Totaled and closed 11/12 Mr F

Totaled 11/09 Mr F 

 

C4 photosynthesis pathways

 

C4 photosynethesis pathways is the functioning in land plants to alter carbon dioxide for the sugar production that undergos the process of photosynthesis. C₄ and CAM actually fix oxygen rather than carbon dioxide and this leads to a loss of energy and carbon and this process is known as photoresperation. This happens because is a more efficient enzyme is used to fix CO₂ in the mesophyll cells and shuttling the fixed carbon via malata or bundle sheath cells, where CO₂ is released by decarboxylation of the malate. These additional steps require energy by ATP because of these tradeoffs, no one of these three photosynthetic pathways is considered superior to the others -- rather, each is best suited to a different set of conditions. The name "C₄" comes from the fact that the first product of CO₂ fixation in these plants has four carbon atoms, rather than three. 

 

Here's a funny "rap" video that explains the what happens to a C4 plant with rapping puppets.  It's funny, but listen, because it'll really help!

Here are the lyrics to the song in the video, which might even go in your notes!

The temperature was rising on an uphill slant

Once upon a leaf in a C3 plant

Stomata were open, releasing too much H2O

"How can I close them when photosynthesis is too slow?"

When the C4 plants started sprouting on the hill

They said to C3, Ill live longer than you will.

Ive got these mesophyll cells full of loving PEP

P-E-P carboxylase in Calvins first step

So some CO2 binds with my loving P-E-P

Making O-A-A, oxaloacetate with 4 atoms of C

Oxaloaceate is made to malate, then it flows

Down the plasmodesmata to a special cell, it goes

To the bundle sheath cells where malate changes shape

Into pyruvate and CO2, then pyruvate escapes

Back to the mesophyll cells where it turns to P-E-P

Back to loving PEP, the final step, before we repeat ***(repeat)

A never-ending cycle getting CO2 to where?

To the bundle sheath cells where theres very little air

So rubisco can fix CO2 without a fight

As oxygen is limited, photorespiration's out of sight

Yeah, photorespiration's out of sight

Yeah, you know it's out of sight!

 

 

 

CAM  Crassulacean acid metabolism, 

 

Crassulacean acid metabolism, also known as CAM photosynthesis, is an elaborate carbon fixation pathway in some plants. These plants fix carbon dioxide (CO₂) during the night, storing it as the four carbon acid malate. The CO₂ is released during the day, where it is concentrated around the enzyme RuBisCO, increasing the efficiency of photosynthesis. The CAM pathway allow stomata to remain shut during the day, so it is especially common in plants adapted to arid (dry) conditions.

 

Crassulacean acid metabolism is a system in which CO₂ is concentrated around RuBisCO by day, while the enzyme is operating at peak capacity. This concentration of CO₂ increases RuBisCO's efficiency, as it is likely to operate in the "reverse" direction by means of photorespiration - using oxygen to break down the reaction products the plant would rather it was producing. It differs fromC4 metabolism, which concentrates CO₂ around RuBisCO spatially.

 

During the Night

CAM plants open their stomata during the cooler and more humid night-time hours, permitting the uptake of carbon dioxide with minimal water loss.

The carbon dioxide is converted to soluble molecules, which can be readily stored by the plant at a sensible concentration.

The chemical pathway involves a three-carbon compound phosphoenolpyruvate (PEP), to which a CO₂ molecule is added. This forms a new molecule, oxaloacetate, which in turn forms a malate(an acid). Oxaloacetate and malate are built around a skeleton of four carbons, hence the term C4. Malate can be readily stored by the plant in vacuoles within individual cells.

 

 

During the Day

Malate can be broken down on demand, releasing a molecule of CO₂ as it is converted to pyruvate. The pyruvate can be phosphorylated (i.e. have a phosphate group added by the "energy carrier" ATP) to regenerate the PEP with which the plant started, ready to be spurred into action the next night. But it is the release of CO₂ that makes the cycle worth the plant's while. It is directed to the stroma of chloroplasts: the sites at which photosynthesis is most active. There, it is provided to RuBisCO in greater concentration, increasing the efficiency of the molecule, and therefore producing more sugars per unit photosynthesis.

 

The benefits of CAM

A great deal of energy is expended during CAM by the production and subsequent destruction of malate. This is in part countered by the increased efficiency of RuBisCO, but the more important benefit to the plant is the ability to leave most leaf stomata closed during the day. CAM plants are most common in arid environments, where water comes at a premium. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evapotranspiration, allowing CAM plants to grow in environments that would otherwise be far too dry. C3 plants, for example, lose 97% of the water they uptake through the roots to transpiration - a high cost avoided by CAM plants.

 

Example of CAM plant: Cacti

 

Cacti are an example of a CAM plant because during the cooler night hours is when their stomata open. Considering that cacti are most often located in desert conditions, they do this in order to prevent water evaporation during the intense heat and dryness during the day. The Calvin Cycle for these plants is performed during the day when the stomata are closed. Other examples of CAM plants include sedums and pineapples.

 

Here is an interesting rap produced by some random kids about CAM.

http://www.youtube.com/watch?v=PHfzmKSJktA&NR=1 

This image shows the difference in how the CAM and C4 plants proccess CO₂:

 

   The C4 plant seperates the reactions by location      Whereas the CAM plant seperates the rections by time

 

CAM stands for crassulacean acid metabolism

CAM plants, like C4 plants live in hot and dry places. Unlike any other type of plant, the can close their stomates during the day to conserve water. The also use PEPCase to fix carbon dioxide at night, instead of using RuBP.

Note that, only the Cam plants fix CO2 later during the night because they have their stomata closed during the day.

 

• Some C₄ plants — called CAM plants — separate their C₃ and C₄ cycles by time.
• Other C₄ plants have structural changes in their leaf anatomy so that
  • their C₄ and C₃ pathways are separated in different parts of the leaf with
  • RUBISCO sequestered where the CO₂ level is high; the O₂ level low.

 

Details of C4 Cycle

• After entering through stomata, CO₂ diffuses into a mesophyll cell.
  • Being close to the leaf surface, these cells are exposed to high levels of O₂, but
  • have no RUBISCO so cannot start photorespiration (nor the dark reactions of the Calvin cycle).
• Instead the CO₂ is inserted into a 3-carbon compound (C₃) called phosphoenolpyruvic acid (PEP) forming
• the 4-carbon compound oxaloacetic acid (C₄).
• Oxaloacetic acid is converted into malic acid or aspartic acid (both have 4 carbons), which is
• transported (by plasmodesmata) into a bundle sheath cell. Bundle sheath cells
  • are deep in the leaf so atmospheric oxygen cannot diffuse easily to them;
  • often have thylakoids with reduced photosystem II complexes (the one that produces O₂).
  • Both of these features keep oxygen levels low.
• Here the 4-carbon compound is broken down into
  • carbon dioxide, which enters the Calvin cycle to form sugars and starch.
  • pyruvic acid (C₃), which is transported back to a mesophyll cell where it is converted back into PEP.

 

Example of C4 plant: Corn

 

Corn is an example of a C4 plant because it performs the C4 Cycle (CO2 diffuses into mesophyll which then forms the 4-Carbon compound oxaloacetic acid (C4)). C4 Plants are often located in areas with high daytime temperatures and intense sunlight. Other examples inlcude crabgrass, sugarcane, and sorghum.

 

 

C4 Leaf Anatomy

 

The C4 plants have two rings of cells surrounding their vascular bundles. The inner ring is called the Bundle Sheath cell which contains starch rich chloroplasts that do not have grana that is in the outer layer of mesophyll cells. This particular anatomy is called the kranz anatomy. The function of it is to provide an area where the CO2 can be concentrated around the Rubsico, and by doing this photoresperation is reduced.

 

Although most plants have the kranz anatomy some species of C4 plants operate without any distinctive bundle sheath tissue. This plants are mostly terrestrial plants that inhabit dry, salty areas. These plants operate on a single cell C4 C02 concentrating mechanism which is very unique.

 

 

The Video gets to the good stuff around 2:15. sorry for the corny beginning, but i didn't make it.

 

C4 Plant Anatomy The picture below displays the differences in anatomy of a C4 plant versus a C3 plant. As you can see a C4 plant is much more condensed then the C3 or a typical leaf cell we had been studying previously. The most noticeable difference is that there is only a Palisade parenchyma (we know them as mesophyll) in the C4 plant while the typical plant has both the Palisade and the Spongy parenchyma. Another difference between the two is that in the C4 plant, the chloroplasts are in the bundle sheath cells, unlike a typical leaf where the chloroplats are located mesophyll.

 

 

 

CAM Plant 

What allows CAM plants to survive in their harsh enviroments? 

• These are C4 plants, yet instead of segregating the pathways in different parts of the leaf, it seperates them by time of day

 

At Night

• The plants take in CO2 through their open stomata (which are often closed during the day to retain moisture within the leaf)
• The CO2 joins with PEP to form a 4-carbon oxaloacetic acid.
• This converted into 4-carbon malic acid which accumlates over night in the central vacuole

 

In the Morning

• Stomata close to conserve moisture (oxygen diffusion is low also)
• The stored 4-carbon malic acid leaves the vacuole and is broken down to release CO2
• The CO2 is used in the Calvin Cycle

 

CAM plants have made adaptations to live in conditions such as

• Low soil moisture
• Intense sunlight exposure
• High temperatures

 

HOW CAM AND C4 PLANTS WORK:

C4 and CAM Plants

C4 and CAM plants are plants that use certain special compounds to gather carbon dioxide (CO₂) during photosynthesis. Using these compounds allows these plants to extract more CO₂ from a given amount of air, helping them prevent water loss in dry climates.

All photosynthetic plants need carbon to build sugars, and all get their carbon from CO₂ in the air. CO₂ must first be bound, or "fixed," to another molecule inside the plant cell in order to begin its transformation into sugar. In most plants, carbon fixation occurs when CO₂ reacts with a five-carbon compound called RuBP (ribulose 1,5-bisphosphate). The product splits immediately to form a pair of three-carbon compounds, and therefore this pathway is called the C3 pathway. Further reaction leads to the creation of a sugar (glyceraldehyde-3-phosphate) and the regeneration of RuBP. This series of reactions is known as the Calvin-Benson cycle after the two scientists who elucidated it.

The enzyme that catalyzes the joining of RuBP and CO₂ is known as RuBP carboxylase, also called Rubisco. Rubisco is believed to be the most abundant protein in the world. However, Rubisco is not very efficient at grabbing CO₂, and it has an even worse problem. When the concentration of CO₂ in the air inside the leaf falls too low, Rubisco starts grabbing oxygen instead. The ultimate result of this process, called photorespiration, is that sugar is burned up instead of being created. Photorespiration becomes a significant problem for plants during hot, dry days, when they must keep their stomates (leaf pores) closed to prevent water loss.

Diverse groups of plants have evolved different systems for coping with the problem of photorespiration. These plants, called C4 plants and CAM plants, initially bind carbon dioxide using a much more efficient enzyme. This allows a more efficient harvest of CO₂, allowing the plant to trap sufficient CO₂ without opening its stomates too often. Each then uses the CO₂ in the Calvin-Benson cycle.

C4 ("four-carbon") plants initially attach CO₂ to PEP (phosphoenolpyruvate) to form the four-carbon compound OAA (oxaloacetate) using the enzyme PEP carboxylase. This takes place in the loosely packed cells called mesophyll cells. OAA is then pumped to another set of cells, the bundle sheath cells, which surround the leaf vein. There, it releases the CO₂ for use by Rubisco. By concentrating CO₂ in the bundle sheath cells, C4 plants promote the efficient operation of the Calvin-Benson cycle and minimize photorespiration. C4 plants include corn, sugar cane, and many other tropical grasses.

CAM ("crassulacean acid metabolism") plants also initially attach CO₂ to PEP and form OAA. However, instead of fixing carbon during the day and pumping the OAA to other cells, CAM plants fix carbon at night and store the OAA in large vacuoles within the cell. This allows them to have their stomates open in the cool of the evening, avoiding water loss, and to use the CO₂ for the Calvin-Benson cycle during the day, when it can be driven by the sun's energy. CAM plants are more common than C4 plants and include cacti and a wide variety of other succulent plants.