8.3 Photosynthesis Flashcards
Where does photosynthesis take place?
In the chloroplast
Photosynthesis can be roughly divided into ___ processes
Two
What are the two processes that photosynthesis can be roughly divided into?
-Light-dependent reactions
-Light-independent reactions.
What happens in photosynthesis in the light dependent reactions?
The light-dependent reactions convert light energy into a flow of excited electrons.
What are the steps of the process of the light-dependent reactions converting light energy into a flow of excited electrons?
1) Photoactivation
2) Photolysis
3) Electron transport chain
4) Chemiosmosis
5) ATP synthesis
6) NADP reduction.
Where do the light-dependent reactions take place?
In the thylakoids (more specifically in the intermembrane space of the thylakoids), special membrane structures found within the chloroplast.
Just like in cellular respiration, some of the subsequent steps take place in another compartment of the ___. (reword)
Chloroplast
What happens to the energy generated in the light-dependent reactions of photosynthesis?
-It needs to be stored.
-Again, as is the case with cellular respiration, the energy is transferred to electron carriers, but in the chloroplast, it is in the reduced form of NADP (nicotinamide adenine dinucleotide phosphate).
-The light-dependent reactions also generate ATP.
What does each NADP molecule accept?
-It accepts two hydrogen atoms (i.e. two H + ions and two electrons) to form NADPH + H + (second plus is small).
-For simplicity, reduced NADP will be referred to as NADPH throughout the text.
What are the light-independent reactions called?
The Calvin cycle
Where does the Calvin cycle take place?
In the stroma (the cytoplasm of the chloroplast).
What are the steps of the Calvin cycle?
1) Carbon fixation
2) Carboxylation of ribulose bisphosphate (RuBP)
3) Triose phosphate production.
What happens to the NADPH and ATP produced in the light-dependent reactions?
They are used in the light-independent reactions.
When do light-independent reactions occur and stop?
-Although these reactions are called light-independent, in reality, they can only continue for a short while in the absence of light.
-Once the stock of NADPH and ATP runs out, light-independent reactions stop.
Diagram of the chloroplast: light-dependent and light-independent reactions (Calvin cycle)
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What is the difference between the electron carrier in photosynthesis and cellular respiration?
-Electron carrier in Photosynthesis: reduced form of NADP.
-Electron carrier in cellular respiration: reduced form of NAD.
What is photosynthesis?
The process during which an organism (usually a plant) uses light energy to carry out chemical reactions to produce sugars or other organic molecules.
What does visible light consist of?
Photons with a particular wavelength.
What do different wavelengths of the photon mean?
-A shorter wavelength (of the photon) means a higher energy content.
-So, a ‘blue’ photon has a higher energy level than a ‘red’ photon, because blue light has a shorter wavelength than red light.
-Chlorophyll is a light-sensitive molecule that can absorb photons with certain wavelengths.
-The absorption spectrum of chlorophyll shows this.
What is a photosystem made up of?
-Hundreds of chlorophyll molecules (up to 300) and other accessory pigments (around 30–40) aggregate (collect) together with a protein to form a protein complex called a photosystem.
-These pigments transfer all the energy that they have absorbed from light photons to a central chlorophyll a molecule that forms the reaction center of the photosystem.
What are accessory pigments?
-Any pigment, other than chlorophyll a, that can absorb light.
-Examples include chlorophyll b and carotenoids.
Examples of accessory pigments
Chlorophyll b and carotenoids
How many types of photosystems are there embedded in the thylakoid membrane?
Two
What are the two types of photosystems embedded in the thylakoid membrane?
Photosystem I and Photosystem II.