Photosynthesis: Light Reactions Overview
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Questions and Answers

What is the primary purpose of the Calvin Cycle?

  • To absorb light energy
  • To split water molecules
  • To produce glucose (correct)
  • To return ADP to the light reactions

Which molecule provides the energy required for the Calvin Cycle?

  • Glucose
  • Adenosine Triphosphate (ATP) (correct)
  • NADP+
  • Oxygen

Where does the Calvin Cycle occur within a plant cell?

  • In the cytoplasm
  • In the thylakoid
  • In the reaction center
  • In the stroma (correct)

What happens to P680 after it loses an electron?

<p>It becomes positively charged (P680+) (B)</p> Signup and view all the answers

What is produced when water is split by P680?

<p>Oxygen and hydrogen ions (A)</p> Signup and view all the answers

Which process helps to pump hydrogen ions across the membrane during light reactions?

<p>Chemiosmosis (B)</p> Signup and view all the answers

What happens to NADP+ after the Calvin Cycle?

<p>It returns to the light reactions (A)</p> Signup and view all the answers

Which statement about the light reactions is true?

<p>They generate ATP and NADPH (A)</p> Signup and view all the answers

What molecule is produced from ADP through the action of ATP synthase?

<p>ATP (D)</p> Signup and view all the answers

What causes the P700 chlorophyll in Photosystem I to become positively charged?

<p>Loss of electrons to the primary electron acceptor (C)</p> Signup and view all the answers

Which enzyme transfers an electron to NADP+ in the light reactions?

<p>NADP+ reductase (B)</p> Signup and view all the answers

What is produced from the process of cyclic electron flow?

<p>ATP (B)</p> Signup and view all the answers

Which component is involved in the transfer of photo-excited electrons after Photosystem I?

<p>Ferredoxin (B)</p> Signup and view all the answers

From which molecule does the carbon in your body originate?

<p>Carbon dioxide (D)</p> Signup and view all the answers

What happens during a short-circuited path of cyclic electron flow?

<p>Electrons are transferred to the cytochrome complex (B)</p> Signup and view all the answers

What characterizes the high-energy phosphate bonds in ATP?

<p>They store energy (B)</p> Signup and view all the answers

What are the primary products of the light reactions in photosynthesis?

<p>ATP and NADPH (C)</p> Signup and view all the answers

Where do the light reactions of photosynthesis occur?

<p>Thylakoids (B)</p> Signup and view all the answers

What role does sunlight play in the light reactions of photosynthesis?

<p>It provides the energy needed for electron transfer. (B)</p> Signup and view all the answers

What happens to water during the light reactions?

<p>It is split, producing oxygen as a byproduct. (A)</p> Signup and view all the answers

Why is photosynthesis deemed essential for life on Earth?

<p>It provides food and oxygen for living organisms. (C)</p> Signup and view all the answers

What is formed through phosphorylation during the light reactions?

<p>ATP (C)</p> Signup and view all the answers

Which molecule is reduced to form NADPH during the light reactions?

<p>NADP+ (C)</p> Signup and view all the answers

What gas is primarily released as a byproduct of the light reactions?

<p>Oxygen (A)</p> Signup and view all the answers

What is the main product of the Calvin Cycle as described?

<p>Glyceraldehyde-3-Phosphate (G3P) (A)</p> Signup and view all the answers

How many molecules of ATP are required to make one molecule of G3P?

<p>9 (C)</p> Signup and view all the answers

Which of the following molecules is not needed to produce G3P in the Calvin Cycle?

<p>Sucrose (C)</p> Signup and view all the answers

What happens to Glyceraldehyde-3-Phosphate (G3P) after its release from the Calvin Cycle?

<p>It combines to form sucrose. (C)</p> Signup and view all the answers

How many times does the Calvin Cycle need to 'spin' to make one molecule of G3P?

<p>3 (D)</p> Signup and view all the answers

What is the primary product formed in the Calvin cycle?

<p>Glucose (B)</p> Signup and view all the answers

Which enzyme is crucial for the carbon fixation phase of the Calvin cycle?

<p>Rubisco (B)</p> Signup and view all the answers

In which part of the chloroplast does the Calvin cycle occur?

<p>Stroma (D)</p> Signup and view all the answers

How many molecules of G3P are produced in one turn of the Calvin cycle?

<p>Six (D)</p> Signup and view all the answers

What happens to five out of the six produced G3P molecules in the Calvin cycle?

<p>Used to regenerate RuBP (A)</p> Signup and view all the answers

What is the initial carbon molecule that enters the Calvin cycle?

<p>Carbon dioxide (CO2) (A)</p> Signup and view all the answers

What is produced at the end of the reduction phase of the Calvin cycle?

<p>Glyceraldehyde-3-phosphate (G3P) (A)</p> Signup and view all the answers

Why is the Calvin cycle important to all living organisms?

<p>It provides food and energy for plants and indirectly for herbivores and carnivores. (C)</p> Signup and view all the answers

Flashcards

Light Reactions in Photosynthesis

The first stage of photosynthesis, using sunlight to initiate an electron transfer chain, converting light energy into chemical energy. This results in the production of NADPH and ATP.

NADP+ to NADPH conversion

Light energy converts the electron carrier NADP+ into NADPH, storing energy in the form of electrons.

ATP production

Light reactions create ATP (adenosine triphosphate) through a process called phosphorylation, a crucial energy-carrying molecule.

Water splitting

The process in light reactions where water molecules are split, releasing oxygen as a byproduct.

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Thylakoids

Membranous sacs within chloroplasts where light reactions take place.

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Photosynthesis importance

Photosynthesis is essential for life because it's how plants make their food and produces oxygen, which supports other life forms.

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Two-stage process

Photosynthesis occurs in two stages: light reactions and the Calvin cycle.

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Importance of sunlight to Photosynthesis

Sunlight is the primary energy source driving light reactions, initiating the entire process of converting light energy into chemical energy.

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Calvin Cycle

The second stage of photosynthesis that uses ATP and hydrogen to convert carbon dioxide into glucose.

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Light Reactions

The first stage of photosynthesis that captures light energy to produce ATP and hydrogen.

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Photosystem II

A protein complex in the thylakoid membrane that absorbs light energy and splits water to release oxygen.

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Electron Transport Chain (ETC)

A series of proteins in the thylakoid membrane that transfer electrons from Photosystem II to Photosystem I, generating ATP.

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ATP Synthase

A protein that uses the proton gradient to produce ATP from ADP and inorganic phosphate.

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P680

A chlorophyll molecule in Photosystem II that initiates the light-dependent reactions by absorbing light energy.

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Chemiosmosis

The process of generating ATP using the proton gradient across the membrane.

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Glucose

A sugar (C6H12O6) produced in the Calvin Cycle as a result of combining carbon dioxide with hydrogen. Energy source for cells.

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RuBP Regeneration

A process in the Calvin Cycle where five molecules of G3P are converted into three molecules of RuBP, requiring ATP and another set of RuBP to continue the cycle.

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G3P Uses

The G3P produced in the Calvin Cycle can be used to form various molecules, including glucose, fructose, sucrose, starch, lipids, and proteins.

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Glyceraldehyde-3-Phosphate (G3P)

A three-carbon sugar produced in the Calvin Cycle, which can be used to make glucose and other important molecules.

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Calvin Cycle 'Spin'

The Calvin Cycle needs to complete three cycles to produce one molecule of G3P from three molecules of CO2.

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Calvin Cycle Sugar

The sugar produced directly in the Calvin Cycle is not glucose, but a three-carbon sugar called G3P.

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What is the purpose of the Calvin Cycle?

To create glucose (a sugar) from carbon dioxide using the energy stored in ATP and NADPH, providing food for the plant or algae.

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Carbon Fixation

The process in the Calvin Cycle where carbon dioxide from the atmosphere is incorporated into an organic molecule, specifically RuBP, initiating sugar production.

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Where does the Calvin Cycle take place?

It occurs in the stroma, the fluid-filled region inside chloroplasts.

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RuBP

Ribulose bisphosphate, a 5-carbon sugar that serves as the primary carbon acceptor in the Calvin Cycle.

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What is the role of ATP and NADPH in the Calvin Cycle?

ATP provides the energy required for the reactions of the Calvin Cycle, while NADPH provides reducing power (electrons) to convert carbon dioxide into sugar.

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What is Rubisco?

An enzyme that helps attach CO2 to RuBP, the first step in the Calvin Cycle.

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What is RuBP?

A five-carbon sugar molecule that binds with CO2 in the first stage of the Calvin Cycle.

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What is the end product of the Calvin Cycle?

Glucose (C6H12O6), a simple sugar that serves as the building block for more complex carbohydrates and other vital organic molecules.

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Regeneration

The final step in the Calvin Cycle where RuBP, the carbon acceptor, is regenerated to continue the cycle.

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What is 3-phosphoglycerate?

A three-carbon molecule formed after CO2 is attached to RuBP.

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What is G3P?

A three-carbon sugar molecule that is produced in the Calvin Cycle and can be used to make glucose.

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How does the Calvin Cycle relate to the light reactions?

The Calvin Cycle is directly dependent on the energy produced by the light reactions. ATP and NADPH, products of the light reactions, provide the energy and electrons needed for the Calvin Cycle to function.

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What are the phases of the Calvin Cycle?

The Calvin Cycle is divided into three main phases: carbon fixation, reduction, and regeneration.

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What is the significance of the Calvin Cycle to life?

The Calvin Cycle is the foundation of food webs, providing energy and food for all organisms, directly or indirectly.

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Study Notes

Photosynthesis: Light Reactions

  • Photosynthesis is a vital process for life on Earth
  • Plants (autotrophs) use water, carbon dioxide, and sunlight to make food
  • Humans and other organisms depend on plants for survival
  • If photosynthesis stops, organic matter and oxygen levels will decrease significantly
  • Chemosynthetic bacteria are independent of light energy

Stages of Photosynthesis

  • Photosynthesis is a two-stage process: light reactions and the Calvin cycle
  • Light reactions take place in the thylakoids of chloroplasts
  • Light reactions use sunlight to produce ATP and NADPH

Light Reactions Events

  • Light energy excites electrons in Photosystem II (P680)
  • Water molecules are split, releasing oxygen as a byproduct, and providing electrons
  • Electrons move through an electron transport chain, generating ATP
  • Electrons are transferred to Photosystem I (P700), which generates NADPH
  • ATP and NADPH are used in the Calvin cycle
  • The process happens in thylakoids

Cyclic Electron Flow (Alternative Pathway)

  • Electrons can take a short-circuited path via Photosystem I, bypassing Photosystem II
  • This route produces ATP but not NADPH

Photosynthesis: Calvin Cycle

  • Calvin cycle occurs in the stroma of chloroplasts
  • The Calvin cycle fixes carbon dioxide from the air into organic molecules
  • The Calvin cycle occurs in three phases: carbon fixation, reduction, and regeneration.
  • Rubisco is the key enzyme in carbon fixation
  • The Calvin cycle produces G3P, a three-carbon sugar
  • G3P is used to make glucose, sucrose, starch, and other molecules
  • The cycle uses ATP and NADPH, produced in the light reactions.

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Biology 1 Quarter 2 Week 2A Energy Transformation (Light Reactions) PDF

Description

This quiz explores the light reactions of photosynthesis, a crucial process that allows plants to convert sunlight into chemical energy. Key stages include the excitation of electrons, water splitting, and the generation of ATP and NADPH. Understanding these processes is essential for recognizing how plants support life on Earth.

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