Photosynthesis

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What is the function of chloroplastswithin photosynthetic organisms?

Photosynthesis is the process by which light energy is changed into chemical energy that is both storable and useable.

Sunlight Energy Rich Organic MoleculesBiochemical Pathways are series of chemical

reactions in which the product of one reaction becomes the reactants for the next reaction.

Phototrophs are organisms that use photosynthesis.

H2O + CO2 O2 + C6H12O6

Cell Respiration Equation:

Photosynthesis Equation:

Photosynthesis is divided into the Light and Dark Reactions .

The Light Reaction depends on the absorption of light to drive it.

Thylakoids :(1) flattened membrane sacks found in groups called

grana within chloroplasts(2) where the light reaction occurs

Stroma :(1) the liquid that surrounds the grana within the

chloroplasts

(2) analogous to the matrix of the mitochondria(3) where the dark reaction occurs

Fig. 6-17

Free ribosomesin the mitochondrial matrix

Intermembrane spaceOuter membrane

Inner membraneCristae

Matrix

0.1 µm

Visible spectrum - Light which can be seen by the human eye. It is also the portion of the electromagnetic spectrum that is used to drive photosynthesis

Wavelength indicates the strength of a photon of light. Short wavelength = high energy; long wavelength = low energy

Pigments absorb light at one wavelength or more.Chlorophyll

Pigment found in chloroplasts which is responsible for absorbing light to excite electrons

There are three types (A, B, and C) found in different organisms

Accessory Pigments - pass absorbed light energy over to chlorophyll to be further converted into chemical energy

Carotenoids are red, orange, or yellow pigments Phycobins are pigments used in algae and bacteria

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1. What does sunlight do in photosynthesis?

2. How many photosystems do plants and cyanobacteria have and how are they organized?

3. What is different about the origin of electrons in bacterial and plant photosynthesis?

4. What are the similarities between this part of photosynthesis and the electron transport chain?

5. What is the role of photosystem II? How does that role compare with the role of photosystem I?

Question of the Day!!

If glucose is broken down for energy in respiration, is carbon dioxide broken down for energy in photosynthesis?

http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm

Procedure : Your task is to use the simulation to determine how wavelength and intensity affect the rate of photosynthesis (and the production of ATP). Keep in mind you are dealing with two variables, so in order to determine absolutely how each factor affects photosynthesis, you must keep one variable constant while manipulating the other variable.

Lab Report must contain the following typed section s.

1. Introduction: Describe briefly the light dependent reactions and propose a hypothesis to answer the experimental question.

2. Data: Include data tables for the simulation. The tables must show clearly trends resulting from changes of intensity and changes of wavelength. Multiple data tables would probably be best here. In Microsoft Word, use the "table" function to organize your data.

3. A graph showing how the percentage of ATP changed (Y axis) as a result of changes in wavelength and intensity (X axis). Two graphs would be best here.

4. Conclusion: Use your data to answer the experimental question. Answer clearly how light wavelength affects the reaction, and how light intensity affects the reactions. Offer an explanation of the results, taking into account the principles of photosynthesis and the light reaction.

The light reaction of photosynthesis:(1) produces the energy needed to assemble

sugars in the dark cycle(2) is similar to the ETC from cellular respiration(3) “extracts” electrons from water by splitting it

apartThe reactions within the light reaction look like:

(1) 2 H2O → 4 H+ + 4e- + O2

(2) ADP + Phosphate → ATP(3) NADP+ + H+ + 2e- → NADPH

Enzymes close to Photosystem II break apart water. The electrons move through/along the photosystems and the hydrogen ions are pumped during ETC and back through ATP synthase.

LightReaction

DarkReaction

Gylcolysis

KrebsCycle

ETC

CO2

NADPH & ATP

NADP+ & ADP

O2

Glucose

NADHNADH

& FADH2

NAD+ & FAD

Pyruvate

ATP

Fig. 10-7

Reflectedlight

Absorbedlight

Light

Chloroplast

Transmittedlight

Granum

The light reaction is separated into two photosystems that occur in order. Both systems are embedded within the thylakoidmembrane.

A chlorophyll reaction array is the place where light energy excites electrons.

Photosystem II (the first one!?!?) contains a chlorophyll reaction array, carrier proteins (hydrogen pumps), and ATP synthase.

Photosystem I (the second one) contains a chlorophyll reaction array and an enzyme that makes NADPH.

Fig. 10-14

MillmakesATP

e–

NADPH

Ph

oto

n

e–

e–

e–

e–

e–

Ph

oto

n

ATP

Photosystem II Photosystem I

e–

Fig. 10-17

Light

Fd

Cytochromecomplex

ADP+

i H+

ATPP

ATPsynthase

ToCalvinCycle

STROMA(low H + concentration)

Thylakoidmembrane

THYLAKOID SPACE(high H + concentration)

STROMA(low H + concentration)

Photosystem II Photosystem I

4 H+

4 H+

Pq

Pc

LightNADP+

reductase

NADP+ + H+

NADPH

+2 H+

H2OO2

e–e–

1/21

2

3

Photosystem II:(1) Enzymes in the thylakoid membrane capture

and break apart water into hydrogen ions, electrons, and oxygen.

(2) An electron pair that was passed to chlorophyll and excited by a photon of light is handed over to proteins similar to ETC.

(3) Hydrogen ions are pumped across the membrane creating a gradient that is used to make ATP via movement through ATP synthase.

(4) Two oxygen ions bond to create O2 which is released by the plant into the atmosphere.

It’s Time for Draw-rings!

Student drawings must include (1)an enzyme for splitting water(2) two chlorophyll reaction arrays(3) one hydrogen pump (ETC)(4) ATP synthase(5) the reactants and products of splitting water(6) the reactants and products of making ATP, and (7) an arrow-trail or something that relates the path of an electron.

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Why do plants need water?

Question of the Day!Why does a plant make sugar in photosynthesis as

opposed toanother type of molecule, like ATP?

The energized electrons each move from Photosystem II to Photosystem I by traveling down the electron transport chain. The electron transport chain pumps H+ across the thylakoidmembrane to the inside using energy lost by the electron. This strengthens the concentration and charge gradient across the thylakoidmembrane.

The Calvin Cycle is also called the dark reaction. It uses the ATP and the NADPH from the light reaction to make a more storable and stable energy rich molecule, sugar.

Fig. 10-16

Key

Mitochondrion Chloroplast

CHLOROPLASTSTRUCTURE

MITOCHONDRIONSTRUCTURE

Intermembranespace

Innermembrane

Electrontransport

chain

H+ Diffusion

Matrix

Higher [H +]Lower [H +]

Stroma

ATPsynthase

ADP + P i

H+ATP

Thylakoidspace

Thylakoidmembrane

1. The Calvin Cycle “starts” as 6 five-carbon chains and 6 single carbon molecules in the form of carbon dioxide come together to form 12 three carbon chains.

2. The energy from 12 ATP being turned into 12 ADP and from 12 NADPH being turned into 12 NADP+ is absorbed to create higher energy levels in the 12 three-carbon molecules

3. Two of the 12 three-carbon molecules come together to form one single sugar molecule that will leave the system for storage.

4. The remaining 10 three-carbon molecules will then take the energy from 6 more ATP breaking down into ADP and reconfigure into 6 five-carbon molecules.

5. The five carbon molecules that are left at the end reenter step one with 6 new CO2 molecules and that completes the cycle

Fig. 10-18-1

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

Fig. 10-18-2

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

ATP6

6 ADP

P P61,3-Bisphosphoglycerate

6

P

P6

66 NADP+

NADPH

i

Phase 2:Reduction

Glyceraldehyde-3-phosphate(G3P)

1 POutput G3P

(a sugar)

Glucose andother organiccompounds

CalvinCycle

Fig. 10-18-3

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

ATP6

6 ADP

P P61,3-Bisphosphoglycerate

6

P

P6

66 NADP+

NADPH

i

Phase 2:Reduction

Glyceraldehyde-3-phosphate(G3P)

1 POutput G3P

(a sugar)

Glucose andother organiccompounds

CalvinCycle

3

3 ADP

ATP

5 P

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)

G3P

All fuel sources are recycled between the light and the dark reaction. ATP made in the light reaction is used in the Calvin Cycle and the ADP returns to the light reaction, Similarly, NADPH made in the light reaction is used in the Calvin Cycle and NADP+ then returns to the light reaction where it can regain its hydrogen and electrons.

The Calvin Cycle is also known as the Dark Reaction but does not occur only at night. It occurs at all times and in fact slows down at night due to a decrease in available fuel from the light reaction

Fig. 10-21

LightReactions:

Photosystem IIElectron transport chain

Photosystem IElectron transport chain

CO2

NADP+

ADPP i+

RuBP 3-PhosphoglycerateCalvinCycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

It’s Time for Draw-rings!

Student drawings must include (1)an enzyme for splitting water(2) two chlorophyll reaction arrays(3) one hydrogen pump (ETC)(4) ATP synthase(5) the reactants and products of splitting water(6) the reactants and products of making ATP, and (7) an arrow-trail or something that relates the path of an electron.

Procedure Day 1

Each lab group will get:• one plant (that has been kept in the dark for 24 hours)• four clear plastic squares slightly larger than the leaf• paper clips• two paper cut outs and/or film negatives smaller than the leaf• scissors• clear tape

1. Take one paper cut out and tape it to one side of the clear plastic square. Then take the other paper cut out and tape it to one side of another clear plastic square.

2. Cut out a large leaf shaped whole in the two other plastic squares

3. Take one plastic square with a cut out on it and one plastic square with a hole cut out of it and use the paper clips to sandwich the leaf between both squares. The square with the hole cut out goes on the underside of the leaf and the square with the cut out goes on the upper side of the leaf. Repeat this step on another leaf using the other two squares.

http://www.science.smith.edu/departments/Biology/Bio231/calvin.html

Day 2Materials:

• hot plate• ethanol• beakers • tweezers or tongs• paper towels• iodine solution• aluminum foil

1. Carefully remove the plastic squares from the plant2. Cut the leaf from the plant.3. Hold the leaf with forceps, tweezers or tongs, and

drop it in a beaker of boiling water to kill the cells.4. Place it in a beaker of hot ethanol for two minutes to remove most of the

chlorophyll.5. Place it in a beaker of room temperature ethanol for one minute. The leaf

should be almost white.6. Blot the leaf on paper towels7. Place the leaf in iodine solution on a square of aluminum foil for one minute

or less. Remove it when you can see the picture. Remove both the leaf and the foil together and place in water to rinse. You may blot the leaf and press it in a book if desired.

Make a prediction for how you think the leaf will look at the end of the experiment.

1. Why are certain parts of the leaf darker than oth ers?

2. Is there a relationship between the areasthat received light and the areas of starch product ion?

3. Think about what you have learned about photosyn thesis to fully explain the relationship you observe.

Review Time1. One of the principal chemical compounds that living things use to store energy is:

a) DNA b) ATP c) H2O d) CO2

2. In addition to light and chlorophyll, photosynthesis requires:

a) H2O & O2 b) H20 & Sugar c) O2 & CO2 d) H2O & CO2

3. The products of photosynthesis are:

a) sugars & O2 b) sugar & CO2 c) H2O & CO2 d) H2 & O2

4. The first process in light dependent reactions of photosynthesis is:

a) light absorption b) electron transport

c) oxygen production d) ATP formation

5. Which substance from the light-dependent reactions of photosynthesis is a source of energy for the Calvin Cycle?

a) ADP b) NADPH c) H2O d) pyruvic acid

If plants make their own foods, why do some plants, like Venus fly-traps, appear to be consumers rather than

producers?