Photosynthesis: Light-Dependent & Independent Reactions
What are the two sets of photosynthesis?
light-dependent reactions and light-independent reactions
What is the order of the sets in photosynthesis?
Light-dependent reactions
Light-independent reactions
Why do plants need light ?
Because the light-dependent reactions can not take place without it
Where do the light dependent reactions take place?
In the thylakoids of chloroplast
What are photosystems?
groups of chlorophyll and proteins found in the thylakoids
What is the role of the photosystems?
take in sunlight and use it to add energy to the electrons
What happens to the electrons that the photosystems add energy to?
they are passed on to a set of carriers in the membrane
How many photosystems are there?
2
What do the pigments in Photosystem II do?
absorb light-energy and release high-energy electrons
What happens to the electrons released by Photosystem II?
they get passed down the electron transport chain
What is the electron transport chain?
a group of carrier proteins that use energy from the electrons to pump hydrogen ions inside the thylakoid
What happens as light shines on the chlorophyll?
more and more electrons enter the electron transport chain
When does chlorophyll get new electrons?
when enzymes break up water molecules
What happens as plants take electrons from water?
oxygen and hydrogen are left behind
What happens to the oxygen and hydrogen left behind from Photosystem II?
oxygen goes into the air we breathe and hydrogen becomes ions that are left inside the thylakoid
Where do hydrogen ions build up in Photosystem II?
Inside the thylakoid
Where do the hydrogen ions come from in Photosystem II ?
the break up of water and the electron transport chain
How does the build up of hydrogen ions inside the thylakoid affect the outside?
makes the outside more negatively charged than the inside
What powers the making of ATP?
The difference in charge and number of Hydrogen Ions on either side of the membrane
Can hydrogen Ions cross the membrane directly?
no
ATP synthase
Large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP.
How do Hydrogen Ions cross the membrane?
The large protein ATP synthase is forced to turn by the build up of hydrogen ions and adds a phosphate group to ADP making it ATP
What happens tot he electrons in Photosystem II?
they lost energy when they pumped ions across the membrane
What does Photosystem I do to the electrons from Photosystem II?
they give them energy again
What happens to the electrons in Photosystem I after they have been given energy again?
they go through another electron transport chain and are used to make NADP+ into NADPH for the next set of reactions
What happens during the light dependent reactions?
use water and energy from the sunlight to make oxygen and change ADP and NADP+ into the energy carriers ATP and NADPH
What happens during the light independent reaction?
plants build high-energy sugars that are stable, enabling them to store energy for a long time
What can the light -independent reactions also be referred to as?
The Calvin Cycle named after American scientist melvin Calvin