Ch 10 Photosynthesis

Introductory Questions #8

1. Where is the Casparian strip located?

2. Why must plants use active transport in order to take in ions into the root hair cells?

3. Name the two types of cells that make up the mesophyll layers in a leaf. What kind of tissue (cell types) are they?

4. Briefly explain how the stomata open and close. Name the ions involved. What color light cause the stomata to open?

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

Introductory Questions #101) Name the three parts that make up a photosystem.

2) How does NADPH differ from NADH?

3) What does it mean when we “FIX” carbon? Does this happen in the light or dark reactions?

4) What is required in order for the light reactions to proceed?

5) How does non-cyclic photophosphorylation differ from cyclic photophosphorylation? Which process is more common?

Introductory Questions #111) 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.

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)

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 (Plank’s constant-ER

can be quantized ) and DeBroglie (objects move in waves)

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

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”.

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 (hairlike structures)

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

Cell Layers Observed in Leaves

The Chloroplast and Light (pg. 186)

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

Introductory Questions #91) How is an autotroph different from a heterotroph?

2) Briefly explain what light is and how it is generated.

3) In plant tissue, where are chloroplasts highly concentrated?

4) How are chloroplasts similar to mitochondria? How are they different?

5) 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?

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

The Leaf: The Site for Photosynthesis

Structure of the Chloroplast

• Double membrane

• Has its own DNA

• Internal membrane system called Thylakoids

• Contains protein pigmets: ex chlorophyll a

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

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

Determining Absorbance of a Pigment (pg. 187)

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 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• Light Harvesting 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

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

Photosystem II (P680)Photosystem I (P700)

• 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.

Photosystems in the Thylakoid Membrane

Noncyclic Electron Flow

Build up of Hydrogen ions in the thylakoid space

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

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

Photosynthesis-Light & Dark Reactions

The Calvin Cycle-C3 pathway

3 molecules of CO2 are ‘fixed’ into glyceraldehyde 3-phosphate (G3P)

3 Phases:1- Carbon fixation~

Each CO2 is attached to RuBP (rubisco enzyme)

2- Reduction~ electrons 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 intially 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.

Content Breakdown for Test #1Topic # Questions

• Chapter 20: Origin of the Earth 4• Chapter 26: Bryophytes & Ferns 4• Chapter 27: Gynosperms & Angiosperms 4• Chapter 35: Lifecycle of Angiosperms & Fruit 8• Chapter 36: Hormonal responses 3• Chapter 31: Tissues 4• Chapter 33: Stems 8• Chapter 34: Roots 10• Chapter 32: Leaves 8• Chapter 8: Photosynthesis 12• Cumulative (1st Semester content) 10

Controlling Stomata Activity• Typically open during the day and closed at night (except in CAM

plants) – for CO2

• Two Guard Cells that surround the opening change their shape when H2O enters and leaves. (osmotically)

• Yellow pigments are thought be abundant in the guard cells which absorb Blue light.

• Uptake of potassium & chloride ions = OPENS the stomata (driven by actively transporting H+ ions out of guard cells)• Decrease in sucrose concentration = CLOSES the stomata• Low CO2 = stomata open High CO2 = Stomata close• Dehydration• Circadian rhythms also contribute

Transpiration in Plants• Loss of water by evaporation• Cuticle helps to reduce this loss (1-3%)• Occurs mostly through open stomata• Light, higher temperatures, wind, and dry air all increase

transpiration• Decreased by high humidity• Can prevent plants from overheating• Responsible for water movement in plants (to leaves)• Distributes minerals throughout the plant• Important part of the hydrologic cycle

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.

Stomata Opening and Closing

Controlling Stomata Activity

• Typically open during the day and closed at night (except in CAM plants) – for CO2

• Two Guard Cells that surround the opening change their shape when H2O enters and leaves. (osmotically)

• Yellow pigments are thought be abundant in the guard cells which absorb Blue light.

• Uptake of potassium & chloride ions = OPENS the stomata (driven by actively transporting H+ ions out of guard cells)• Decrease in sucrose concentration = CLOSES the stomata• Low CO2 = stomata open High CO2 = Stomata close• Dehydration• Circadian rhythms also contribute

Transpiration in Plants• Loss of water by evaporation• Cuticle helps to reduce this loss (1-3%)• Occurs mostly through open stomata• Light, higher temperatures, wind, and dry air all

increase transpiration• Decreased by high humidity• Can prevent plants from overheating• Responsible for water movement in plants (to leaves)• Distributes minerals throughout the plant• Important part of the hydrologic cycle

Leaf Morphology

Leaf Morphology-Chapter 32

• Leaves can be used to identify different species of plants.

• (3) Characteristics are used:– Simple vs. Compound Leaves (Pinnate or Palmate)– Leaf arrangement on the stem:

(alternate, whorled, or opposite)– Venation Pattern (parallel, branched)