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PHOTOSYNTHESISSBI4U

Diana Puia

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CURRICULUM EXPECTATIONSC3.2 explain the chemical changes and energy conversions associated with the process of photosynthesis (e.g., carbon dioxide and water react with sunlight to produce oxygen and glucose)

C3.3 use the laws of thermodynamics to explain energy transfer in the cell during the processes of cellular respiration and photosynthesis.

C3.4 describe, compare, and illustrate (e.g., using flow charts) the matter and energy transformations that occur during the processes of cellular respiration (aerobic and anaerobic) and photosynthesis, including the roles of oxygen and organelles such as mitochondria and chloroplasts.

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AGENDA Which organisms perform

photosynthesis? What is photosynthesis? (Overview) Where does it happen? Light as a source of energy Light-dependent reactions

Photosystem I Photosystem II

Calvin cycle

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Which Organisms perform Photosynthesis? PHOTOAUTOTROPHS Plants(a) Sunflowers Algae (b)Spirogyra Protists(c)Euglena gracilis Cyanobacteria(d) Anabaena

NOTE: blue-green algae bacteria in oceans produce the most O2.

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What is Photosynthesis?

The process which transforms light energy into chemical energy.

OVERALL REACTION:

6CO2 + 6H2O C6H12O6 + 6O2

light energy

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What is Photosynthesis?LIGHT-DEPENDENT REACTIONS(the photo part) Requires H2O,

chlorophyll, and light energy (from any light).

Produces O2, ATP, and NADPH

CALVIN CYCLE(the synthesis part) Requires ATP,

NADPH, and CO2. Produces glucose

(sugars), ADP+Pi, and NADP+

6CO2 + 6H2O C6H12O6 + 6O2

light energy

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Photosynthesis Overview

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Why is photosynthesis important?

Directly or indirectly, photosynthesis nourishes almost the entire living world:

Makes energy-rich organic molecules (glucose) from energy-poor inorganic molecules (CO2 and H2O)

It is the start of all food chains & webs. It also makes oxygen.

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Where does photosynthesis happen?

Photosynthesis happens in:

• Palisade layer

• Spongy layer

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ChloroplastsENDOSYMBIOTIC THEORY: An ancestor of cyanobacteria was engulfed

by an ancestor of today’s eukaryotic cells. Symbiotic relationship – eukaryote offered

protection, cyanobacteria offered food. Chloroplasts are structurally similar to and

likely evolved from photosynthetic bacteria.

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Structure of a chloroplast

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Light as a Source of Energy 60% absorbed by the atmosphere 40% reaches plants on Earth. Only 5% of that is used in

photosynthesis.

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What is light? A form of electromagnetic (EM) radiation. Travels in wave packs as photons (also known as

quanta). Photon wavelength is inversely proportional to

energy (the shorter the wavelength, the “bluer” the light, the higher the energy).

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T.W. Engelmann’s Experiment (1882) Used Spirogyra – has a

long spiral chloroplast throughout its length.

Added aerobic bacteria to the slide.

Placed a triangular prism between the light source and the stage.

Found that bacteria accumulated where oxygen was produced the most (in areas exposed to red and blue-violet light).

Engelmann video

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The Absorption Spectrum of Chlorophyll A and B

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Photosynthetic Pigments

Chlorophyll a (blue-green) Chlorophyll b (yellow-green) Carotenoids (yellow-orange) Xanthophylls (yellow) Anthocyanins (red, violet, blue)

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CHLOROPHYLL

Click icon to add picture

COMPOSED OF 2 PARTS:• Porphyrin ring• Hydrocarbon chain

TWO COMMON TYPES:Chlorophyll a – methyl (CH3)

Chlorophyll b – aldehyde (CHO)

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Coloured leaves? Right: mosaic forest (same season) Bottom: summer vs. autumn leaves

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Capturing light energy: photosystemsPHOTOSYSTEMS CONSIST OF: Antenna complex – captures light first Reaction centre – chlorophyll a molecule

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Capturing light energy: photosystems

Main photosynthetic pigment: Chlorophyll a (two types:

p680 and p700)

Accessory pigments: Chlorophyll b – broader

spectrum used for photosynthesis.

Carotenoids – absorb excessive light that would damage chlorophyll.

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Photoexcitation

Before light strikes the molecule, electrons are at ground state.

Photon of light hits. Electron excited to higher energy state. Electron falls back down to ground state and gives off a photon of energy (flourescence) and some heat.

What happens when a chlorophyll molecule interacts with light energy (photons)?

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Chlorophyll Fluorescence Isolated chlorophyll molecules fluoresce when

separated from the photosynthetic membrane in which they are normally embedded.

If illuminated in bright white light, an isolated solution of chlorophyll will fluoresce, giving off red light and heat.

Fluorescence DEMO

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Photosystems

Photosystem I (PSI)

Contains p700 chlorophyll a.

Absorption peaks at 700nm red light.

Found in the thylakoid membrane.

Photosystem II (PSII)

Contains p680 chlorophyll a.

Absorption peaks at 680nm red light.

Found in the thylakoid membrane.

The two photosystems work together to start the process of photosynthesis

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Non-cyclic (linear) electron flow and chemiosmosis

Electron transport

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Non-cyclic electron flow (Z-diagram)Pathways and energy changes are shown in a graph form.

Energy video

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Cyclic electron flow A non-sustainable pathway.

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Melvin Calvin (1911-1997) Determined the details of the cycle in

the early 1960’s. Received a Nobel prize in Chemistry in

1961.

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Calvin Cycle (dark light-independent reactions) The Calvin Cycle needs: ATP (from the light reactions) H atoms from NADPH (from the light reactions) CO2(from the environment)

3 phases: Carbon fixation Reduction reactions Regeneration of RuBP

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Calvin Cycle video