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Quizzes > Science

Chloroplast Thylakoids Quiz: Name the Flattened Sacs

Quick, free quiz to test your knowledge of thylakoid membranes. Instant results.

Editorial: Review CompletedCreated By: Karen BrownUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration of a chloroplast with stacked flattened membrane sacs called thylakoids on a sky blue background

This quiz helps you identify and name chloroplast thylakoids, the flattened membrane sacs where the light reactions start. Strengthen recall of their structure and job in photosynthesis, then keep practicing with our organelle identification quiz and photosynthesis practice quiz, or review more cell structures in the cell organelles quiz.

What is the term for the flattened sacs of internal membranes inside chloroplasts?
Stroma
Grana
Lamellae
Thylakoids
Thylakoids are pancake-like flattened sacs of membrane inside chloroplasts where light reactions occur. Each thylakoid encloses a compartment called the lumen. These structures provide a large surface area for chlorophyll molecules and protein complexes required in photosynthesis.
In chloroplasts, thylakoids are arranged in stacks called what?
Grana
Stroma
Lumen
Lamellae
Grana are stacks of thylakoids, resembling stacks of coins within chloroplasts. They increase surface area for light capture and house the protein complexes of the light-dependent reactions. Grana are interconnected by stroma lamellae to allow energy distribution.
The fluid inside a chloroplast surrounding the thylakoids is known as what?
Stroma
Lumen
Matrix
Cytosol
The stroma is the aqueous fluid surrounding the thylakoid membranes within chloroplasts. It contains enzymes for the Calvin cycle, DNA, ribosomes, and starch granules. Carbon fixation takes place in this compartment following the light reactions.
Which pigment is located in the thylakoid membrane and is the primary molecule for light absorption?
Hemoglobin
Xanthophyll
Chlorophyll a
Anthocyanin
Chlorophyll a is the primary photosynthetic pigment embedded in the thylakoid membrane and is essential for capturing light energy. It absorbs blue-violet and red wavelengths most effectively. Accessory pigments transfer energy to chlorophyll a, but chlorophyll a is the main pigment.
The site of the light-dependent reactions in photosynthesis is located in which part of the chloroplast?
Outer membrane
Stroma
Cytoplasm
Thylakoid membrane
Light-dependent reactions occur in the thylakoid membrane, where photosystems, electron carriers, and ATP synthase are embedded. Here, sunlight drives electron transport, water splitting, and proton pumping. The resulting ATP and NADPH fuel the Calvin cycle in the stroma.
During the light reactions, a proton gradient is established across which membrane?
Thylakoid membrane
Plasma membrane
Inner mitochondrial membrane
Cell wall
The proton gradient that drives ATP synthesis is established across the thylakoid membrane during the light reactions. Protons are pumped into the thylakoid lumen by the cytochrome b6f complex and water splitting. The gradient is used by ATP synthase to generate ATP.
What is the name of the interior compartment inside each thylakoid sac?
Matrix
Lumen
Periplasm
Stroma
The thylakoid lumen is the interior aqueous space of each thylakoid sac. It accumulates protons during light-driven electron transport. This acidification drives ATP synthesis as protons flow back to the stroma.
Photosystem II, which initiates the light-dependent reactions, is embedded in which structure?
Cytoskeleton
Thylakoid membrane
Stroma
Outer chloroplast membrane
Photosystem II is located in the thylakoid membrane, mostly in the grana stacks. PSII captures light energy to split water and initiate electron flow. Its localization optimizes light absorption and water oxidation.
What are the unstacked thylakoid membranes that interconnect grana called?
Thylakoid lumen
Outer membrane
Thylakoid membrane
Stroma lamellae
Stroma lamellae are unstacked thylakoid membranes that interconnect grana stacks. They enable lateral diffusion of electron carriers and balance energy distribution between photosystems. These membranes ensure cohesive function of the light reactions.
Which enzyme complex synthesizes ATP during photophosphorylation in the thylakoid membrane?
NADP+ reductase
ATP synthase
Rubisco
Cytochrome b6f
ATP synthase is a transmembrane enzyme in the thylakoid membrane that synthesizes ATP using the proton gradient across the membrane. It consists of CF0 embedded in the membrane and the CF1 catalytic domain protruding into the stroma.
What term describes the light-driven splitting of water molecules in photosynthesis?
Hydrolysis
Photolysis
Fermentation
Decarboxylation
Photolysis refers to the light-driven splitting of water molecules into protons, electrons, and oxygen in photosystem II. This reaction supplies electrons for the electron transport chain and releases O2 as a byproduct.
The oxygen released in the light-dependent reactions of photosynthesis originates from which molecule?
Water
Carbon dioxide
Chlorophyll
Glucose
The oxygen released during the light-dependent reactions originates from the splitting of water by the oxygen-evolving complex of photosystem II. No oxygen comes from CO2 during these reactions.
Compared to the stroma, the pH inside the thylakoid lumen is typically:
Neutral
Lower (more acidic)
Equal
Higher (more basic)
Proton pumping into the thylakoid lumen lowers its pH relative to the stroma, making the lumen more acidic. The resulting pH gradient drives protons back into the stroma through ATP synthase to form ATP.
Which special chlorophyll a pair in photosystem II absorbs light at 680 nm?
P550
P760
P700
P680
P680 is the special chlorophyll a pair in the reaction center of photosystem II. It absorbs light maximally at 680 nm and donates excited electrons to the electron transport chain.
Which mobile electron carrier shuttles electrons between photosystem II and the cytochrome b6f complex?
Cytochrome c
Plastoquinone
Plastocyanin
ATP
Plastoquinone is a lipid-soluble electron carrier that shuttles electrons between PSII and the cytochrome b6f complex within the thylakoid membrane. It also transports protons from the stroma into the lumen.
The stacking of thylakoids into grana primarily serves to increase what?
Stroma volume
Surface area for light absorption
Inner membrane potential
Volume for carbon fixation
Stacking thylakoids into grana increases the surface area available for pigment-protein complexes and maximizes light absorption efficiency. This organization optimizes the light reactions.
In cyclic electron flow around photosystem I, electrons are returned to which component?
Cytochrome b6f complex
NADP+
Photosystem II
Oxygen
In cyclic electron flow, electrons from photosystem I are redirected back to the cytochrome b6f complex instead of reducing NADP+. This process boosts ATP production without generating NADPH.
Which lipid is most abundant in the thylakoid membrane and affects its fluidity?
Galactolipids
Sphingolipids
Cholesterol
Phosphatidylcholine
Thylakoid membranes are rich in galactolipids such as monogalactosyldiacylglycerol (MGDG), which influences membrane curvature and fluidity. These lipids are essential for optimal function of protein complexes.
During non-cyclic photophosphorylation, which complex transfers electrons from plastoquinol to plastocyanin?
ATP synthase
Photosystem II
Cytochrome b6f complex
Photosystem I
Cytochrome b6f complex mediates electron transfer from plastoquinol to plastocyanin and pumps protons into the lumen. It bridges photosystem II and photosystem I in the electron transport chain.
The stroma lamellae primarily house which photosystem?
Photosystem I
Cytochrome b6f
Rubisco
Photosystem II
Photosystem I is predominantly located in the unstacked stroma lamellae, where it interacts efficiently with soluble electron carriers like plastocyanin. This spatial separation prevents energetic conflicts with PSII.
The thylakoid lumen's primary role in the light reactions is to:
Fix carbon dioxide
Split water
Consume NADPH
Accumulate protons to drive ATP synthesis
The thylakoid lumen accumulates protons during electron transport, creating an electrochemical gradient. This gradient is harnessed by ATP synthase to produce ATP in the stroma.
Which protein complex in the thylakoid membrane contains CF1 and CF0 components?
NADP+ reductase
Cytochrome b6f
ATP synthase
Photosystem I
The CF1CF0-ATP synthase complex spans the thylakoid membrane, with CF0 forming the proton channel and CF1 catalyzing ATP formation. It couples proton flow to phosphorylation of ADP.
Photoprotection in the thylakoid membrane involves excess energy dissipation via which cycle?
Xanthophyll cycle
Photorespiration
Calvin cycle
Glycolate pathway
The xanthophyll cycle involves the reversible conversion of xanthophyll pigments to dissipate excess light energy as heat, protecting the thylakoid membrane from photodamage. It's a key photoprotective mechanism.
The Q cycle is associated with which thylakoid membrane complex?
ATP synthase
Cytochrome b6f complex
Photosystem II
Photosystem I
The Q cycle describes how plastoquinone oxidation in the cytochrome b6f complex contributes to proton translocation, enhancing the proton gradient used for ATP synthesis.
Variations in the ratio of grana to stroma lamellae in different plant species are primarily adaptations to what?
Light intensity environment
CO2 concentration
Chlorophyll concentration
Temperature
Plants adapted to high light environments often have more grana stacks relative to stroma lamellae to maximize light capture, while shade-adapted plants have fewer grana. These structural variations optimize photosynthetic efficiency.
Phosphorylation of LHCII in the thylakoid membrane facilitates what process?
State transitions between photosystems
Calvin cycle activation
Starch synthesis
Photolysis
Phosphorylation of LHCII triggers its migration between grana and stroma lamellae, facilitating state transitions that balance excitation energy between photosystems I and II. This dynamic redistribution optimizes photosynthetic performance.
Which subunit of the CF1 domain of ATP synthase interacts directly with ADP and inorganic phosphate to form ATP?
Gamma subunit
Beta subunit
Alpha subunit
Delta subunit
The beta subunit of the CF1 domain of ATP synthase contains the catalytic site where ADP and inorganic phosphate combine to form ATP. It plays a direct role in substrate binding and catalysis.
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Study Outcomes

  1. Identify thylakoids -

    Recognize thylakoids, the flattened sacs of internal membranes associated with photosynthesis, and describe their location within the chloroplast.

  2. Explain light-dependent reactions -

    Outline how light energy is captured by photosystems in the thylakoid membrane and used to generate ATP and NADPH.

  3. Analyze proton gradient formation -

    Describe how electron transport across the thylakoid membrane creates a proton gradient and drives ATP synthesis.

  4. Distinguish chloroplast compartments -

    Compare the structure and function of thylakoids versus the stroma in ch 8 photosynthesis processes.

  5. Link to carbon fixation -

    Connect ATP and NADPH produced in thylakoids to their roles in the carbon fixation reactions of the Calvin cycle.

Cheat Sheet

  1. Thylakoid Definition -

    In ch 8 photosynthesis you learn that the flattened sacs of internal membranes associated with photosynthesis are called thylakoids. These disk-shaped structures house chlorophyll and form the site for the light-dependent reactions. A simple mnemonic is "Think LID" (Light-Dependent Interior Disks) to recall their shape and function.

  2. Grana and Stroma Structure -

    Thylakoids stack to form grana, which resemble stacks of coins and increase surface area for photon capture, a concept often tested in photosynthesis quizzes. The surrounding stroma is where carbon fixation quiz topics like the Calvin cycle occur, highlighting compartmentalization in chloroplasts. Visualize a "green pancake stack" to remember grana composition and stroma location.

  3. Photosystems I and II -

    Embedded in the thylakoid membrane are Photosystem II and Photosystem I, each absorbing specific light wavelengths (680 nm and 700 nm respectively), a key point in any light-dependent reactions quiz. The Z-scheme path illustrates how electrons move from H2O to NADP+, forming NADPH: H2O→PSII→ETC→PSI→NADP+→NADPH. To memorize order, recall "Z-flow" like a zigzag slide of energy transfer!

  4. Chemiosmosis and ATP Synthase -

    Protons accumulate in the thylakoid lumen during electron transport, creating a proton gradient (ΔpH) that drives ATP synthase to produce ATP from ADP + Pi (ADP + Pi → ATP). This proton-motive force is central in light-dependent reactions quiz questions and highlights chemiosmotic coupling as proposed by Peter Mitchell. Imagine protons "rushing" through ATP synthase like water through a turbine to generate energy.

  5. Link to Carbon Fixation -

    Although thylakoids focus on light reactions, the ATP and NADPH they generate fuel the Calvin cycle in the stroma, which is often featured in the carbon fixation quiz section. The Calvin cycle fixes CO2 into G3P using the equation 3CO2 + 9ATP + 6NADPH → G3P + 9ADP + 8Pi + 6NADP+, tying both quizzes together. A handy mnemonic is "CAR Fix" (CO2 + ATP + NADPH → Carbohydrate).

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