ib photosynthesis with standards. 3.8.1 state that photosynthesis involves the conversion of light...

IB PhotosynthesisIB Photosynthesis

With StandardsWith Standards

3.8.1 State that photosynthesis 3.8.1 State that photosynthesis involves the conversion of light involves the conversion of light energy into chemical energy. energy into chemical energy.

State means to give a specific name, value or other brief answer without explanation or calculation.

Location: chloroplast or prokaryotic Location: chloroplast or prokaryotic equivalent. equivalent.

Reaction: Traps light energy Reaction: Traps light energy (photons) and converts it into (photons) and converts it into chemical energy.chemical energy.

Organisms: Prokaryotic and Organisms: Prokaryotic and EukaryoticEukaryotic

Substrate: Inorganic CO2 and H2OSubstrate: Inorganic CO2 and H2O Products: Organic compounds Products: Organic compounds

(sugars) and O2(sugars) and O2

Environments:Environments:

Aquatic environments with lightAquatic environments with light Terrestrial environments with lightTerrestrial environments with light Extremophiles can do photosynthesis at Extremophiles can do photosynthesis at

some extreme latitudes and altitudes. At some extreme latitudes and altitudes. At extreme high temperatures we see extreme high temperatures we see photosynthesis in geothermal active photosynthesis in geothermal active regions.regions.

3.8.2 State that light from the Sun 3.8.2 State that light from the Sun is composed of a range of is composed of a range of

wavelengths (colours). wavelengths (colours).


Light from the sun is composed of a range Light from the sun is composed of a range of wavelengths (colours).of wavelengths (colours).

The visible spectrum illustrates the The visible spectrum illustrates the wavelengths and associated colour of wavelengths and associated colour of light.light.

Combined together these wavelengths Combined together these wavelengths give the 'white' light we associate with full give the 'white' light we associate with full sunlight. sunlight.

The shortest wavelengths are the 'blues' The shortest wavelengths are the 'blues' which have more energy.which have more energy.

The longer wavelengths are the 'reds' The longer wavelengths are the 'reds' which have less energy.which have less energy.

3.8.3 State that chlorophyll is the 3.8.3 State that chlorophyll is the main photosynthetic pigment. main photosynthetic pigment.


Chlorophyll is the main Chlorophyll is the main photosynthetic pigment. photosynthetic pigment. This is where This is where light energy is trapped and turned into light energy is trapped and turned into chemical energy. chemical energy.

The head of the molecule is polar and The head of the molecule is polar and composed of a ring structure. At the heart composed of a ring structure. At the heart of this ring structure is the inorganic ion of this ring structure is the inorganic ion magnesium. This is the light trapping magnesium. This is the light trapping region of the chlorophyll molecule. region of the chlorophyll molecule.

The tail of the molecule is non polar and The tail of the molecule is non polar and embeds itself in membranes in the embeds itself in membranes in the chloroplast. chloroplast.

There are other pigments, reds, yellows There are other pigments, reds, yellows and browns but these are only usually and browns but these are only usually seen in the experimental chromatography seen in the experimental chromatography or the autumnal colours of deciduous or the autumnal colours of deciduous trees in a temperate climate. trees in a temperate climate.

3.8.4 Outline the differences in 3.8.4 Outline the differences in absorption of red, blue and green absorption of red, blue and green

light by chlorophyll.light by chlorophyll.

Outline means to give a brief account or summary

The 'peaks' show which wavelength of The 'peaks' show which wavelength of light are being absorbed.light are being absorbed.

Look at the x-axis for colours of light Look at the x-axis for colours of light absorbed at the 'peaks'.absorbed at the 'peaks'.

The main colour of light absorbed The main colour of light absorbed by chlorophyll is red and blue.by chlorophyll is red and blue.

The main colour reflected (not The main colour reflected (not absorbed) is green. absorbed) is green.

Hence why so many plants are seen Hence why so many plants are seen as green, the light is reflected from as green, the light is reflected from the chlorophyll to your eye.the chlorophyll to your eye.

3.8.5 State that light energy is used 3.8.5 State that light energy is used to produce ATP, and to split water to produce ATP, and to split water

molecules (photolysis) to form molecules (photolysis) to form oxygen and hydrogen.oxygen and hydrogen.


(a) Light is absorbed by (a) Light is absorbed by chlorophyll molecules (green) chlorophyll molecules (green) on membranes inside the on membranes inside the chloroplast. chloroplast.

This is the light trapping stage This is the light trapping stage in which photons of light are in which photons of light are absorbed by the chlorophyll absorbed by the chlorophyll and turned into chemical and turned into chemical energy (electrons). energy (electrons).

(b) The chemical energy (b) The chemical energy (electrons) is trapped in (electrons) is trapped in making ATP.making ATP.

Photolysis(c):Photolysis(c): Water used in photosynthesis Water used in photosynthesis

is split which provides:is split which provides: Hydrogen for the formation of Hydrogen for the formation of

organic molecules. (Corganic molecules. (C66HH1212OO66) ) Oxygen gas is given off.Oxygen gas is given off.

3.8.6 State that ATP and hydrogen 3.8.6 State that ATP and hydrogen (derived from the photolysis of (derived from the photolysis of water) are used to fix carbon water) are used to fix carbon

dioxide to make organicdioxide to make organicmolecules.molecules.


H+ from the splitting of water are combined with H+ from the splitting of water are combined with carbon dioxide to form organic compounds like carbon dioxide to form organic compounds like sugar. sugar.

Bonds are formed between the carbon, hydrogen Bonds are formed between the carbon, hydrogen and oxygen using the energy from ATP (which and oxygen using the energy from ATP (which came form the sun).came form the sun).

C, H, O are enough to form lipids and C, H, O are enough to form lipids and carbohydrates.carbohydrates.

With a Nitrogen source amino acids and therefore With a Nitrogen source amino acids and therefore proteins can be made.proteins can be made.

Plants have this remarkable ability to Plants have this remarkable ability to manufactory all their own organic molecules and manufactory all their own organic molecules and by definition all the basic organic molecules by definition all the basic organic molecules required by all life forms.required by all life forms.

3.8.7 Explain that the rate of 3.8.7 Explain that the rate of photosynthesis can be measured photosynthesis can be measured

directly by the production of oxygen directly by the production of oxygen or the uptake of carbon dioxide, or or the uptake of carbon dioxide, or

indirectly by an increase in indirectly by an increase in biomass. biomass.

Explain means to give a detailed account of causes, reasons or mechanisms.

Processes like photosynthesis and Processes like photosynthesis and respiration can be measured by either:respiration can be measured by either:

Depletion of substrate.Depletion of substrate. Accumulation of products Accumulation of products InvestigationInvestigation: Photosynthesis: : Photosynthesis: Carbon dioxide + water ---> Organic molecule + OxygenCarbon dioxide + water ---> Organic molecule + Oxygen The rate of photosynthesis can therefore be measured The rate of photosynthesis can therefore be measured

by:by: Depletion of substrateDepletion of substrate which includes measuring which includes measuring

how much carbon dioxide has been used or how much how much carbon dioxide has been used or how much water is used.water is used.

Accumulation of productAccumulation of product which might include which might include measuring how much oxygen is produced or organic measuring how much oxygen is produced or organic molecules (biomass) produced.molecules (biomass) produced.

In this simple experiment the accumulation of In this simple experiment the accumulation of oxygen is measure of rate of reaction.oxygen is measure of rate of reaction.

Independent variable: Light Intensity or wavelength Independent variable: Light Intensity or wavelength of light.of light.

Dependent variable O2 vol. against timeDependent variable O2 vol. against time Method the collection of gas over water.Method the collection of gas over water. Specimen: Pond weed ElodeaSpecimen: Pond weed Elodea

3.8.8 Outline the effects of 3.8.8 Outline the effects of temperature, light intensity and temperature, light intensity and

carbon dioxide concentration on the carbon dioxide concentration on the rate of photosynthesis rate of photosynthesis

Outline means to give a brief account or summary.

The effect of temperature on the The effect of temperature on the rate of photosynthesis:rate of photosynthesis:

Photosynthesis is a biological reaction and like all Photosynthesis is a biological reaction and like all other such reactions there are steps that require other such reactions there are steps that require the presence of enzymes.the presence of enzymes.

Temperature as we have already met is a change in Temperature as we have already met is a change in the average kinetic energy of the particle. the average kinetic energy of the particle.

The graph the left should look familiar as this is the The graph the left should look familiar as this is the same one covered in the section on the effect of same one covered in the section on the effect of temperature on the rate of an enzyme catalysed temperature on the rate of an enzyme catalysed reaction. reaction.

(a) Increasing rate of photosynthesis as the kinetic (a) Increasing rate of photosynthesis as the kinetic energy of reactants increases.energy of reactants increases.

(b) Maximum rate of reaction of photosynthesis at (b) Maximum rate of reaction of photosynthesis at the 'optimal' temperature.the 'optimal' temperature.

(c) Decrease in rate of photosynthesis as the (c) Decrease in rate of photosynthesis as the enzymes become unstable and denature.enzymes become unstable and denature.

The effect of carbon dioxide concentration The effect of carbon dioxide concentration on the rate of photosynthesison the rate of photosynthesis

Carbon dioxide is one of the reactants of the Carbon dioxide is one of the reactants of the reaction so this graph is very much like the effect of reaction so this graph is very much like the effect of substrate on the rate of reaction. substrate on the rate of reaction.

(a) O2 is used up as the plant is not (a) O2 is used up as the plant is not photosynthesizing but only respiring.photosynthesizing but only respiring.

(b) As the concentration of the carbon dioxide (b) As the concentration of the carbon dioxide (substrate) increases the rate of reaction increases. (substrate) increases the rate of reaction increases.

(c) The atmospheric levels of carbon dioxide and the (c) The atmospheric levels of carbon dioxide and the associate rate photosynthesis.associate rate photosynthesis.

(d) Maximum rate of photosynthesis (see section e). (d) Maximum rate of photosynthesis (see section e). (e) The is a range of values for different plants (e) The is a range of values for different plants

reaching their saturation level with carbon dioxide. reaching their saturation level with carbon dioxide. One the saturation level has been reached there is One the saturation level has been reached there is no further increase in the rate of photosynthesisno further increase in the rate of photosynthesis

The effect of light concentration on The effect of light concentration on the rate of photosynthesis the rate of photosynthesis

The effect of light intensity on the rate of reaction.The effect of light intensity on the rate of reaction. Light energy absorbed by chlorophyll is converted to Light energy absorbed by chlorophyll is converted to

ATP and H+ see section 3.8.5.ATP and H+ see section 3.8.5. At very low light levels (a) the plant will be respiring At very low light levels (a) the plant will be respiring

only not photosynthesizing.only not photosynthesizing. As the light intensity increases then the rate of As the light intensity increases then the rate of

photosynthesis increases.photosynthesis increases. At high light intensities the rate becomes constant, At high light intensities the rate becomes constant,

even with further increases in light intensity there even with further increases in light intensity there are no increases in the rate.are no increases in the rate.

The plant is unable to harvest the light at these high The plant is unable to harvest the light at these high intensities and indeed the chlorophyll system can be intensities and indeed the chlorophyll system can be damaged by very intense light levels.damaged by very intense light levels.

8.2.1 Draw and label a diagram 8.2.1 Draw and label a diagram showing the structure of a showing the structure of a

chloroplast as seen in electron chloroplast as seen in electron micrographs. micrographs.

Draw means to represent by means of pencil lines

(a) Cell wall(a) Cell wall (b) Double membrane(b) Double membrane (c) Starch grain(c) Starch grain (d) Grana(d) Grana (e) Thylakoid(e) Thylakoid (f) Stroma (f) Stroma

Internal membranes called thylakoids Internal membranes called thylakoids which is the location of the light dependent which is the location of the light dependent reaction reaction

Stroma surrounding the thylakoids and Stroma surrounding the thylakoids and inside the double membrane. This is the inside the double membrane. This is the location of the light independent reaction location of the light independent reaction that includes the Calvin cycle. that includes the Calvin cycle.

The stroma often contains starch grains The stroma often contains starch grains and oil droplets both products of and oil droplets both products of photosynthesisphotosynthesis

8.2.2 8.2.2 State that photosynthesis State that photosynthesis consists of light-dependent and consists of light-dependent and light-independent reactions. light-independent reactions.


Light Dependent ReactionLight Dependent Reaction

Energy of sun is trapped by chlorophyll molecules Energy of sun is trapped by chlorophyll molecules (oxidation) (oxidation)

Photon energy is used to raise the energy of Photon energy is used to raise the energy of electrons which escape the chlorophyll (oxidation)electrons which escape the chlorophyll (oxidation)

This energy is coupled to the reduction of ADP to This energy is coupled to the reduction of ADP to ATP and the coenzyme NADP+ is reduced to ATP and the coenzyme NADP+ is reduced to NADPH + H+ . NADPH + H+ .

The reaction must have light to take place. The reaction must have light to take place. This reaction takes place on the thylakoid This reaction takes place on the thylakoid

membranes. membranes.

Light Independent ReactionLight Independent Reaction

Uses the chemical energy from the Uses the chemical energy from the LDR to fix atmospheric carbon into LDR to fix atmospheric carbon into organic molecules such as glucose. organic molecules such as glucose.

The process does not require light The process does not require light and can occur in both the light and and can occur in both the light and dark periods. dark periods.

This reaction takes place in the This reaction takes place in the stroma stroma

8.2.3 8.2.3 Explain the light-Explain the light-dependent reactions. dependent reactions.

Explain means give a detailed account of causes, reasons or mechanisms.

Light energy is converted into chemical energy. Light energy is converted into chemical energy. Chlorophyll molecules are attached to the thylakoid Chlorophyll molecules are attached to the thylakoid

membranes.membranes.

They are often associated with accessory pigments They are often associated with accessory pigments and other proteins to form and other proteins to form Photosystem.Photosystem.

At the centre of all photosystem are forms of At the centre of all photosystem are forms of chlorophyll achlorophyll a each of which is specialised to absorb each of which is specialised to absorb a particular wavelength of light.a particular wavelength of light.

Electrons within the chlorophyll absorb the energy Electrons within the chlorophyll absorb the energy from photons and this raises them to higher 'excited' from photons and this raises them to higher 'excited' states.states.

Excited electrons are more easily lost from the Excited electrons are more easily lost from the chlorophyll which is a form of oxidationchlorophyll which is a form of oxidation

Summary of Non-Cyclic Summary of Non-Cyclic Photophosphorylation:Photophosphorylation:

1. Light energy is 1. Light energy is trapped in two trapped in two Photosystem.Photosystem.

2. ATP is 2. ATP is produced.produced.

3. The co-enzyme 3. The co-enzyme

NADP+is reducedNADP+is reduced

1) PS II absorbs light at a peak of 680 nm 1) PS II absorbs light at a peak of 680 nm 2) Electrons in chlorophyll are 'excited' and raised to the next 2) Electrons in chlorophyll are 'excited' and raised to the next

energy level.energy level. 3) Electrons are lost (oxidation) from PS II and picked up by 3) Electrons are lost (oxidation) from PS II and picked up by

acceptors like cytochromeacceptors like cytochrome 4) The electrons transfer to other membrane proteins releases 4) The electrons transfer to other membrane proteins releases

free energy in pumping H+into the thylakoid space which in turn free energy in pumping H+into the thylakoid space which in turn birng about the synthesis of ATP birng about the synthesis of ATP

5) The electron is taken up by PS I reducing this back to ground 5) The electron is taken up by PS I reducing this back to ground state.state.

6) PS I has already absorbed lower energy electrons 700nm and 6) PS I has already absorbed lower energy electrons 700nm and released electrons at the more 'excited' higher energy level.released electrons at the more 'excited' higher energy level.

7) The electron is passed in a series of redox reactions along 7) The electron is passed in a series of redox reactions along membrane proteins.membrane proteins.

8) Free energy released is coupled to the reduction of co-enzyme 8) Free energy released is coupled to the reduction of co-enzyme NADP+NADP+ Cyclic Photophosphorylation

Cyclic PhotophosphorylationCyclic Photophosphorylation

When the ratio of NADPH + H+: When the ratio of NADPH + H+: NADP+ is high then only ATP is NADP+ is high then only ATP is produced in a cyclic process.produced in a cyclic process.

PS I does not generate NADPH + H+ PS I does not generate NADPH + H+ but sends its 'excited' electron to a but sends its 'excited' electron to a proton pump.proton pump.

1. PS I is oxidised releasing an 'excited' electron.1. PS I is oxidised releasing an 'excited' electron. 2. The electron reduces the membrane proton 2. The electron reduces the membrane proton

pump. Protons are pumped into the thylakoid pump. Protons are pumped into the thylakoid space. This generates ATP.space. This generates ATP.

3. The electrons are cycled back to PS I for its 3. The electrons are cycled back to PS I for its own reduction.own reduction.

8.2.4 8.2.4 Explain Explain photophosphorylation in terms photophosphorylation in terms

of chemiosmosis of chemiosmosis State that State that photosynthesis involves the photosynthesis involves the

conversion of light energy into conversion of light energy into chemical energy. chemical energy.


Chemiosmosis theory is based Chemiosmosis theory is based on:on:

Accumulation of a high concentration of H+ which Accumulation of a high concentration of H+ which is due to proton pumping.is due to proton pumping.

There being a concentration difference between There being a concentration difference between two places which is the high concentration of two places which is the high concentration of H+in the thylakoid space and a lower H+in the thylakoid space and a lower concentration in the stroma. concentration in the stroma.

The protons diffuse through the core of the ATP The protons diffuse through the core of the ATP synthetase.synthetase.

This drives the motor mechanism of the structure This drives the motor mechanism of the structure resulting the in the reduction of ADP to ATP.resulting the in the reduction of ADP to ATP.

Note how the same mechanism was seen on the Note how the same mechanism was seen on the cristae membranes in respiration.cristae membranes in respiration.

8.2.5 Light-Independent Reaction8.2.5 Light-Independent Reaction

The energy trapped from sunlight in the The energy trapped from sunlight in the light dependent reaction (ATP and NADPH) light dependent reaction (ATP and NADPH) is used to fix carbon from carbon dioxide is used to fix carbon from carbon dioxide into organic molecules.into organic molecules.

The reaction called the Calvin Cycle takes The reaction called the Calvin Cycle takes place in the stroma and is controlled by place in the stroma and is controlled by enzymes. enzymes.

Ribulose Bisphosphate Carboxylase Ribulose Bisphosphate Carboxylase (Rubisco) allows carbon (carbon dioxide) (Rubisco) allows carbon (carbon dioxide) to be fixed into an initial organic molecule to be fixed into an initial organic molecule

Carbon FixationCarbon Fixation

The single carbon in carbon dioxide is first The single carbon in carbon dioxide is first trapped by Ribulose bisphosphate (5C) to trapped by Ribulose bisphosphate (5C) to form a 2 molecules of Glycerate-3-form a 2 molecules of Glycerate-3-phosphate (GP).phosphate (GP).

ReductionReduction

GP is reduced to a Triose-phosphate(TP) in the process GP is reduced to a Triose-phosphate(TP) in the process NADPH and ATP are oxidised to provide the energy NADPH and ATP are oxidised to provide the energy

TP is used to manufacture a variety of organic molecules including Glucose-phosphate

Regeneration Regeneration

Some of the TP is used to regenerate Some of the TP is used to regenerate Ribulose Bisphosphate. This will allow Ribulose Bisphosphate. This will allow more carbon dioxide to be fixed from more carbon dioxide to be fixed from the atmosphere. the atmosphere.

8.2.6 8.2.6 Explain the relationship Explain the relationship between the structure of the between the structure of the chloroplast and its function chloroplast and its function

Explain means to give a detailed account of causes, reasons or mechanisms.

ib photosynthesis with standards. 3.8.1 state that photosynthesis involves the conversion of light...

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