photosynthesis Flashcards
granum
stacks of thylakoid disks
what connects the granum?
Granum are connected by lamellae
why do plants appear green?
In green range of light they absorb very poorly, so they reflect it, which is why plants look green
where are thylakoid disks found?
Found in the middle space of chloroplast called the stroma
Plants absorb visible light via ____
chlorophyll
structure of chlorophyll and functions?
- Long hydrophobic tail (anchors in membrane of thylakoid discs) & porphyrin ring (which absorbs light)
difference between chlorophyll a, b?
absorb different spectrums of light
what are the light reactions and their purpose?
Light energy is converted to chemical energy during the first stage of photosynthesis, which involves a series of chemical reactions known as the light-dependent reactions.
where do the light reactions take place?
in the thylakoid membranes of chloroplasts
what do the light reactions produce?
the energy storage molecule ATP and the reduced electron carrier NADPH
photosystem
large complexes of proteins and pigments (light-absorbing molecules) that are optimized to harvest light. two types of photosystems: photosystem I (PSI) and photosystem II (PSII).
what do photosystems do when light hits?
Photons come in and get passed around to the reaction center chlorophyll and gets shared among all pigments- Also called antenna complex
energetically, how does photosystem 1 work?
- photosystem 1 absorbs light (max 700 wavelength—less energy), electron gets energy and passed on to another acceptor. Then gets placed onto acceptor, NADP+ (same molecule as NAD+ but with a phosphate)
- NADP+ becomes NADPH (stored reducing power)
non-cyclic photophosphorylation
electrons are removed from water and passed through PSII and PSI before ending up in NADPH. This process requires light to be absorbed twice, once in each photosystem, and it makes ATP . In fact, it’s called photophosphorylation because it involves using light energy (photo) to make ATP from ADP (phosphorylation)
cyclic photophosphorylation
in cyclic photophosphorylation, (the non standard form of light reactions ) electrons follow a different, circular path and only ATP (no NADPH) is produced.
If a typical plant cell finds itself in need of some additional ATP, over and above that produced by the standard dual photosystem photosynthesis process, what options are available to make more ATP?
cyclic photophosphorylation (Electron can be passed in the opposite direction back towards photosystem 2 to make extra ATP)
yield from photosystems absorbing light in non-cyclic phosphorylation?
NADPH & ATP & O2 gas as a waste product
does non cyclic phosphorylation utilize oxygen?
no
in which photosystem is O2 released?
PSII
describe light absorption in PSI.
The electron arrives at photosystem I and joins the P700 special pair of chlorophylls in the reaction center. When light energy is absorbed by pigments and passed inward to the reaction center, the electron in P700 is boosted to a very high energy level and transferred to an acceptor molecule. The special pair’s missing electron is replaced by a new electron from PSII (arriving via the electron transport chain).
describe light absorption in PSII
When light is absorbed by one of the many pigments in photosystem II, energy is passed inward from pigment to pigment until it reaches the reaction center. There, energy is transferred to P680, boosting an electron to a high energy level. The high-energy electron is passed to an acceptor molecule and replaced with an electron from water. This splitting of water releases the \text O_2O2O, start subscript, 2, end subscript we breathe
Metabolism
sum total of all biochemical reactions in an organism
Anabolism
the buildup of organic molecules (sugars, proteins, etc)
catabolism
breakdown of organic molecules
