Photosynthesis Flashcards
What is photosynthesis responsible for?
the conversion of light energy from the sun into chemical energy in the form of complex carbohydrates. As a process it supports all life on earth
How is photosynthesis a transduction?
It converts of 1 form of energy into another
Why are plants photoautotrophs
They convert light energy into the food they need to release energy
What is the equation of photosynthesis
6CO2 + 6H2O -> C6H1206 + 6O2
What problems come from the photosynthesis equation?
It is very simplistic as the process is a lot more complex
How are leaves adapted for photosynthesis
The palisade cells in the mesophyll layer are highly adapted for this role. They are close to the surface of the upper leaf, are tightly packed together and have numerous chloroplasts in their cytoplasm. The spongy mesophyll layer has cells lees tightly packed with numerous air spaces that form a continuous pathway with the stomata in the lower epidermis. This facilities gas exchange with the palisade cells and the outside environment.
Where does photosynthesis occur in the plant
In the chloroplasts
How are chloroplasts adapted for photosynthesis
Thylakoids contain chlorophyll and other pigments along with systems of electron carriers and enzymes
Thylakoids are arranged in stacks – grana – where most light harvesting occurs
Thylakoids are linked by intergranal lamellae
CO2 is fixed with the stroma, and the reactions that occur in the stroma depend on a ready supply of products from the reactions associated with the absorption of light in the thylakoids.
What are the 3 stages of photosynthesis
Light harvesting, light dependant, light independent stage
What happens during the light harvesting stage? (Simple)
The absorption of light in the thylakoid to raise the energy level of the electrons in chlorophyll
What happens at the light dependent stage (simple)
energises electrons make energy rich compounds eg ATP and reduced NADP on the thylakoid membranes
What happens at the light independent stage (simple)
the products of the light reaction make carbohydrates, CO2 is also fixed in a series of cyclical reactions in the stroma.
What does the absorption spectra show?
the absorption of light of different wavelengths by chlorophyll.
What is the absorption spectrum
The absorption spectrum is the relative absorption of light at particular wavelengths. It is not necessarily linked to light intensity.
What is chlorophyll made of?
Chlorophyll is a combination of different pigments: chlorophyll a and b and another group of pigments called the carotenoids. The chlorophyll molecules have very similar chemical structures
What is chlorophyll made of?
Chlorophyll is a combination of different pigments: chlorophyll a and b and another group of pigments called the carotenoids. The chlorophyll molecules have very similar chemical structures
What carotenoids exist?
molecules such as the xanthophylls and carotenes and are not green – they are yellow, orange (e.g β carotene – the pigment found in carrots), red and brown. These pigments may be described as accessory pigments
What is the significance of accessory pigments?
absorb light of different wavelengths and pass the energy onto the chlorophyll to assist in the process of photoactivation. It is the combined absorption of all these pigments that gives rise to the overall absorption spectrum of “chlorophyll”.
What is the action spectrum
the rate of photosynthesis that takes place at different wavelengths
What do we see if a graph of rate of photosynthesis vs. wavelength is plotted
the rate is dependent on the wavelength, with the highest rate for those wavelengths over which most light is absorbed.
Where does the light harvesting take place
in particles attached to the thylakoid membranes of the chloroplast. These particles are more accurately described as photosystems and they exist in 2 forms - PSI and PSII
What is the difference between the photosystems
Photosystem I contains the primary pigment P700 (as it absorbs light with a wavelength of 700nm).
Photosystem II contains the primary pigment P680 (as it absorbs light with a wavelength of 680nm).
What is the light harvesting
The process of absorbing light in the photosystems
What does chlorophyll a do?
acts at the reaction centre and is referred to as the primary pigment;
What are accessory pigments responsible for
funneling the photons of light onto the primary pigment
What is the antenna complex
All of the accessory pigments considered together are known as the antenna complex.
What does the antenna complex do?
harvests light over a range of wavelengths, as the different pigments have different absorption maxima. As light is absorbed through the complex, special proteins help the absorbed energy move from one molecule to another by resonance transfer, and the energy is funneled to the reaction centre.
Where does the light dependent stage occur?
In the thylakoids and are tightly linked to process of light harvesting
What happens to the light energy harvested by both photosystems
used to excite electrons within the primary pigment to a higher energy level (photoactivation). These electrons are then passed to an electron acceptor.
What happens when their is sufficient light in the antenna complex
The arrangement of the accessory pigments in the antenna complex ensured that if there is sufficient light, enough energy can pass to the reaction centre allowing electrons in chlorophyll a to move to higher energy levels, they become excited in the process of photoactivation. If enough energy is available, the electrons emitted are taken up by an electron acceptor – ie chlorophyll becomes the electron donor. The electron that accepts the emitted electrons is arranged at the start of an electron carrier chain with cytochromes forming the carriers in the chain itself.
What is reduction
Removal or loss of oxygen
Addition of hydrogen
Gain of electrons
How are chloroplasts reducing agents
The chlorophyll molecules in the photosystem can be seen to act as reducing agents for the acceptor - they are donating electrons to them causing them to be reduced. These electrons are passed through a series of acceptors via a series of REDOX reactions. As each of the acceptors in the chain is at a slightly lower energy level than the preceding one enough energy is released from the electrons to allow the formation of ATP from ADP and inorganic phosphate (Pi) -the ADP is phosphorylated through the use of light energy - photophosphorylation.
