Overview All organisms need a constant supply of energy to survive. - PowerPoint Presentation

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Slide2

Overview

All organisms need a constant supply of energy to survive.

For most life on earth, the ultimate source of energy is

the sun

.

Converting that energy source into something usable is accomplished by

photosynthesis

.

Slide3

Overview

Photosynthesis

:

the overall process by which sunlight (solar/light energy) chemically converts water and carbon dioxide into chemical energy stored in glucose (a sugar/carbohydrate.)Water is absorbed in roots CO2 is absorbed through stomataIt can be represented by the following chemical equation:6CO2 + 6H2O C6H12O6 + 6O2

Solar energy

Slide4

Overview

6CO

2

+ 6H2O C6H12O6 + 6O2Reactants = ingredientsCO2 (carbon dioxide) and H2O (water)Products = resultsC6H12

O6

(glucose) and

O

2 (oxygen)Note: Solar energy from the sun is necessary for photosynthesis to happen (as well as some enzymes) but isn’t considered a reactant or product.

Solar energy

Slide5

Structure of Chloroplast

Photosynthesis takes place in the

chloroplast

which has 2 main parts: Grana: pancake-like stacks of thylakoid membraneStroma: fluid-like substance that fills the space between the grana

grana

thylakoid membrane

Slide6

Why are plants green?

The presence of the pigment

chlorophyll

Chlorophyll a, chlorophyll b, and other pigments called carotenoids absorb every color of light in sunlight except green Therefore, green is leftover and is reflected and is what we see

Slide7

Two Stages of Photosynthesis

Photosynthesis can be divided into two sets of reactions:

1.

Light-dependent (“photo”) ReactionRequires solar energy.AKA the Electron Transport Chain (or light rxn)2. Light-independent (“synthesis”) ReactionDoes not require any solar energy.AKA the Calvin Cycle (or dark rxn)

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Light-Dependent Reaction

Purpose

=

Capture energy from the sun and store energy in “energy-carrying molecules” (ATP and NADPH)Location = occurs in the grana (specifically the thylakoid membrane) where the chlorophyll is stored.

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Light-Dependent Reaction

Summary

:

Water molecules are split into hydrogen and oxygen. Oxygen is released as a waste product. ATP and NADPH are charged up by the sun.

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Light-Dependent Reaction

Details

:

Energy from sun is passed down the Electron Transport Chain and is stored in the bonds of ATP and NADPHLight energy excites e- (electrons)e- move down ETC At end they combine with “final electron acceptors/carriers” of NADP+ and ADP, making NADPH and ATPChemiosmotic process b/c H+ ions move down the gradient to make ATPATP, NADPH, and H+ leave the grana and go into the stroma for the next stage!

Slide11

How is light absorbed?

Photosystems

absorb light

They are clusters of chlorophyll and proteins that trap energy from the sunChlorophyll is a pigment that can absorb sunlightEnergy is transferred to electrons  makes “excited” electrons

Slide12

What are electron carriers?

Molecules that

carry electrons

in order to pass on their energyEx. Compound (NADP+) that can accept a pair of high-energy electrons and transfer them to another molecule NADP+ grabs/carries 2 electrons and a H+  becomes NADPHATP and NADPH carry energy from the light-dependent rxn to the light-independent rxn.

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Light-Dependent Reaction

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Light-Independent Reaction

Purpose

= use the energy from the

“energy-carrying molecules” from the light-dependent reaction to make sugar (glucose)Location = occurs in the stroma

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Light-Independent Reaction

Summary

=

Calvin Cycle Series of enzyme-assisted chemical reactions powered by ATP and NADPH that produce three-carbon (3-C) sugars from CO2 and the H+ from water.The cycle happens twice and then these 3-C sugars combine to make glucose = C6H12O6

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Light-Independent Reaction

Details

Grab

CO2 diffuses into stromaEnzyme attaches CO2 to 5-C RuBPProduce unstable 6-C molecules Split Energy from ATP and NADPH and an enzyme break the 6-C molecule into 2 3-C molecules (PGA)

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Light-Independent Reaction

Details

Leave

Each 3-C molecule (PGA) is converted to a different 3-C molecule (G3P)One G3P leaves the cycle to become glucoseThe other G3P moves on to next stepSwitchRemaining G3P converts back to 5-C RuBP by using a phosphate from ATP and the cycle starts again!

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Light-Independent Reaction

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Rate of Photosynthesis

Speed is affected by

3 factors

: Light intensityExcites more e- causing light reactions to happen fasterAmount of CO2More ingredients to work with and process through cycleTemperatureIncreased temperature accelerates chemical reactions to a degree

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Why do root cells in a plant not need chloroplasts?

Chloroplasts catch sunlight! Since roots are underground, they are not exposed to the sun!

So they

can’t do photosynthesis.

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Alternate Pathways

Stomata

= pores on underside of leaf. Where…

Plants lose water CO2 entersO2 exitsIf it is too hot or dry out, the plant will close its stomata so that it doesn’t lose too much water and become dehydratedHowever this eliminates the gas exchange!!SO  the levels of CO2 drop and the levels of O2 increaseThis results in…. PHOTORESPIRATIONPhotorespiration adds oxygen to the Calvin Cycle instead of carbon dioxide - This makes NO sugar or ATP 

- This wastes all of the plants resources!

Two types of alternative pathways in plants to avoid this

:

1. CAM 2. C4

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Alternate Pathways

CAM

Done by

cacti and pineapplesOpen stomata at night and close during dayOpposite of normal plantsCauses them to grow slowly

Slide23

Alternate Pathways

C

4

Done by corn and sugarcanePartially close stomata during hottest part of dayAllows them to only need ½ as much water as normal plants!