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

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