Photosynthesis and ATP

Photosynthesis and ATP

High School

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Learning Objectives

• Describe the roles of ATP and ADP in storing and releasing cellular energy.

• Explain the overall process of photosynthesis, including its reactants and products.

• Detail the two major stages of photosynthesis: light-dependent and light-independent reactions.

• Identify key structures in the chloroplast and explain the function of chlorophyll.

Key Vocabulary

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ATP

Adenosine triphosphate is an energy-carrying molecule used by cells to power metabolic and cellular processes.

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Photosynthesis

The process where plants use sunlight, water, and carbon dioxide to create their own food.

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Chloroplast

An organelle in plant cells where the entire process of photosynthesis takes place.

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Chlorophyll

The green pigment in chloroplasts that absorbs light energy from the sun for photosynthesis.

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Thylakoid

A sac-like membrane inside chloroplasts where the light-dependent reactions of photosynthesis occur.

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Stroma

The fluid-filled space in a chloroplast that surrounds thylakoids and where the Calvin Cycle occurs.

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ATP: The Cell's Energy Currency

ATP (High Energy)

• Adenosine Triphosphate (ATP) is a key molecule that stores energy for cellular activities.

• It is a high-energy molecule that features a total of three phosphate groups.

• Energy is released for the cell’s use when the bond to the third phosphate group breaks.

ADP (Low Energy)

• Adenosine Diphosphate (ADP) is what remains after ATP releases its stored energy.

• This lower-energy molecule has only two phosphate groups instead of three.

• Energy can be used to add a phosphate group back to ADP, reforming it into ATP.

Multiple Choice

How does the ATP-ADP cycle work to store and release energy for the cell?

• Energy is stored when a phosphate group is added to ADP to form ATP, and released when a phosphate is removed.

• Energy is only stored in ATP and cannot be released.

• Energy is stored when a phosphate group is removed from ATP, and released when one is added to ADP.

• Energy is released by adding a phosphate group to ATP.

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What is Photosynthesis?

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Solved Example 1
A plant produces 2 moles of glucose (C₆H₁₂O₆) through photosynthesis. How many moles of oxygen (O₂) are released? The balanced equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

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Step 1: Analyze and Sketch the Problem

• Goal: Find the moles of oxygen (O₂) produced.

• Knowns: Moles of glucose (C₆H₁₂O₆) = 2 mol.

• Unknown: Moles of oxygen (O₂).

• Formula: The molar ratio between C₆H₁₂O₆ and O₂ is 1:6.

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Solved Example 1
A plant produces 2 moles of glucose (C₆H₁₂O₆) through photosynthesis. How many moles of oxygen (O₂) are released? The balanced equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

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Step 2: Solve for the Unknown

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Solved Example 1
A plant produces 2 moles of glucose (C₆H₁₂O₆) through photosynthesis. How many moles of oxygen (O₂) are released? The balanced equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

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Step 3: Evaluate the Answer

Multiple Choice

According to the chemical equation for photosynthesis, what are the primary reactants and products?

• Reactants: Water, Carbon Dioxide, and Sunlight; Products: Oxygen and Glucose.

• Reactants: ATP and NADPH; Products: Oxygen and Glucose.

• Reactants: Oxygen and Glucose; Products: Water, Carbon Dioxide, and Sunlight.

• Reactants: Water and Oxygen; Products: Glucose and Carbon Dioxide.

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Capturing Light Energy

• Photosynthesis occurs inside cell organelles known as chloroplasts.

• ​Chlorophyll, the main pigment, absorbs light and gives plants their green color.

• When chlorophyll absorbs light, it creates a supply of high-energy electrons.

• In the fall, other pigments become visible as chlorophyll starts to break down.

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Multiple Choice

What is the primary role of chlorophyll in photosynthesis?

• To take in carbon dioxide from the atmosphere.

• To store glucose after it has been produced.

• To give leaves their fall colors by breaking down.

• To absorb light energy and transfer it to high-energy electrons.

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The Machinery of Photosynthesis

• A chloroplast is enclosed by an outer and inner membrane, containing several structures.

• Thylakoids, stacked into grana, are where the light-dependent reactions happen.

• The stroma is the fluid-filled space where the light-independent reactions occur.

• Stomata are leaf openings that let carbon dioxide (CO₂) enter the plant.

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Multiple Choice

Where do the light-dependent reactions and the light-independent reactions (Calvin cycle) take place, respectively?

• Stomata and Granum

• Stroma and Thylakoids

• Thylakoids and Stroma

• Outer membrane and Inner membrane

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Phase 1: Light-Dependent Reactions

• This phase occurs in the thylakoids, using water and sunlight as reactants.

• Light energy splits water (H₂O), releasing oxygen and providing electrons to Photosystem II.

• Hydrogen ions (H⁺) create a gradient that powers the production of ATP.

• NADP⁺ accepts electrons to make NADPH; both are energy carriers for the next phase.

Multiple Choice

What are the main products of the light-dependent reactions that are used to power the next phase of photosynthesis?

• Water and Sunlight

• ATP and NADPH

• Carbon Dioxide and Water

• Oxygen and Glucose

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Phase 2: Light-Independent Reactions (Calvin Cycle)

• The Calvin Cycle occurs in the stroma and does not need direct light.

• ​Energy from ATP and NADPH produced in the light-dependent phase is used.

• The cycle’s main reactant is carbon dioxide (CO₂) from the atmosphere.

• The final product is glucose, a sugar used for plant energy and growth.

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Multiple Choice

What are the essential inputs required for the Calvin Cycle to produce glucose?

• Carbon Dioxide, ATP, and NADPH

• Water, Sunlight, and Oxygen

• Oxygen and ATP

• Sunlight and Carbon Dioxide

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Common Misconceptions about Photosynthesis

Misconception	Correction
Photosynthesis is the plant's 'breathing'.	Plants 'breathe' through respiration. Photosynthesis is for making food.
Light-independent reactions only happen at night.	They occur during the day, using products from light-dependent reactions.
All parts of a plant can photosynthesize.	Photosynthesis mainly occurs in leaves and stems, not in the roots.
Plants get their food from the soil.	Plants create their own food (glucose) through photosynthesis, not from soil.

Multiple Choice

Why is the splitting of water essential for the light-dependent reactions to continue?

• It provides the carbon atoms needed to build glucose.

• It replaces the high-energy electrons that are passed to the electron transport chain.

• It creates the NADPH needed for the Calvin Cycle.

• It releases oxygen, which powers ATP synthase.

Multiple Choice

What is the direct relationship between the light-dependent and light-independent reactions?

• The light-dependent reactions produce glucose, which the light-independent reactions break down.

• The light-independent reactions produce oxygen, which is used by the light-dependent reactions.

• There is no relationship; they are separate processes that occur at different times.

• The light-dependent reactions produce ATP and NADPH, which power the light-independent reactions to make sugar.

Multiple Choice

A scientist discovers a plant with a mutation that causes its stomata to be closed all the time. How would this most likely impact the Calvin Cycle?

• The cycle would produce oxygen instead of sugars.

• The cycle would accelerate because more water is conserved.

• The cycle would halt because it cannot take in the CO₂ needed to produce sugars.

• The cycle would not be affected because it is dependent on light, not CO₂.

Multiple Choice

Imagine a plant is exposed to light that only contains green wavelengths. What would be the predicted outcome for photosynthesis and why?

• Photosynthesis would produce a different type of sugar.

• Photosynthesis rates would be very high because plants are green.

• Photosynthesis would stop completely, but the plant would survive on stored energy.

• Photosynthesis rates would be very low because chlorophyll primarily reflects green light, rather than absorbing it.

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Summary

Poll

On a scale of 1-4, how confident are you with the key concepts of photosynthesis and ATP covered today?

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