Photosynthesis

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

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

carbohydrates, lipids, proteins, DNA, RNA, vitamins

from inorganic molecules, using an energy source.

Photoautotrophs

• Do photosynthesis

• Use energy from sunlight

• Include:

Plants from the phylum __________

algae from the phylum __________

bacteria from the phylum __________

Chemoautotrophs

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

• E.g. Nitrifying bacteria

Nitrosomonas

Nitrobacter

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

Photosynthesis: 2 stage process

• 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-

• Organelle where photosynthesis takes place

• Pigment which absorbs light energy

• Stage of photosynthesis which uses water and produces oxygen

• Stage which uses CO2 and produces carbohydrate

How does the structure of chloroplasts enable

them to carry out their functions?

• Draw and label a diagram of a chloroplast

• Annotate it to show how it is adapted for photosynthesis

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

Double Membrane Envelope

Stroma

Thylakoid Disc

Granum

Chloroplast

Chloroplast

Photosynthetic pigments

• Define the term:

• Chemicals that absorb light energy

• On thylakoid membranes

• Absorbs light energy of a specific wavelength

• E.g.

Chlorophyll a, b, carotenoids, xanthophylls

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

• Tear up leaves; grind them up in acetone and a little sand

• Draw pencil line 1 cm from bottom of paper.

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

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

• Remove when solvent reaches top and mark the top of solvent. Allow to dry.

• Identify pigments Solvent

Identifying pigments

• Measure distance of solvent front.

• Measure distance from 1st spot to centre of each new spot.

• Find Rf values

• Match up value with name of pigment

Distance travelled by solvent

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

Light harvesting clusters

Quite complex animation!• http://www.learnerstv.com/animation/animation.php?ani=179&cat=biology• http://www.uic.edu/classes/bios/bios100/lectures/ps01.htm(useful info!)

The light dependent stage

• Can you remember where it happens?

Thylakoid membranes

• And the light independent stage?

Stroma

The light dependent stage

• 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.

Making ATP by Photophosphorylation and Chemiosmosis

Photon of light hits chlorophyll molecule2 electrons get excited!Released from chlorophyll to electron acceptorsPassed on electron carriers (on _____________ )Energy released during electron transport is used

to pump H+ into thylakoid spaceH+ (proton) gradient is formedH+ move down gradient through ATP synthase

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

Key terms (Hints for ‘Spot the term’)

• Photon • Chlorophyll• Electron• Proton• Thylakoid membrane

• Energy• Chemiosmosis• Enzyme• Photophosphorylation• Electron acceptor

The role of water: explain using these words-

Photolysis

Photosynthesis biochemistry The light dependent stage

Called photophosphorylation – using light energy to make ATP

There are 2 parts – cyclic and non-cyclic photophosphorylation

P680

P700

Light

Light

2e-Photolysis of water

1/2O2

2H+ 2e-

2e-NADP+2H+

reduced NADP

ADP+Pi

ATP 2e-

Non-cyclic photophosphorylation

Non-cyclic photophosphorylation

Non-cyclic photophosphorylation

cyclic photophosphorylation

chlorophyll a in photosystem I

P 700

excited electrons 2e-

chain of electron carriers

ADP+Pi ATP

2e-

Cyclic or non-cyclic phosphorylation?

photosystem I light energy

photosystem II excited electrons

chlorophyll a P700 ATP

chlorophyll a P680water

chain of electron carriers oxygen

photolysis reduced NADPhttp://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html

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

Light independent stage

• The Calvin cycle

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

• Limiting factors-

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

• time for plant to adjust to expt conditions

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

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

Measuring photosynthesis using density of leaf discsMethod • 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

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 is used as a measure of the rate of photosynthesis

Independent variables can be light intensity, wavelength, temp.

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

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.