2.9 Photosynthesis (SL)

Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life.

Essential idea

2.9 Photosynthesis (SL)

Vocabulary

https://quizlet.com/_886c73?x=1qqt&i=28b19k

​

https://quizlet.com/_88lhtd?x=1qqt&i=28b19k

​

8.3 Photosynthesis

Vocabulary

2.9 Photosynthesis (SL)

Syllabus Reference

8.3 Photosynthesis

Syllabus Reference

* ‘across the thylakoid membrane’ is a more accurate statement as reactions occur on either side of the integral proteins.

Photosynthesis is conversion of light energy to the synthesise chemical energy in the form of carbon compounds.

2.9 Photosynthesis (SL)

2.9 U1 Photosynthesis is the production of carbon compounds in cells using light energy.

8.3 Photosynthesis

8.3.U1 Light-dependent reactions take place in the intermembrane space of the thylakoids.*

8.3.U2 Light-independent reactions take place in the stroma.

2.9 Photosynthesis (SL)

What do plants use their glucose for?

• Cellulose for strong Cell walls
• Respiration
• Amino acids for protein synthesis (nitrates from the soil)
• Insoluble starch for storage
• Lipids for storage in seeds

​

​

Challenge: How do you test for starch?

CRASS

2.9 Photosynthesis (SL)

2.9.U2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.

Blue light has a shorter wavelength and more energy.

Red light has a longer wavelength and less energy.

• Photolysis is the splitting of water molecules using light (photons)

2.9 Photosynthesis (SL)

2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water.

• Excite electrons to create an electrochemical gradient in order to phosphorylate ADP
• Reduce NADP to NADPH + H+
• Split water to recycle electrons and H⁺
• The ATP is used to phosphorylate carbon compounds to synthesise 2 x 3 carbon compounds
• These 3 carbon compounds are phosphorylated to form glucose molecules

2.9 Photosynthesis (SL)

Light energy is used to:

2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

• Epidermis
• Waxy Cuticle
• Palisade Mesophyll
• Spongey Mesophyll
• Chloroplasts
• Air space
• Stomata
• Guard Cell
• Xylem (Water)
• Phloem (Food)

https://www.youtube.com/watch?v=co0JdqUlycg

​

Plant Tissues and Organs

What is the structure of a leaf?

Task 1

Waxy Cuticle

Chloroplasts

Palisade Mesophyll

Spongey Mesophyll

Air Spaces

Guard Cells

Stomata

Xylem

Phloem

Epidermis

Epidermis

2.9 Photosynthesis (SL)

Vascular Bundles

2.9 Photosynthesis (SL)

Chlorophyll traps sunlight.

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

It is the main photosynthetic pigment in plants

Why do leaves look green?

visible light

Red and blue light is absorbed by the leaf.

​

Green light is reflected and reaches our eyes

2.9 Photosynthesis (SL)

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

visible light

Green light is reflected and reaches our eyes

The amount of red and blue,light absorbed can be measured using a spectrophotometer

Leaf extract (chlorophyll)

2.9 Photosynthesis (SL)

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

2.9 Photosynthesis (SL)

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

2.9 Photosynthesis (SL)

Absorption Spectrum

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

If we pass light through a leaf extract and measure how much of each wavelength of light is absorbed we produce an absorption spectrum.

The main colours of light absorbed are red and blue. The main colour reflected is green.

​

2.9 Photosynthesis (SL)

Action Spectrum (Photosynthetic Rate)

2.9 S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

If we pass different wavelengths of light through a leaf extract and measure the rate of photosynthesis we get an action spectrum.

​

• There are five main types of chlorophylls: chlorophylls a, b, c and d, (plus a related molecule found in prokaryotes called bacteriochlorophyll).
• In plants, chlorophyll a and chlorophyll b are the main photosynthetic pigments.
• Chlorophyll molecules absorb blue and red wavelengths, as shown by the peaks in the absorption spectra above.

2.9 Photosynthesis (SL)

Extra Information

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

2.9 Photosynthesis (SL)

Extra Information

2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

2.9 Photosynthesis (SL)

Structure of Chlorophyll

• Carotenoids are another key group of pigments that absorb violet and blue-green light (reflect yellow, orange and red )
• The brightly colored carotenoids found in fruit—such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene)—are often used as advertisements to attract animals, which can help disperse the plant's seeds.

2.9 Photosynthesis (SL)

Other Photosynthetic Pigments

chlorophyll a

chlorophyll b

carotenoids

2.9 Photosynthesis (SL)

2.9 Photosynthesis (SL)

2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

(Edited by Chris Paine)

https://app.box.com/s/88edjbrgbff0febtiyfk8x9l0cdnyshr

https://app.box.com/s/88edjbrgbff0febtiyfk8x9l0cdnyshr

http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm

2.9 Photosynthesis (SL)

Extra: Build a spectra

Light energy is converted into chemical energy.

8.3 Photosynthesis

What are these visual representations of?

Essential idea

Remember this number 2680

Where is the chlorophyll found in the chloroplasts?

​

Why are there so many membranes in a chloroplast?

​

How does the chloroplast convert sunlight energy into chemical energy (as glucose)?

​

​

8.3 Photosynthesis

8.3.U1 Light-dependent reactions take place in the intermembrane space of the thylakoids.*

8.3.U2 Light-independent reactions take place in the stroma.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

Thylakoid

Granum

Grana

Stroma

Lamellae connects the grana

70s ribosomes

Naked DNA

Starch granules

1

2

3

4

5

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

Stroma is the location of the light independent reaction that includes the Calvin cycle.

Internal membranes called thylakoids are the location of the light dependent reaction.

8.3 Photosynthesis

How are pancakes related to photosynthesis?

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

thylakoids

grana (sing. granum)

stroma

How is the chloroplast adapted to suit its function?

Large SA for absorption of light

​

Concentrates H⁺ ions

​

Compartmentalisation of enzymes for Calvin cycle

​

8.3 Photosynthesis

8.3.U14 The structure of the chloroplast is adapted to its function in photosynthesis.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

1.

2.

3.

4.

8.3 Photosynthesis

8.3.S1 Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

• Photosystems are groups of photosynthetic pigments (including chlorophyll) embedded within the thylakoid membrane
• Photosystems are classed according to their maximal absorption wavelengths (PS I = 700 nm ; PS II = 680 nm)
• When a photosystem absorbs light energy, delocalised electrons within the pigments become energised or ‘excited'
• These excited electrons are transferred to carrier molecules within the thylakoid membrane

8.3 Photosynthesis

Put the following statements in the correct order

8.3.U3 Reduced NADP and ATP are produced in the light-dependent reactions.

1

2

3

4

5

6

7

8.3 Photosynthesis

Put the following statements in the correct order

8.3.U4 Absorption of light by photosystems generates excited electrons. 8.3.U5 Photolysis of water generates electrons for use in the light-dependent reactions. 8.3.U6 Transfer of excited electrons occurs between carriers in thylakoid membranes.

8.3 Photosynthesis

8.3.U4 Absorption of light by photosystems generates excited electrons. 8.3.U5 Photolysis of water generates electrons for use in the light-dependent reactions. 8.3.U6 Transfer of excited electrons occurs between carriers in thylakoid membranes.

Excited electrons from Photosystem I reduce NADP+

The electrons lost from Photosystem I are replaced by de-energised electrons from Photosystem II

 Electrons lost from Photosystem II are replaced by electrons released from water via photolysis

Water is split by light energy into H+ ions (used in chemiosmosis) and oxygen (released as a by-product)

8.3 Photosynthesis

Annotate your diagram

8.3.U6 Transfer of excited electrons occurs between carriers in thylakoid membranes.

8.3 Photosynthesis

Can you remember the number?

8.3 Photosynthesis

An overview of photosynthesis

A.K.A: Light Independent Reaction (Independent from Light)

Light Dependent Reaction

Light Independent Reaction (Calvin Cycle)

Thylakoid membranes

• Uses light (absorbed by chlorophyll)
• Uses H₂O

• Produces O_2, ATP & to NADPH + H⁺

• Photolysis
• Photophosphorylation

Stroma

• Uses ATP & to NADPH + H^+, CO₂ and RuBiSco

• Glucose (Triose Phosphate)

• Carbon Fixation

8.3 Photosynthesis

What are the functions of light in photosynthesis?

8.3.U4 Absorption of light by photosystems generates excited electrons.

• Photoactivation is electrons becoming excited, which then allows photophosphorylation to occur.
• initiates the photolysis (splitting) of water.
• allows the reduction of NADP to NADPH.

When a pigment absorbs a photon of light, it becomes excited, meaning that it has extra energy and is no longer in its normal, or ground, state

At a subatomic level, excitation is when an electron is bumped into a higher-energy orbital that lies further from the nucleus.

2.9 Photosynthesis (SL)

What is photoactivation?

8.3.U4 Absorption of light by photosystems generates excited electrons.

Photophosphorylation is the process of utilising light energy from photosynthesis to convert ADP to ATP

It excites the electrons (photoactivation), which then allows photophosphorylation to occur.

8.3 Photosynthesis

8.3.U3 Reduced NADP and ATP are produced in the light-dependent reactions.

The addition of phosphate using light energy.

e.g. ADP + P_i ATP

​

​

​

​

e.g. when light energy is used to form ATP from ADP and phosphate.

​

8.3 Photosynthesis

Photophosphorylation is the process of utilising light energy from photosynthesis to convert ADP to ATP

8.3.U3 Reduced NADP and ATP are produced in the light-dependent reactions.

It excites the electrons, which then allows the reduction of NADP to NADPH.

​

-

Reduction is the loss of oxygen atom from a molecule or the gaining of one or more electrons.

8.3 Photosynthesis

8.3.U3 Reduced NADP and ATP are produced in the light-dependent reactions.

8.3 Photosynthesis

It initiates the photolysis (splitting) of water.

​

​

8.3.U5 Photolysis of water generates electrons for use in the light-dependent reactions.

e^- e^- e^- e^-

8.3 Photosynthesis

The splitting of water into H⁺, e^– and oxygen using light energy.

8.3.U5 Photolysis of water generates electrons for use in the light-dependent reactions.

8.3 Photosynthesis

8.3 Photosynthesis

intermembrane space of the thylakoids

Stroma

Thylakoid Membrane

Light (680nm)

strikes PSII

Excited electron leaves the chlorophyll molecule

Exciting an electron in the chlorophyll molecule

And is passed along a series of electron carriers (plastoquionine) to PSI

​

Electrons in PSII are replaced through photolysis

H+ produced by photolysis and also pumped into the thylakoid membrane accumulate in the thylakoid space

Protons pass through ATP Synthase by chemiosmosis

This photophosphorylates ADP + Pi 🡪ATP

This create an electrochemical gradient

H⁺ ions reduce NADP⁺ 🡪 NADPH + H⁺

Electrons in PSI (700nm) are excited and the energy is transferred to reduce NADP⁺ 🡪 NADPH + H⁺

8.3 Photosynthesis

Excited electrons from Photosystem II are used to contribute to generate a proton gradient.

8.3 U7. Excited electrons from Photosystem II are used to contribute to generate a proton gradient

• As electrons move down the electron transport chain they lose energy. This energy is used to pump H+ (protons) across the thylakoid membrane into the thylakoid space.
• This creates an H+ concentration gradient and the potential energy needed, that will drive chemiosmosis and produce ATP from ADP during photophosphorylation (similar to oxidative phosphorylation in mitochondria)
• The photolysis of water also helps create the proton gradient as H+ is produced when water is split

8.3 Photosynthesis

returns to same molecule

doesn’t return to same molecule

PS II

PSI

PSI and PSII

PSI only

NADP

PSI

8.3 Photosynthesis

• Chlorophyll molecules are grouped together into photosystems contained within the thylakoid membranes.
• Chlorophyll a within the photosystem II (PS II) absorbs a photon of light (most efficient at 680 nm).�
• This photon of light excites an electron from the chlorophyll a molecule to a higher energy state.�
• The chlorophyll is now in a photoactivated state.�
• The excited electron is released by the oxidized Chlorophyll a molecule to the primary electron acceptor in photosystem II.�
• There are two excited electrons and the electrons are transferred along a series of electron carriers in the thylakoid membrane�

8.3 Photosynthesis

Excited electrons from Photosystem I are used to reduce NADP.

• A photon of light strikes photosystem I, re-exciting the electron to a higher energy state (photoactivation)
• This electron is passed along a second electron transport chain (includes ferredoxin) until it is accepted by the final electron carrier NADP+.
• A second electron that follows the same path is also accepted by NADP+.
• These electrons reduce NADP+ to form NADPH (NADP+ + 2e- + H+ --> NADPH).
• This reaction is catalyzed by an enzyme called NADP reductase.
• Since the electrons are not returned to photosystem II, this path for making ATP is called non-cyclic photophosphorylation.
• New electrons are passed to PSI from PSII through a carrier called plastocyanin.
• If NADP+ runs out and it cannot accept the excited electron from photosystem I, electrons return to the electron transport chain (PQ) where they can reflow back to PS I thus pumping more protons into the thylakoid space; producing more ATP.
• This is called cyclic photophosphorylation.

8.3 Photosynthesis

What is chemiosmosis?

8.3.U8 ATP synthase in thylakoids generates ATP using the proton gradient.

• The diffusion of ions across a partially permeable membrane through ATP Synthase.

​

• As electrons pass along the ETC energy is released.

​

• This energy is used to pump protons across the thylakoid membrane into the thylakoid space.

​

• As protons build up a gradient is created.

​

• The flow of protons from the thylakoid to the stroma generates ATP.

​

​

​

8.3 Photosynthesis

Compare Cyclic and Non-Cyclic Light Dependent Reactions

Whilst juggling balls, can you explain Cyclic and Non-Cyclic Light Dependent Reactions

8.3 Photosynthesis

Organise the solo hexagon cards

Checkpoint

8.3 Photosynthesis

Suggested Answers

8.3 Photosynthesis

Try this with pairs of hexagons

Checkpoint

Start by choosing pairs that go together, then highlight key words, e.g.

8.3 Photosynthesis

Some possible pairs

Then make up a fun vivid animated story in 3D which links the words.

You can do this in your own mind without writing it down ... but also try doodling as you make up the story if you like.

8.3 Photosynthesis

Example story

Theo the thylakoid membrane went into a cafe and bought a large Chloro-cola (a green drink!) which he spilt all over the large surface area of the table making a terrible sticky mess.��Chlorophyll the assistant in this cafe (which was called Photosystem II Cafe) tried cleaning up by photolysis, separating electrons from water��These electrons got excited about this as there was a lot of bright light in the cafe so they jumped up and were carried off the table by electron carriers

8.3 Photosynthesis

What do you wonder?

How does the chloroplast trap CO₂ from the air?

​

Which 'carbohydrates' do the light independent reactions make?

​

Which products from the light dependent reactions are used in the light independent reactions?

​

8.3 Photosynthesis

1 Carbon fixation

​

​

​

2 Reduction

​

​

3 Regeneration

CO₂ is added to a 5 carbon compound called ribulose bisphosphate (RuBP)

RuBP splits to form glycerate 3 phosphate (G3P)

G3P is reduced to triose phosphate (TP)

⅙ TP molecules is used to make hexose bisphosphate

⅚ TP molecules are used to regenerate RuBP

8.3 Photosynthesis

8.3.U11 Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP. 8.3.U12 Triose phosphate is used to regenerate RuBP and produce carbohydrates.

8.3.U13Ribulose bisphosphate is reformed using ATP.

1C

5C

Ribulose Bisphosphate Carboxylase

Glycerate 3 Phosphate

2 x 3C

Carbon Fixation

Triose Phosphate

2 x 3C

1C per cycle

8.3 Photosynthesis

8.3.U11 Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP. 8.3.U12 Triose phosphate is used to regenerate RuBP and produce carbohydrates.

8.3.U13Ribulose bisphosphate is reformed using ATP.

• Organic compounds are carbon containing compounds found in living or once living things
• In organic compounds, C atom is covalently bonded to H atom
• CO₂ is considered inorganic

8.3 Photosynthesis

Carbon Fixation

8.3.U10 In the light-independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate.

8.3 Photosynthesis

Match the images of the LIR with the statements on the SOLO Hexagons to create a multimedia answer to the IB style question below.

Checkpoint

What are limiting factors with regards to photosynthesis?

​

​

​

2.9 Photosynthesis (SL)

2.9 Skill2: Design of experiments to investigate the effect of limiting factors on photosynthesis.

8.3 Photosynthesis

Effect on the concentration of TP, GP and RuBP

8.3.U12 Triose phosphate is used to regenerate RuBP and produce carbohydrates.

8.3 Photosynthesis

8.3 Photosynthesis

(a) Draw a labelled diagram of the structure of a chloroplast as seen with an electron microscope (4)

​

Starter

Award [1] for each of the following clearly drawn and correctly labelled.

double/inner and outer membrane/envelope—shown as two concentric continuous lines close together;

granum/grana —shown as a stack of several disc-shaped subunits;

(intergranal) lamella — shown continuous with thylakoid membrane;

thylakoid — one of the flattened sacs;

stroma;

(70S) ribosomes/(circular) DNA / lipid globules / starch granules /thylakoid space;

Increasing the light intensity has no effect on the rate. Other factors are limiting (carbon dioxide or temperature).

​

​

As the light intensity increases the rate of photosynthesis also increases.

At low light intensity the plant is respiring.

​

2.9 Photosynthesis (SL)

What is the effect of changing light intensity?

2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

Effect of changing carbon dioxide

Increasing the carbon dioxide has no effect on the rate. Leaves are saturated with carbon dioxide. Other factors are limiting.

​

​

As the carbon dioxide increases the rate of photosynthesis also increases. The limiting factor is the carbon dioxide concentration.

2.9 Photosynthesis (SL)

What is the effect of change carbon dioxide concentration?

2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

The light-independent reaction of photosynthesis is controlled by enzymes. Temperature affects enzyme reactions.

As temperature increases, collision frequency between reactant particles and between reactant and enzyme increases. This increases the rate of reaction up to the optimum temperature.

Beyond the optimum temperature however, enzymes begin to be denatured. Their tertiary structure breaks down, changing the shape of the active site so that reactant molecules no longer fit.

up to optimum temperature

enzyme denatured at high temperature

2.9 Photosynthesis (SL)

Why is temperature important?

2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

Effect of changing temperature

​

​

Plant enzymes have an optimum of about 25^oC and are denatured at 45^oC

​

As the temperature and kinetic energy increase the rate of photosynthesis also increases. Enzymes needed for photosynthesis work better in warmer temperatures.

​

​

Maximum rate at optimum temperature

2.9 Photosynthesis (SL)

What is the effect of changing temperature?

2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

2.9 Photosynthesis (SL)

Direct Measurement 1

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

Aquatic plants can submerged in water in a closed space with a gas syringe attached. Alternatively gas volume can be measured by displacing water in an inverted measuring cylinder or by simply counting bubbles.

Oxygen probes can be used with terrestrial plants kept in closed environments to measure increases in oxygen concentration.

• Placing the plant in a closed space with water.
• CO₂ reacts with the water producing bicarbonate and hydrogen ions
• Which increases the acidity of the solution.
• Increased CO₂ uptake -> increased pH -> increased rate of photosynthesis.

2.9 Photosynthesis (SL)

Direct Measurement 2

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

2.9 Photosynthesis (SL)

Indirect Measurement

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

Glucose production can be (indirectly) measured by a change in a plant's dry biomass.

​

Starch levels in a plant (glucose is stored as starch) can be identified by staining with iodine solution, this can be quantitated using a colorimeter.

What can we measure? How?

​

How quickly raw materials are used:

e.g. water and carbon dioxide

​

How quickly products are formed:

e.g. oxygen production and biomass

2.9 Photosynthesis (SL)

How?

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

Controlling Variables

2.9 Photosynthesis (SL)

Controlling the variables?

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

Try this - Virtual Photosynthesis Lab

2.9 Photosynthesis (SL)

Try this Virtual Lab

Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.

Try this:

2.9 Photosynthesis (SL)

Plant pigment chromatography

2.9.S3 Separation of photosynthetic pigments by chromatograph. (Practical 4)

• The evolution of photosynthesis
• Composition of the early atmosphere and how photosynthesis changed it
• Photosynthesis and the maintenance of the current atmosphere
• The role of photosynthesis in the current climate and its  changes
• Oceans and photosynthesis

2.9 Photosynthesis (SL)

Create a story board to explain photosynthesis and you must also include the changes from the early atmosphere until now.

Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.

• Composition of the early atmosphere and how photosynthesis changed it
• Early photosynthetic organisms
• Chemoautotrophs
• Evolution of chloroplasts
• Creation of the ozone layer
• Photosynthesis and the maintenance of the current atmosphere
• Photosynthesis and climate change
• Photosynthesis and rock deposition
• Oceans

2.9 Photosynthesis (SL)

Extra Detail

Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.

8.3 Photosynthesis

Outline the light-dependent reactions of photosynthesis (6)

Exam-Style Questions

• (chlorophyll/antenna) in photosystem II absorbs light;
• absorbing light/photoactivation produces an excited/high energy/
• free electron;
• electron passed along a series of carriers;
• reduction of NADP+ / generates NADPH + H+;
• absorption of light in photosystem II provides electron for photosystem I;
• photolysis of water produces H+ / O₂;
• called non-cyclic photophosphorylation;
• in cyclic photophosphorylation electron returns to chlorophyll;
• generates ATP by H+ pumped across thylakoid membrane /
• by chemiosmosis / through ATP synthetase/synthase;

8.3 Photosynthesis

Explain the effect of light intensity and temperature on the rate of photosynthesis. (8)

• both light and temperature can be limiting factors;
• other factors can be limiting;
• graph showing increase and plateau with increasing light / description of this;
• graph showing increase and decrease with increasing temperature /description of this;
• light:
• affects the light-dependent stage;
• at low intensities insufficient ATP;
• and insufficient NADPHH + H+ produced;
• this stops the Calvin cycle operating (at maximum rate);
• temperature:
• affects light-independent stage / Calvin cycle;
• temperature affects enzyme activity;
• less active at low temperatures / maximum rate at high temperatures;
• but will then be denatured (as temperature rises further);
• Award [5 max] if only one condition is discussed.

8.3 Photosynthesis

Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions. (6 marks)

Exam Style Question

• Light causes photoactivation / excitation of electrons;
• This leads to the generation of both ATP and NADPH in the light dependent reactions;
• The flow of electrons causes pumping of protons into thylakoid; ATP formation when protons pass back across thylakoid membrane; ATP needed to regenerate RuBP for use in the light dependent reactions; The photoactivated electrons are passed to NADP / NADP+ reducing it (to NADPH);
• Light-independent reaction fixes CO₂ to make glycerate 3-phosphate; glycerate 3-phosphate becomes reduced to triose phosphate;
• The reduction uses both NADPH and ATP;

8.3 Photosynthesis

Compare Chloroplasts and Mitochondria

Exam Style Question

8.3 Photosynthesis

8.3 Application: Calvin’s experiment to elucidate the carboxylation of RuBP

8.3 Photosynthesis

What is the lollipop experiment – by Melvin Calvin?

Application: Calvin’s experiment to elucidate the carboxylation of RuBP.

8.3 Photosynthesis

Application: Calvin’s experiment to elucidate the carboxylation of RuBP

• Radioactive carbon-14 is added to a ‘lollipop’ apparatus containing green algae (Chlorella)
• Light is shone on the apparatus to induce photosynthesis (which will incorporate the carbon-14 into organic compounds)
• After different periods of time, the algae is killed by running it into a solution of heated alcohol (stops cell metabolism)
• Dead algal samples are analysed using 2D chromatography, which separates out the different carbon compounds
• Any radioactive carbon compounds on the chromatogram were then identified using autoradiography (X-ray film exposure)
• By comparing different periods of light exposure, the order by which carbon compounds are generated was determined
• Calvin used this information to propose a sequence of events known as the Calvin cycle (light independent reactions)  

8.3 Photosynthesis

What is the lollipop experiment – by Melvin Calvin?

Application: Calvin’s experiment to elucidate the carboxylation of RuBP.

8.3 Photosynthesis

What is the lollipop experiment – by Melvin Calvin?

Application: Calvin’s experiment to elucidate the carboxylation of RuBP.

8.3 Photosynthesis

Checkpoint

8.3 Photosynthesis Kahoot

8.3 Photosynthesis Quiz