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Autotrophs Organisms capture and store free energy for use in biological processes.

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Presentation on theme: "Autotrophs Organisms capture and store free energy for use in biological processes."— Presentation transcript:

1 Autotrophs Organisms capture and store free energy for use in biological processes

2 Name to methods that autotrophs use to capture energy from physical sources in the environment. Photosynthetic Organisms – capture free energy present in sunlight Plants, Algae, Cyanobacteria Chemosynthetic Organisms – capture free energy from small inorganic molecules present in their environment, and this process can occur in the absences of oxygen Bacteria

3 Chloroplasts The Structure and Function of Subcellular components, and their interactions, provide essential cellular processes

4 How are chloroplasts specialized to capture energy for photosynthesis? Chloroplasts have a double outer membrane that creates a compartmentalized structure – to support function Within the chloroplasts are membrane-bound structures called thylakoids Energy-capturing reactions housed in the thylakoids are organized in stacks, called grana to produce ATP and NADPH 2, which fuel carbon-fixing reactions in the Calvin Cycle Carbon fixation occurs in the stroma, where molecules of CO 2 are converted to carbohydrates

5 Fig. 10-3b 1 µm Thylakoid space Chloroplast Granum Intermembrane space Inner membrane Outer membrane Stroma Thylakoid

6 Lighter Reactions of Photosynthesis Organisms capture and store free energy for use in biological processes

7 What is the electron carrier/acceptor for photosynthesis? NADPH

8 How does photosynthesis trap the energy from the sun to form ATP and NADPH? Chlorophyll reflects and transmits green light Chlorophyll absorbs energy in red and blue light When Chlorophyll absorbs free energy from light, the energy is used to boost electrons to a higher energy level in Photosystems I and II Reflected light Absorbed light Light Chloroplast Transmitted light Granum

9 Does chlorophyll work alone? No – it is aided by accessory pigments that absorb different wavelengths of light Chlorophyll a is the main photosynthetic pigment Chlorophyll b and carotenoids are accessory pigments that help the organism capture the maximum about of energy available

10 Fig Wavelength of light (nm) (b) Action spectrum (a) Absorption spectra (c) Engelmann’s experiment Aerobic bacteria Rate of photosynthesis (measured by O 2 release) Absorption of light by chloroplast pigments Filament of alga Chloro- phyll a Chlorophyll b Carotenoids

11 Where are photosystems I and II? Photosystems I and II are embedded in the internal membranes of chloroplasts (in thylaykoids) and are connected by the transfer of higher free energy electrons through and electron transport chain. Photosystem II is located in from of photosystem I – named by the order in which they were discovered. Photosystem I – PSI or P700; absorbs light best at a wavelength of 700nm Photosystem II – PSII or P680; absorbs light best at a wavelength of 680nm

12 Fig THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA e–e– Pigment molecules Photon Transfer of energy Special pair of chlorophyll a molecules Thylakoid membrane Photosystem Primary electron acceptor Reaction-center complex Light-harvesting complexes

13 What happens when light strikes chlorophyll a? When chlorophyll a absorbs light, its electrons go from a ground state to an excited state. Electrons at the excited state are passed onto the the primary electron acceptor within the reaction center of the photosystem The electrons are then passed between molecules as they move through the ETC. The movement of electrons creates an electrochemical gradient of H + across the thylakoid membrane

14 What is the final acceptor of electrons in the Light Reactions of Photosynthesis? NADP + H + → NADPH Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I ) Light Primary acceptor e–e– P700 6 Fd Electron transport chain NADP + reductase NADP + + H + NADPH 8 7 e–e– e–e– 6 Photosystem II (PS II )

15 How are electrons replaced at each photosystem? PSII / P680 A water molecules is split Electrons go to chlorophyll a H+ adds to electrochemical gradient across the thylakoid Oxygen atoms join to form Oxygen gas – released into atmosphere thru stomata PSI / P700 Electrons from PSII flow thru ETC to PSI

16 What happens with the elctrochemical gradient? Build up of H+ within the lumen of the thylakoid is used to create ATP by adding Pi to ADP H+ pass thru ATP synthase in the thylakoid – as they move down the concentration gradient, energy is harnessed to phosphorylate ADP making ATP

17 Fig Light Fd Cytochrome complex ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H + concentration) Thylakoid membrane THYLAKOID SPACE (high H + concentration) STROMA (low H + concentration) Photosystem II Photosystem I 4 H + Pq Pc Light NADP + reductase NADP + + H + NADPH +2 H + H2OH2O O2O2 e–e– e–e– 1/21/

18 What are the products of the light reactions of photosynthesis NADPH and ATP are produced and used to power the production of carbohydrates in the Calvin Cycle Oxygen is released as a waste product (from the splitting of H 2 O)

19 Do all photosynthetic autotrophs produce ATP to drive the Calvin cycle in a linear process (PSII to PSI)? No – some organisms only have one photosystem (PSI) These organisms use cyclic electron flow Cyclic electron flow does not produce NADPH; it only produces ATP Some organisms can switch between linear and cyclic electron flow to supplement ATP production ATP Photosystem II Photosystem I Primary acceptor Pq Cytochrome complex Fd Pc Primary acceptor Fd NADP + reductase NADPH NADP + + H +

20 Where did photosynthesis first evolve? Prokaryotic organisms Scientific evidence supports that prokaryotic photosynthesis was responsible for the production of an oxygenated atmosphere Prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis


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