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GRADE 12A: Biology 1
UNIT 12AB.1
15 hours
Biological energetics
About this unit
Previous learning
Resources
This unit is the first of seven units on biology for
Grade 12 advanced.
To meet the expectations of this unit, students should already be able to
describe the structural features of mitochondria and how these relate to the
chemical processes of respiration. They should know that ATP is the
immediate energy source in cellular processes and be able to relate this to
respiration. They should be able to outline the reaction steps in the
glycolysis, Krebs cycle and oxidative phosphorylation stages of respiration.
They should be able to describe the structural features of chloroplasts and
know how these relate to the chemical processes of photosynthesis. They
should know that ATP is the immediate energy source in cellular processes
and be able to relate this to photosynthesis. They should be able to outline
the reaction steps in the light-dependent and light-independent stages of
photosynthesis. They should be able to relate the structure of a plant leaf to
its function in photosynthesis and understand the factors limiting the rate of
photosynthesis.
The main resources needed for this unit are:
The unit is designed to guide your planning and
teaching of biology lessons. It provides a link
between the standards for science and your
lesson plans.
The teaching and learning activities should help
you to plan the content and pace of lessons.
Adapt the ideas to meet your students’ needs.
For consolidation activities, look at the scheme of
work for Grades 10A and 11A.
You can also supplement the activities with
appropriate tasks and exercises from your
school’s textbooks and other resources.
Introduce the unit to students by summarising
what they will learn and how this builds on earlier
work. Review the unit at the end, drawing out the
main learning points, links to other work and real
world applications.
Expectations
By the end of the unit, students understand the basic biochemistry of
anaerobic respiration and compare this with aerobic respiration. They know
the structure of ATP and ADP, the reactions in the three stages of aerobic
respiration and the role of NAD and ATP. They understand why aerobic and
anaerobic respiration yield different amounts of energy in the form of ATP.
They understand respiratory quotient and relate this to energy values of
respiratory substrates. They know the reactions in the two stages of
photosynthesis and the importance of the Calvin cycle. They know about
cyclic and non-cyclic photophosphorylation and the use of ATP in the lightindependent stage of photosynthesis. They know how carbon-14 has been
used to investigate photosynthesis. They understand the absorption
spectrum of chlorophyll and know that the pigments of chlorophyll can be
separated by chromatography.
Students who progress further have a more detailed knowledge and
deeper understanding of the biochemistry involved in the processes studied.
They know that there is more than one form of chlorophyll and that different
forms of chlorophyll have different absorption spectra. They understand the
principles of chromatography.
391 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
• overhead projector (OHP), whiteboard
• yeast culture, thermostatically controlled water baths
• video clip of a sprint race
• models of ATP, ADP and glucose
• photomicrographs of mitochondria
• sets of prepared cards (e.g. for glycolysis, Krebs cycle)
• Internet access
• model waterwheel or OHT diagram
• calorimeter
• cabbage, centrifuge, buffer solution, dichlorophenolindophenol
• chromatography paper and/or thin-layer plates
• hand spectrometer and strong light source
Key vocabulary and technical terms
Students should understand, use and spell correctly:
• anaerobic respiration, aerobic respiration
• glycolysis, the Krebs cycle, oxidative phosphorylation
• pyruvate, lactic acid, fermentation, oxygen debt
• NAD, FAD, ATP, chemiosmosis
• respiratory quotient
• light-dependent reactions, light-independent reactions
• cyclic photophosphorylation, non-cyclic photophosphorylation
• photolysis, NADP
• carbon-14
• absorption spectrum, action spectrum
• photosystems 1 and 2
• thylakoid membranes
• chlorophyll pigments
© Education Institute 2005
Objectives for the unit
15 hours
1 hour
Comparing
anaerobic with
aerobic respiration
1 hour
ATP: its structure,
function and
synthesis
1 hour
SUPPORTING STANDARDS
11A.5.1 Describe the structure of mitochondria
… and relate [this] to the biochemical
… reactions of respiration …
11A.6.1 Describe the role of ATP as the universal
energy currency in all living organisms
and relate this to respiration …
11A.6.2 Describe the reaction steps in the three
stages of aerobic respiration
(glycolysis, Krebs cycle and oxidative
phosphorylation), including the roles of
oxygen and ATP.
Biochemistry of
the light-dependent
reaction
2 hours
Biochemistry of the
light-independent
reaction
3 hours
Light and pigments
respiration differ from those of aerobic respiration and how anaerobic
respiration builds up an oxygen debt.
12A.5.2 Explain the structure and function of ADP and ATP and the synthesis of ATP
in the electron transport chain on the membranes of the mitochondria.
12A.5.3 Outline glycolysis as the phosphorylation of glucose and the subsequent
splitting of hexose phosphate (6C) into two triose phosphate molecules, which
are further oxidised with a small yield of ATP and reduced NAD.
12A.5.4 Explain that when oxygen is available, pyruvate is converted into acetyl coenzyme
12A.5.6 Explain the role of oxygen in the process of oxidative phosphorylation.
2 hours
1 hour
12A.5.1 Explain how the biochemistry, products and energy release of anaerobic
reactions in the matrix of the mitochondria that reconvert citrate to
oxaloacetate; explain the role of NAD.
The ‘link reaction’
and the Krebs cycle
Respiratory
quotients
EXTENSION STANDARDS
12A.5.5 Explain the Krebs cycle as a series of decarboxylation and dehydrogenation
2 hours
2 hours
CORE STANDARDS
Grade 12 standards
A (2C), which then combines with oxaloacetate (4C) to form citrate (6C).
Glycolysis
Oxidative
phosphorylation
Unit 12AB.1
12A.5.7 Explain respiratory quotient and the relative energy values of carbohydrates,
proteins and lipids as respiratory substrates.
11A.5.1 Describe the structure of …
chloroplasts and link [this] to the
biochemical and photochemical
reactions of … photosynthesis.
11A.6.1 Describe the role of ATP as the
12A.6.1 Explain that energy is transferred by the photoactivation of chlorophyll
resulting in the splitting of water molecules and the transfer of energy to ATP
and NADPH; that this involves cyclic and non-cyclic photophosphorylation;
that this generates hydrogen for the light-independent stage of the process;
that gaseous oxygen is produced.
universal energy currency in all living
organisms and relate this to …
photosynthesis.
11A.6.3 Describe the reaction steps in the light-
dependent and light-independent
stages of photosynthesis, including the
role of ATP.
12A.6.2 Explain that the Calvin cycle involves the light-independent fixation of carbon
dioxide by combination with RuBP (5C) to form two molecules of GP (3C), that
ATP and NADP are required for the reduction of GP to carbohydrate, and that
RuDP is regenerated.
12A.6.3 Describe how carbon-14 has been used to establish the biochemistry of
photosynthesis.
12A.6.4 Know that chlorophyll reflects green light and absorbs in the red and blue areas
of the spectrum, and that the pigments of chlorophyll can be separated by
chromatography.
392 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
© Education Institute 2005
Activities
Unit 12AB.1
Objectives
Possible teaching activities
1 hour
Introduce this topic by quizzing students on their knowledge of respiration by recalling earlier
work, such as that from Unit 11AB.1. Ask students such questions as:
Comparing anaerobic with
aerobic respiration
Explain how the biochemistry,
products and energy release
of anaerobic respiration differ
from those of aerobic
respiration and how
anaerobic respiration builds
up an oxygen debt.
Notes
School resources
Use this column to note
your own school’s
resources, e.g.
textbooks, worksheets.
• What is respiration?
• How does the body release the energy in food? And why does the process yield energy?
• Why does the body need energy?
Make sure students appreciate that food contains potential energy and the cell systematically
breaks down complex organic molecules that are rich in energy to simpler substances that have
less energy. Some of the energy released from food can be used to do work while the rest is
released as heat.
Ask students to write the word and formula equations for aerobic respiration in animals and
plants (recall from Standard 9.8.1). Help them, if necessary, to reproduce the correct equations.
Now ask them to explain what the process involves in the cell. Where does it occur? What
happens to the sugar, glucose? Try to establish that the glucose is completely oxidised to
carbon dioxide and water; compare the process with combustion. Ask them if they think the
same combustion process happens inside our cells? Establish that body temperature does not
support rapid combustion with oxygen but rather a slower enzyme-regulated process in which
the enzymes lower the activation energy (recall from Unit 10AB.3). Glucose is broken down
gradually, in a series of steps, with each step catalysed by a different enzyme. Show using an
OHT that a large amount of energy is released and one molecule of glucose yields in excess of
30 molecules of ATP.
Now compare the process of anaerobic respiration by asking students if they know whether
respiration can occur in the absence of oxygen. Prompt them with questions about what
happens to the body when you run very fast, and about fermentation. Show them the word and
formula equations for anaerobic respiration in animals and plants: lactic acid fermentation and
alcohol fermentation, respectively. Explain that most of the potential energy remains in the
organic molecules present at the end of the process (lactic acid in animals, alcohol in plants) –
the glucose molecule is incompletely oxidised and yields only two molecules of ATP in
anaerobic respiration. Also point out that the cell’s supply of the coenzyme NAD would run out
(and anaerobic respiration stop) unless there was a stage to regenerate it from NADH as, for
example, in the production of lactic acid by reduction of pyruvate.
Ask students to work in pairs to investigate the effect of temperature on the rate of fermentation
in yeast as follows. Use a yeast culture and thermostatically controlled water baths at 20 °C,
35 °C and 50 °C. Invert fermentation tubes full of yeast culture carefully into test-tubes
containing10 cm3 of yeast culture into each water bath. Record the length of the carbon dioxide
bubble within each fermentation tube at intervals of 10 minutes. Does the rate of fermentation
change? Most enzyme-controlled processes double in rate for each 10 °C rise in temperature.
Do the results confirm this general rule or not?
Enquiry skills 12A.1.3, 2A.1.4, 2A.3.1–2A.3.3.
Visit a bakery to see how fermentation is used in one of the earliest examples of biotechnology.
Visit opportunity: Visit a bakery.
393 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
© Education Institute 2005
Objectives
Possible teaching activities
Notes
School resources
Show students a video of a sprint race and discuss with the class why the athletes breathe
heavily for several minutes after the race. Discuss the development of an oxygen debt in the
cells, particularly in the muscles of the legs, and show a graph of how the sprint produces a
rapid oxygen debt which is repaid when the race is over. Discuss the fate of lactic acid
(eventually oxidised by liver).
Ask students to produce a chart displaying the reactions in anaerobic respiration. Establish
pyruvic acid (pyruvate) as the intermediate metabolite at the cross-roads of anaerobic and
aerobic respiration.
1 hour
ATP: its structure,
function and synthesis
Explain the structure and
function of ADP and ATP and
the synthesis of ATP in the
electron transport chain on
the membranes of the
mitochondria.
Ask students if they can tell you what ATP is. After establishing its full name and the fact that it is a
nucleotide, show a diagram on the OHP to compare it with ADP. Ask students what ATP does in
the cell. Confirm its status as the intermediary molecule in the cell between the energy-producing
reactions and energy-consuming reactions: it is the cell’s ‘energy currency’ molecule. The process
of cell respiration replenishes the ATP supply by powering the phosphorylation of ADP.
Show students models of ATP and ADP. Discuss the potential energy involved in the two
molecules and how they are interconvertible if inorganic phosphate is available.
Examine photomicrographs of mitochondria from different tissue cells (e.g. liver, skeletal
muscle). Ask students to measure them if a scale or magnification is provided.
Ask students to draw diagrams of the mitochondria and to find out the names of parts and what
their functions are.
Explain that ATP can be synthesised in two different ways: either by substrate-level
phosphorylation (in glycolysis and the Krebs cycle) or, mainly, by oxidative phosphorylation in
the electron transport chain. Show students a diagram of the crista (inner mitochondrial
membrane) with a portion showing the electron transport chain and the enzyme ATP synthase
and explain the chemiosmotic process of ATP synthesis. (See further details of chemiosmosis
in oxidative phosphorylation later.)
1 hour
Recall introductory work on the biochemistry of respiration (e.g. in Unit 11AB.1).
Glycolysis
Introduce the biochemistry by giving an overview of the whole process in outline so students
can appreciate that glycolysis is just the first stage of three main stages: glycolysis, the Krebs
cycle and oxidative phosphorylation. Ask students to find out where each of the stages occurs
in the cell.
Outline glycolysis as the
phosphorylation of glucose
and the subsequent splitting
of hexose phosphate (6C)
into two triose phosphate
molecules, which are further
oxidised with a small yield of
ATP and reduced NAD.
Prepare OHT diagrams.
Illustrate with a suitable electron microscope
picture.
Use a molecular model of glucose to demonstrate its structure while explaining glycolysis.
Tell students that the word glycolysis means ‘splitting of sugar’ and that is exactly what happens
in this pathway: the six-carbon sugar, glucose, is split into two three-carbon sugars. These
smaller sugars are then oxidised and the remaining atoms rearranged to form two molecules of
pyruvate. Show this on the OHP or build up on the whiteboard.
Give more details of glycolysis. Show that glucose must first be activated by two ATP molecules
which phosphorylate the glucose to hexose diphosphate (6C). This is then split into two triose
phosphate molecules. The trioses are then oxidised in an energy-yielding phase to produce two
molecules of pyruvate and four ATP molecules (but only two net, see above) and two reduced
NAD molecules.
394 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
© Education Institute 2005
Objectives
Possible teaching activities
Ask students to carry out a card-sort activity that requires them to put the intermediates of the
glycolytic pathway (e.g. glucose, glucose phosphate, ADP + Pi, NAD, ATP, hexose
diphosphate) in the correct order. Divide the class into two teams and challenge students to see
who can produce the quickest solution. The first team to finish may not win if they have taken
less care with accuracy.
2 hours
The ‘link reaction’ and the
Krebs cycle
Explain that when oxygen is
available, pyruvate is
converted into acetyl
coenzyme A (2C), which then
combines with oxaloacetate
(4C) to form citrate (6C).
Explain the Krebs cycle as a
series of decarboxylation and
dehydrogenation reactions in
the matrix of the mitochondria
that reconvert citrate to
oxaloacetate; explain the role
of NAD.
Notes
School resources
Prepare sets of cards for students to sort.
Tell students that when oxygen is present, the pyruvate enters the mitochondria for the aerobic
stages of respiration: the Krebs cycle and oxidative phosphorylation. The pyruvate still contains
most of the energy from the glucose.
Show students a summary diagram of the Krebs cycle, including the ‘link reaction’ from
pyruvate to acetyl coenzyme A. Give them a copy. Ask them to study what is happening and
then ask one student to explain the link reaction (this is the junction between glycolysis and the
Krebs cycle). Make sure students know that this is the first step in aerobic respiration where
CO2 is released. The pyruvate is also oxidised (NAD+ is reduced to NADH) to an acetyl group
and combined with a coenzyme, coenzyme A, to activate the remaining molecule to acetyl
coenzyme A. The acetyl coenzyme A then feeds its two-carbon molecule into the Krebs cycle
by adding to the four-carbon compound oxaloacetate to form the six-carbon citrate.
Prepare OHT diagram and copies for students.
Ask students to find out about coenzymes using the Internet.
ICT opportunity: Use of the Internet.
Ask students, in turn, to tell the rest of the class something about the reactions in the Krebs
cycle (e.g. eight steps; take place in mitochondrial matrix; each involving a specific enzyme;
reactions include a sequence of decarboxylations and dehydrogenations; oxidation of the
organic acids in the cycle results from production of reduced coenzymes: NADH and FADH;
production of ATP by substrate phosphorylation; oxaloacetate is regenerated, which can then
accept another two-carbon acetyl coenzyme A for another turn of the cycle).
Ask students to summarise the total numbers of CO2, NADH and FADH molecules produced in
one turn of the Krebs cycle, including the link reaction, starting from pyruvate (three CO2, four
NADH and one FADH from each pyruvate molecule).
Ask students what has been the fate of each pyruvate? (They have been oxidised to release
three CO2 and reduced coenzymes, as above.)
Ask students to carry out a card-sort activity that requires them to put the intermediates of the
Krebs cycle in the correct order. Divide the class into two teams and challenge students to see
who can produce the quickest solution. The first team to finish may not win if they have taken
less care with accuracy.
Prepare sets of cards for students to sort.
Encourage students to find out about Hans Krebs and why a series of reactions is named after
him.
ICT opportunity: Use of the Internet.
395 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
© Education Institute 2005
Objectives
Possible teaching activities
2 hours
Ask students where the energy that was in the pyruvate molecule has gone (most is still in the
reduced coenzymes).
Oxidative phosphorylation
Explain the role of oxygen in
the process of oxidative
phosphorylation.
Notes
School resources
Ask students how much energy in the form of ATP molecules has been produced from the
original glucose molecule (four by substrate-level phosphorylation: two from glycolysis and two
from the Krebs cycle).
Tell students that the final stage of aerobic respiration is oxidative phosphorylation which,
coupled to the electron transport chain, powers the production of most of the ATP molecules
produced in respiration.
This is a difficult concept for students to understand; using the following waterfall analogy may
help. Show students, on the OHP or board, a diagram of a series of waterfalls with water
flowing. Now add the ‘inflowing molecules’ (NADH) and show by arrows the downward flow of
molecules to the next level (FADH) and then further arrows down to other molecules in turn,
such as cytochromes b, then c and then a, and finally, at the very bottom, oxygen.
Prepare a suitable OHT diagram, or use a
model.
The above analogy can illustrate the gradual release of energy that the real electron transport
chain achieves by being arranged sequentially in the inner mitochondrial membrane at
successively lower energy levels.
Ask students how the mitochondrion couples this (electron transport) process to ATP synthesis.
The answer is a mechanism called chemiosmosis.
Show students a diagram of the crista (inner mitochondrial membrane) with a portion showing
the electron transport chain and the membrane protein, the enzyme ATP synthase, and explain
the chemiosmotic process of ATP synthesis. (Explain how an ion gradient of H+ is created by
the electron chain pumping H+ into the intermembrane space. The H+ then diffuses down the
proton gradient through the membrane protein channels, which are protein complexes called
ATP synthases, and this ‘fall’ of H+ drives the phosphorylation of ADP to ATP.)
Prepare an OHT diagram.
Ask students what the relationship is between the reduced coenzymes NADH and FADH and
the number of ATP molecules produced (each NADH that enters the electron transport chain
generates a maximum of three ATP molecules and each FADH, with less energy, produces a
maximum of two ATP molecules).
Ask students to use their textbook or the Internet to find information on energy production and
then to work out the total energy production (as ATP molecules) from one glucose molecule.
Ask them to draw up a summary table to show where all the energy-containing molecules
(NADH, FADH, ATP) are produced. Compare aerobic and anaerobic ATP yields.
ICT opportunity: Use of the Internet.
They should arrive at a figure of around 36 ATP molecules produced during aerobic respiration.
(The ‘mitochondrial shunt’ or ‘shuttle’ has to be taken into account, in which the two NADH
molecules from glycolysis enter the mitochondria but, because of some losses, these produce
an average of four ATP molecules and not the expected six ATP from oxidative
phosphorylation.)
A figure of just two ATP molecules produced during anaerobic respiration shows that aerobic
respiration yields 18 times more ATP than fermentation.
Ask students to produce a wall chart of the biochemistry of respiration.
396 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
Enquiry skill 12A.3.4
© Education Institute 2005
Objectives
Possible teaching activities
2 hours
Ask students whether glucose is the sole substrate in respiration. Their answers should indicate
that lipids and even proteins can act as substrates as well as other carbohydrates.
Respiratory quotients
Explain respiratory quotient
and the relative energy
values of carbohydrates,
proteins and lipids as
respiratory substrates.
Notes
Ask students to find out the energy value of different respiratory substrates from their textbook
or from the library or Internet.
ICT opportunity: Use of the Internet.
Demonstrate how the energy value of a substrate is determined by burning a known mass of
the substance in pure oxygen in a calorimeter. Knowledge of the calorimeter’s water equivalent
will be required to carry out the calculation. Record the temperature at the start and when it
reaches its maximum, and use these to calculate the substrate’s energy content. Use different
substrates and compare the values. The values obtained may be significantly less than given in
the official tables. Ask students to explain. The loss of heat to the surroundings is the main
reason for the difference.
Use a simple calorimeter with a supply of
oxygen
School resources
Enquiry skills 12A.1.1, 12A.3.1, 12A.3.3
Ask students to write down the simple equation for the aerobic respiration of glucose:
C6H12O6 + 6O2  6CO2 + 6H2O + energy
Ask them to work out the ratio of O2 taken in to the volume of CO2 released; a ratio of 1:1 is
produced by 6CO2 given out compared with 6O2 taken in. However, different substrates will give
different ratios of the volumes of oxygen used and carbon dioxide given off. Measuring this ratio
produces the respiratory quotient (RQ) and this indicates what substrate is being used in
respiration. Ask students what the RQ of glucose is (6/6 = 1.0).
The aerobic respiration of the fatty acid oleic acid produces the following equation:
C18H34O2 + 25.5O2  18CO2 + 17H2O + energy
Ask students to work out its RQ (18/25.5 = 0.7).
Ask students what happens to the RQ when the respiration is anaerobic.
C6H12O6  2C2H5OH + 2CO2 + energy
(RQ = 2/0 = infinity, although in reality some respiration is likely to be aerobic so a small volume
of O2 will be taken up so the RQ will be above 2.)
1 hour
Biochemistry of the light
dependent reaction
Explain that energy is
transferred by the
photoactivation of chlorophyll
resulting in the splitting of water
molecules and the transfer of
energy to ATP and NADPH;
that this involves cyclic and noncyclic photophosphorylation;
that this generates hydrogen for
the light-independent stage of
the process; that gaseous
oxygen is produced.
Ask students to use the Internet to find out about the work of Robert Hill at Cambridge on
chloroplasts and C.B. van Niel at Stanford University on photosynthesis in bacteria.
ICT opportunity: Use of the Internet.
Enquiry skill 12A.2.1
Describe the discovery by Robert Hill that isolated chloroplasts can evolve oxygen if provided
with light, water and a suitable hydrogen acceptor. Ask students what conclusions can be drawn
from this ‘Hill reaction’.
The possible conclusions are:
• oxygen production requires light;
• oxygen comes from water and not from carbon dioxide;
• chloroplasts can produce oxygen without other cell components;
• a hydrogen acceptor molecule is needed.
Ask students what happens to water in this light-dependent reaction.
The answer is that chloroplasts split water molecules using light energy (photolysis) and so the
simple equation for photosynthesis that suggests carbon dioxide as the source of oxygen needs
to be rewritten.
397 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
© Education Institute 2005
Objectives
Possible teaching activities
Notes
School resources
To describe the reaction steps, use an OHT or whiteboard to illustrate:
• how the absorption of light affects the photosynthetic pigments, especially chlorophyll;
• that, in the thylakoid membranes of the chloroplast, electrons from the two chlorophyll
photosystems are each raised to a higher energy level.
During the light reactions there are two possible routes for electron flow: a cyclic route and a
non-cyclic route, which both result in photophosphorylation.
Ask students to produce a flow chart of the processes of:
• cyclic photophosphorylation;
• non-cyclic photophosphorylation.
Cyclic photophosphorylation
Explain that this is the simpler pathway and involves only photosystem 1 and produces only
ATP.
The electrons from the photoactivated chlorophyll molecule from photosystem 1 are passed
along the electron transport chain in the thylakoid membrane, during which energy is released
and used to synthesise ATP from ADP and inorganic phosphate (very similar to chemiosmosis
in mitochondria explained earlier in this unit). This process is known as cyclic
photophosphorylation since the same electrons that left the chlorophyll return to it again.
Non-cyclic photophosphorylation
Explain that this electron pathway involves the cooperation of both photosystems (in the familiar
‘Z scheme’) and results in the production of both ATP and NADPH, as well as the release of O2.
The electrons from the photoactivated chlorophyll molecule from photosystem 1 are captured by
an electron acceptor and used to reduce NADP. Electrons from the photoactivated chlorophyll
molecule from photosystem 2 are used to stabilise photosystem 1 and produce ATP by passing
along the same electron path as described in the non-cyclic path above.
The photosystem 2 chlorophyll’s lost electrons are replaced by those from the splitting of water
(photolysis), resulting in the release of oxygen gas and hydrogen ions. The electrons that have
passed along the electron transport chain are used, together with the hydrogen ions, to reduce
NADP to NADPH.
Demonstrate the Hill reaction by the following procedure (or ask small groups of students to
carry out the procedure). Extract chloroplasts from cabbage leaves and isolate them. Then add
them to the blue dye DCPIP (dichlorophenol-indophenol), expose the mixture to light and note
the change of colour from blue to colourless. This occurs because the blue dye is readily
reduced to a colourless compound by reducing agents.
398 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
You will need dark green leaves (e.g. cabbage
leaves), chilled sucrose/phosphate buffer at
pH 6.5, and a bench centrifuge.
Enquiry skills 12A.1.3, 12A.4.1
© Education Institute 2005
Objectives
Possible teaching activities
2 hours
Use the OHP or board to outline the light-independent reactions that take place in the stroma of
the chloroplasts. Carbon dioxide from the atmosphere is fixed using ATP and reduced NADP
from the light-dependent reaction. Carbon dioxide is reduced to carbohydrate.
Biochemistry of the light
independent reaction
Explain that the Calvin cycle
involves the light-independent
fixation of carbon dioxide by
combination with RuBP (5C)
to form two molecules of GP
(3C), that ATP and NADP are
required for the reduction of
GP to carbohydrate, and that
RuDP is regenerated.
Describe how carbon-14 has
been used to establish the
biochemistry of
photosynthesis.
Ask students to investigate on the Internet how Melvin Calvin helped contribute to our
understanding of photosynthesis.
Notes
School resources
ICT opportunity: Use of the Internet.
Teach students about the experimental investigations carried out by Calvin as follows.
• Use the OHP to show students Calvin’s ‘lollipop’ apparatus, which he used to feed singlecelled algae carbon-14 labelled carbon dioxide for progressively longer light periods.
Prepare suitable OHTs.
• Use the OHP to show students Calvin’s two-dimensional chromatography technique
separating the carbon-14 labelled products and developed to display a radiochromatogram.
• Ask students to work in pairs to arrange a set of cards in the correct sequence displaying the
events of the Calvin cycle. Each card should have only a single reaction described or a single
chemical intermediate or even enzyme named (e.g. ribulose bisphosphate carboxylase – the
commonest enzyme in the world). Begin by using a simple set of cards showing just the
number of carbon atoms in each compound rather than names of compounds. Then add
more detailed cards for more advanced students as required.
Write out sets of suitable cards: a simple set and
a more complex set.
• Create a set of OHT cutout shapes of the events of the Calvin cycle, as described above, and
build the cycle up sequentially on the OHP, with a logical progression and explanation.
• Provide students with a template of the Calvin cycle with blank boxes to be filled with the
names of the intermediates. Either ask students to complete the exercise from their own
research or use the template in conjunction with the card activity above.
Prepare OHT cutout shapes of Calvin cycle
components.
Prepare a Calvin cycle template.
Ask students to identify the way that the light-dependent reaction helps the light-independent
reaction (through ATP and reduced NADP).
3 hours
Light and pigments
Know that chlorophyll reflects
green light and absorbs in the
red and blue areas of the
spectrum, and that the
pigments of chlorophyll can
be separated by
chromatography.
Ask students to work in pairs to extract the pigments from leaves and carry out a leaf pigment
separation and identification by a chromatographic technique. This could be either
• paper chromatography
Students will need chromatography paper or
previously made up thin-layer plates of silica gel
on microscope slides.
or
• thin-layer chromatography.
Demonstrate the absorption of light by plant pigments by shining a light through a solution of the
pigments and observing the transmitted light using a spectrometer (red and blue spectral
regions may appear black but the green region will be seen clearly because this is not absorbed
but reflected).
You will need a hand-held spectrometer.
Show students an OHT of an absorption spectrum of the plant pigments and ask them to
explain its shape.
Prepare OHTs of an absorption spectrum and
an action spectrum for photosynthesis.
Show students an action spectrum of photosynthesis and ask them to explain its shape.
Demonstrate fluorescence. Shine a strong light onto a tube of extracted pigment and turn all the
lights out; the chlorophyll solution will fluoresce deep red in the darkened room.
399 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
Use a projector lamp as the strong light source.
© Education Institute 2005
Assessment
Examples of assessment tasks and questions
Assessment
Explain what the term oxygen debt means and how such a debt is produced.
Set up activities that allow
students to demonstrate what
they have learned in this unit.
The activities can be provided
informally or formally during
and at the end of the unit, or
for homework. They can be
selected from the teaching
activities or can be new
experiences. Choose tasks
and questions from the
examples to incorporate in
the activities.
a. Explain the process of glycolysis and lactic acid production.
Unit 12AB.1
Notes
School resources
b. What is the fate of lactic acid when aerobic conditions return?
Calculate the number of reduced NAD and FAD molecules produced by each glucose molecule
entering the respiratory pathway when oxygen is available.
Explain how ATP is produced by electron transport and oxidative phosphorylation.
Explain the processes of:
a. cyclic photophosphorylation;
b. non-cyclic photophosphorylation.
a. Complete the spaces in the diagram of the Calvin cycle.
b. Explain how the reactions of the light-dependent stage help the reactions of the lightindependent stage of photosynthesis.
400 | Qatar science scheme of work | Grade 12 advanced | Unit 12AB.1 | Biology 1
Provide a suitable diagram of the Calvin cycle to
be completed by students.
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