Photosynthesis Mrs Martin

Plants and animals are dependent upon the products of photosynthesis. They use the products of photosynthesis to for respiration 6CO2 + 6H2O (+ light energy) - C6H12O6 + 6O2 C6H12O6 + 6O2  6CO2 + 6H2O Photoautotrophs and heterotrophs can release the chemical potential energy in complex organic molecules during photosynthesis. They can also use the waste product Oxygen produced by photosynthesis for aerobic respiration.

Autotroph Chemoautotroph Organisms that can produce their own complex organic compounds, using light energy or chemical energy, from inorganic sources. Chemoautotroph Prokaryotes that use the energy from exergonic reactions (chemical reactions that release heat) to synthesise complex organic compounds Nitrifying bacteria that oxidise ammonia to nitrate or oxidising nitrite to nitrate. Bacteria using sulphur rich substances bubbling from the vents of volcanoes. These bacteria help to support food chains living in those areas.

Photoautotroph Heterotrophs Use the sun as their energy source and the inorganic molecules carbon dioxide and water. Most of the world’s food chains have photoautotrophs as their producers Heterotrophs These organisms cannot make their own food and are reliant on digesting other organisms to obtain their complex organic molecules into more simple soluble molecules. These simple molecules can then be rebuilt to produce proteins, lipids and nucleic acids.

Structure of the chloroplast

Chloroplasts- main regions Stroma Fluid filled matrix contains starch grains, oil droplets, DNA and and prokaryote-type ribosomes Chloroplast DNA and ribosomes can make some proteins needed for photosynthesis Site of light independent reactions Enzymes needed for these reactions are found here Surrounds Grana so products of light dependent reactions can easily pass into the stroma

Chloroplasts- main regions Grana Stacks of flattened membrane compartments – thylakoids Up to 100 stacks Provides large surface area for photosynthetic pigments, electron carriers and ATP synthase (required for light dependent reactions) Can only be seen using an electron microscope Site of light dependent reactions Light is absorbed and ATP synthesised Contain Photosynthetic pigments arranged into photosystems

Photosystem Photosystem, a funnel shaped light harvesting cluster of photosynthetic pigments held in place by proteins in the thylakoid membrane. The primary pigment reaction centre is a molecule of Chlorophyll a. The accessory pigments consist of molecules of chlorophyll b and carotenoids.

Structure of chlorophyll a Essential molecule in the process of photosynthesis. Gives plants their intense green colour When vegetation is cooked the central magnesium is replaced with a hydrogen ion. This changes the colour of the leaves

Chlorophyll a Active part of the chlorophyll molecule. Central Mg bonded to 4 N atoms. Changes in the electrons in this part of the molecule enable it to absorb light very strongly Hydrocarbon tail is non-polar. It is hydrophilic so sticks into the thylakoid membrane

Photosynthetic pigments Substances that absorb some wavelengths of light and reflect others. The colour they appear is the colour they are reflecting This light is reflected

Pigments Two forms of chlorophyll a P680 absorbs at 680nm- found in photosystem II P700 absorbs at 700nm- found in photosystem I Both also absorb blue light at around 450nm Chlorophyll b absorbs around 500nm & 640nm Carotenoids absorb blue light and reflect orange/yellow light Pigments

Knowledge check What is a chemoautotroph? Can you name an example What type of trophic organism are the majority of food chains reliant upon? Name the membrane that makes up the grana Suggest what this membrane is composed of Suggest why scientists have proposed the idea of endosymbiosis State where the light independent reactions of photosynthesis take place Explain why the majority of plants are green Suggest why in the autumn leaves may turn red Explain how a chlorophyll molecule is adapted for its function Describe how a photosystem is able to maximise the amount of energy it can obtain from light

(b) Formation of ATP during non-cyclic photophosphorylation (a) The distribution of photosystems on granal and intergranal lamellae; (b) Formation of ATP during non-cyclic photophosphorylation (b) © Pearson Education Ltd 2009 This document may have been altered from the original 14

The Z-scheme 15 © Pearson Education Ltd 2009 This document may have been altered from the original 15

Light dependent reactions- non-cyclic photophosphorylation Light energy strikes photosystem II and cascades through to the primary pigment reaction centre If enough energy strikes the primary pigment molecule the energy levels of a pair of electrons are raised. The electrons leave the chlorophyll molecule to an electron transport chain As the electrons go down the electron transport chain they lose energy which is used to convert ADP + Pi  ATP New electrons are needed to replace the electrons lost from photosystem II

Photolysis of water H20  2H+ + 2e- + ½ O2 enzyme Protons Used for NADP Waste product Electrons used as a Replacement for PS II

OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons Light energy also hits photosystem I. If enough light hits the photosystem II electrons are lost from the primary pigment centre. The electrons are replaced by the electrons from photosystem II The electrons again leave to the electron transport chain The electrons lose energy as they go down the chain. This energy is used to make reduced NADP (rNADP) OILRIG OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons

OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons NADP + 2H+ + 2e-  Reduced NADP Energy source Protons from photolysis of water From Photosystem II OILRIG OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons

OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons REMEMBER!!! OILRIG OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons

Cyclic Phosphorylation Only photosystem I is used Excited electrons are passed to an electron receptor and back to the chlorophyll molecule from which they were lost No photolysis of water Small amounts of ATP are produced which maybe used in photosynthesis or by guard cells to bring in K ions lowering water potential and causing water to enter by osmosis. This causes the guard cells to swell and open, allowing exchange of gas.

Light dependent photosynthesis The Z-scheme © Pearson Education Ltd 2009 This document may have been altered from the original 22

(b) Formation of ATP during non-cyclic photophosphorylation (a) The distribution of photosystems on granal and intergranal lamellae; (b) Formation of ATP during non-cyclic photophosphorylation (b) © Pearson Education Ltd 2009 This document may have been altered from the original 23

Explain the role of carbon dioxide in the light-independent stage. Week 10 Outline how the products of the light-dependent stage are used in the light-independent stage (Calvin cycle) to produce triose phosphate (TP), referring also to ribulose bisphosphate (RuBP), ribulose bisphosphate carboxylase (rubisco) and glycerate 3-phosphate (GP). Explain the role of carbon dioxide in the light-independent stage. State that TP (and GP) can be used to make carbohydrates, lipids and amino acids. State that most TP is recycled to RuBP. © Pearson Education Ltd 2009 This document may have been altered from the original 24

Light independent photosynthesis The reactions are not truly independent of light as the ATP and rNADP could not be produced without light. The light independent reactions occur within the stroma. Carbon Dioxide is needed to produce all large organic molecules. These molecules are used as structures or act as energy stores or sources for all the carbon based life forms on this planet

Calvin Cycle Inorganic form Of Carbon 3CO2 Rubisco 2x Glycerate 3 phosphate GP (2x 3C, not sugar) Now has carboxy group 5C acceptor Ribulose bisphosphate (RuBP) 5C Sugar This reaction is catalysed by Ribulose Bisphosphate Carboxylase Oxygenase Rubisco. Described as the most important enzyme on earth. Read Stretch and challenge on page 65!

Calvin Cycle GP Reduced and phosphorylated ATP ADP + Pi 2x triose phosphate (3C) Ose= sugar NADP rNADP 5 of every 6 molecules of TP are recycled by phosphorylation (using ATP from light dependent reaction, to 3 molecules of RuBP (5C)

Calvin cycle 28 © Pearson Education Ltd 2009 This document may have been altered from the original 28

Limiting Factors Lesson Objective To discuss the factors that limit photosynthesis Design an experiment to test one factor that affects photosynthesis

Limiting Factors Law of limiting Factors states At any given moment, the rate of metabolic process is limited by the factor that is present at its least favourable (lowest) value

Limiting factors At any given moment, the rate of metabolic process is limited by the factor that is present at its least favourable (lowest) value

Light Intensity When light is the limiting factor the rate of photosynthesis is directly proportional to the light intensity. What does this mean? Light causes the stomata to open so that Carbon dioxide can enter the leaves Light is trapped by chlorophyll where it excites electrons It splits water molecules to produce protons Electrons and protons are involved are involved in photophosphorylation producing ATP for the fixation of carbon dioxide

Questions Which stage of photosynthesis will affected by temperature? And why? Why does light intensity affect the rate of photosynthesis? Why would burning an oil-fired stove in a greenhouse increase the growth of plants in a greenhouse?

Questions Which stage of photosynthesis will affected by temperature? And why? The light independent Calvin cycle. As many of the reactions are catalysed by enzymes, the rate rises between 0-25oC. At the rate plateaus and fall as enzymes work less efficiently and as oxygen competes more successfully than carbon dioxide for the active site of rubisco

Questions Why does light intensity affect the rate of photosynthesis? Which stage of photosynthesis will affected by temperature? And why? Why does light intensity affect the rate of photosynthesis? Light is required for the light dependent phase, as photons hit the photosystem electrons are excited which then leave the photosystem via electron carriers and passed along a series of protein electron carriers which eventually produce ATP and rNADP. A reduced light intensity will reduce these levels. G3P will accumulate as it is not reduced to triose phosphate (calvin cycle). Ribulose bisphosphate levels will fall as it is not being regenerated

Questions Which stage of photosynthesis will affected by temperature? And why? Why does light intensity affect the rate of photosynthesis? Why would burning an oil-fired stove in a greenhouse increase the growth of plants in a greenhouse Burning hydrocarbons (oil, coal, natural gas) will produce Carbon Dioxide Burning fuel will also increase the temperature of the greenhouse

Use your knowledge to explain the graph

Use your knowledge to explain the graph