Autotrophs Autotrophs are organisms that use Light Energy or Chemical Energy and inorganic molecules (carbon dioxide and water) to synthesis complex organic molecules. Examples of autotrophs include:

Heterotrophs Heterotrophs are organisms that Ingest and Digest complex organic molecules, releasing the chemical potential energy released in them. Examples of heterotrophs include:

Capturing Light In the inner membranes of the Chloroplast,. By photosynthetic pigments. LOCATION Chlorophyll in thylakoids.

The light Dependent Reaction SUMMARY: Light is converted into chemical energy Electrons passed through a membrane as a result of photons of light effect on chlorophyll Water is split into Protons, Electrons and Oxygen PRODUCTS: ATP and reduced NADP Oxygen LOCATION : Thylakoids.

Nicotinamide adenine dinucleotide Reduced in the light dependent reaction. It gains electrons and then uses these to reduce CO2 in turn becoming oxidised

The light independent Reaction Summary: Protons are used to reduce carbon dioxide to produce sugars and other organic molecules. Location: Stroma

The light dependent reaction of photosynthesis

light dependent reaction Collective memory light dependent reaction ADP + P ATP NADP NADPH water oxygen

Can be summarised like thus: light dependent reaction ADP + P ATP NADP NADPH water oxygen

Chlorophyll is the most important photosynthetic pigment Chlorophyll is the most important photosynthetic pigment. It absorbs light in the blue-violet and the red regions of the visible spectrum. The porphyrin ring contains a central magnesium atom. It is hydrophilic and rests on the membrane surface The hydrocarbon tail is hydrophobic and is embedded in the thylakoid membrane.

Chlorophyll is a mixture of pigments. Chlorophyll a- 2 forms P680 and P700 Appear .............................. colour Both absorb Red Light at slightly different wavelengths. Both absorb blue light at around 450nm Chlorophyll b Absorbs light of wavengths 500nm and 640nm It appears blue green. Accessory Pigments Carotenoids, reflect yellow and orange light and absorb blue light. No porphyrin ring. Carotene (orange) and Xanthophyll (yellow) main pigments.

Light harvesting Complex

Electron Loss! Chlorophyll absorbs light energy and then emits a pair of excited electrons. Electrons are passed on to an electron carrier. The electrons are passed along a chain of electron carriers in the thylakoid membrane. A series of redox reactions Electrons lose energy in this process as each electron carrier is at a slightly lower energy than the previous one. The lost energy is used to combine ADP + Pi in a condensation reaction

There is a problem! Look at your sheet s to determine the solution

Photolysis Using light energy to split water into electrons, hydrogen ions and oxygen. H2O  2 H+ + 2e- + ½ O2 Replacing the electrons and hydrogen ions now carried by NADP, as this coenzyme has gained electrons we call it reduced NADP (NADPH)

Reduction of NADP The Hydrogen ions(protons) from photolysis associate with the coenzyme NADP which becomes reduced. Reduced NADP (NADPH) is required by the light independent stage of Photosynthesis.

The Z scheme What is going on here?

Well done- 2 Photosystems

COMPARTMENTALISATION Integral membrane proteins PSII Electron carrier PSI Electron carrier ATP synthase

NonCyclic photophosphorylation: (The Z-scheme) Light strikes PSI and electrons have been lost These electrons along with the protons (produced by photolysis @ PSII) , join NADP which becomes reduced NADP. The protons pass through ATPsynthase in chemiosmosis before joining NADP making ATP Electrons from oxidised PSII replace those lost by PSI. Electrons from photolysed water reduce PSII. Light strikes PSII Pair of electrons leave primary pigment reaction centre Electrons pass along a chain of electron carriers., energy released is used to synthesise ATP.

light dependent reaction Collective memory light dependent reaction ADP + P ATP NADP NADPH water oxygen

Cyclic- Photophosphorylation. Only used in PSI (P700), Electrons pass to an electron acceptor and are then passed back to the chlorophyll molecule from which they were lost. No photolysis of water and no generation of reduced NADP. Small amounts of ATP are generated. Guard cells of Stomata only contain PSI.

The Light-Independent Reaction

Light Independent stage Energy from ATP, hydrogens and electrons from reduced NADP are used to reduce carbon dioxide to produce carbohydrate. This happens in the stroma.

Light independent stage Reduced NADP NADP light independent reaction Carbon dioxide glucose ATP ADP + Pi

2X Glycerate-3-Phosphate Ribulose Biphosphate CO2 (1C) ATP 2X Glycerate-3-Phosphate (3C) NADPH ATP 2X Triose Phosphate (3C) (6C) Glucose

CO2 REDUCTION Ribulose Biphosphate 2X Glycerate-3-Phosphate 2X Triose Phosphate Glucose Ribulosebisphosphate carboxylase oxisdase (Rubisco) Amino Acids/Fatty Acids CO2 (1C) (5C) (3C) (3C) (6C) REDUCTION ADP NADP returned to light dependent stage. NADPH NADP + H+ ATP ADP +Pi Revision Card sort.

Exam question Suggest why after the light was switched off the amount of GP... a) Increased immediately b) levelled out after a time

Sketch the curve to show what happens to the amount of RuBP after the light has been switched off. Explain your answer. Sketch what would happen if CO2 was removed with the light left on.

Melvin Calvin Deciphering Photosynthesis The scientific process.

Stretch and Challenge Questions: Rubisco has been described as the most important enzyme on Earth. It is also the most abundant as it makes up 50% of the leaf protein. When chloroplasts are illuminated, protons are pumped from the stroma into the thylakoid space. The pH of the Stroma increases from pH7 to pH8. Rubisco is short for ribulose bisphosphate carboxylase-oxygenase. Oxygen can also fit onto the active site of this enzyme resulting in a reaction called photorespiration. It undoes a lot of the work of photosynthesis and wastes some of the ATP made during the light-dependent stage. It also leads to the formation of hydrogen peroxide which may be toxic. As temperature increases, the oxygenase activity of rubisco increases more than its carboxylase activity. When photosynthesis evolved, the Earth’s atmosphere contained very little or no free oxygen and , therefore, a relatively higher proportion of carbon dioxide. Questions: A: explain why illumination of chloroplasts will lead to optimum condidtions for teh enzyme rubisco, involved in the light-independent stage. B: Suggest how geneticaly modified plants, with an altered tertiary structure of rubisco, could improve the efficiency of photosynthesis. C: Suggest why there has been no selection of plants with rubisco enzymes having reduced oxygenase activit. D:It has been suggested that with the increased carbon dioxide lin the atmosphere, plants will carry out photosynthesis more efficiently. However, some studies of teh greenhose effect show that the opposite occurs and teh rate of photosynthesis is reduced...suggest how. E: Why do plant tissues contain the enzyme catalase? F: Why is rubisco described as the most important enzyme on earth?