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32 terms

Biology, Chap. # 7 Photosynthesis: Using light to make food

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Photosynthesis
Transform light energy to chemical engergy stored in the bonds of sugar they make from carbon dioxide and water
Autotrophs
Organisms that make their own food and thus sustain themselves without consuming organic molecules derived from any other organisms
Producers
Make the food for the organisms in the biosphere
Photoautotrophs
Organisms that produce organic molecules from inorganic molecules using the energy of light
Chlorophyll
A light-absorbing pigment in the chloroplasts that plays a central role in the chloroplasts
Mesophyll
The green tissue in the interior of the leaf
Stomata
Tiny pores where carbon enters and oxygen exits
Stroma
A thick fluid that is enclosed by the two membranes of the chloroplast
Thylakoids
Interconnected membranous sacs suspended in the stroma
Grana
Stacks of thylakoids
Light reactions
Absorb solar energy and convert it to chemical energy stored in ATP and NADPH
Calvin cycle
Consists of Carbon fixation, reduction, release of G3P, and regeneration of RuBP. Using carbon from CO2, electrons from NADPH, and energy from ATP, the cycle constructs G#P, which is used to build glucose and other organic molecules
Wavelength
The distance between the crest of two adjacent waves
Photon
A fixed quantity of light energy
Photosystem
Consists of a number of light-harvesting complexes surrounding a reaction center complex
Reaction center complex
Contains a pair of chlorophyll a molecules and a molecule called the primary electron acceptor, which is capable of accepting electrons and becoming reduced
Carbon fixation
Rubisco combines CO2 with a five-carbon sugar called ribulose bisphosphate (RuBP). The unstable product splits into two molecules of the three-carbon organic acid, 3-phosphoglyceric acid (3-PGA). For three CO3 entering, six 3-PGA result
Reduction
Two chemical reactions consume energy from six molecules of ATP and oxidize six molecules of NADPH. Six molecules of 3-PGA are reduced, producing six molecules of G3P
Release of one molecule of G3P
One molecule of G3P you see leaving the cycle is the net product of photosynthesis. A plant cell uses G3P to make glucose and other organic compounds
Regeneration of RuBP
A series of chemical reactions uses energy from ATP to rearrage the atoms in the five G3P molecules (15 carbons total), forming three RuBP molecules (15 carbons). These can start another turn of the cycle
1st step of the Calvin cycle
Carbon fixation
2nd step of the Calvin cycle
Reducation
3rd step of the Calvin cycle
Release of one molecule of G3P
4th step of the Calvin cycle
Regeneration of RuBP
Inputs of the light reactions
Energy from light, water, ADP + P, NADP+
Outputs of the light reactions
oxygen, ATP, NADPH
Inputs of the Calvin cycle
CO2
Outputs of the Calvin cycle
Sugar, NADP+, ADP + P
C3 plants
First organic compound produced is the three-carbon compound 3-PGA.Common and widely distributed; they include soy beans, oats, wheat and rice.
C4 plants
Alternate modes of carbon fixation have evolved that save water without shutting down photosynthesis. Preced the Calvin cycle by first fixing CO2 into a four-carbon compound. Keeps its stromata mostly closed
CAM plants
These species are adapted to very dry climates. Pineapples, Cacti and succulent plants
Photorespiration
A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP