8.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH Flashcards
Where do the light reactions occur?
The light reaction occurs in the thylakoids where the light is transformed into chemical energy of ATP and NADPH
wavelength
the distance between crests of electromagnetic waves can range from less than a nanometer to more than a kilometer
electromagnetic spectrum
the entire range of radiation
visible light
the segment most important to live is about 380 nm to 750 nm which is this light, drives photosynthesis
photons
the discrete nontangible particle that makes up light
What signifies a high amount of energy?
the shorter the wavelength, the more energy there is, less nm = more energy for electrons
pigments
absorption spectrum: a graph plotting a pigment’s light absorption versus wavelength
absorption spectrum
a graph plotting a pigment’s light absorption versus wavelength
chlorophyll a
the key light-capturing pigment that participates directly in the light reactions
chlorophyll b
accessory pigment, broadens spectrums
carotenoids
another accessory pigment, absorbs damaging lights
photoprotection
absorb and dissipate excess light energy that would otherwise damage chlorophyll or interact with oxygen
What happens when the chlorophyll absorbs the light
When the chlorophyll absorbs the light(not all) and reflects the others in the spectrum, one of the electrons goes to a new level/electron shell
fluorescence
when electrons go back to their ground state, photons are given off, goes to the ETC
Photosystems
where chlorophyll molecules are organized along with other small organic molecules and portion into these complexes
reaction-center complex
surrounded by light-harvesting complex, composes the middle photosystems, proteins holding chlorophyll a, and primary electron acceptors
light-harvesting complex
consists of various pigment molecules ,within this complex, the energy goes from one pigment to another
primary electron acceptor
molecule capable of accepting electrons and becoming reduced
Why doesn’t the energy released from the excited electrons dissipate as heat energy
excited electrons are not dissipated as light and heat due to the readily available electron acceptor
What are the two types of chlorophyll a
photosystem 2: P680(680 nm)
photosystem 1: P700(700 nm)
photosystem 2 works first
What do these 2 systems work to achieve?
these 2 photosystems work together to generate ATP and NADPH
linear electron flow?, cyclic electron flow?
the flow of electrons through photosystems and other molecular components built into the thylakoid membrane
photosystems cycle between each other
What are the 4 enzymes used in the light reactions ?
Pq and Pc help carry out redox reactions as electrons flow down the ETC
Fd accepts electrons from the primary electrons
NADP+ reductase, uses electrons from PS 2 in order to make NADPH
Differences between Chemiosmosis in the Chloroplasts and Mitochondria
One notable difference is that the energy drop in chloroplasts start with water while mitochondria start with organic compounds
One starts with light while the other starts with organic compounds
Explain how light is reflected
Certain light is absorbed while the rest are reflected.
8 steps of light reactions
- The photons from light cause a chain reaction of exciting electrons in each pigment of photosystem 2 until P680 is reached
- P680 is then oxidized since the electron leaves to go to the primary electron acceptor
- H2O is split into 2xH+, Oxygen, and 2 electrons, the
2 electrons reduce the oxidized P680 and the H+ are in the thylakoid space, the Oxygen combines with one another and makes O2 - The photoexcited electrons pass from the primary electron acceptor of PS2 to PS1 through an ETC, Pq, and Pc carry out redox reactions as electrons flow down the ETC, releasing free energy that is used to pump H+
- the potential energy stored in the proton gradient is used to make ATP through chemiosmosis
- P700 in PS 1 is now oxidized due to its exciting electron being taken, the oxidized P700 accepts electrons from PS 2
- protein Fd accepts electrons from the primary electrons
- NADP+ reductase catalyzes the transfer of electrons from Fd to NADP+, the 2 electrons added then create NADPH, and H+ is also removed from the stroma
action spectrum
profiles the relative effectiveness of different wavelengths of radiation in driving the process
