Photosynthesis and Respiration- Photosynthesis Flashcards
What are chloroplasts?
Flattened organelles surrounded by a double membrane that are found in plant cells
What are thylakoids?
Fluid-filled sacs
What are grana?
Structures in the chloroplast that are made from stacked up thylakoids
How are the grana linked together?
By bits of the thylakoid membrane called lamellae
What are photosynthetic pigments?
Coloured substances that absorb the light energy needed for photosynthesis
Where are photosynthetic pigments found?
In the thylakoid membrane attached to proteins
What is a photosystem?
The protein and pigment
Which photosystem absorbs light best at 700nm?
Photosystem I
Which photosystem absorbs light best at 680nm?
Photosystem II
What is the stroma?
A gel-like substance contained within the inner membrane of the chloroplasts and surrounding the thylakoids
What does the stroma contain?
Enzymes, sugars and organic acids
What happens to carbohydrates that are produced by photosynthesis and not used straight away?
They are stored as starch grains in the stroma
What are the two stages that make up photosynthesis?
The light-dependent reaction and the light-independent reaction
Where does the light-dependent reaction take place?
In the thylakoid membranes of the chloroplast
What is the process of the light-dependent reaction?
- Light energy is absorbed by chlorophyll in the photosystems
- The light energy excites the electrons in the chlorophyll, leading the their eventual release from the molecule
- The chlorophyll has been photoionised
- Some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP
- ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction
- During the process H2O is oxidised to O2
What is the light-independent reaction also called?
The Calvin cycle
Where does the light-independent reaction take place?
In the stroma of the chloroplast
What happens in the light-independent reaction?
The ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make simple sugars from CO2
What are electron carriers?
Proteins that transfer electrons
What is an electron transport chain?
A chain of proteins through which excited electrons flow
What happens when light energy excites electrons in chlorophyll?
The electrons move to a higher energy level
What happens to the high-energy electrons?
They are released from the chlorophyll and move down the electron transport chain
What happens after the excited electrons move down the electron transport chain?
Light energy splits water into protons (H+ ions), electrons and oxygen- photolysis
What is the reaction for photolysis?
H2O —> 2H+ + 1/2O2
What happens to the excited electrons as they move down the electron transport chain?
They lose energy
How is the energy from the excited electrons used?
To transport proteins into the thylakoid so that the thylakoid has a higher concentration of protons than the stroma which forms a proton gradient across the thylakoid membrane
How do protons move down their concentration gradient?
Into the stroma via ATP synthase, which is embedded into the thylakoid membrane
How is the energy from the protons moving down their concentration gradient used?
To combine ADP and inorganic phosphate to form ATP
How is reduced NADP formed?
Electrons are transferred to NADP along with a proton from the stroma
What molecule does the light-independent reaction make?
Triose phosphate from CO2, and ribulose biphosphate
How can triose phosphate be used?
To make glucose and other useful organic substances
How does the light-independent reaction start?
CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast
What happens once CO2 has entered the leaf?
It is combined with ribulose biphosphate (RuBP), a 5-carbon compound, and the reaction is catalysed by the enzyme rubisco
After RuBP has combined with CO2, what is produced?
A 6-carbon compound, which is unstable, so is quickly broken down into two molecules of a 3-carbon compound called glycerate 3-phosphate (GP)
What does the hydrolysis of ATP do?
Provides energy to turn GP into a different 3-carbon compound called triose phosphate (TP)
What does the reaction that turns GP to TP require?
H+ ions which come from reduced NADP which is recycled to NADP
What is some TP then converted into?
Useful organic compounds and some continues to regenerate RuBP
How many times does the Calvin cycle need to turn to make one hexose sugar?
Six
