PHOTOSYNTHESIS

Using Bicarbonate Indicator Solution

• This indicator is orange /yellow when acid (much ___________ is present) and purple / red when neutral (very little or no ___________ is present.

Group work: What colour will it be if….?

• Respiration is predominant – explain

• Photosynthesis is predominant – explain

• Design an experiment to demonstrate under what conditions photosynthesis or respiration are predominant.

Starter

• Suggest what colour the bicarbonate indicate solution will turn after 60(!) hrs:

• If light has been shining on the leaf,

• If the leaf has been in the dark.

• Explain ! Now have a look…

• Might there be a time when the colour shows a dynamic equilibrium of CO2 diffusion?

Aims• To check results of respiration vs

photosynthesis exp.• Autotrophs, photoautotrophs,

chemoautotrophs and heterotrophs!• Is the light absorbing pigment in

chloroplasts just made of chlorophyll?

• How are the pigments related to light absorption?

Photosynthesis involves the conversion of light energy

into chemical energy.

What do you know so far?

• Fill in the gaps on p1 of the booklet.• Write the equation for

photosynthesis.• Complete the gaps in the next

section using these key words: Decomposer Respiration Oxygen Light Chemical Consumers Potential Aerobic

Autotrophs (p1 booklet, 58 key definition)

• Autotrophs are organisms that can synthesise complex organic molecules such as

carbohydrates, lipids, proteins, DNA, RNA, and vitamins

from inorganic molecules, using an external energy source.

Heterotrophs

• Heterotrophs digest complex organic molecules into simpler, soluble ones. They then synthesise molecules they need from these.

Examples of heterotrophs are Animals Fungi Some

bacteria

Photoautotrophs (p2)

• Do photosynthesis• Use energy from sunlight• Include: Plants from the kingdom __________ Algae from the kingdom __________ Bacteria from the kingdom _________

Chemoautotrophs

• Use energy from oxidation of inorganic molecules to synthesise complex organic molecules

• e.g. Nitrifying bacteria Nitrosomonas Nitrobacter

How many marks would a definition be worth?

True or False?• Heterotrophs synthesise complex organic

molecules from inorganic molecules. • Chemoautotrophs use chemical energy

released from oxidation reactions to synthesise their own complex organic molecules.

• Autotrophs make food from an external energy source.

• Photoautotrophs use light energy to combine inorganic molecules.

• Photoautotrophs are found in the kingdoms Plantae, Protoctista and Animalia.

Photosynthesis: 2 stage process (p 3)

• Takes place in chloroplasts

CHLOROPHYLLLight

Water

Oxygen

Carbon dioxide

Carbohydrate

Importance to Respiration

• What products of photosynthesis are needed for respiration?

• Which one is a product of the light dependent reaction?

• Which is a product of the light independent reaction?

Check your memory: name these…

1. Organelle where photosynthesis takes place

2. Pigment which absorbs light energy3. Stage of photosynthesis which uses

water and produces oxygen4. Stage which uses CO2 and produces

carbohydrate

So most Elodea leaves are just 2 cells thick except at

the midrib.

Photosynthetic pigments (p 10 and 60)

• Define the term:

• Chemicals that absorb light energy• Within thylakoid membranes• Each pigment absorbs light energy of a

specific wavelength.• e.g. Chlorophyll a, chlorophyll b, carotenoids,

xanthophylls. Learn 3 names!

Is chlorophyll really green? Analysing the pigment using thin layer chromatography

(p10)1. Tear up leaves; grind them up

in acetone and a little sand.2. Draw pencil line 1 cm from

bottom of paper or TLC plate. This is the origin line.

3. Drop spots of the green extract on to chromatography paper: build up the spot gradually and allow to dry.

4. Pour a little solvent into beaker - add paper and allow to ‘run’.

5. Remove when solvent reaches top and mark the top of the solvent. This is the solvent front. Allow to dry.

6. Identify pigments Solvent

Identifying Pigments

• Measure distance of solvent front from origin line.

• Measure distance from origin line to centre of each new spot.

• Find Rf values

• Match up value with name of pigment on a following slide.

Distance travelled by solvent

Interpret chromatography data

Rf value =

Distance travelled by spotDistance travelled by solvent

Calculate the Rf values for all the spots and therefore identify the components of the pigment mixture.

Light from the sun is composed of a range of wavelengths.

Now complete page 11 in your booklet

• Place some filtered chlorophyll extract in a test tube.

• Place some solvent in a second tube as a blank.

• Read the absorbance of light at the different wavelengths of light possible in the colorimeter.

• Note data in table on page 11.

Aims

• Complete work on light absorption by different pigments and action spectrum.

• Introduce light dependent reaction.• Homework - Chloroplast structure

and function. Annotate your diagram page 8 to show how chloroplasts are adapted for photosynthesis and answer page 1 of booklet B.

Answers to excretion question 4.

• a) no protein• b) i) 5.5 out – 4.2 in = 1.3 kPa.• ii) efferent arteriole is narrower than

afferent – so even though plasma is lost from glomerulus, blood pressure is maintained through narrower lumen.

• iii) high b.p. may damage basement membrane – so big proteins may pass through into urine.

• c) i) microvilli increase surface area – therefore speed up absorption at any one time.

• ii) Active transport needs ATP whereas facilitated does not.

• Active can transport up the concentration gradient, whereas facilitated can not.

• iii) Active transport removes sodium from cell, so lowering concentration and stimulating diffusion into the cell.

• d) Water follows salts/solutes – by osmosis, so conc remains the same.

• e) Read the graph!

• Describe…….• Concentration filtered depends on conc of

glucose in plasma – a passive process.• Conc of glucose reabsorbed depends on number

of cotransporter channels available in membrane – number limiting at C.

1. As the ……………….increases,

2. So,

the… A

B

C

Filtered in glomerulus

Reabsorbed from PCT

Both

• f) Non – diabetic person has insulin to stimulate uptake of glucose from blood into liver, muscle e.t.c

• Level of glucose in blood does not normally exceed 250mg per 100 cm³ blood, so is all absorbed by the PCT.

Kwashiorkor

Check your memory: name these…

1. Organelle where photosynthesis takes place.

2. Pigment which absorbs light energy.3. Stage of photosynthesis which uses

water and produces oxygen.4. Stage which uses CO2 and produces

carbohydrate.5. Which products of photosynthesis are

needed for respiration?6. Which one is a product of the light

dependent reaction?7. Which is a product of the light

independent reaction?8. Name 3 photosynthetic pigments.

Absorption spectrum: did yours look like this? Why are plants green? Does the

action spectrum (p30) show any correlation? Explain!

Absorption spectrum of various pigments.

Photosynthetic Pigments – see page 61 in book

1. Chlorophyll a contains a porphyrin ring surrounding a __________ atom.

2. The Absorption Spectrum shows that most absorption of light occurs in the colour _____ (_____ nm) and _____ (______ nm) wavelengths.

3. Chlorophyll a has 2 versions, one absorbing best at ____nm and the other at ____ nm.

4. Chlorophyll b absorbs light of _____nm and ____nm.

5. Carotenoids absorb blue light around _____nm.6. Chlorophylls reflect 520nm – 600nm i.e. _______

colour.

How does the structure of chloroplasts

enable them to carry out their functions?

Homework - Chloroplast structure and function. Draw and label a diagram of a chloroplast on page 8.

Annotate your diagram page 8 to show how chloroplasts are adapted for photosynthesis and answer page 1 of booklet B.

How does the structure of chloroplasts enable them to carry out their functions?

Double Membrane Envelope

Stroma

Thylakoid Disc

Granum

Chloroplast – add labels and adaptations

Light harvesting clusters or photosystems.

(p booklet and 61 book)

Quite complex animation!• http://www.learnerstv.com/animation/animation.php?ani=179&cat=biology

True or False?• Chlorophyll contains the ion Fe++.• Chlorophyll a in photosystem 2

absorbs light of mainly wavelength 700 nm.

• Chlorophyll a and b also absorb light of 450 nm wavelength.

• Chlorophylls and carotenoids reflect most light of 550 nm.

• The absorption spectrum shows at which wavelength plants photosynthesis best.

The light dependent stage

• Can you remember where it happens?

Thylakoid membranes• And the light independent stage? Stroma

The light dependent stage

• Syllabus says:• Outline how light energy is converted

to chemical energy (ATP and reduced NADP) in the light-dependent stage.

• Explain the role of water in the light-dependent stage.

Aim of light dependent reaction

• To split water to release Hydrogen ions.

• To use hydrogen ions to help make ATP (for use in light independent reaction) via chemiosmosis.

• To produce reduced NADP (for use in ……..)• What is ATP?• (Arrow on Z scheme page 63 is back to

front!)

e- e-

chlorophyll

Light

Light energyabsorbed –photoexcitation.

++

2 e-

2H+

NADP

NADPH2

2e-

H2O

½ O2 + 2H+

The effect of light energyon a chlorophyll moleculewithin a photosystem.

In stroma

Now look at Z scheme!

P680

P700

Light

Light

2e-Photolysis of water

1/2O2

2H+ 2e-

2e-NADP+2H+

reduced NADP

ADP+Pi

ATP 2e-

Non-cyclic photophosphorylation

Aims

• Check structure and function of chloroplasts homework.

• Complete light dependent reaction.• Homework for Monday – Page 15, 19,

18 and in Booklet B page 4• Light independent reaction.

Chloroplast

Match the pairs

A Double membraned envelope

1 Connect grana

B Stroma 2 Transport proteins embedded within

C Intergranal lamellae 3 Surrounds grana so ATP + NADPH can easily pass into it for light independent reaction

D Granum – thylakoid discs 4 Outer membrane permeable to ions

E Lamellae 5 Provides large surface area for pigments, electron carriers and ATP synthase enzyme.

1C, 2E, 3B, 4A, 5D Now check question page 1, Booklet B

Photosynthesis biochemistry The light dependent stage

Called photophosphorylation – using light energy to make ATP

There are 2 parts – cyclic and non-cyclic photophosphorylation

e- e-

chlorophyll

Light

Light energyabsorbed –photoexcitation.

++

2 e-

2H+

NADP

NADPH2

2e-

H2O

½ O2 + 2H+

The effect of light energyon a chlorophyll moleculewithin a photosystem.

In stroma

Now look at Z scheme!

The Light-dependent reaction takes place within the _______ of the _____

• Having studied and coloured in the Z scheme diagram of Non-cyclic photophosphorylation (page 2, Booklet B) have a look at the first animation (half way through) which shows the Z scheme.

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

Non-cyclic photophosphorylation

Cyclic or non-cyclic phosphorylation?Draw table on page 15

photosystem I light energy

photosystem II excited electrons

chlorophyll a P700 ATP

chlorophyll a P680water

chain of electron carriers oxygen

photolysis reduced NADP

Quick questions on the light dependent

stage

• Where does it happen?

• What raw materials are needed?

• Which products are needed in the light independent stage?

• Which product is needed for respiration?

• State 1 similarity and 1 difference between cyclic and non-cyclic photophosphorylation

Now for the chemiosmosis….

• Find the diagram (on page 3 of Booklet B) of the thylakoid membrane containing the photosystems and ATP synthase.

• Colour it in, add chemiosmosis to the title, make sure you understand it and note what is happening at each number before watching the second animation.

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

Making ATP by Photophosphorylation and

Chemiosmosis1. Photon of light hits chlorophyll molecule and 2 electrons get excited! They are released from chlorophyll

to electron acceptors.2. Passed on down electron carriers (in ______ _______ )4. Energy released during electron transport is used to pump H+

into thylakoid space H+ (proton) gradient is formed (lowering the pH in lumen)5. Electrons from chain replace those excited by light (700nm) in

PS1. 6. The electrons move to ferrodoxin.7. NADP accepts electrons along with protons to form NADPH3. Meanwhile, water is split by photolysis, 2 electrons from H move

into PS2, and H protons and oxygen are left in lumen.8. Accumulated H+ move down gradient through ATP synthase

enzymes. 9. H flow allows ATP to be made by ____ ________ from ADP and P

http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atpsynthase_an.html

AIMS

• Starter – Cut out statements on page 17 and stick in correct order on next sheet.

• Check homework answers.• Calvin Cycle.• Can you find real stomata?• Linking the light dependent and

independent reactions together.• Homework – Using page 66, 67, 72 and

73, in the text book, complete pages 23 – 25 and page 27 of your booklet.

Key terms (Answers for ‘Spot the term’ page 15)

1. Photon 2. Chlorophyll3. Electron4. Electron acceptor 5. Thylakoid membrane6. Electrons7. Energy8. Protons9. Thylakoid disc

10. Chemiosmosis11. Enzyme12. Photophosphorylation

Homework Answers – page 191. Grana / thylakoid membranes.2. PS2 = 680nm / PS1 = 700nm3. Splitting water using light energy.4. Using light energy to add phosphate to

(phosphorylate) ADP, in a non cyclical reaction.

5. 1A, 2E, 3D, 4B, 5F, 6C, O2 , ATP, NADPH

6. Many enzymes.7. Carbon dioxide.8. Cyclic, Non – cyclic, Non - cyclic

Page 18

i) Lower pH = more acid• More H+ ions = more acidicii) More H+ ions in the lumen produce a steeper

concentration gradient between the lumen and stroma.

• Therefore more H+ ions will flow through the ATP synthase to release more ATP.

b) Herbicides will accept the electrons instead of electron transport chain

• No reduced NADP or ATP will be made.• No glucose will be made as NADPH and ATP are

both needed for the Light independent reaction.

and 4 of booklet B

• a) Photosystems 2 (E) and 1(F)• b) chlorophyll a• c) electron acceptor / carrier• d) Lower pH = more acid More H+ ions = more acidic e) More H+ ions in the lumen produce a steeper concentration gradient between the lumen and stroma.• Therefore more H+ ions will flow through

the ATP synthase to release more ATP.

Light independent stage is where CO2 is “fixed” and used to build organic

molecules. (note down)

• Where does it take place?• Draw cycle (next slide) onto

page 20 and add extra detail from page 64 (book).

• http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

• Try quiz!• http://www.science.smith.edu/departments/Biology/

Bio231/calvin.html

Ribulose bis-phosphate(RuBP) 5C

CO2

RUBISCO

2 GP glycerate-3-phosphate (3C)

2 TP triose phosphate (3C)

RuPATP

ADP

Hexose etc

ATP

ADP + Pi

NADPH

NADP

Calvin Cycle / Light independent Reaction

(Show with plasticine)

1/6th

5/6ths

CO2

RuBP (5C)

2 x GP(2 x 3C)

2 x triose P(2 x 3C)

Hexose sugar (6C), etc

ATP

ADP + Pi

NADPH

NADP

ADP ATP

the Calvin cycle in the stroma of the chloroplast

Where does nitrogen come in?

• Nitrates are needed to make ______ ______ and then be built into protein.

• RUBISCO is an enzyme, so made of p_______

• Nitrogenous bases and phosphate are found in nucleic acids, NADP, RuBP, and ATP (and N in electron carriers and molecules with porphyrin rings.

• Now complete page 21

CO2 diffuses into air spaces through open _______.

Would number of stomatalimit CO2 uptake?

Would leaves in the shade

or light need more stomata?

CO2 diffuses to the _____ of a chloroplast in a palisade cell

via……?

Note storybottom of page 5.

Find stomata onthe lower epidermisof geranium and one other leaf.

Starter

• Calvin Cycle Quiz, page 5 Booklet B – 10 min test!

• AIMS• Collect in homework exam questions.• Linking light dependent and

independent reactions.• Introduce practicals used to

investigate the factors which affect the rate of photosynthesis – CO2 and light intensity.

Linking light dependent and independent (Calvin Cycle) reactions

Light

Light DependentReaction

NADP

NADPH

Calvin Cycle

hexoses

CO2

ATP

ADP + Pi

H2O

O2

(You draw in the arrows and cut and stick you own A3 sheets at home)

Limiting Factors (check homework)

• Key definition • The limiting factor for a metabolic process

is the factor that is present at the lowest or least favourable value.

• Why might temperature affect rate of PHS?

• Usual + high rate of transpiration and therefore stomata closure and therefore lack of carbon dioxide!

• Why might high light intensity affect rate of PHS?

• Usual + Very high might lower rate due to damaged chloroplasts!

Investigating the factors that affect the rate of photosynthesis

Aim: Describe how to investigate experimentally the factors that affect the rate of photosynthesis.

TO BE CONSIDERED:• What strategy to use

• independent variable and how to change it

• dependent variable and how to measure it

• factors to keep constant and how you will do this.

• time for plant to adjust to expt conditions

• how to obtain reliable data e.g. how many measurements to record and

what apparatus to use

To find rate of photosynthesis:possible strategies

• Rate of oxygen production• Rate of carbon dioxide uptake

• Rate of carbohydrate production

• Rate of water uptake

Photosynthometer

Remember the leaf cross section? What will happen to the density if we remove the air from the air

spaces?What effect will that have on the leaf’s ability to

float?

Measuring photosynthesis using density of leaf discs

Method • Cut 5 leaf discs using a straw• Suck 5ml sodium hydrogen carbonate solution into a 10ml

syringe• Turn syringe upside down and pull plunger to bottom• Put a finger over hole, turn syringe right way up and remove

plunger• Blow leaf discs into solution, replace plunger and push up to

remove air from syringe• Put finger tight on hole again and pull plunger down to

remove air bubbles from leaf discs• Tap to allow air bubbles to rise and escape – continue until

leaf discs sink• Put syringe near lamp and record time for discs to rise

Results and conclusion• Record results in a table and explain why the discs sank and

then floated

Revision of Rate Experiments

• http://www.biology4all.com/resources_library/source/61c.swf Photosynthometer

• What would you keep constant if light intensity was changed?

• Light intensity = _1_ where d = distance

d2

Leaf discs

• http://www-saps.plantsci.cam.ac.uk/worksheets/ssheets/ssheet3.htm

• http://www.elbiology.com/labtools/Leafdisk.html

Using immobilised algal balls to investigate photosynthesis

http://www-saps.plantsci.cam.ac.uk/worksheets/ssheets/ssheet23.htm

Dependent variable is uptake of carbon dioxide

Rate of uptake of CO2 is used as a measure of the rate of photosynthesis

Independent variables can be light intensity, wavelength, temp.

Effect of number of stomata

• Plants with more stomata will have greater rate of gas exchange but may will also lose more water by transpiration when stomata are open.

• Paint thin layer of nail varnish on to underside of leaf and allow to dry.

• Peel off layer, mount on slide with water and cover slip.

• Observe using microscope and count stomata.

Brain warm-up

Oxygen has 2 isotopes – O16 and O18.(neither are radioactive – just different masses)

A plant is given carbon dioxide with O16 and water with O18.

After photosynthesis, which oxygen atom would you expect in the carbohydrate and in the oxygen?

Explain your answer.

Answer O16 in carbohydrate as it is formed using carbon

dioxide in the light independent stage; O18 in oxygen as it is formed from water in the

light dependent stage

Limiting Factors

• Key definition • The limiting factor for a metabolic

process is the factor that is present at the lowest or least favourable value.

• Task – in pairs draw graphs of mean rate of photosynthesis against either CO2 conc, temperature (both at low and high light intensity) and light intensity itself.

• Now lets check those pages 23 – 25 and 27, and answer quest 4, page 77.

Now for some more questions….

• MAIN TOPICS ARE……• Biochemistry of light dependent

(light provides energy to reduce NADP and form ATP and O2) and independent (Calvin Cycle) reactions.

• Linking two stages including graphs.• Adaptations of chloroplasts.• Limiting factors and why.

Making algal balls

• Pour 3 cm3 sodium alginate into container• Add 3 cm3 conc. algal cells. Mix well.• Pour algal mixture through open syringe

into 2% calcium chloride solution.• Swirl mixture gently as you add it.• Leave for 5 mins. Wash in cold water, then

in distilled water.

• http://www-saps.plantsci.cam.ac.uk/worksheets/ssheets/ssheet23.htm

Aims• Check answer to question 7.• Pair and share “Limiting Factors”• Using books, complete pages 21, 22

and 23• Recap with OHT questions.• Homework – Page 20, Practical data

question, quiz page 14, 15, 16 and questions 2 and 8 for Tuesday.

Now use the books to…….

• Answer questions on pages 21 – 23.

• Finally lets recap with questions on OHT.

Limiting factors in Photosynthesis

• Discuss the limiting factors in photosynthesis with reference to carbon dioxide concentration, light intensity and temperature.

Carbon dioxide concentration

• Average carbon dioxide content of the atmosphere is 0.03-0.04%

• Increase in CO2 up to 0.5% will increase the rate of photosynthesis

• BUT optimum is 0.1%

0.1 0.5 Carbon dioxide conc

Rateof photosynthesis

With reference to the graph:

• What makes 0.1% the optimum figure?

• Why is there little point in recording rates above the 0.5% CO2

concentration?

Light intensity

• Experiments carried out by Blackmann

• At low light intensities, the rate of photosynthesis increases as light increases

• Beyond 20 kilolux the rate levels off

Effect of light

• Allows opening of stomata so CO2 can enter

• Absorbed by chlorophyll excites electrons• Splits water molecules photolysis

Light intensity and the compensation point

Effect of temperature

• Mostly affects enzyme controlled reactions of Calvin cycle

• At high light intensity, increase in temperature increase in rate.

• At low light intensity, little change.• Above 30oC photosynthesis is

reduced at both high and low light intensity- can you suggest why?

Effect of temp. and light together

Rate of photosynthesis

Temperature/oC

High light intensity

Low light intensity

• What temperature is likely to be the optimum temperature at high light intensity?

• What is likely to be the temperature at which photosynthesis stops?

• Explain why this happens.

Now do stretch and challenge questions on p73.

Graphs and quiz

• http://www.cix.co.uk/~argus/Dreambio/fertilisers%20and%20crops/limiting%20factors.htm