Photosynthesis Flashcards
What is photosynthesis?
The process by which photosynthetic organisms harness light energy and convert it to chemical energy in order to produce macromolecules from simple organic precursors.
Oxygenic photosynthesis
02 producing photosynthesis
Organisms which are able to carry out photosynthesis
- Plants
2. Micro-organisms eg. algae and cyanobacteria
Light-dependent reaction facts
- require light in the visible spectrum
- convert light energy to chemical energy
- produce ATP and NADPH-H+
- produce O2 as by-product
Light-independent reaction facts
- Doesn’t require light
- must be preceded by light-dependent reaction
- use ATP and NADPH-H+ from light-dependent
- carbon fixation occurs
- sugars/carbs produced
Where does photosynthesis occur?
Within chloroplasts.
Describe the structure of a chloroplast.
Within a chloroplast there are grana (singular = granum) which are made up of thylakoid discs. The granum are connected to one another via thylakoid lamellae and it is at the membrane of the thylakoid discs which is where the light-dependent reaction takes place. Furthermore each chloroplast contains 2 membranes and the inner membrane is impermeable to most ions and molecules (much like mitochondria).
Name the different types of chlorophyll found in both plants and algae.
Plants: chlorophyll a, chlorophyll b
Algae: chlorophyll a, chlorophyll c, chlorophyll d and chlorophyll e
Where does the light-independent reaction occur?
Within the stroma of the chloroplast.
Why do chlorophyll molecules contain Mg2+ ions?
They are important in the process of capturing light.
From which areas of the visible spectrum does chlorophyll absorb light?
The extremes of the visible spectrum - the violet/blue end and the ulterior red end.
What is the chlorophyll molecule within the middle of the antennae molecule referred to as?
It is referred to as the reaction centre. Antennae themselves are embedded within photosystems.
Name the type of chlorophyll acting as the reaction centre and wavelength at which said reaction centre becomes excited within photosystem 1.
The reaction centre is chlorophyll a and the wavelength at which it becomes excited is P700.
Name the type of chlorophyll acting as the reaction centre and wavelength at which said reaction centre becomes excited within photosystem 2.
The reaction centre can either be chlorophyll a or b and the wavelength at which it becomes excited is P680.
Why are plants green?
Green light Is reflected whereas other coloured light is absorbed by plant.
- Describe the first step in the light-dependent reaction.
A photon of light comes in and hits an accessory pigment within the antennae. The energy from this process is passed along via different accessory pigments until it reaches the reaction centre within the chlorophyll molecule. The reaction centre becomes excited and donates 2e- to the primary electron acceptor (pheophytin, otherwise referred to as Q). This begins an electron transport chain.
- What occurs after P680 loses an electron pair and give the 2 names for this process.
P680 then becomes a strong oxidant and as a result pulls e- from H2O, splitting 2H20 to 2e-, 2H+ (which are released into the lumen) and 02. This process is known as photo-oxidation or photolysis.
- Where does the electron pair go after it has been accepted be pheophytin the primary electron acceptor?
The electron pair is then donated to plastoquinone (PQ), and 2H+ are once again released into the lumen. The donation of the electron pair causes PQ to be reduced to PQH2, otherwise known as plastoquinol.
- How is PQH2 able to carry electrons to Cytb6f?
When PQ becomes PQH2 this results in its release from P680 meaning that it is able to travel freely along the thylakoid membrane. Therefore it is able to physically carry 2e- to Cytb6f, with PQH2 simultaneously releasing 2H+ into the lumen. Furthermore as Cytb6f takes up 2e- it also releases 2H+ into lumen.
What is cytochrome Cytb6f?
Cytochrome Cytb6f is a protein complex in the thylakoid membrane comprising of Cytb6 and Cytf subunits.
- What happens after Cytb6f takes up the electron pair?
Cytb6f then donated the electron pair to plastocyanin (PC). PC then carries the electrons to the reaction centre of P700 (photosystem 1). This ends the first electron transport chain, when the process of passing the electron pair from photosystem 2 to photosystem 1 is complete.
- How does the second electron transport chain begin?
P700 becomes reduced and then passes the electron pair to Fx, which is how the new electron transport chain begins.
- What happens after Fx accepts the donated electrons?
Fx then donates the electron pair to Fdx (ferredoxin).
- Where does ferredoxin donate the electron pair to and what process does this kick start?
Fdx passes the pair to ferredoxin: NADPH+ reductase which leads to NADPH+ being reduced to NADPH+-H+, the process of photoreduction which occurs in the stroma.
