Chapter 10

Chapter 10Photosynthesis

The conversion of radiant energy into chemical energy

&Converting inorganic

matter into organic matter

Overview of Chapter 10 • Autotrophs vs. Hetertrophs• Properties and Characteristics of Light • Chloroplast Structure & Function Key Pigments: Chlorophyll a &

b, & Carotenoids• Light Reactions (Light Dependent)-Photosystems• Cyclic vs. Non-cyclic flow of Electrons-------------------------------------------------------------------------------• Dark Reactions (Light independent)-Calvin Cycle• Photorespiration: ↓ Photosynthetic efficiency• C3, C4, and CAM Metabolic Pathways of Plants

Photosynthesis in Nature

Autotrophs are biotic Producers;

Ex. Photoautotrophs and chemoautotrophs; obtains organic food without eating other organisms

Heterotrophs: are biotic Consumers; obtains organic food by eating other organisms or their by-products (includes decomposers)

Visible Light

• Wavelength range of: 380 nm – 760 nm

• Colors include:

R O Y G B I V Red: Lowest energy, Longest wavelength

Violet: Highest energy, smallest wavelength

Leaves: The Solar Collectors for Plants

• Considered to be an organ of the plant• Site for Photosynthesis (lots of chloroplasts)• Cutin-thin wax layer helps to reduce or control water loss• Other features worth noting:

-Upper & Lower epidermis-Stomata & Guard cells-Xylem & Phloem (vascular bundle sheaths)-Palisade & spongy Mesophyll-Trichomes

• High surface area: Can cause water to be lost • See a definite trade off

Properties of Light

• Electromagnetic Radiation• Possesses properties of a particle and a wave• Generated when electrons move from a high

energy state to a lower energy state. • Small portion of the EM spectrum (pg .157)• Composed of small “packets” or quantized

amount of energy called PHOTONS• Described by Max Plank and DeBroglie

Properties of Light (Pg. 186)

Photons and Electrons

• Photons interact with electrons and move electrons to higher energy levels from the “ground state”

• When electrons “fall” to the lower ground state, and light is emitted as it falls. This light is called “Fluorescence”.

The Chloroplast and Light (pg. 186)

• The (3) Fates of Light as it interacts with a chloroplast.

Structure of the Chloroplast

• Double membrane

• Has its own DNA

• Internal membrane system called Thylakoids

• Contains protein pigmets: ex chlorophyll a

Internal Structure of a Leaf

Introductory Questions #9

1. Name three factors that can affect transpiration in plants.

2. How do plants absorb light energy? Name some features that allow plants to absorb light. What are some differences between chlorophyll a and chlorophyll b?

6) What did Engelmann’s experiment measure? What organisms did he use?

7) Which reactant does the oxygen produced from photosynthesis directly come from?

8) Where specifically do the light and dark reaction take place within a plant cell?

9) Name the three parts that make up a photosystem.10) How does NADPH differ from NADH?

The Leaf: The Site for Photosynthesis

The Chlorophyll Molecule (Pg. 188)• Porphyrin ring (absorbs light)• Central Magnesium

Atom• Hydrocarbon tail• Alternating double &

single bonds• Similar to

hemoglobin• History of Discovering Chlorophyll:

http://www.chm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.htm

Typical Pigments Found in the Thylakoid Membrane

• Chlorophyll a - important in light reactions

• Chlorophyll b - accessory pigment

- has a yellow/green reflection

• Carotenoids – are yellow & orange

• Anthocyanins– are red pigments

• Fucoxanthin – is a brown pigment

• Xanthophylls – are typically yellow

Determining Absorbance of a Pigment (pg. 187)

Lab #14: Plant Pigments & Photosythesis • Computer guided Lab using our typical Ph_school

lab bench site• Two Parts:

– Separation of pigments (Hon. Bio/Reg Bio.)– Oxidation/Reduction with DPIP

• Key point about the lab:– The pigments separated by chromatography were: (top to bottom)

• Carotene (orange)---Xanthophyll (yellow)----Chlorophyll a ----Chlorophyll b

– DPIP has blue color acting as an electron acceptor: changes to colorless when it is reduced (gains the electron)

– Oxidized DPIP will turn back to a blue color– As the samples become reduced (DPIP becomes colorless) the transmittance

will be high and as it becomes oxidized (DPIP changes to blue) the transmittance will be low because of the amount of absorbance.

Absorption & Action Spectra (pg. 187)

Engelmann’s Experiment (pg. 187)

• Obtained the first action spectrum in 1883• Used Spirogyra w/spiral shaped chloroplasts• Exposed this alga to a color spectrum using a prism• Measured photosynthesis by using certain motile

bacteria that would be attracted to the oxygen released by photosynthesis.

• Control: Ensure that the bacteria were not attracted to the colors, he conducted the experiment without spirogyra. No preference was shown by the bacteria.

Discovering the Process of Photosynthesis

• For centuries gardeners have asked the perplexing question:

“Where does the mass of a tree that weighs several tons come from when it starts as a seedling weighing only a few grams?:”

• Does it come from:-Soil-air-water

Experiments conducted probing this Question

• Jan Van Helmont - accounted for the water (hydrate) aspect of photosynthesis

• Joseph Priestly – accounted for the release of oxygen by photosynthesis using a a burning candle, glass jar and a mint leaf.

• Jan Ingenhousz – same as Priestly except showed that light was required.

Photosynthesis Equation

Photosynthesis-Chemical Equation

• Reactants: carbon dioxide & water• Products: Glucose and oxygen gas• Also: Light energy, enzymes, pigments

Another Perplexing Question about Photosynthesis

• Where does the oxygen released by photosynthesis come from directly? Does it come from the carbon dioxide or water?

• First challenged by C.B. Van Niel using photosynthetic bacteria which showed that CO2 is not split.

• Isotopic Oxygen (18O) was used to trace and track the fate of oxygen.

Tracking the Fate of Isotopic Oxygen

Photosynthesis: an overview

Redox processH2O is split into:

2e- and 4 H+ The H’s are transferred to CO2 and a

sugar is produced (CH2O)

2 Major steps to Photosynthesis:• Light Reactions (“photo”)

-occurs in the thylakoids • Dark Reactions

-Also called “Carbon fixation”-occurs in the stroma-Involves the Calvin Cycle

Photosynthesis: an overview

A Photosystem (located in the thylakoid membranes)

• Light Harvesting Protein Pigments

• Have “antennae pigments complexes”

(200-300 pigment molecules)

• Chlorophyll a and chlorophyll b are present

• Chlorophyll a = Reaction Center

• Primary Electron Acceptor will receive the electron (reduced) and chlorophyll a will be oxidized and lose the electron.

Structure of a Photosystem

• Light harvesting units of the thylakoid membrane

• Composed mainly of protein and pigment antenna complexes

• Antenna pigment molecules are struck by photons

• Energy is passed to reaction centers (redox location)

• Excited e- from chlorophyll is trapped by a primary e- acceptor

Photosystems in the Thylakoid Membrane

Mechanical view of Photosynthesis

Build up of Hydrogen ions in the thylakoid space

Introductory Questions #9

1. Name three factors that can affect transpiration in plants.

2. How do plants absorb light energy? Name some features that allow plants to absorb light. What are some differences between chlorophyll a and chlorophyll b?

6) What did Engelmann’s experiment measure? What organisms did he use?

7) Which reactant does the oxygen produced from photosynthesis directly come from?

8) Where specifically do the light and dark reaction take place within a plant cell?

9) Name the three parts that make up a photosystem.10) How does NADPH differ from NADH?

Photosystems in the Thylakoid Membrane

Noncyclic Electron Flow

Noncyclic Electron Flow• Most common light reaction pathway• Involves (2) Photosystems:

Photosystem II (P680)-absorption peakPhotosystem I (P700)-absorption peak

• Exhibits A “Z scheme” or Zig-Zag flow of electrons• Electrons flow in one direction• ATP and NADPH are produced• Electrons do not cycle back to the ground state to

chlorophyll.

Cyclic Electron flow• Alternative cycle when ATP is deficient• Photosystem I used but not II; produces ATP

but no NADPH• Why? The Calvin cycle consumes more ATP

than NADPH…….• Cyclic photophosphorylation

Review of Light reactions:http://web.mit.edu/esgbio/www/ps/light.html

Cyclic Electron flow

Cyclic Flow of Electrons• Utilizes Photosystem I (P700) only

• Electrons cycle back to chlorophyll

• NADPH is not produced.

• Helps to produce more ATP that is used in the Calvin Cycle

• Stimulated by the accumulation of NADPH

Photosynthesis-Light & Dark Reactions

The Calvin Cycle-C3 pathway3 molecules of CO2 are ‘fixed’ into

glyceraldehyde 3-phosphate (G3P)

3 Phases:1- Carbon fixation

Each CO2 is attached to RuBP (rubisco enzyme)

2- Reductionelectrons from NADPH reduces to

G3P; ATP used up

3- Regeneration G3P rearranged to RuBP; ATP used;

cycle continues

The Calvin Cycle-C3 pathway

Calvin Cycle: First PhaseCarbon Fixation:(1 carbon) + (5 carbon) (3 carbon)

CO2 + Ribulose Bisphosphate (RuBP) →2 Phosphoglycerate (PGA)

w/ help of: RUBISCO(Ribulose Bisphosphate Carboxylase)-most abundant protein on earth

**Carbon is converted from an inorganic form into an organic form and thereby “FIXED”.

**A Total of Six carbons must be fixed for one glucose molecule or some other hexose.

Calvin Cycle: Second PhaseReduction Phase:

Phosphoglycerate (PGA) ↓ is phosphorylated (use ATP)

1,3-bisphosphoglycerate↓ Redox Rxn w/NADPH

Glyceraldehyde-3-Phosphate (G3P)

*G3P is a sugar also seen in glycolysis*For every 3 CO2 → 6 G3P is produced but only ONE

can be counted as a gain in carbohydrate and can exit the cycle.

Calvin Cycle: Third Phase

Regeneration of RUBP:

5 G3P are phosphorylated 3 RuBP

3 ATP’s are used to do the chemical rearrangement

RuBP can now accept more CO2 molecules

Calvin Cycle - Net Synthesis

• For every G3P molecule produced:

3 CO2 are brought in

9 ATP’s are consumed

6 NADPH are used

**G3P can then be used by the plant to make glucose and other organic compounds

Website for review of the Calvin Cycle: http://web.mit.edu/esgbio/www/ps/dark.html

To Make a Six Carbon Molecule You need:

• 6 CO2 molecules (6 carbons)

• 6 molecules of RuBP (30 carbons)

(remain in the cycle from TEN G3P’s)

• 18 ATP molecules

-Produced-

• 12 molecules of PGA (36 carbons)

• 2 molecules of G3P (6 carbons)

C3 Metabolic Pathway in Plants

• CO2 enters directly into the Calvin Cycle

• The first organic compound made is a 3 carbon molecule called PGA (phosphoglycerate)

• Close their stomata on hot, dry days to conserve water.

• Photorespiration occurs typically in these plants.

• Examples include: Rice, Wheat, and Soybeans.

Photorespiration• Observed in C3 plants when stomata are closed during

hot, dry days• CO2 levels ↓ & O2 levels • Rubisco binds with O2 instead of CO2

• Drains the Calvin cycle (↓ photosynthetic output)• No ATP is produced• No food molecules (G3P) are made• Thought to be an evolutionary relic (Rubisco’s affintiy

for O2 remains)• Considered to be wasteful and no benefit known• TWO Adaptations have emerged to minimize

photorespiration: They are observed in the C4 and CAM plants

C4 Metaboic Pathway in Plants• CO2 and PEP (phosphoenolpyruvate) combine to produce a 4-Carbon

compound called “Oxaloacetate”

• Unique anatomy is present w/Bundle Sheath cells that are photosynthetic surrounding the veins of the leaf.

• Calvin cycle is confined to the chloroplasts within the bundle sheath cells.

• PEP carboxylase is used initially instead of Rubisco (higher affinity for CO2)

• A high CO2 concentration is maintained for the Calvin cycle which minimizes photorespiration.

• CO2 is continually fed into the Calvin cycle from the mesophyll cells even when the stomata are closed.

• Examples include: Corn & Sugarcane

Cell Layers Observed in Leaves

Unique Anatomy of C4 Plants

CAM Plants

• ‘CAM” – Crassulacean Acid Metabolism• Adapted in arid environments• Close their stomata during the day and open them

only at night. (reverse of typical plants)• Organic compounds made are “stored” at night in

their vacuoles when the stomata are open then used later during the day.

• Common in succulent plants such as: ice plants, pineapple and cacti.

Comparing CAM and C4 Plants

A Review of Photosynthesis

Review of Key PointsPhotons → Food

• Light Reactions ATP and NADPH• Calvin Cycle → Sugar “Fixes CO2”• The sugar produced: supplies the plant w/chemical

energy & carbon skeletons needed for other cellular parts.

• 50% of the sugar produced is used for cellular respiration in the plants mitochondria.

• Typically, plants produce more organic material than they need and store it away as starch.

Introductory Questions #11. Plants have thought to evolved from a group of green

algae called ? 2. Name the four main groups of plants.3. Name the four main challenges faced by plants and

animals as they emerged on land.4. Name three key adaptations in plants allowing them to

be successful on land.5. What is the significance of lignin and the vascular tissue

found in land plants? 6. Moss, hornworts, and liverworts are all part of which

group of plants? 7. Looking at the life cycle of the moss, what is the name

of the male and female reproductive structures?

Introductory Questions #21. Which generation is dominant for the ferns? How is the

Gametophyte generation different from the Sporophyte generation?

2. How is a frond different from a rhizome?3. Ferns have several leaflets that make up their structure. What do

we call this type of structure?4. Another name for the sporangia in the fern is: ??5. Why are seedless vascular plants referred to as “homosporous”?6. Name the three key reproductive adaptations that led to plants

becoming successful on land. (pg. 596) 7. Give the name for the ancestral seedless vascular plants

that are thought to be the link to Gymnosperms. (pg. 596)

8. List the four main phylum groups found in Gymnosperms. (See pg. 594-595)

Introductory Questions #31. Which generation is dominant for the ferns? How is the

Gametophyte generation different from the Sporophyte generation?

2. How is a frond different from a rhizome?3. Ferns have several leaflets that make up their structure. What do

we call this type of structure?4. Another name for the sporangia in the fern is: ??5. Why are seedless vascular plants referred to as “homosporous”?6. Name the three key reproductive adaptations that led to plants

becoming successful on land. (pg. 596) 7. Give the name for the ancestral seedless vascular plants

that are thought to be the link to Gymnosperms. (pg. 596)

8. List the four main phylum groups found in Gymnosperms. (See pg. 594-595)

Introductory Questions #51. Using Pgs. 718-719 name the three types of tissue systems found

in plants. Rank the tissues according to their flexibilities?2. How can we tell the difference between Parenchyma,

Collenchyma, and Sclerenchyma?3. Tracheids and vessel elements are part of the vascular tissue

called .4. How is the stele in monocots different from the stele in the

dicots?5. Lateral roots that form arise from the _________. 6. How is primary growth different from secondary growth? The

specific areas that plant grow in their body are known as .

7. An increase in girth is due to cell division occurring in the .

Introductory Questions #61. Match each cell with the tissue(s) they’re found in.

Parenchyma cells A. Ground TissueVessels elements B. Dermal TissueTrichomes C. Vascular TissueSieve tube cellsSclerenchymaGuard cellsCompanion cells

Introductory Questions #71. Name the layer of cells that serve as a gatekeeper to regulate

what solutes are taken into the xylem. What is the thin layer of waxy substance (suberin) that is found in this layer of cells?

2. Why is nitrogen one of the most difficult elements for plants to take up? Give two reasons.

3. How is mycorrhizae different from a root nodule? Name the bacteria that is found in a root nodule of a legume.

4. How is nitrogen fixing bacteria different from ammonifying bacteria? Name the type of bacteria that converts ammonium to nitrate.

5. Fill in the missing layers found in a stem of a woody dicot tree: pith secondary xylem primary

phloem6. Name the type of cells that make up the phloem fiber cap

located in the vascular bundles.

Introductory Questions #81. What is the driving force behind the movement of water in the

xylem and sugar through the phloem in plants? 2. As Sugar is produced in the leaves during photosynthesis,

what is the driving force to move the product down the plant (other than gravity)? What is considered to be the “source” and what is considered to be the “sink”? Why is this movement explained by the “pressure-flow hypothesis”?

3. Why must plants open their stomata? When does this usually occur?

4. Briefly explain what guttation is and why it is more significant in smaller plants. (pg. 746) Why does this occur at night? How far can water be “pushed” up through the plant as root pressure builds? How much water pressure can accumulate in the roots?

5. Name the three solutes that accumulate in the guard cells allowing for water to move in. What type of protein channel allows for potassium to enter into the cell?

6. How is a pinnate leaf different from a palmate leaf? Name the two mesophyll cell layers in a dicot leaf. How are these two layers different from each other?

Introductory Questions #91. Name three factors that can affect transpiration in plants.2. How do plants absorb light energy? Name some features that

allow plants to absorb light. What are some differences between chlorophyll a and chlorophyll b?

6) What did Engelmann’s experiment measure? What organisms did he use?

7) Which reactant does the oxygen produced from photosynthesis directly come from?

8) Where specifically do the light and dark reaction take place within a plant cell?

Introductory Questions #101) How does non-cyclic photophosphorylation differ from cyclic

photophosphorylation? Which process is more common?2) What does it mean when we “FIX” carbon? Does this happen in

the light or dark reactions?3) Name the three phases of the Calvin Cycle. Which phases

require ATP and how much ATP would be needed for producing on glucose molecule?

4) What are the substrates that attach to the active sites of Rubisco?

5) How does a C3 plant differ from a C4 plant? Give 3 examples of a C3 & C4 plant.

6) What happens as a result of stomata closing? 7) Which type of plant undergoes photorespiration? Does

photorespiration occur at night or during the day? How is photorespiration different from cellular respiration seen in the mitochondria?

8) How are C4 and CAM plants similar and how are they different? Give an example of both.

Introductory Questions #11

1) Name the three phases of the Calvin Cycle. Which phases require ATP and how much ATP would be needed for producing on glucose molecule?

2) What are the substrates that attach to the active sites of Rubisco?

3) How does a C3 plant differ from a C4 plant? Give 3 examples of a C3 & C4 plant.

4) What happens as a result of stomata closing? 5) Which type of plant undergoes photorespiration?

Does photorespiration occur at night or during the day? How is photorespiration different from cellular respiration seen in the mitochondria?

6) How are C4 and CAM plants similar and how are they different? Give an example of both.