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Photosynthesis. PS Learning Targets 1-8. Photosynthesis Outline. LT’s 1-3: Energy and Old Dead Dudes LT’s 4 & 5: Light and Structures of PS LT’s 6-8: Reactions and Factors of PS . ENERGY. LT 1. All living things need energy to live!

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PS Learning Targets 1-8

photosynthesis outline
Photosynthesis Outline

LT’s 1-3: Energy and Old Dead Dudes

LT’s 4 & 5: Light and Structures of PS

LT’s 6-8: Reactions and Factors of PS


LT 1

All living things need energy to live!

  • Heterotrophs-get their food by eating other organisms and turning them into energy

(Ex: herbivores, carnivore, decomposers, etc)

  • Autotrophs-get their energy by converting light or chemical energy into sugar, and then converting that into energy

(Ex: plants, bacteria, and some protists)

  • The cell will store energy in molecules like sugars and ATP
    • Most cells have small stores of ATP that only last a few seconds, but cannot store energy there long-term.
    • Cells will store it long term in carbohydrates/


    • Sugar energy > ATP energy

90x greater


What are the uses for ATP in biochemical reactions?

  • Active Transport
  • Energy to move cell organelles
  • Making proteins or nucleic acids
photosynthesis reaction

LT 3

Photosynthesis Reaction

6CO2 + 6H2OlightC6H12O6 + 6O2

Made in the dark rxn

Made in the light rxn

From the roots

From the sun

From the air

Will be made into ATP later in Cellular Respiration

light and pigments

LT 4

Light and Pigments

6CO2 + 6H2Olight C6H12O6 + 6O2

  • Photosynthesis starts with SUNLIGHT!
  • The light that comes from the sun is WHITE LIGHT or ROYGBIV(R O Y G B I V)
  • The red end is lower

energy and longer


  • The violet end has

higher energy and

smaller wavelength

light and pigments1
Light and Pigments

? If plants use visible light, are all colors/wavelengths/energies equally valuable to PS?

Let’s see…

Read the results of the experiment from Thomas Engelmann in 1803

light and pigments2
Light and Pigments
  • Most plants are GREEN. This means that

ROY BIV is absorbed andG is reflected.

  • This means that if ROY and BIV are absorbed these are the colors of light that power PS

Pigment – any substance that absorbs light

Chlorophyll a – the main pigment in plants

that absorbs the sun’s light to power PS

light and pigments3
Light and Pigments
  • There are also other pigments, beside chlorophyll a, called ACCESSORY PIGMENTS

chlorophyll b and carotenoids

  • Each pigment has its optimal portion of ROYGBIV for absorptionand to fuel PS
  • Chlorophyll a is the main pigment for PS, while the accessory pigments help chlorophyll a by expanding the portion of ROYGBIV it can use!
light and pigments4
Light and Pigments

Chlorophyll a best absorption occurs around 425nm AND 660nm

Chlorophyll b best absorption occurs around 475nm AND 640nm

Carotenoids best absorption occurs around 450nm AND 490nm

Therefore, the accessory pigments expand the absorption from about 425nm (V) to 425-490nm (V-B) AND from 660nm (R) to 640-660nm (O-R). More light absorbed = More PSing!!

why do leaves change color in the fall
Why do leaves change color in the fall?
  • What are the three kinds of pigments?
  • What two factors cause the color to change?
  • What three factors will give good fall color, especially reds?
why do leaves change color in the fall1
Why do leaves change color in the fall?
  • Remember…leaves get their colors from their pigments
why do leaves change color in the fall2
Why do leaves change color in the fall?

So how do they know to change color??

  • Fewer hours of sunlight/days are shorter
    • Trees produce less and less chlorophyll
    • Now carotenoids (already in leaf) can show through
  • Drop in temperature
why do leaves change color in the fall3
Why do leaves change color in the fall?

But what about the anthocyanins?

    • This is dependent upon…
      • Temperature and cloud cover
      • Warm days and cool nights = good reds
      • Help plants get all the remaining sugar out of the leaves before they fall off

So for good fall leaf color…

  • A warm, wet summer
  • A summer that is not too hot or dry
  • A fall with many warm days and cool nights
cell structures we already know

LT 5

Cell Structures We Already Know….

Cell Membrane

  • A phospholipid bilayer embedded with proteins
  • Selectively permeable
  • Maintains homeostasis for the cell via
    • PASSIVE (diffusion, osmosis, or facilitated diffusion)
    • ACTIVE TRANSPORT (active transport, endocytosis or exocytosis)

Now…The Leaf and Chloroplasts

  • The structures plants use for PS
the leaf

Cuticle- the waxy outer covering of a leaf that prevents water loss

The Leaf

Palisdade Layer-layer of long cells where chloroplastsare found and where most of PS occurs

Spongy Mesophyll-random collection of cells with large spaces in between them. Some PS occurs here, but mostly this is where the gases taken in & given off by PS are exchanged between palisade layer and stoma

the leaf cont
The Leaf (cont.)

Guard Cells-the cells on either side of the stoma that open/close them to let gases in or out OR to keep gases in

Stoma- openings on the underside of leaves that allow for gas exchange between the leaf and atmosphere.

the chloroplast
The Chloroplast
  • Organelle responsible for PHOTOSYNTHESIS!
  • Disc-like in shape
  • Green due to the presence of the pigment Chlorophyll a
  • Found mostly within the palisade layer, but some are in the mesophyll too.
  • Internal structures include
    • Thylakoids
    • StRoma
    • Granum (sing.) or Grana (pl.)
    • Lumen

Let’s see this

the chloroplast cont
The Chloroplast (cont.)

1 of 2 membranes that surround the organelle

Fluid between the thylakoidswhere the dark rxn occurs

Disc where the pigments of PS are. Where the light rxn occurs

how photosynthesis occurs


6 & 7

How Photosynthesis Occurs

? So what about the rest of the PS equation; like CO2, Water, Glucose and O2 ?

6CO2+ 6H2Olight C6H12O6 + 6O2

PS occurs in 2 parts

  • Light Dependent (or Light Reaction)
    • This part of the rxn requires LIGHT, H2O, and gives off O2
  • Light Independent (or Dark Reaction)
    • This part of the rxnrequires CO2and produces the sugar or glucose



the light reaction
The Light Reaction



“I’m So Excited!”



electron carriers receive

chlorophyll’s electrons the excited e-’s and pass get very excited from the them along to other sun’s energy molecules. These e-’s carriers molecules are

called the


the light reaction1
The Light Reaction

Examples of a Carrier Molecule:


  • Takes 2e-’s from chlorophyll and 1H+ from water

NADP+ + 2e- + 1H+NADPH

  • Takes energy with it to other cell rxns
  • Think of it like a UPS truck, picking up “packages” and dropping them off


the light reaction key concepts
The Light Reaction: Key Concepts
  • Occurs in the thylakoid membrane of the chloroplast
  • IncludesPhotosystem IIandPhotosystem I
  • NeedsLight and H2O to start
  • ProducesO2, NADPH and ATP


the light reaction photosystem ii
The Light Reaction: PhotosystemII

PS II - In the Thylakoid Membrane (TM)

  • 1. e- absorb sun’s energy and get highly energized
  • 2. The proteins in the TM split a water (hydrolysis) to make

H+’s , e-’s , and O2

  • 3. e-’s go to ETC (a series of protein carriers)
  • 4. Energy from the e-’s pumps H+’s into the TM, changing the [H+] ions (low to high-active transport)
the light reaction photosystem i
The Light Reaction: PhotosystemI

PS I - In the Thylakoid Membrane (TM)

  • 5. Light is energized again
  • 6. e-’s move to the final e- acceptor which adds them to NADP+ to make NADPH
  • 7. High [H+] (left over from hydrolysis) diffuse through the enzyme protein ATP synthase to make ATP form ADP (H+ give energy to add a phosphate to ADP)

Let’s See This

the light reaction the thylakoid membrane1
The Light Reaction: The Thylakoid Membrane

A Little Quiz:

  • Put a #1 where there is a higher concentration of H+
  • Draw a squiggly line between PSII and PSI
  • Put a #2 on the thylakoid membrane
  • Put a #3 in the stroma
  • Put a #4 where the e-’s are first energized
  • Put a #5 where the e-’s are re-energized
  • Put a #6 where hydrolysis occurs
  • Put a #7 where active transport is occurring.
the dark reaction key concepts



The Dark Reaction: Key Concepts
  • The secondpart of PS is called the Dark Reaction,the Calvin Cycle, or the Light Independent Cycle
  • It is called the Dark Rxn because this part can take place without light (that is not to say it must be dark,

but if it were,

this part could

still proceed)

the dark reaction key concepts1
The Dark Reaction: Key Concepts
  • The two products from the Light Reaction, NADPH and ATP go to the Dark Reaction
  • NADPH and ATP have lots of energy intheir bondsbut they can only hold it for a few minutes
  • If the cell wants to hold the energy long-term, they will have to build high energy moleculesthat can hold it…like GLUCOSE (savings account!)
  • This process takes place in the stRoma (outside of chloroplast)
the dark reaction

From Light Rxn

The Dark Reaction


5 C’s


3 -CO2

3-6C Compound-Unstable!

6-3C PGA’s


6-3C PGAL’s

3-5C RuBP’s


Calvin Cycle Video

1 exits and will become GLUCOSE

5 stay in cycle

limiting factors to ps



Limiting Factors to PS

There are factors that limit the amount of PS

  • H2O –slow or decrease PS
  • Temperature
    • Recall that enzymes have particular optimal


    • Functions best between 0-35°C
    • Temperatures above or below these temps slow PS
    • Very low temps STOP PS
  • Light Intensity- increase intensity = increase PS
  • Color of Light – RO and BV preferred
photosynthesis review



Photosynthesis Review
  • Two rxns: Light and Dark
  • Reactants: H2O, CO2, and Light
  • Products: O2 and Glucose
  • Two Locations:
    • Light –Thylakoid Membrane
    • Dark- StRoma
photosynthesis review1
Photosynthesis Review

Word Bank


ATP (2)



Light Energy from the sun

High energy sugars



Light-depentdent reaction

Calvin Cycle