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Questions and Answers
What is the main product of photosynthesis?
Which pigment is essential for the absorption of sunlight energy during photosynthesis?
What is the role of stomata in plants?
Which part of chlorophyll is involved in absorbing sunlight?
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How do water and carbon dioxide enter the leaf for photosynthesis?
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What is a potential disadvantage of stomata opening for gas exchange?
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What type of organisms possess chlorophyll a?
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What is the function of accessory pigments in photosynthesis?
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What is formed when two of the 12 molecules of glyceraldehyde phosphate (PGAL) are removed from the cycle?
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Which factor can limit the rate of photosynthesis when increased too much?
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At which wavelengths do photosystems I and II absorb light most efficiently?
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What happens to the rate of photosynthesis as the temperature approaches the optimal range?
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Which molecule is regenerated in the cycle to allow the continuation of photosynthesis after the production of PGAL?
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What is the first process that occurs in Photosystem II (PSII)?
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What is produced during the photolysis of water in PSII?
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Which photosystem is named because it was the second to be discovered?
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What is synthesized from ADP and phosphate as a result of the energy changes in the electron transfer process?
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What role does the positively charged chlorophyll ion serve in the light-dependent reactions?
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Which of the following best describes the Z scheme in photosynthesis?
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What is the final electron acceptor in the electron transfer chain during the light-dependent reactions?
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Which of the following statements about non-cyclic phosphorylation is incorrect?
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What is the primary function of thylakoids in chloroplasts?
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During photosynthesis, what is produced when chlorophyll a absorbs light energy?
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What happens to water molecules during the light-dependent reactions of photosynthesis?
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What is the role of NADP+ in photosynthesis?
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What are the main products of the light-dependent reactions?
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What is the significance of the stroma in the chloroplast?
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Which of the following correctly describes the compartments of chloroplasts?
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Which process is responsible for the initial formation of glyceraldehyde 3-phosphate in photosynthesis?
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What drives the production of ATP during chemiosmosis in chloroplasts?
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Which component does NOT participate in cyclic phosphorylation?
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What is produced when carbon dioxide is incorporated into ribulose 1,5-biphosphate (RuBP)?
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What is the role of ATP in the light-independent reactions of photosynthesis?
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What is the end product formed from every pair of glyceraldehyde 3-phosphate (GALP) molecules during photosynthesis?
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Which process generates more ATP to drive light-independent reactions?
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What is the primary function of electrons transferred from photosystems during photosynthesis?
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Which of the following is an outcome of the Calvin Cycle?
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Study Notes
Photosynthesis
- Photosynthesis is the process by which plants, some bacteria and some protistans use sunlight energy to produce glucose from carbon dioxide and water.
- Glucose can be converted into pyruvate which releases adenosine triphosphate (ATP) by cellular respiration.
- Oxygen is also formed during photosynthesis.
Chlorophyll
- Chlorophyll is a complex molecule essential for photosynthesis.
- All photosynthetic organisms have chlorophyll a.
- Accessory pigments, including chlorophyll b, xanthophylls, and carotenoids, absorb energy that chlorophyll a does not.
- Chlorophyll a absorbs energy from the violet-blue and reddish orange-red wavelengths, and little from the green-yellow-orange wavelengths.
- All chlorophylls have a lipid-soluble hydrocarbon tail and a flat hydrophilic head with a magnesium ion at its centre
- Different chlorophylls have different side-groups on the head.
Leaves
- Leaves are specialized structures for photosynthesis in plants, acting like "solar collectors" packed with photosynthetic cells.
- Water enters the root and is transported to the leaves via xylem vessels.
- Land plants have evolved specialized structures called stomata to allow gas exchange.
- Carbon dioxide enters and oxygen exits the leaf through the stomata.
- Water is also lost through the stomata during gas exchange.
Chloroplast Structure
- The thylakoid is the structural unit of photosynthesis, found in both prokaryotes and eukaryotes.
- Thylakoids are flattened sacs containing photosynthetic chemicals.
- Eukaryotes have chloroplasts surrounded by a membrane.
- Thylakoids are stacked in grana, with the areas between grana referred to as stroma.
- The chloroplast has three membrane systems, forming three compartments.
Stages of Photosynthesis
- Photosynthesis is a two-stage process.
- The light-dependent reactions occur in the grana and require direct sunlight energy to make energy-carrier molecules.
- The light-independent reactions occur in the stroma and use the energy-carrier molecules to create carbohydrates from carbon dioxide.
Light-Dependent Reactions
- Light energy is trapped by chlorophyll to make ATP (photophosphorylation).
- Water is split into oxygen, hydrogen ions and free electrons (photolysis).
- The electrons react with NADP+, changing it to its reduced state (NADPH).
Light-Independent Reactions
- Carbon dioxide from the atmosphere is captured and modified by the addition of hydrogen to form carbohydrates.
- This process is called carbon fixation.
- Energy for this process comes from the light-dependent reactions.
Electron Transfer System
- Chlorophyll a absorbs light energy, exciting its electrons.
- The excited electrons are transferred to a primary electron acceptor.
- The chlorophyll molecule is oxidized and becomes positively charged.
- Energy from photoactivation is transferred to ATP and NADPH.
- Photoionisation of chlorophyll releases electrons that are transferred to an electron acceptor.
- The positively charged chlorophyll ion receives electrons from an electron donor, such as water.
Photosystems
- Two photosystems, Photosystem II (PSII) and Photosystem I (PSI), are involved in electron transfer.
- PSII occurs before PSI, though it was discovered second.
- Energy changes accompanying the electron transfer create a "Z scheme".
- Energy released during electron transfer produces ATP.
Non-cyclic phosphorylation
- Both ATP and NADPH are produced.
- Photoionisation of chlorophyll in PSII transfers electrons to an electron acceptor.
- Photolysis of water produces oxygen, hydrogen ions, and electrons, which replace those lost from chlorophyll.
- Electrons are transferred through the electron transport chain to PSI.
- Light energy further excites electrons in PSI, leading to the reduction of NADP+ to NADPH.
Chemiosmosis
- Electrons passing through the transport chain provide energy to pump H+ ions from the stroma into the thylakoid compartment.
- The electrochemical gradient drives the diffusion of H+ ions back into the stroma.
- This diffusion powers the production of ATP.
Cyclic phosphorylation
- Only PSI is involved, generating excited electrons.
- Electrons are transferred to the electron transport chain between PSII and PSI, but not to NADP+.
- No NADPH is formed.
- Electrons are transported back to PSI, completing the cycle.
The Calvin cycle
- Carbon dioxide combines with RuBP, a five-carbon sugar.
- An unstable six-carbon sugar is formed, which breaks down into two glycerate 3-phosphate (GP) molecules.
- ATP phosphorylates GP into glycerate diphosphate molecules.
- NADPH reduces glycerate diphosphate to two molecules of glyceraldehyde 3-phosphate (GALP).
- One GALP molecule is used to create glucose and other carbohydrates, lipids, or amino acids.
- The other GALP molecule is converted back into RuBP, initiating the cycle again.
Factors affecting photosynthesis
- Light intensity, carbon dioxide concentration, and temperature are key factors.
- As light intensity increases, the rate of photosynthesis generally increases.
- An increase in carbon dioxide concentration increases the rate of carbon fixation.
- Photosynthesis is dependent on temperature, as it is driven by enzymes.
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Description
Test your knowledge on the process of photosynthesis, the role of chlorophyll, and the structure of leaves in this comprehensive quiz. Explore how these components work together to convert light energy into chemical energy in plants and other organisms.