Alternative Pathways oi palm

7/29/2019 Alternative Pathways oi palm

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Photosynthesis Quest Number 3

Monkemeier

CP Biology 2011


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The incorporation of carbondioxide into organic compoundsis known as carbon fixation.

Carbon fixation occurs during the

light independent reactions akaCalvin Cycle or Dark Reactions.


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Carbon dioxide diffuses into the stroma of thechloroplast.

The enzyme, RibuloseBiphosphatase (akaRubisco) enables Carbon Dioxide to combinewith a 5-carbon sugar known as Ribulose

biphosphate. This six carbon compound is UNSTABLE and

splits into two 3-Carbon sugars. 3-PGA The two 3-Carbon sugars then get rearranged

and form G3P One of the G3P will go on to make glucose The other G3P will go to regenerate the 5-Carbon

sugar known as RibuloseBiphosphatase.


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The Calvin Cycle just described isknown as the C3 pathway becausethe first stable organic moleculeformed is a three carbon sugar!

Examples of C3 plants are: grass,oak trees, maple trees, rosebushes, etc.


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C3 plants keep their stomata OPEN during theday when the sun is out and CLOSED at nightwhen sun is not shining.

The carbon dioxide can get IN and Oxygencan get OUT during the day when the stomataare open.

ON hot, dry, days, water loss (transpiration) is

a PROBLEM. C3 Plants have decreased levelsof photosynthesis due to water loss!


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When the stomata are closed, carbon dioxidecan not enter the leaf and oxygen can notleave the leaf.

Oxygen competes with carbon dioxide in TheCalvin Cycle.

When too much oxygen is inside the leaf, itwill bind with RUBISCO (aka ribulose

biphosphatase) and shut down the CalvinCycle. This is known as photorespiration.


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When oxygen combines with the enzyme ofthe Calvin Cycle (Rubisco, aka ribulosebiphosphatase), it then combines with the5-Carbon sugar and the combination breaks

down.

The Calvin Cycle shuts down because: the5-Carbon sugar is not available to make asugar and it breaks down into water andcarbon dioxide.


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Plants have had to evolve indifferent climates.

In HOT and DRY climates, plants

have evolved alternativepathways. Plants fight transpiration,photorespiration and the needfor carbon dioxide to enter theleaf.


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Corn, sugar cane and crab grass. Help fight transpiration by keeping their stomata

partially closed during the day and partially closed atnight.

Fix carbon dioxide into a temporary storage moleculethat has four carbons!

It is called a C4 pathway because the first stablecompound that carbon dioxide is fixed into is a fourcarbon compound.

The four carbon compound is transported tospecialized cells where Calvin Cycle is taking place!

The four carbon compound releases carbon dioxideto run Calvin Cycle.


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Jade plants, succulent plants, pineapple, Keep stomata CLOSED during the day and

OPEN at night.

Store carbon dioxide as an organic acid.

The organic acid then releases carbon dioxidedirectly to the Calvin Cycle.

CAM plants grow very slowly, but they require

less water than C3 or C4 plants.


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C3 Plants C4 Plants CAM Plants

Stomata Open at NightClosed duringDay

Partially closedduring day andpartially closedat night

Closed duringday and Open atnight

Carbon fixation Carbon dioxideis fixed into athree carboncompound thatis stable

Carbon dioxideis temporarilystored as a 4carbon stablecompound

Carbon dioxideis temporarilystored as anorganic acid.

Water Loss Has trouble withwater loss dueto transpiration.Trouble withphotorespiration

Less water lossthan C3 plants.Photorespirationis not a problem

Grow very slowlyand noproblems withphotorespiration

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Alternative Pathways oi palm