Topics 2.9 & 8.3 Photosynthesis Topics 2, 7 & 8 Biochemistry Topics 2.9 & 8.3 Photosynthesis

1 – Chloroplasts & Light Read & Consider Understandings 2.9.2-2.9.3 & 8.3.14 What are the different types of light or electromagnetic radiation? How do they impact living organisms?

Light Energy – Visible Spectrum Visible light or white light is actually composed of a continuous spectrum from red to violet. Different colors have different wavelengths with blues having the shortest wavelengths and therefore more energy, while reds have long wavelengths and less energy overall.

Photosynthetic Pigment: Chlorophyll The head of the molecule is polar and composed of a ring structure. At the heart of this ring structure is the inorganic ion magnesium. This is the light trapping region of the chlorophyll molecule. The tail of the molecule is non polar and embeds itself in membranes in the chloroplast.

Light Absorption The chemical structure of the chlorophyll molecule allows absorption of the energy of blue and red light.

Action Spectrum The action spectrum is the range of visible light wavelengths that bring about the greatest rate of photosynthesis

Absorption Spectrum The absorption spectrum is specific to the pigments of chlorophyll. It indicates the specific wavelengths that each pigment absorbs.

Annotation of Chloroplast Diagram Chloroplasts are the organelles in which photosynthesis occurs. Photosynthetic pigments Enzymes Electron-transport proteins

Chloroplast Features  Function Double membrane Thylakoids Grana (granum) Stroma Chlorophyll Starch grains, lipid droplets, ribosomes

Chromatograph Pigment Separation

2 - Photosynthesis Read & Consider Understandings 2.9.1, 2.9.4-2.9.5 & 8.3.1-8.3.13 What are the products of photosynthesis? How are these products used?

Photosynthesis 6CO2 + 6H2O + light  C6H12O6 + 6O2 Water and carbon dioxide are used to produce carbohydrates, with oxygen as a waste product. Carbon Dioxide + Water + Light Energy  organic compounds (sugars) + oxygen 6CO2 + 6H2O + light  C6H12O6 + 6O2

Part One - 1 - Light energy is used to split water (photolysis) This releases oxygen (2H2O + light  O2 + 4H) as a waste product and allows hydrogen atoms to be retained by hydrogen acceptor molecules. At the same time ATP is formed from ADP and phosphate, also using energy from light.

Part Two - 2 Sugars are built up from carbon dioxide using ATP and hydrogen H+ from the splitting of water is combined with carbon dioxide to form organic compounds like sugar. Bonds are formed between the carbon, hydrogen and oxygen using the energy from ATP (which came from the sun).

Light-Dependent Reaction Light-dependent reactions – in which light is used directly to split water (photolysis). Hydrogen is them retained by the hydrogen acceptor NADP+ (photophosphorylation). Oxygen is given off as a waste product of the light-dependent reaction. This stage occurs in the grana of the chloroplast.

Light-independent reactions – in which sugars are built up using carbon dioxide. Products of the light-dependent reaction are needed (ATP & NADPH + H+) for sugar production. This stage occurs in the stroma of the chloroplast. It requires a continuous supply of products from the light- dependent reaction but does not directly involve light.

Light-Dependent Process The light-dependent stage requires energy trapped in chlorophyll which occurs in grouped structures called photosystems found in the thylakoid membranes of the grana. Photosystem I – has a reaction center that is activated by and absorbs 700nm wavelengths – P700 Photosystem II – has a reaction center that is activated by and absorbs 680nm wavelengths – P680

Proteins - Enzymes catalyzing: Splitting of water Formation of ATP Conversion of oxidized H-carrier (NAPD+) to reduced carrier (NADPH + H+) Electron carrier molecules ground-state electrons of the key chlorophyll molecules are raised to an ‘excited state’. High-energy electrons are released from the chlorophyll molecule and bring about the changes of the light-dependent reaction.

The Process -

Light-Dependent Reaction Steps Photosystem II absorbs light (P680). Water is split by an enzyme (H2O  2H + 2e- + 1/2O2) The reaction center causes ground-state electrons to be raised to excited state. Excited electrons are accepted and passed along the electron carrier chain. As the electrons pass, some of the energy is used to pump excess hydrogen into the thylakoid space. Hydrogen accumulates in the thylakoid space lowering pH.

Continued… This results in a concentration gradient of H across the thylakoid membrane which drives the synthesis of ATP. As the result of these energy transfers, electrons fall back to ground state filling vacancies in photosystem I (p700). Meanwhile the vacancies in photosystem II are filled with electrons from the splitting of water. Excited electrons from photosystem I are then picked up by a different electron transport chain. Electrons are passed two at a time to NADP+, which is then reduced to NADPH + H+ (NADPH2)

8.2.4 Explain photophosphorylation in terms of chemiosmosis. Additionally ATP production (photophosphorylation) is coupled to electron transport. This occurs by chemiosmosis or the movement of an ion down its concentration gradient. Here excess hydrogen ions trapped in the thylakoid space flow out via ATP synthase (ATPase). This causes the synthesis of ATP form ADP + Pi

Light-Independent Reaction

Light-independent Reaction Fixation CO2 from the atmosphere is combined with ribulose biphosphate (5 carbon molecule) The enzyme ribulose biphosphate carboxylase or rubisco completes this to form glycerate 3- phosphate

Continued… Calvin Cycle Reduction The initial product is immediately reduced to 2 three-carbon sugar phosphates called triose phosphate. NADPH2 and ATP are used in this step. Triose phosphate may follow any one of two paths at this point. Product synthesis - triose phosphate is further metabolized to produce carbohydrates such as sugars, starches, and later lipids. Regeneration of acceptor – some triose phosphate is metabolized to produce the molecule that first reacts with CO2 (ribulose biphosphate).

3 – Limiting Factors Read & Consider Understanding 2.9.6 Define limiting factor and give an example.

Temperature Photosynthesis is a biological reaction and like all other such reactions there are steps that require the presence of enzymes. Temperature as we have already met is a change in the average kinetic energy of the particle.

Carbon Dioxide Concentration Carbon dioxide is one of the reactants of the reaction so this graph is very much like the effect of substrate on the rate of reaction.

Light Intensity Light energy absorbed by chlorophyll is converted to ATP and H+. At very low light levels (a) the plant will be respiring only not photosynthesizing, as the light intensity increases the rate of photosynthesis increases.

Limiting Factors Under a given set of conditions only one factor will affect the rate of photosynthesis this factor is at its minimum and is called the limiting factor.

Measuring Photosynthesis Depletion of substrate which includes measuring how much carbon dioxide has been used or how much water is used. Accumulation of product which might include measuring how much oxygen is produced or organic molecules (biomass) produced.

Works Cited Biology Guide - First Assessment 2016. International Baccalaureate Diploma Program. N.p., Dec. 2013. Web. Dec. 2013. Encyclopedia Britannica. "White Light." Encyclopedia Britannica Online. N.p., n.d. Web. 2 July 2015. Propwnge. "Chlorophyll Chromatography." YouTube, 29 Nov. 2011. Web. 18 July 2015. Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge, UK: Cambridge UP, 2014. Print.