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1. Photosynthesis •Plants and Oxygen •Plant Respiration •Parts of Photosynthesis •Light Reactions

1. Photosynthesis Plants and Oxygen Plant Respiration Parts of Photosynthesis Light Reactions

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1. Photosynthesis Plants and OxygenPlant RespirationParts of PhotosynthesisLight Reactions


Photosynthesis is essential to all life on earth; both plants and animals depend on it. It is the only biological process that can capture energy that originates in outer space (sunlight) and convert it into chemical compounds (carbohydrates) that every organism uses to power its metabolism.2Photosynthesis

Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a waste product into the atmosphere.3The Plant Cell

NucleusCell WallCentral VacuoleChloroplastsLike all organisms, plants have cells. But unlike animal cells, plant cells have more components in them, such as the cell wall.

Major components in a plant cellsCell wall- gives the cell a definite shapeCell membrane- controls the movement of substances in and out of a cellCytoplasm- allows substances in the cell to move aboutCentral vacuole- a large part in a plant cell to store food the plant needsNucleus- controls activities in a cell and contains genetic informationChloroplasts- contains chlorophyll which photosynthesizes and makes food for the plantHowever, some parts of the plant do not contain chloroplasts, such as the roots as no sunlight reaches underground and no photosynthesis can take place.4Plants and Oxygen ProductionCyanobacteria, like these in Yellowstone National Park, were the worlds first Oxygen Producers.

This Oxygen Revolution transformed early earths atmosphere. It was good for some (allowing for increased efficiency with O2 respiration) but bad for others (in the form of mass extinction of anaerobes)

5StromatolitesStromatolitesare special rock-like structures that form in shallow water.

They are formed bycyanobacteria that use water, carbon dioxide, and sunlight to create their food, and put out oxygenas a by-product. The Earliest Evidence of Stromatolites: 3.5 BYA!

6This world map shows Earths distribution of photosynthesis as seen via chlorophyllaconcentrations. On land, this is evident via terrestrial plants, and in oceanic zones, via phytoplankton.

Percentage of Earth's Surface Area

Pretty Big! HUGE!

Average net primary production (g/m2/yr)Low Productivity! High Productivity! Percentage of Earth's net primary productionWay higher than the others!Oceans and Rainforest are vital to oxygen production on Earth! What will happen if they arent protected?Photosynthesis/RespirationPhotosynthesis:Plants use H2O and carbon dioxide and produce starch and oxygen

H2O + CO2 = Starch/sugar + O2RespirationAnimals use starch/sugar and oxygen, and produce H2O and carbon dioxide

Starch/sugar + O2 = H2O + CO2 1111Respiration and photosynthesis are complementary processes

Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (low in energy) and water as substrates.

Photosynthesis releases oxygen and produces simple carbohydrate molecules (which are high in energy) that can subsequently be converted dozens of other sugar molecules.

These sugar molecules contain energy and the energized carbon that all living things need to survive.1212Point out that equation is balancedStomata on the underside of a leaf

1313a stoma (also stomate; plural stomata) is a tiny opening or pore that is used for gas exchange.

Air containing carbon dioxide and oxygen enters the plant through these openings where it is used in photosynthesis and respiration. Waste oxygen produced by photosynthesis exits through these same openings. Also, water vapor gets into the atmosphere through these pores in a process called transpiration.

The pore is formed by a pair of specialized cells known as guard cells which are responsible for regulating the size of the opening and found mostly on the under-surface(epidermis) of a plant leaf.An open (left) and closed (right) stoma of a spider plant (Chlorophytum colosum) leaf. When guard cells are turgid, the stoma is open (left).

Stomata on the underside of a leaf141415

1515Oxygen bubbles form on underwater plants. 16The Chloroplast

Most of the living world depends on chloroplasts for its energy!

Two membranes on outsideComplex membrane structure on inside

161617Photosynthesis Summary

1717Photosynthesis Summary

Photosynthesis takes place in two sequential stagesIn thelight-independent reactions, the chemical energy harvested during the light-dependent reactions drive the assembly of sugar molecules from carbon dioxide.In thelight-dependent reactions, energy from sunlight is absorbed by chlorophyll and that energy is converted into stored chemical energy. 1818

Absorbed and Reflected LightAbsorbed LightReflected LightTransmitted LightPlants are green because chlorophyll reflects green light.1919Light comes in spectrum plants dont use all light, only certain wavelengths = we will see this in later labs

2020Plants use visiable light Diff plants use diff parts of specThey have pigments to harness energy we will talk about that later

Leaf > Cell with Chloroplasts > Chloroplasts Interior > Pigment molecules around the light reaction chamber. 21

PhotosystemExcited electrons are the key to photosynthesis.

Grannum (stack of thylakoids)Within the membrane of each thylakoid arecountless clusters of pigments. These pigments are inside Photosystems.

The pigments act as antenna, bouncing photons towards the Primary Electron Receptor2222A photosystem consists of a light-harvesting complex and a reaction center. The first photosystem of photosynthesis is called photosystem 2.

Light harvesting complexReaction CenterPhotosystem 2 23

Pigments in the light-harvesting complex pass light energy (in the form of photons) to two special chlorophyllamolecules in the reaction center.

Chlorophyllamolecules Click once to animate this slide. 24

The light excites an electron from the chlorophyllapair, which passes to the primary electron acceptor.Primary Electron Acceptore-Photosystem 2 Click once to animate this slide. 25

The chlorophyll molecule must get a new electron from somewhere! Its electron is replaced by the splitting of a watermolecule. When a molecule of water is split energy (and oxygen) is released.OHHOHHe-For every two water molecules that are split, one molecule ofO2, the oxygen we breathe, is produced.Click once to animate this slide. 26

Meanwhile, the excited electron that was raised to the primary electron acceptor is transferred to a mobile carrierprotein, that moves it along the electron transfer chain.

As it moves along the electron transfer chain it releases works to produce ATP, the currency of energy, that a cell uses. However, as it produces ATP becomes less and less excited.e-ATPATPATPPhotosystem 2 Click once to animate this slide. 27


At the end of the Electron Transfer Chain, the electron is no longer excited. It enter Photosystem 1 and is excited again by the photons boosting it back into its high energy state.

e-Photosystem 1 Photosystem 2 Click once to animate this slide. 28

ATPATPATPThe re-excited electron is again transferred to a mobile carrierprotein, that moves it along the electron transfer chain, however this time it is combined with another electron, one proton, and a molecule of NADP+to create a molecule ofNADPH.e-NADP+e-HNADPHPhotosystem 1 Click once to animate this slide. 29Active Transport: Proton pumpsThe ATP released during the ETC transfer is used to drive proton pumps which sets up a concentration gradient of high H+ inside the thylakoid (lumen) and a low H+ outside the thylakoid (stroma)

HHInside of ThylakoidOutside of ThylakoidATPATPHHHHClick once to animate this slide. 30

ATPase ActivityHInside of ThylakoidOutside of ThylakoidADPProtons (H+) flow down concentration gradient through ATPase, an enzyme that synthesizes ATP.PATPHHHHHHH

323233Light ReactionsLight boosts electrons in Photosystem II, high energy electrons passed along chain of carriers Electrons replaced by splitting waterPassage of electrons down chain releases energy used to fuel proton pumps to generate ATPChain ends in Photosystem I, electron energy boosted again, passed on to NADPHATP, NADPH (fuel) produced by light reactions provide energy to power Calvin Cycle (making sugar)3333