This might be a bad question, but is there a difference in the equations for each path of photosynthesis?

This is not a bad question! The pathway and reaction is all the same but when/how it occurs varies.

Why is it that C3 plants are more abundant in nature than C4 plants? Afterall C4 are more efficient than C3 as they lack photorespiration

A likely explanation for this is that C4 plants arose later on the evolutionary timeline than C3 plants. If C4 plants indeed happen to be more efficient than C3 plants, we can expect the proportion of C4 plants in nature to gradually rise over time, over millions of years...

what role does temperature have in this

The high temperature will make the plant close its stomata to reduce water loss by evaporation. If the stomata is closed, the oxygen from photosynthesis will build up inside the leaf while the carbon dioxide will not get into the leaf. This situation will make the concentration of oxygen inside the leaf higher than carbon dioxide. The rubisco will more likely bind the oxygen. So, the photorespiration happens. For more details, you could visit the photorespiration article https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/a/c3-c4-cam-plants

What would be the result of a competition between aCAM plant and a C4 plant in a hot, very wet, environment?

Many plants will not grow well in soils that are constantly moist or wet. However, several plants are tolerant of and have adapted to perform well under these conditions. both CAM and C4 plants are dominant in very hot, dry environments like deserts so thriving in very wet soil would not be an advantage for them. However, there are epiphytic CAM plants in very moist forests during the rainy season. _Bromeliaceae_. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4242292/

The mesophylls are tightly packed so oxygen cannot enter the bundle sheath in C4 Plants. However how does Carbon dioxide enter?

It reacts with water to form (HCO3)- ... this can then enter and react with the PEP carboxylase

Which enzyme is involved in the breakdown of malic acid to CO2 and pyruvate (in C4 pathway)?

Malate dehydrogenase — you can start learning more about two different forms of this enzyme in the following wikipedia links: •https://en.wikipedia.org/wiki/Malate_dehydrogenase_(oxaloacetate-decarboxylating)_(NADP%2B) •https://en.wikipedia.org/wiki/NAD-malic_enzyme

The plant in which water use efficiency is higher is

C4 have higher water efficiency than C3 plants. C3 grasses release 833 molecules of water per co2 molecule while C4 grasses release 277 molecules of water.

Which type of plants are most efficient

It could be argued that CAM plants are the most efficient because they create the most amount of energy from the least amount of water. However, these plants won't do very well in a very wet environment because they're used to opening their stomata for only small amounts of water. It really all depends on the environment, each plant adapts to be the most efficent for where they are!

Main content

Course: Biology library > Unit 13

Lesson 4: Photorespiration: C3, C4, and CAM plants

C3, C4, and CAM plants

Google Classroom

How the C4 and CAM pathways help minimize photorespiration.

Key points:

Photorespiration is a wasteful pathway that occurs when the Calvin cycle enzyme rubisco acts on oxygen rather than carbon dioxide.
The majority of plants are $C_{3}$ ‍ plants, which have no special features to combat photorespiration.
$C_{4}$ ‍ plants minimize photorespiration by separating initial ${CO}_{2}$ ‍ fixation and the Calvin cycle in space, performing these steps in different cell types.
Crassulacean acid metabolism (CAM) plants minimize photorespiration and save water by separating these steps in time, between night and day.

Introduction

High crop yields are pretty important—for keeping people fed, and also for keeping economies running. If you heard there was a single factor that reduced the yield of wheat by

20 %

and the yield of soybeans by

36 %

in the United States, for instance, you might be curious to know what it was

^{1}

As it turns out, the factor behind those (real-life) numbers is photorespiration. This wasteful metabolic pathway begins when rubisco, the carbon-fixing enzyme of the Calvin cycle, grabs

O_{2}

rather than

{CO}_{2}

. It uses up fixed carbon, wastes energy, and tends to happens when plants close their stomata (leaf pores) to reduce water loss. High temperatures make it even worse.

Some plants, unlike wheat and soybean, can escape the worst effects of photorespiration. The

C_{4}

and CAM pathways are two adaptations—beneficial features arising by natural selection—that allow certain species to minimize photorespiration. These pathways work by ensuring that Rubisco always encounters high concentrations of

{CO}_{2}

, making it unlikely to bind to

O_{2}

In the rest of this article, we'll take a closer look at the

C_{4}

and CAM pathways and see how they reduce photorespiration.

$C_{3}$ ‍ plants

A "normal" plant—one that doesn't have photosynthetic adaptations to reduce photorespiration—is called a

C_{3}

plant. The first step of the Calvin cycle is the fixation of carbon dioxide by rubisco, and plants that use only this "standard" mechanism of carbon fixation are called

C_{3}

plants, for the three-carbon compound (3-PGA) the reaction produces

^{2}

. About

85 %

of the plant species on the planet are

C_{3}

plants, including rice, wheat, soybeans and all trees.

$C_{4}$ ‍ plants

C_{4}

plants, the light-dependent reactions and the Calvin cycle are physically separated, with the light-dependent reactions occurring in the mesophyll cells (spongy tissue in the middle of the leaf) and the Calvin cycle occurring in special cells around the leaf veins. These cells are called bundle-sheath cells.

To see how this division helps, let's look at an example of

C_{4}

photosynthesis in action. First, atmospheric

{CO}_{2}

is fixed in the mesophyll cells to form a simple,

4

-carbon organic acid (oxaloacetate). This step is carried out by a non-rubisco enzyme, PEP carboxylase, that has no tendency to bind

O_{2}

. Oxaloacetate is then converted to a similar molecule, malate, that can be transported in to the bundle-sheath cells. Inside the bundle sheath, malate breaks down, releasing a molecule of

{CO}_{2}

. The

{CO}_{2}

is then fixed by rubisco and made into sugars via the Calvin cycle, exactly as in

C_{3}

photosynthesis.

This process isn't without its energetic price: ATP must be expended to return the three-carbon “ferry” molecule from the bundle sheath cell and get it ready to pick up another molecule of atmospheric

{CO}_{2}

. However, because the mesophyll cells constantly pump

{CO}_{2}

into neighboring bundle-sheath cells in the form of malate, there’s always a high concentration of

{CO}_{2}

relative to

O_{2}

right around rubisco. This strategy minimizes photorespiration.

The

C_{4}

pathway is used in about

3 %

of all vascular plants; some examples are crabgrass, sugarcane and corn.

C_{4}

plants are common in habitats that are hot, but are less abundant in areas that are cooler. In hot conditions, the benefits of reduced photorespiration likely exceed the ATP cost of moving

{CO}_{2}

from the mesophyll cell to the bundle-sheath cell.

CAM plants

Some plants that are adapted to dry environments, such as cacti and pineapples, use the crassulacean acid metabolism (CAM) pathway to minimize photorespiration. This name comes from the family of plants, the Crassulaceae, in which scientists first discovered the pathway.

Instead of separating the light-dependent reactions and the use of

{CO}_{2}

in the Calvin cycle in space, CAM plants separate these processes in time. At night, CAM plants open their stomata, allowing

{CO}_{2}

to diffuse into the leaves. This

{CO}_{2}

is fixed into oxaloacetate by PEP carboxylase (the same step used by

C_{4}

plants), then converted to malate or another type of organic acid

^{3}

The organic acid is stored inside vacuoles until the next day. In the daylight, the CAM plants do not open their stomata, but they can still photosynthesize. That's because the organic acids are transported out of the vacuole and broken down to release

{CO}_{2}

, which enters the Calvin cycle. This controlled release maintains a high concentration of

{CO}_{2}

around rubisco

^{4}

The CAM pathway requires ATP at multiple steps (not shown above), so like

C_{4}

photosynthesis, it is not an energetic "freebie."

^{3}

However, plant species that use CAM photosynthesis not only avoid photorespiration, but are also very water-efficient. Their stomata only open at night, when humidity tends to be higher and temperatures are cooler, both factors that reduce water loss from leaves. CAM plants are typically dominant in very hot, dry areas, like deserts.

Comparisons of $C_{3}$ ‍, $C_{4}$ ‍, and CAM plants

C_{3}

C_{4}

and CAM plants all use the Calvin cycle to make sugars from

{CO}_{2}

. These pathways for fixing

{CO}_{2}

have different advantages and disadvantages and make plants suited for different habitats. The

C_{3}

mechanism works well in cool environments, while

C_{4}

and CAM plants are adapted to hot, dry areas.

Both the

C_{4}

and CAM pathways have evolved independently over two dozen times, which suggests they may give plant species in hot climates a significant evolutionary advantage

^{5}

Type	Separation of initial ${CO}_{2}$ ‍ fixation and Calvin cycle	Stomata open	Best adapted to
$C_{3}$ ‍	No separation	Day	Cool, wet environments
$C_{4}$ ‍	Between mesophyll and bundle-sheath cells (in space)	Day	Hot, sunny environments
CAM	Between night and day (in time)	Night	Very hot, dry environments

This article is licensed under a CC BY-NC-SA 4.0 license

Attribution:

This article is a modified derivative of "Photosynthetic pathways," by Robert Bear and David Rintoul, OpenStax CNX, CC BY 4.0. Download the original article for free at http://cnx.org/contents/d0b6df3d-22b7-411f-8f28-5eeed0e1c82d@9.

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Walker, Berkeley J., VanLoocke, Andy, Bernacchi, Carl J., and Ort, Donald R. (2016). The cost of photorespiration to food production now and in the future. Annual Review of Plant Biology 67, 107. ://dx.doi.org/10.1146/annurev-arplant-043015-111709.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Alternative mechanisms of carbon fixation have evolved in hot, arid climates. In Campbell biology (10th ed.) San Francisco, CA: Pearson, 201.
Crassulacean acid metabolism. (2016, May 29). Retrieved July 22, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism#Biochemistry.
Raven, Peter H., Johnson, George B., Losos, Mason, Kenneth A., Losos, Jonathan B., and Singer, Susan R. (2014). Photorespiration. In Biology (10th ed., AP ed.). New York, NY: McGraw-Hill, 165.

5.Guralnick, Lonnie J., Amanda Cline, Monica Smith, and Rowan F. Sage. (2008). Evolutionary physiology: the extent of C4 and CAM photosynthesis in the genera Anacampseros and Grahamia of the Portulacaceae. Journal of Experimental Botany, 59(7), 1735-1742. http://dx.doi.org/10.1093/jxb/ern081.

References:

Bareja, B. (2015). Plant types: II. In C4 plants, examples, and C4 families. Retrieved from http://www.cropsreview.com/c4-plants.html.

Berg, J. M., Tymoczko, J. L., and Stryer, L. (2002). The Calvin cycle synthesizes hexoses from carbon dioxide and water. In Biochemistry (5th ed., section 20.1). New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK22344/.

Bowsher, C., Steer, M., and Tobin, A. (2008). Photosynthetic carbon assimilation. In Plant biochemistry (pp. 93-141). New York, NY: Garland Science.

C4 carbon fixation. (2015, September 26). Retrieved October 26, 2015 from Wikipedia: https://en.wikipedia.org/wiki/C4_carbon_fixation.

Crassulacean acid metabolism. (2015, September 16). Retrieved October 26, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism.

De, D. (2000). Crassulacean acid metabolism. In Plant cell vacuoles: an introduction (pp. 186-187). Collingwood, VIC: CSIRO Publishing.

Guralnick, Lonnie J., Amanda Cline, Monica Smith, and Rowan F. Sage. (2008). Evolutionary physiology: the extent of C4 and CAM photosynthesis in the genera Anacampseros and Grahamia of the Portulacaceae. Journal of Experimental Botany, 59(7), 1735-1742. http://dx.doi.org/10.1093/jxb/ern081.

Koning, R. E. (1994). Photorespiration. In Plant physiology information website. Retrieved from http://plantphys.info/plant_physiology/photoresp.shtml.

Photorespiration. (2015, September 4). Retrieved October 26, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Photorespiration.

Photosynthesis - an overview. (n.d.) In Biomes. Retrieved fromhttp://w3.marietta.edu/~biol/biomes/photosynthesis.htm.

Purves, W.K., Sadava, D., Orians, G.H., and Heller, H.C. (2003). Photosynthesis: energy from the sun. In Life: the science of biology (7th ed., pp. 145-162). Sunderland, MA: Sinauer Associates, Inc.

Raven, Peter H., Johnson, George B., Losos, Mason, Kenneth A., Losos, Jonathan B., and Singer, Susan R. (2014). Photorespiration. In Biology (10th ed., AP ed., pp. 163-165). New York, NY: McGraw-Hill.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Alternative mechanisms of carbon fixation have evolved in hot, arid climates. In Campbell biology (10th ed., pp. 201-204). San Francisco, CA: Pearson.

RuBisCO. (n.d.) In Combining algal and plant photosynthesis. Retrieved from https://cambridgecapp.wordpress.com/improving-photosynthesis/rubisco/.

Trueman, Shanon. (n.d.). CAM plants: survival in the desert. In History of botany. Retrieved from http://botany.about.com/od/HistoryBotany/a/Cam-Plants-Survival-In-The-Desert.htm.

Walker, Berkeley J., VanLoocke, Andy, Bernacchi, Carl J., and Ort, Donald R. (2016). The cost of photorespiration to food production now and in the future. Annual Review of Plant Biology 67, 107-129. http://dx.doi.org/10.1146/annurev-arplant-043015-111709. Vascular bundle. (2015, October 19). Retrieved October 26, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Vascular_bundle.

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Gina G
Posted 7 years ago. Direct link to Gina G's post “What are the average acid...”
What are the average acidity levels on the PH scale of C3, C4, and CAM?
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(6 votes)
Answer
- Jay Bird
  Posted 6 years ago. Direct link to Jay Bird's post “Not always true. How muc...”
  Not always true. How much deuterium is in the plant determines its pH. This is related to soil, latitude, and the rain water consumption by photosynthesis. Deuterium content inside the tropics in rain water is massively different and this has huge implications to plant food webs and acidity More deuterium means more acidity and inflammatory effect due to the kinetic isotope effect of the extra atomic mass in deuterium compared to H+.
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Spandan
Posted 6 years ago. Direct link to Spandan's post “In CAM cycle, doesn't the...”
In CAM cycle, doesn't the oxygen produced in light dependent reaction cause photorespiration (the stomata is closed)? When almost all the CO2 is utilized there will be much higher quantity of O2 compared to CO2.
Thanking you for your help.
Button navigates to signup pageComment on Spandan's post “In CAM cycle, doesn't the...”
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Grace Idachaba
Posted 6 years ago. Direct link to Grace Idachaba's post “what role does temperatur...”
what role does temperature have in this
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(2 votes)
Answer
- Klln Nda
  Posted 6 years ago. Direct link to Klln Nda's post “The high temperature will...”
  The high temperature will make the plant close its stomata to reduce water loss by evaporation. If the stomata is closed, the oxygen from photosynthesis will build up inside the leaf while the carbon dioxide will not get into the leaf.
  
  This situation will make the concentration of oxygen inside the leaf higher than carbon dioxide. The rubisco will more likely bind the oxygen. So, the photorespiration happens.
  
  For more details, you could visit the photorespiration article
  https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/a/c3-c4-cam-plants
  Comment on Klln Nda's post “The high temperature will...”
  (5 votes)
sks.replies
Posted 4 years ago. Direct link to sks.replies's post “This might be a bad quest...”
This might be a bad question, but is there a difference in the equations for each path of photosynthesis?
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(4 votes)
Answer
- Saivishnu Tulugu
  Posted 4 years ago. Direct link to Saivishnu Tulugu's post “This is not a bad questio...”
  This is not a bad question! The pathway and reaction is all the same but when/how it occurs varies.
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  (2 votes)
liyaalhayat
Posted 6 years ago. Direct link to liyaalhayat's post “Why is it that C3 plants...”
Why is it that C3 plants are more abundant in nature than C4 plants? Afterall C4 are more efficient than C3 as they lack photorespiration
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(3 votes)
Answer
- Vivek Menon
  Posted 2 years ago. Direct link to Vivek Menon's post “A likely explanation for ...”
  A likely explanation for this is that C4 plants arose later on the evolutionary timeline than C3 plants. If C4 plants indeed happen to be more efficient than C3 plants, we can expect the proportion of C4 plants in nature to gradually rise over time, over millions of years...
  Button navigates to signup page
  (2 votes)
SHASHWAT11111111
Posted 5 years ago. Direct link to SHASHWAT11111111's post “Which enzyme is involved ...”
Which enzyme is involved in the breakdown of malic acid to CO2 and pyruvate (in C4 pathway)?
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(1 vote)
Answer
- tyersome
  Posted 5 years ago. Direct link to tyersome's post “Malate dehydrogenase — yo...”
  Malate dehydrogenase — you can start learning more about two different forms of this enzyme in the following wikipedia links:
  •https://en.wikipedia.org/wiki/Malate_dehydrogenase_(oxaloacetate-decarboxylating)_(NADP%2B)
  •https://en.wikipedia.org/wiki/NAD-malic_enzyme
  Button navigates to signup page
  (5 votes)
shaktiprakash258
Posted 7 years ago. Direct link to shaktiprakash258's post “The plant in which water ...”
The plant in which water use efficiency is higher is
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(1 vote)
Answer
- Sparsh Jandial
  Posted 7 years ago. Direct link to Sparsh Jandial's post “C4 have higher water effi...”
  C4 have higher water efficiency than C3 plants. C3 grasses release 833 molecules of water per co2 molecule while C4 grasses release 277 molecules of water.
  Button navigates to signup page
  (5 votes)
goell21
Posted 4 years ago. Direct link to goell21's post “What would be the result ...”
What would be the result of a competition between aCAM plant and a C4 plant in a hot, very wet, environment?
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(2 votes)
Answer
- Ivana - Science trainee
  Posted 4 years ago. Direct link to Ivana - Science trainee's post “Many plants will not grow...”
  Many plants will not grow well in soils that are constantly moist or wet. However, several plants are tolerant of and have adapted to perform well under these conditions.
  
  both CAM and C4 plants are dominant in very hot, dry environments like deserts so thriving in very wet soil would not be an advantage for them.
  
  However, there are epiphytic CAM plants in very moist forests during the rainy season.
  Bromeliaceae.
  
  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4242292/
  Button navigates to signup page
  (3 votes)
Angelarpita54
Posted 6 years ago. Direct link to Angelarpita54's post “Which type of plants are ...”
Which type of plants are most efficient
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(1 vote)
Answer
- celiaq18
  Posted 6 years ago. Direct link to celiaq18's post “It could be argued that C...”
  It could be argued that CAM plants are the most efficient because they create the most amount of energy from the least amount of water. However, these plants won't do very well in a very wet environment because they're used to opening their stomata for only small amounts of water. It really all depends on the environment, each plant adapts to be the most efficent for where they are!
  Button navigates to signup page
  (4 votes)
Ghalib
Posted 4 years ago. Direct link to Ghalib's post “The mesophylls are tightl...”
The mesophylls are tightly packed so oxygen cannot enter the bundle sheath in C4 Plants. However how does Carbon dioxide enter?
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(2 votes)
Answer
- Carson Arnold
  Posted 7 months ago. Direct link to Carson Arnold's post “It reacts with water to f...”
  It reacts with water to form (HCO3)- ... this can then enter and react with the PEP carboxylase
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  (2 votes)

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