coenzyme A sometimes abbreviated by CoA,
a sulfur-containing compound is attached via its sulfur atom to the two-carbon
intermediate, forming acetyl CoA. The Acetyl CoA has a high potential energy,
which is used to transfer the acetyl group to a molecule in the citric acid cycle
(Krebs cycle), a reaction that is therefore highly exergonic producing great
number of energy in the form of ATP.

Application activity 2.2

Application activity 2.2
1) Using the chemical equations explain the synthesis and the hydrolysis
    of ATP in a living cell.
2) The hydrolysis and synthesis of ATP are reversible reactions. Estimate
    the amount of energy for each process.
3) Calculate the amount of energy produced by 5 moles of ATP
a) Under standard conditions
b) In a living cell

2.3 Respiratory substrates and their relative energy values

Activity 2.3

Activity 2.3: Simple combustion experiments to determine the relative energy
values of different food substances.
– Cut up a range of dried foods into small pieces around 1 cm square
   or 0.5 cm cubed.
– Use the measuring cylinder to measure 20 cm³ of water into the
    boiling tube.
– Clamp the boiling tube to the clamp stand.
– Measure the temperature of the water with the thermometer. Record
    the temperature in a suitable table.
– Impale the piece of food carefully on a mounted needle.

– Light the Bunsen burner and hold the food in the flame until it
    catches a light.
– As soon as the food is alight, put it under the boiling tube of water as
    shown on figure and keep the flame under the tube.
– Hold the food in place until the food has burnt completely.
– As soon as the food has burned away completely and the flame
    has gone out, stir the water carefully with the thermometer and
    measure the temperature of the water again. Note down the highest
   temperature reached.
– Repeat the procedure for other foods.
– Calculate the rise in temperature each time and Calculate the energy
    released from each food by using this formula.

Where 4.2 represents the value of the specific heat capacity of water, in
joules per gram per degree Celsius. If the number is more than 1000 J/g,
express it as kilojoules (kJ):
1 kilojoule = 1000 joules
Compare obtained results.
Follow the set up below:

A respiratory substrate refers to the substance required for cellular respiration
to derive energy through oxidation. They include carbohydrates, lipids and
proteins.

Carbohydrates include any of the group of organic compounds consisting
of carbon, hydrogen and oxygen, usually in the ratio 1:2:1. The examples of
carbohydrates include sugars, starch and cellulose. Carbohydrates are the
most abundant of all classes of biomolecules, and glucose whose chemical

formula is C₆H₁₂O₆ is the most known and the most abundant. Its breakdown
produces energy in the following way: C₆H₁₂O₆ +6 O₂→6 CO₂ +6 H₂O+Energy
(ATP + heat).

This breakdown is exergonic metabolic reaction, having a free-energy change of
-686 kcal (-2,870 kJ) per mole of glucose decomposed.

Lipids include diverse group of compounds which are insoluble in water but
dissolved readily in other lipids and in organic solvents such as ethanol (alcohol).
Lipids mainly fats and oils contain carbon, hydrogen and oxygen, though the
proportion of oxygen is lower than in carbohydrates. Fats and oils have a higher
proportion of hydrogen than either carbohydrates or proteins. This property
makes them a more concentrated source of energy, where each gram of fat or
oil yields about 38kJ (38 kJ/g) more than twice the energy yield of a gram of
carbohydrate.

Proteins are other respiratory substrate. They are large and complex biological
molecules which play many and diverse roles during respiration. They mainly
work as enzymes. Enzyme is a biological catalyst that controls biochemical
reactions in living organisms.

Back to glucose when it is broken down during the process called glycolysis,
the dehydrogenases enzymes transfer electrons from substrates, here glucose,
to NAD⁺ which in turn forms NADH. At this stage the electron transport chain
accepts electrons from NADH and passes these electrons from one molecule
to another in electron chain transfer leading to a controlled release of energy
for the synthesis of ATP. At the end of the chain, the electrons are combined
with molecular oxygen and hydrogen ions (H⁺) to form one molecule of water.
When NAD is oxidized, its oxidized form NAD⁺ is converted into its reduced
from NADH, and two molecules of ATP are produced.

Application activity 2.2

1) Calculate the amount of energy produced by 5moles of glucose in kcal
     and kJ if one mole of glucose produce -686 kcal and 2,870 kJ per mole
     of glucose.
2) Specify the number of ATP produced by glycolysis during respiration
    process.

2.4 Measurement of respiration and respiratory quotients

Activity 2.3

– Set up the boiling tube so it is vertical and supported in a water bath
    such as a beaker.
– Use pea seeds that have been soaked for 24 hours and rinsed in 1%
   formaldehyde for 5 minutes.
– Kill an equal quantity of soaked seeds by boiling them for 5 minutes.
– Cool the boiled seeds in cold tap water; rinse them in bleach or
   formaldehyde for 5 minutes as before.
– Start with a water bath at about 20 °C and allow the seeds to adapt
   to that temperature for a few minutes before taking any readings.
– Record the initial and final positions of the water drop with a
   permanent marker with small label onto the glass.
– Measure the distance travelled by colored dye (or drop of water) with
   a ruler.
– Repeat the procedure (introducing a new bubble each time) at a
   range of different temperatures, remembering to allow time for the
   seeds to adapt to the new conditions before taking further readings.
– Interpret your observation. Follow the set up below:

The rate of respiration is measured by the use of respirometer device, typically
by measuring oxygen consumed and the carbon dioxide given out. It can also
be used to measure the depth and frequency of breathing, and allows the
investigation on how factors such as; age, or chemicals can affect the rate of
respiration. Currently, the computer technology is also used to automatically
measure the volume of gases exchanged and drawing off small samples to
analyze the proportions of oxygen and carbon dioxide in the gases.

The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide
produced to the volume of oxygen used in respiration during the same period
of time. The RQ is often assumed to equal the ratio of carbon dioxide expired:
oxygen inspired during a given time as it is summarized in the following formula:

The RQ is important as it can indicate whether the respiration is aerobic or
anaerobic.

As each molecule of gas occupies the same volume, this would give RQ =
1.0, and this is common for all carbohydrates. Further studies indicated the
respiratory quotient to be 0.9 for proteins and 0.7 for fats, and concluded that
an, RQ greater than 1.0 indicates anaerobic respiration, while RQ equals or less
than 1.0 indicates aerobic respiration.

Note that respiration during germination, especially in early stages was also
studied. Results indicated that it is difficult for oxygen to penetrate the seed
coat, so that at this stage, the RQ is about 3 to 4. Later when the seed coat is
shed, it becomes easier for oxygen to reach respiration tissues and the levels of
RQ falls. Results indicated that eventually seeds with large carbohydrate stores
have an RQ around 1.0 and those with large lipid stores have RQs of 0.7 to 0.8.

a. Measuring and obtaining the RQ values in invertebrate (e.g. woodlice)
In this particular respirometer, woodlice have been placed in a boiling tube
which is connected to a U-tube. The U-tube acts as a manometer (a device for
measuring pressure changes). The other end of the U-tube is connected to a
control tube which is treated in exactly the same way as the first tube, except
that it has no woodlice but instead glass beads which take up the same volume
as the woodlice. The two boiling tubes (but not the manometer) are kept in
water bath at constant temperature. The U-tube contains a colored liquid which
moves according to the pressure exerted on it by the gases in the two boiling
tubes. Both tubes contain potassium hydroxide solution which absorbs any
carbon dioxide produced. The setup is summarized below:

When the woodlice respire aerobically, they consume oxygen, which causes
the liquid to move in the U- tube in the direction of arrows. The rate of oxygen
consumption can be estimated by timing how long it takes for the liquid to
rise through a certain height. The experiment can be repeated by replacing the
potassium hydroxide solution with water. Comparing the changes in manometer
liquid level with and without potassium hydroxide solution gives an estimate of
carbon dioxide production can be used to measure the respiratory quotient.

If the internal radius of the manometer tube is known, the volumes of gases can
be calculated using the equation:

Volume of gases = π r² h,

Where π is equal to 3.14, r is the internal radius of the tube and h is the
distance moved by the liquid.

b. Measuring and obtaining the RQ values during seed germination
     process

During seed germination, CO₂ is released. To test its presence, chemicals
including Sodium hydroxide or Potassium hydroxide are used due to their ability
to absorb CO₂. As the germinating seeds use oxygen, pressure reduces in tube
A so the manometer level nearest to the seeds rises (figure 2.8). The syringe is
used to return the manometer fluid levels to normal. The volume of oxygen used
is calculated by measuring the volume of gas needed from the syringe to return
the levels to the original values. If water replaces the sodium hydroxide, then the
carbon dioxide evolved can be measured. The setup is summarized below:

This graph suggests that the seed begins with carbohydrate as a metabolite,
changes to fat/oil then returns to mainly using carbohydrate.

Application activity 2.4

1) Using the following equation of oleic acid (a fatty acid found in olive
     oil):

a) Calculate the RQ for the complete aerobic respiration.
b) Based on your findings, state which substrate is being respired
2) Measurements of oxygen uptake and carbon dioxide production by
germinating seeds in a respirometer showed that 25 cm³ of oxygen
was used and 17.5 cm³ of carbon dioxide was produced over the
same time period.
i) Calculate the RQ for these seeds.
ii) Identify the respiratory substrate used by the seeds.

2.5 Aerobic respiration and Glycolysis

Activity 2.5

Glycolysis process
Observe the figure below and do the following activities

a) If this representation on figure above (→ATP) shows energy used and
     this (ATP→) represent energy produced during this process. Identify the
     energy used and energy produced then calculate net energy produced
     during this process.
b) According to your observation, what are the end products of this
     process above?

Cellular respiration is the complex process in which cells make adenosine
triphosphate (ATP) by breaking down organic molecules. The energy stored
in ATP can then be used to drive processes requiring energy, including
biosynthesis, locomotion or transportation of molecules across cell membranes.
The main fuel for most cells is carbohydrate, usually glucose which is used by
most of the cells as respiratory substrate. Some other cells are able to break
down fatty acids, glycerol and amino acids.

Glucose breakdown can be divided into four stages: glycolysis, the link
reaction, the Krebs cycle and oxidative phosphorylation.

Glycolysis is the splitting or lysis of a glucose molecule. It is a multi-step
process in which a glucose molecule with six carbon atoms is eventually split
into two molecules of pyruvate, each with three carbon atoms. Energy from ATP
is needed in the first steps, and it is released in the later steps to synthesize ATP.
There is a net gain of two ATP molecules per molecule of glucose broken down.

Glycolysis takes place in the cytoplasm of a cell. Within the mitochondrion, the
citric acid cycle occurs in the mitochondrial matrix, and oxidative metabolism
occurs at the internal folded mitochondrial membranes (cristae). Glucose enters

the cell and is phosphorylated by the enzyme called hexokinase, which transfers
a phosphate group from ATP to the sugar. The ATP used in this process has
2 advantages: the charge of the phosphate group traps the sugar in the cell
because the plasma membrane is impermeable to large ions. Phosphorylation
also makes glucose more chemically reactive. Even though glycolysis consumes
two ATP molecules, it produces a gross of four ATP molecules (4 ATP), and
a net gain of two ATP (2 ATP) molecules for each glucose molecule that is
oxidized. Glycolysis results in a net gain of two ATP (2ATP), two NADH and two
pyruvate molecules

Application activity 2.5

1) Why is ATP needed for glycolysis?
2) How many gross ATP molecules are produced during glycolysis from
one glucose molecule?
3) How many NADH are made during glycolysis?
4) The following flowchart summarizes the reactions that take place in
glycolysis
Glucose → 2 × glyceraldehydes 3-phoshate → 2 × pyruvate
a) How many carbon atoms are there in glucose, glyceraldehydes
3-phoshate and pyruvate?
b) What is the net gain of ATP in glycolysis?

2.6 Link reaction and Krebs cycle (TCA cycle)

Activity 2.6

Use the figure below and do the following activities:

a) The above figure summarizes two stages that take place during
      respiration, observe it and identify the number of CO₂, ATP, reduced
      FAD and reduced NAD.
b) Knowing that the above stages involve two molecule of pyruvates
      calculate the total number of CO₂, ATP, reduced FAD and reduced NAD.

2.6.1 Link reaction
Pyruvate, the end product of glycolysis is oxidized to Acetyl-CoA by enzymes
located in the mitochondrion of eukaryotic cells as well as in the cytoplasm
of prokaryotes. In the conversion of pyruvate to Acetyl-CoA, one molecule of
NADH and one molecule of CO2 are formed (Figure 2.10). This step is also
known as the link reaction or transition step, as it links glycolysis to the Krebs
cycle.

Krebs cycle (Citric acid cycle)
The coenzyme has a sulphur atom, which attaches the acetyl fragment by an
unstable bond. This activates the acetyl group for the first reaction of the Krebs
cycle also called citric acid cycle or Tricarboxylic Acid Cycle (TCA). It is also
known as the citric acid cycle, because the first molecule formed when an acetyl
group joins the cycle. When oxygen is present, the mitochondria will undergo
aerobic respiration which leads to the Krebs cycle.

In the presence of oxygen, when acetyl-CoA is produced, the molecule then
enters the citric acid cycle inside the mitochondrial matrix, and gets oxidized
to CO₂ while at the same time reducing NAD+ to NADH. NADH can then be
used by the electron transport chain to create more ATP as part of oxidative
phosphorylation. For the complete oxidation of one glucose molecule, two
Acetyl-CoA must be metabolized by the Krebs cycle. Two waste products
namely H₂O and CO₂, are released during this cycle.

The citric acid cycle is an 8-step process involving different enzymes and co-
enzymes. Throughout the entire cycle, Acetyl-CoA (2 carbons) combines with
oxaloacetate (4 carbons) to produce citrate. Citrate (6 carbons) is rearranged
to a more reactive form called isocitrate (6 carbons). Isocitrate (6 carbons) is
modified to α-Ketoglutarate (5 carbons), Succinyl-CoA, Succinate, Fumarate,
Malate, and finally to Oxaloacetate. The net energy gain from one cycle is 3 NADH,
1 FADH₂, and 1 Guanosine Triphosphate (GTP). The GTP may subsequently
be used to produce ATP. Thus, the total energy yield from one whole glucose
molecule (2 pyruvate molecules) is 6 NADH, 2 FADH₂, and 2 ATP. 2 molecules
of carbon dioxide are also produced in one cycle (for a total of 4 molecules of
carbon dioxide from one glucose molecule).

Application activity 2.6

1) Use the chemical equation to show the conversion of pyruvate into
     acetyl-coA.
2) Identify and note the main products of the Krebs cycle from one
    glucose molecule

2.7 Oxidative phosphorylation

Activity 2.7

Observe the figure below and do the following activities

a) This figure summarizes last stage that take place during cellular
      respiration, observe it and identify the role of reduced NAD, reduced
      FAD and oxygen in this stage.
b) Give the explanation of the above figure.

In the final stage of aerobic respiration known as the oxidative phosphorylation,
the energy for the phosphorylation of ADP to ATP comes from the activity of the
electron transport chain. Oxidative Phosphorylation is the production of ATP
using energy derived from the redox reactions of an electron transport chain.

In eukaryotes, oxidative phosphorylation occurs in the mitochondrial cristae. It
comprises the electron transport chain that establishes a proton gradient across
the inner membrane by oxidizing the NADH produced from the Krebs cycle. ATP
is synthesized by the ATP synthase enzyme when the chemiosmosis gradient
is used to drive the phosphorylation of ADP. Chemiosmosis is the production
of ATP from ADP using the energy of hydrogen ion gradients. The electrons
are finally transferred to oxygen and, with the addition of two protons, water is
formed. The average ATP yield per NADH is probably 3 and for FADH₂ of this
electron carrier is worth a maximum of only two molecules of ATP.

Role of oxygen in chemiosmosis
ATP can be synthesized by chemiosmosis only if electrons continue to move
from molecule to molecule in the electron transport chain. Oxygen serves as
the final acceptor of electrons. By accepting electrons from the last molecule in
the electron transport chain, and allows additional electrons to pass along the
chain. As a result, ATP can continue to be synthesized. Oxygen also accepts
the protons that were once part of the hydrogen atoms supplied by NADH and
FADH₂. By combining with both electrons and protons, oxygen forms water as
shown in the following equation:

Overview of aerobic respiration
A considerable number of ATP is produced during oxidative phosphorylation and
it is estimated between 32 and 34 ATPs. These are added to 2 ATP produced
during glycolysis and 2 ATP produced during citric cycle. The total number
of ATP produced during a complete respiration process for one molecule of
glucose is then estimated between 36 and 38 ATPs.

Note that the amount of ATP produced from glucose is usually less than 38
ATP for the following reasons: some ATP is used to transport pyruvate from the
cytoplasm into the mitochondria and some energy is used to transport NADH
produced in glycolysis from the cytoplasm into the cristae of mitochondria.

Overall net gain of energy from glucose

Application activity 2.7

1) a) How many ATP are formed from 1 NADH?
b) How many ATP are formed from 1 FADH?
2) How many ATP are formed after a complete oxidation of one glucose
molecule.

2.8 Efficiency of aerobic respiration

Activity 2.8

During the complete oxidation of a molecule of glucose it is estimated to
produce 686Kcal. Knowing that inside the cell each ATP produced is
equivalent to 7.3 Kcal,

Considering all the amount of ATP produced, find out the percentage of
energy that is equivalent to amount of total ATP produced during aerobic
respiration. Use below formula for your calculations:

The complete oxidation of glucose produces the energy estimated at 686 Kcal.
Under the condition that exists inside most of the cells, the production of a
standard amount of ATP from ADP absorbs about 7.3 Kcal. Glucose molecule
can generate up to 38 ATP molecules in aerobic respiration. The efficiency of
aerobic.

This result indicates that the efficiency of aerobic respiration equals 40%. The
remained energy (around 60%) is lost from the cell as heat.

Application activity 2.8

1) 1. Under which conditions can aerobic respiration take place in animal
cells?
2) 2. Calculate the efficiency aerobic respiration, when a complete
oxidation of glucose produce the energy estimated at 500Kcal under a
production of a standard amount of ATP from ADP absorbed is about
7.3 Kcal.

2.9 Efficiency of anaerobic respiration

Activity 2.9

Anaerobic respiration in yeast
a) Boil some water to expel all the dissolved oxygen.
b) When cool, use the boiled water to make up a 5% solution of glucose
and a 10% suspension of dried yeast.
c) Place 5 Cm3 of the glucose solution and 1 Cm3 of the yeast suspension
in a test-tube and cover the mixture with a thin layer of liquid paraffin to
exclude atmospheric oxygen
d) Fit a delivery tube as shown in figure below and allow it to dip into clear
limewater.

Observe the change that takes place in test tube containing, then explain the
bases of such change.

Without oxygen, pyruvate (pyruvic acid) is not metabolized by cellular respiration
but undergoes a process of fermentation. The pyruvate is not transported into
the mitochondrion, but it remains in the cytoplasm, where it is converted to
waste products like alcohol or lactic acid or other compounds depending on
the kind of cells that are active which may be removed from the cell. This serves
the purpose of oxidizing the electron carriers so that they can perform glycolysis
again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD+
so it can be re-used in glycolysis.

In the absence of oxygen, fermentation prevents the build-up of NADH in
the cytoplasm and provides NAD+ for glycolysis. This waste product varies
depending on the organism. In skeletal muscles, the waste product is lactic acid.
This type of fermentation is called lactic acid fermentation. In yeast and plants,
the waste products are ethanol and carbon dioxide. This type of fermentation is
known as alcoholic or ethanol fermentation. The ATP generated in this process
is made by substrate-level phosphorylation, which does not require oxygen.

Fermentation is less efficient at using the energy from glucose since only 2 ATP
are produced per glucose, compared to the 38 ATP per glucose produced by
aerobic respiration. This is because the waste products of fermentation still
contain plenty of energy. Glycolytic ATP, however, is created more quickly.

Due to the fact that anaerobic respiration produces only 2 ATP, the efficiency
of anaerobic respiration is less than that of aerobic respiration. It is calculated
as follows:

Efficiency of aerobic respiration = Energy required to make ATP x 100 Energy
released by oxidation of glucose 2 ATP x 7.3 Kcal x 100 687 Kcal =2%.

The production of a small yield of ATP from anaerobic respiration in yeast and
mammalian muscle tissue, including the concept of oxygen debt.

Standing still, the person absorbs oxygen at the resting rate of 0.2 dm³ min−1.
(This is a measure of the person’s metabolic rate.) When exercise begins,
more oxygen is needed to support aerobic respiration in the person’s muscles,
increasing the overall demand to 2.5 dm³ min−1. However, it takes four minutes for
the heart and lungs to meet this demand, and during this time lactic fermentation
occurs in the muscles. Thus the person builds up an oxygen deficit. For the next
three minutes, enough oxygen is supplied. When exercise stops, the person
continues to breathe deeply and absorb oxygen at a higher rate than when
at rest. This post-exercise uptake of extra oxygen, which is ‘paying back’ the
oxygen deficit, is called the oxygen debt.

The oxygen is needed for:
• Conversion of lactate to glycogen in the liver
• Re-oxygenation of haemoglobin in the blood
• A high metabolic rate, as many organs are operating at above resting
   levels.

The presence of the lactic acid is sometimes described as an “oxygen debt”.
This is because significant quantities of lactic acid can only be removed
reasonably quickly by combining with oxygen. However, the lactic acid was
only formed due to lack of sufficient oxygen to release the required energy to
the muscle tissue via aerobic respiration. Lactic acid can accumulate in muscle
tissue that continues to be over-worked. Eventually, so much lactic acid can
build-up that the muscle ceases working until the oxygen supply that it needs
has been replenished, this is called muscle cramps

To repay such an oxygen debt, the body must take in more oxygen in order to
get rid of the additional unwanted waste product lactic acid. Mineral depletion,
inadequate blood supply and Nerve compression can be the causes of muscle
cramps.

Application activity 2.9

1) Under which conditions can anaerobic respiration take place in animal
     cells?
2) Calculate the efficiency of anaerobic, when a complete oxidation of
     glucose produce the energy estimated at 200 Kcal under a production
    of a standard amount of ATP from ADP absorbed is about 7.3 Kcal

2.10 Factors which affect the rate of respiration

Activity 2.10

– Fill a small vacuum flask with beans grains or pea seeds that have
    been soaked for 24 hours and rinsed in 1% formaldehyde for 5
    minutes.
– Kill an equal quantity of soaked seeds by boiling them for 5 minutes.
– Cool the boiled seeds in cold tap water, rinse them formaldehyde for
    5 minutes as before and then put them in a vacuum flask of the same
    size as the first one.
– Place a thermometer in each flask so that its bulb is in the middle of
   the seeds.
– Plug the mouth of each flask with cotton wool and leave both flasks
   for 2 days, noting the thermometer readings whenever possible. Set
   it as follow:

a) What is the purpose of soaking seeds for 24 hours and in formaldehyde
    for 5 minutes.
b) Why do you need flask containing dead seeds?
c) Compare the temperature change in those two flasks and explain those
   changes.

Cellular respiration is the process of conversion of chemical energy stored in
the food to ATP or higher energy compounds. The factors that affect the cellular
respiration are:

a. Amount of nutrients
If the amount of nutrients is high, then the energy is high in the cellular respiration.
The nutrients which can go through cellular respiration and transform into

energy are fat, proteins and carbohydrates. The amount of nutrients available to
transform into energy depend upon the diet of the person.

b. Temperature
The rate of the cellular respiration increases if the body temperature is warmer.
The lower the temperature, the slower the rate of cellular respiration. The reason
for this is enzymes which are present in cellular respiration process. Enzyme
reactions require optimum temperatures.

c. State of the cell
Metabolically active cells such as neurons, root of human hair have higher
respiration rate than the dormant cells such as skin cells and bone cells. This is
because metabolically active cells can store energy in the body because of the
many metabolic reactions that take place in them.

d. Water
It is the medium where the reaction happens. When a cell is dehydrated the
respiration and other metabolism decreases.

e. Cellular activity
Some cells need more energy than others. For example, growing cells or very
active cells such as neurons need a lot of energy.

f. O₂ /CO₂ content
When there is high mount of O₂ and lower amount of CO₂ there is increase of the
rate of respiration. This is because oxygen is needed during aerobic respiration.

g. ATP/ADP range
When there is more ATP than ADP, respiration rate slows down to avoid excess
of ATP.

Application activity 2.10

1) Explain how proteins and lipids are metabolized for energy during
     respiration
2) Explain why the body does not use fats to produce energy as
    carbohydrates given that they produce much energy than carbohydrates.

2.11 Use of other substrates in respiration.

Activity 2.11

When someone has eaten carbohydrates such as cassava and sweet pota-
toes you do not feel hungry in the same time as another one who has con-
sumed milk or cheese.
1) Can you suggest the reason for this?
2) Which one can take a short time for digestion and why?

Carbohydrates are the first nutrients that most organisms can catabolize for
energy. In some cases, living things must be able to metabolize other energy-
rich nutrients to obtain energy in times of starvation. Most organisms possess
metabolic pathways that, when necessary, metabolize proteins, lipids. In each
case, the larger molecules are first digested into their component parts, which
the cell may reassemble into macromolecules for its own use. Otherwise, they
may be metabolized for energy by feeding into various parts of glycolysis or the
Krebs cycle

Carbohydrates, fats and proteins can all be used for cellular respiration.
Monomers of these foods enter glycolysis or the Krebs cycle at various points.
Glycolysis and the Krebs cycle are catabolic pathways through which all kinds
of food molecules are channeled to oxygen as their final acceptor of electrons.

Application activity 2.11

1) Explain how proteins and lipids are metabolized for energy during
     respiration
2) Explain why the body does not use fats to produce energy as
    carbohydrates given that they produce much energy than carbohydrates.

Skill lab 2

Fried breads are slices of bread that have been fried in oil or butter.
1) On a sheet of paper write down the ingredients used to make fried
    bread.
2) Write down all requirement to make fried bread.
3) Investigate the procedures and make your own fried bread according
    to that procedures investigated.
4) Compare your fried bread with the one sold in shops.
5) Present some samples to your teacher.

End unit assessment 2

1. Explain the reasons why chemical energy is the most important type of
    energy for living organisms.
2. Why do all organisms need energy and where does this energy come
   from?
3. Give the structure of ATP and specify its importance to living organisms?
4. The equation C₅₇H₁₀₄O₆ + 80O₂→ 57CO₂ + 52H₂O + Energy represents
   oxidation of lipids. Calculate RQ for this equation.
5. Calculate the total amount of energy produced for:
a) 3 moles of hydrolysed ATP
b) moles of synthesized ATP
c) 5 moles of decomposed glucose
6. Active mitochondria can be isolated from liver cells. If these mitochondria
are then incubated in a buffer solution containing a substrate, such as
succinate, dissolved oxygen will be used by mitochondria. The concentration
of dissolved oxygen in the buffer solution can be measured using an electrode.
When this experiment was done, the concentration of dissolved oxygen was
measured every minute for five minutes. Sodium azide (NaN3) which combines
with cytochromes and prevents electron transport was added thereafter. The
results are shown in the graph below.

a) Suggest what effect the addition of sodium azide will have on the
     production of ATP and give an explanation for your answer.
b) Explain why the concentration of oxygen decreased during the first
    five minutes.

c) Suggest what effect the addition of sodium azide will have on the
    production of ATP and give an explanation for your answer

7. During an experiment, the mouse was inside the bell jar. The air pipe from
the bell jar was connected to the first beaker containing lime water and filter
pump. The glass wool containing soda lime covered by a piece of paper was
connected to the second beaker by air pipe. Another air pipe was connected
from the second beaker containing lime water to the belly jar in the first step.
The set of the experiment looked like the following:

8. What are the major differences between cellular respiration and
    photosynthesis?
9. Compare aerobic respiration with anaerobic respiration or fermentation.
10. A student set up an experiment using germinating seeds and boiled seeds
     as shown in the diagram below:

a) State the objective of this experiment and the observation made after
24 hours?
b) Account for the observation made in (a) above?
c) Suggest why vacuum flasks were used in the experiment?
d) What was the purpose of the set-up B?
11) The diagram summarizes how glucose can be used to produce ATP,
without the use of oxygen

Which compounds are represented by the letters X, Y and Z?
12) Complete the table below: