Chapter 8: Photosynthesis Flashcards
What is photosynthesis?
Fixation of CO₂ and reduction to carbohydrates using light energy.
Where does photosynthesis occur?
In chloroplasts.
What are the two main stages of photosynthesis?
Light-dependent reactions and light-independent reactions.
What is the role of chlorophyll in photosynthesis?
It absorbs light and acts as the primary pigment in reaction centers.
What is the difference between primary and accessory pigments?
Primary pigments directly participate in light reactions; accessory pigments transfer light energy to them.
What is the primary pigment of photosystem I?
Chlorophyll a.
What are photosystems
and how many types are there?
What process splits water during photosynthesis?
Photolysis.
What is the main purpose of light-dependent reactions?
To produce ATP and NADPH.
What is the role of NADP in photosynthesis?
Final electron acceptor in light-dependent reactions.
What occurs during non-cyclic photophosphorylation?
Electrons flow through both photosystems in the ‘Z scheme.’
What happens to excited electrons in photosystem II?
They are transferred to electron carriers after photoactivation.
How is ATP generated in photosynthesis?
Through chemiosmosis.
What is cyclic photophosphorylation?
ATP synthesis using only photosystem I.
When does cyclic photophosphorylation occur?
When NADPH accumulates or light is not limiting.
What is the Calvin cycle?
Light-independent reactions for carbon fixation.
Where does the Calvin cycle take place?
In the stroma of chloroplasts.
What is the first step of the Calvin cycle?
CO₂ fixation with RuBP.
What enzyme catalyzes the first step of the Calvin cycle?
Rubisco.
What happens to triose phosphates in the Calvin cycle?
Most regenerate RuBP; some form starch
What structures in the chloroplast are key for light-dependent reactions?
Thylakoid membranes.
What are grana?
Stacks of thylakoids in chloroplasts.
How do chloroplasts store energy products?
As starch grains and lipid droplets.
What factors affect the rate of photosynthesis?
Light intensity
What happens at the light compensation point?
Photosynthesis equals respiration.
What is photophosphorylation?
ATP synthesis using light energy.
What connects grana in chloroplasts?
Intergranal membranes.
Why do plants store glucose as starch?
Starch is insoluble and suitable for storage.
How is oxygen produced in photosynthesis?
From the splitting of water during photolysis.
What is the role of the stroma?
Site for the Calvin cycle and storage of materials like DNA and ribosomes.
What is chemiosmosis?
The process of generating ATP using a proton gradient.
Why is rubisco considered inefficient?
It can bind to O₂ instead of CO₂
What are the by-products of photosynthesis?
Oxygen and glucose.
What are chemoautotrophs?
Organisms using chemical energy instead of light.
Give an example of a chemoautotroph.
Nitrifying bacteria.
What role do nitrifying bacteria play in the nitrogen cycle?
They oxidize ammonia to nitrites or nitrates.
Why is photosynthesis crucial for life on Earth?
It provides energy and oxygen for living organisms.
What is the primary role of light in the light-dependent reactions?
To excite electrons in chlorophyll.
What molecule donates replacement electrons to photosystem II during photolysis?
Water (H₂O).
What is the main product of photolysis?
Oxygen (O₂).
What is the ‘Z scheme’ in photosynthesis?
The pathway of electron flow involving both photosystems.
What happens to electrons in photosystem I during cyclic photophosphorylation?
They return to photosystem I via electron carriers.
What are the two energy molecules produced during the light-dependent reactions?
ATP and NADPH.
Where in the chloroplast do light-dependent reactions take place?
In the thylakoid membranes.
What is the role of ATP synthase in light-dependent reactions?
To produce ATP from ADP and inorganic phosphate.
What creates the proton gradient in the thylakoids?
The splitting of water and the activity of electron carriers.
What is the final electron acceptor in the light-dependent reactions?
NADP⁺.
What energy source drives the Calvin cycle?
ATP and NADPH from light-dependent reactions.
How many turns of the Calvin cycle are required to produce one glucose molecule?
Six turns.
What happens if rubisco fixes oxygen instead of carbon dioxide?
Photorespiration occurs
Why is NADPH always shown leaving the thylakoid membrane in diagrams?
It is used in the Calvin cycle in the stroma.
