Light energy is trapped and converted into chemical energy during photosynthesis.

Section 2: Photosynthesis 1 Photosynthesis 2

KWhat I Know

WWhat I Want to Find Out

LWhat I Learned

• 9(B) Compare the reactants and products of photosynthesis and cellular respiration in terms of energy and matter.

• 1(A) Demonstrate safe practices during laboratory and field investigations.

• 2(F) Collect and organize qualitative and quantitative data and make measurements with accuracy and precision using tools such as calculators, spreadsheet software, data-collecting probes, computers, standard laboratory glassware, microscopes, various prepared slides, stereoscopes, metric rulers, electronic balances, gel electrophoresis apparatuses, micropipettors, hand lenses, Celsius thermometers, hot plates, lab notebooks or journals, timing devices, cameras, Petri dishes, lab incubators, dissection equipment, meter sticks, and models, diagrams, or samples of biological specimens or structures.

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• 3(A) In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student.

• 4(B) Investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules.

PhotosynthesisCopyright © McGraw-Hill Education

Essential Questions• What are the two phases of photosynthesis?• What is the function of a chloroplast during the light reactions?• How can electron transport be described and diagramed?

PhotosynthesisCopyright © McGraw-Hill Education

Review• carbohydrate

New• thylakoid• granum• stroma• pigment• NADP+• Calvin cycle• rubisco

PhotosynthesisCopyright © McGraw-Hill Education

Vocabulary

PhotosynthesisCopyright © McGraw-Hill Education

Overview of Photosynthesis• Most autotrophs make organic compounds using photosynthesis.

• Photosynthesis is the process of converting light energy into chemical energy.

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Overview of Photosynthesis• Photosynthesis occurs in two phases.

• In the light-dependent phase, light energy is converted into chemical energy.

• In the light-independent phase, chemical energy used to synthesize glucose.

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Phase One: Light Reactions• The absorption of light is the first step in photosynthesis.

• Once light energy is captured, it can be stored as ATP or NAPDH.

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Phase One: Light Reactions

Chloroplasts• Are organelles that capture light energy

• Contain two main compartments:

• Thylakoids: flattened saclike membranes • Stacks of thylakoids are called grana.

• The fluid filled space outside the grana called the stroma

PhotosynthesisCopyright © McGraw-Hill Education

Phase One: Light Reactions

Pigments• Light-absorbing colored molecules called pigments are found in the

thylakoid membranes.

• Different pigments absorb specific wavelengths of light.

• Most common pigment in plants is chlorophyll.

• Plants also have accessory pigments.

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Phase One: Light Reactions

Electron transport• The thylakoid membrane has a large surface area, providing space

for a large number of electron transporting molecules and two types of protein complexes called photosystems.

• Photosystems house the light-capturing pigments.

PhotosynthesisCopyright © McGraw-Hill Education

Phase One: Light Reactions

Electron transport• Light energy excites electrons in photosystem II.

• This light energy causes a water molecule to split – releasing an electron into the electron transport system, a hydrogen ion (H+ or proton) into the thylakoid space, and oxygen as a waste product.

PhotosynthesisCopyright © McGraw-Hill Education

Phase One: Light Reactions

Electron transport• The activated electrons move from photosystem II to an acceptor

molecule in the thylakoid membrane.

• The electron acceptor molecule transfers the electrons along a series of electron carriers to photosystem I.

PhotosynthesisCopyright © McGraw-Hill Education

Phase One: Light Reactions

Electron transport• In the presence of light, photosystem I transfers the electrons to a

protein called ferrodoxin.

• Ferrodoxin transfers the electrons to the carrier molecule NADP+, forming the energy storage molecule NADPH.

PhotosynthesisCopyright © McGraw-Hill Education

Phase One: Light Reactions

Electron transport• ATP is produced in conjunction with the electron transport system

through chemiosmosis

• ATP is produced through the flow of electrons down a concentration gradient

• The breakdown of water provides the necessary protons for ATP synthesis

Visualizing Electron Transport

Animation

FPOAdd link to animation from page 225 (Figure 8) here.

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PhotosynthesisCopyright © McGraw-Hill Education

Phase Two: The Calvin Cycle• In the second phase of photosynthesis, called the Calvin cycle,

energy is stored in organic molecules such as glucose.

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Phase Two: The Calvin Cycle• The first step of the Calvin cycle is called carbon fixation.

• CO2 molecules combine with 5-carbon molecules to form 3-phosphoglycerate (3-PGA)

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Phase Two: The Calvin Cycle• In the second step, chemical energy stored in ATP and NADPH is

transferred to the 3-PGA to form glyceraldehyde 3-phospate (G3P).

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Phase Two: The Calvin Cycle• In the third step, some G3P molecules leave the cycle to be used

for the production of glucose and other organic compounds.

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Phase Two: The Calvin Cycle• In the fourth and final step, an enzyme called rubisco converts the

remaining G3P molecules into 5-carbon molecules called ribulose 1,5-bisphospates (RuBP).

• These molecules combine with new CO2 and continue the cycle.

The Calvin Cycle

Animation

FPOAdd link to animation from page 226 (Figure 9) here.

PhotosynthesisCopyright © McGraw-Hill Education

PhotosynthesisCopyright © McGraw-Hill Education

Alternative Pathways

C4 plants

• The C4 pathway allows plants to maintain photosynthesis while reducing water loss.

• Significant structural modification in the arrangement of cells within the leaves – separate CO2 uptake from location of Calvin cycle

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Alternative Pathways

CAM plants

• Crassulacean acid metabolism (CAM) is found in desert plants.

• Collect CO2 at night and store it in organic compounds

• During the day, release CO2 from organic compounds for the light-dependent cycle of photosynthesis

PhotosynthesisCopyright © McGraw-Hill Education

Review

Essential Questions• What are the two phases of photosynthesis?• What is the function of a chloroplast during the light reactions?• How can electron transport be described and diagramed?

Vocabulary

• thylakoid• granum• stroma

• pigment• NADP+

• Calvin cycle• rubisco