2.2 Photosynthesis

2.2 Photosynthesis

​Photosynthesis

​Captures energy from sunlight to make sugars that store chemical energy.

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​Plants absorb visible light.

​Chloroplasts

​Contain chlorophyll molecules, which absorb some energy from visible light.

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​Two types: Chlorophyll a and b

​They absorb blue and red light

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​Chloroplasts

​Grana: Stacks of

coin-shaped compartments called thylakoids.

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​Stroma: Fluid that surrounds the grana in the chloroplast.

​​Two main parts used for photosynthesis:

​Grana and Stroma

​Photosynthesis Overview

Light-Dependent Reactions

​

​Light-Independent Reactions

​Also called "The Calvin Cycle"

Multiple Choice

What molecules in plant chloroplasts absorb light?

• Grana

• Stroma

• Chlorophyll

• ATP

Multiple Choice

What color is not absorbed by the chlorophyll in chloroplasts?

• Red

• Blue

• Green

Multiple Choice

Light-dependent reactions occur in the...

• Stroma

• Thylakoids

Light-Dependent Reactions​

Steps 1-7​

​Light Dependent Reactions

Chlorophyll absorbs light energy​

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​Water molecules are broken down into hydrogen ions, electrons, and oxygen.

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​No sugars are formed in this reaction

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​Two groups of molecules capture light at the thylakoids:

​Photosystem II

Photosystem I

Multiple Choice

What is not formed during the light-dependent reactions?

• Oxygen

• Sugar

• ATP

​Photosystem II and Electron Transport

Step 1:

​Energy absorbed from sunlight

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Energy transfers to electrons (e-)

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Electrons leave chlorophyll and enter electron transport chain

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​​Electron Transport Chain:

Series of proteins in the membrane of thylakoid

​Photosystem II and Electron Transport

Step 2:

Water molecules split

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Oxygen, hydrogen ions, and electrons separate.

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​Oxygen released as waste

​Electrons replace the electrons that left when light was absorbed.

​Photosystem II and Electron Transport

Step 3:

Hydrogen ions transported

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Movement of electrons down the ETC pumps H⁺ ions across the thylakoid membrane.

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​H⁺ ions build up inside the membrane.

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​Electrons move on to photosystem I.

Multiple Choice

What is energy transferred to, so it can carry energy down the electron transport chain?

• electrons

• hydrogen ions

• oxygen

​Photosystem I and Energy-Carrying Molecules

Step 4:

Energy Absorbed from Sunlight

​

Like in photosystem II,

​chlorophyll absorbs light energy and energizes electrons

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​Electrons leave molecules.

​Photosystem I and Energy-Carrying Molecules

Step 5:

NADPH produced

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Energized electrons are added to an NADP+ molecule, to form NADPH.

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​These molecules function similarly to ATP and ADP.

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​NADPH molecules move to the light-independent reactions.

Multiple Select

Which of the following are high-energy carrier molecules? (select all that apply)

• ATP

• ADP

• NADPH

• NADP

ATP Production

Step 6:

Hydrogen Ion Diffusion

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Hydrogen ions flow through a protein channel in the thylakoid membrane.

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​Move from an area of high concentration of H⁺ ions (inside the thylakoid membrane) to an area of low concentration (outside).

ATP Production

Step 7:

ATP Produced

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Protein channel in step 6 is part of a complex enzyme called

"ATP synthase"

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​As ions flow through the protein, ATP synthase makes ATP by adding phosphates to ADP molecules.

Multiple Choice

The flow of _____ powers ATP synthase to form ATP molecules.

• Hydrogen ions

• Electrons

• Oxygen

• Light

Light-Independent Reactions​

​Also called "The Calvin Cycle"

​The Calvin Cycle

​Uses CO₂ and energy carried by ATP and NADPH to build sugars.

Multiple Choice

What is the major product of the calvin cycle?

• carbon dioxide

• water

• glucose

• oxygen

​The Calvin Cycle

​Step 1:

​Carbon dioxide added

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​CO₂ added to a

5-carbon molecule, forms 6-carbon molecule.

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​The Calvin Cycle

​Step 2:

​3-carbon molecules formed

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ATP and NADPH used by enzymes to break

6-carbon molecule down to two 3-carbon molecules.

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​The Calvin Cycle

​Step 3:

3-carbon molecules exit

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​One 3-carbon molecule exits each cycle.

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​Once two have left the cycle, they bond to form a glucose molecule

(6-carbon sugar)

​The Calvin Cycle

​Step 4:

3-carbon molecules recycled

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Remaining 3-carbon sugars are converted back to 5-carbon sugars that start the Calvin cycle

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​These are added to CO₂ molecules when they join the cycle

Multiple Choice

CO₂ enters the calvin cycle and joins with a carbon molecule to form a...

• 3-carbon sugar

• 6-carbon sugar

• 5-carbon sugar

Multiple Choice

Glucose forms from two ________ molecules that leave the calvin cycle.

• 5-carbon sugars

• CO₂

• 3-carbon sugars

• 6-carbon sugars