Photosynthesis Flashcards
What are Light-Dependent Reactions?
They use water and energy from a photon of light to build the molecules ATP and NADPH.
Oxygen is released as waste.
ATP and NADPH are used as fuel for light-independent reactions
What are Light-Independent Reactions?
They do not require light directly.
In these reactions, carbon dioxide is pulled from the air and attached to an existing molecule.
Then ATP and NADPH are used to turn those molecules into glucose
What are thylakoids?
They are fluid-filled disks, stacks are called grana, they are where light is absorbed for photosynthesis
What is the thylakoids membrane?
It separates the interior chamber which is the lumen, from the stroma, which is the fluid surrounding the thylakoid
What are photosystems?
Clusters of chlorophyll in the thylakoid membrane that capture sunlight
Photosystem 2 comes before photosystem 1
What are the two major regions in the photosystems?
The large antenna complex surrounds the smaller reaction centre
Energy from a photon of light is absorbed by the chlorophyll in the antenna and funnelled to the reaction centre
Explain what happens in Photosystem 2 in Step One of photosynthesis.
When a chlorophyll absorbs a photon, the energy elevates one of the chlorophyll’s electrons to a higher energy state
The electron can’t hold the energy long
It passes it to a neighbouring chlorophyll, exciting it’s electron
The photons energy is passed this way through the antenna complex until it is passed to P680 in the reaction centre.
When P680s electron gathers enough photon energy it gets so excited it pops off photosystem 2 and rides away on a molecule called PQ
How does the P680s electron get replaced in photosystem 2?
We take an electron from water
There’s a region of photosystem 2 called the Oxygen Evolving Complex that splits water into three parts: hydrogen, oxygen, and one of the electrons that knits them together
The hydrogen ions accumulate in the thylakoid lumen, the electron replaces the one lost by P680, and oxygen is given off as a waste product
What is the concentration gradient in the thylakoid lumen?
There are lots of Hydrogen ions inside the lumen but not many in the surrounding stroma
In nature the hydrogen ions that are crammed into the lumen would cross the thylakoid membrane and go into the stroma
The positive charges of all the hydrogen ions repel each other
The hydrogen ions really want to leave the lumen, but the only way across the thylakoid membrane is a protein called ATP Synthase
Explain what happens in Photosystem 1 in Step Two of photosynthesis.
The chlorophyll molecules in the antenna complex absorb a photons energy and pass it around until they pass it to P700 in the reaction centre
When P700 absorbs the photon it’s electron is elevated to a higher energy state
It gets excited and rides away on a molecule called Ferredoxin
Ferredoxin takes the electron from P700 to a molecule called NADP+ Reductase. It uses the electrons energy to make a molecule of NADPH
The electron from Photosystem 2 replaces the one lost in Photosystem 1
What is Carbon Fixation?
Rubisco combines CO2 with a five carbon molecule called RuBP
Plants need to get the carbon from somewhere so they gather it from the air
Explain what happens in the Calvin Cycle in Step Three of photosynthesis.
Step 1: When Rubisco combines CO2 with RuBP it makes an unstable 6 carbon molecule that immediately splits into two molecules of 3-Phosphoglycerate.
Step 2: The chemical energy in ATP and NADPH is used to change the 3-Phosphoglycerate molecules into molecules of G3P
Step 3: For every six molecules of G3P made, 5 stay in the cycle and are modified to make more RuBP. The one other molecule G3P leaves the cycle and goes on to make sugar
What is Chlorophyll?
Green coloured pigment
Collects solar energy
Two types: Chlorophyll A and Chlorophyll B
What is Chlorophyll A?
Primary type in all photosynthetic organisms
The only pigment that can transfer solar energy
Absorbs blue-violet and orange light
What is Chlorophyll B?
Accessory pigment
Absorb other photons
Absorbs blue-green and yellow-orange light
