Difference between C3 and C4 Plants

Content Writer-SME

Plants that utilize the C₃ pathway in the dark reaction are called C₃plants. C₄ plants, on the other hand, are those that use the C₄ pathway during the dark reaction. The primary difference between C₃ and C₄is based on carbon fixation process during photosynthesis.

Photosynthesis is a process of preparing food by green plants in the presence of sunlight and chlorophyll.
Unlike C₃plants, the leaves of C₄ plants shows Kranz anatomy.
Around 5% of all plants on the earth fall under the category of C₄ plants.

Table of Content

Difference between C₃ and C₄ Plants
C₃ Plants
C₄ Plants
C₃and C₄Pathway
C₃ and C₄Plants Similarities
Things to Remember
Sample Questions

Difference between C₃ and C₄ Plants

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C₃ plants account for around 95% of all shrubs, trees, and plants whereas C₄plants account for around 5% of all plants. Apart from the prevalance and anatomy of leaves, there are some other grounds of comparison that differentiate C₃ and C₄ plants from each other.

The differences between C₃ and C₄ plants are mentioned below in a tabular form:

Basis of Comparison	C₃ Plants	C₄ Plants
Season	These plants are typically found in cool and moist environments.	These are warm-season plants that are typically found in dry places.
Product	The end product of the C₃ cycle is phosphoglyceric acid, a three-carbon molecule.	Oxaloacetic acid is a 4-carbon chemical produced during the C₄ cycle.
Prevalence	95% of plants present on earth are C₃ Plants	5% of plants present on earth are C₄ plants
Conditions	In temperate climates, it is abundant.	Tropical environments make it prolific.
Kranz Anatomy	Kranz's anatomy does not exist in leaves of C₃ Plants.	Kranz's anatomy exists in leaves of C₄ Plants.
Chloroplast	The bundle sheath cells in this case lack chloroplasts.	Chloroplasts are found in the bundle sheath cells.
CO₂ Acceptors	C₃plants only have one CO₂ acceptor.	C₄ plants have two CO₂ acceptors.
Secondary Acceptors	C₃ plants do not have secondary CO₂ acceptors.	C₄plants are secondary CO₂ acceptors.
Photosynthesis	It can only do photosynthesis while its stomata are open.	It can accomplish photosynthesis even when the stomata are close together.
Peripheral reticulum	The peripheral reticulum does not exist in chloroplasts.	The peripheral reticulum is made up of chloroplasts.
Temperature	The ideal temperature for photosynthesis is really low.	The ideal temperature for photosynthesis is very high.
Efficiency	C₃ plants have a lower photosynthetic efficiency.	Photosynthesis is more efficient in C₄ plants.
Photorespiration	The rate of photorespiration is high.	There is no photorespiration.
CO₂ fixation	It moves slowly in C₃ plants.	It moves more quickly in C₃ plants.
Mesophyll Cell	The dark reaction occurs only in the mesophyll cells in this case.	In this case, mesophyll cells will only carry out the first phases of the C₄ cycle. The majority of the work is done in bundle sheath cells.
CO₂ Composition	These plants have a high carbon dioxide composition point.	These plants have a low carbon dioxide composition point.
Growth	When the soil temperature is between 4 and 7 degrees, growth begins.	When the soil temperature is between 16 and 21 degrees, growth happens.
Example	Wheat, Oats, Rice, Sunflower, Cotton.	Maize, Sugarcane, Amaranthus.

C₃ Plants

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The plants that follows calvin or C₃cycle for carbon dioxide fixation are called C₃plants. 3-phosphoglyceric acid (3 carbon molecule) is considered as the first stable product of C₃cycle. Mesophyll cells in the leaves are the site of calvin cycle in C₃plants.. The C₃pathway is further divided into three stages:

Carbon Fixation

Carbon fixation is the first step of C₃pathway that involves carboxylation of ribulose 1,5-bisphosphate (RUBP) into three carbon compound. This step is catalyzed by an important enzyme called RuBisCo. This is followed by the condensation of RUBP with CO₂molecule which produces a six carbon intermediate product. The intermediate product is further hydrolyzed to give two molecules of 3-phosphoglyceric acid (3-PGA).

Reduction

The formation of 3-PGA as a first stable product marks the end of fixative phase and the begining of reductive phase. Overall, it is a two step process in which kinase enzyme catalyses the first step of reduction whereas the second step is regulated by triose phosphate dehydrogenase.

First Step: In the first step, six molecules of 3-PGA further undergoes the process of phosphorylation to produce six molecules of 1, 3-biphosphoglyceric acid and ADP each.
Second Step: In the second step, six molecules of 3-PGAL (3-phosphoglyceraldehyde) is formed by the hydrolysis of 1, 3-biphosphoglyceric acid.

Regeneration

Regeneration is the last step of calvin cycle in which ribose biphosphate is further regenerated. This phase is commonly known as pentose phosphate pathway.

C₄ Plants

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Light-dependent processes and the calvin cycle are physically separated in C₄ plants. The light-dependent processes occur in the mesophyll cells. The mesophyll cell is a spongy tissue located in the center of the leaf.

While the Calvin cycle takes place in specific cells located around the leaf veins.
These cells are referred to as bundle-sheath cells.

C₃ and C₄Pathway

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The complete C₃ and C₄pathway can be best understood with the help of diagram given below:

C3 and C4 Pathway

C₃ and C₄ Photosynthesis in Plants

C₃ and C₄ Plants Similarities

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The similarities between C₃ and C₄ plants are as follows:

Both plants are examples of dark photosynthesis responses.
C₃ and C₄ plants use sunlight to store energy.
Carbohydrates are synthesized by both plants.
Photosynthesis requires chloroplasts.
Both are made up of the same light reactions.
RuBP accepts CO₂ in both C₃ and C₄plants.

C₃and C₄Plants Examples

The C₄ or Hatch and Slack pathway is more commonly observed in monocot plants. Moreover, examples of C₃and C₄plants include both annual and perennial plants. Some of them are listed below:

C₃Plants

Wheat,
Rye,
Oats,
Orchard grass

C₄Plants

Maize
Sugarcane
Millet
Sorghum

Things To Remember

Difference between C₃ and C₄ plants depends on the process of photorespiration.
C₄plants are more prolific in hot and dry settings
C₃ consumes three times less water and can flourish in drought or high temperatures.
Metabolic networks can be used to perform a systematic comparison of C₃ and C₄ plants.
Carbon fixation is performed by phosphoenolpyruvate carboxylase (PEPC).

Sample Questions

Ques. Which plants are the most productive and efficient? (4 marks)

Ans. Both C₃ and C₄ plants are productive; however, C₄ plants are more productive and efficient. Corn, sorghum, sugarcane, millet, and Panicum virgatum switchgrass are examples of C₄ plants.

C3 plants use Rubisco to fix carbon dioxide through a process known as photorespiration.
Instead of CO₂, O₂ can bind to Rubisco. As a result, O₂ lowers the photosynthetic efficiency and water use efficiency of C₃ plants.
As a result, even in high-temperature conditions, C₄ plants outperform C₃ plants in terms of productivity.
As a result, the C₄ pathway is unquestionably more efficient than the C₃ pathway in terms of carbon fixation.

Ques. Do C₄ plants need a dark period? (2 marks)

Ans.Plants labelled C₄also collect CO₂ during the night to use during the day. Many C₃ plants, including cannabis, do not require rest. Because sugars are needed by the plant to construct tissue and provide energy, the photosynthetic rate of the plant controls its growth rate.

Ques. What exactly is the issue with C₄ plants? (2 marks)

Ans. The disadvantage of C4 photosynthesis is the extra energy required in the form of ATP to pump the 4-carbon acids to the bundle sheath cell and the 3-carbon complex back to the mesophyll cell for conversion to PEP.

Ques. What are the constraints of C₃ plants? (2 marks)

Ans. C3 plants have the disadvantage that their photosynthetic efficiency diminishes in hot, dry circumstances due to a process known as photorespiration. When the concentration of CO₂ in the chloroplasts falls below roughly 50 ppm, the catalyst rubisco, which aids in carbon fixation, begins to fix oxygen instead.

Ques. What are the benefits of C₃ plants? (2 marks)

Ans. C3 plants comprise some of the world's most important sources of calories: cowpea, cassava, soybean, and rice. Because the places where these crops are grown are frequently hot and dry, they may benefit from the energy-saving mechanisms of C4 photosynthesis.

Ques. What are the similarities between C3 and C4 Plants? (4 marks)

Ans. The similarities between C3 and C4 plants are as follows:

Both plants are examples of dark photosynthesis responses.
C3 and C4 plants use sunlight to store energy.
Carbohydrates are synthesized by both plants.
Photosynthesis requires chloroplasts.
Both are made up of the same light reactions.
RuBP accepts CO₂ in both C3 and C4 plants.

Ques. What are the difference between C3 and C4 plants? (5 marks)

Ans. The difference between C3 and C4 plants are as follows:

C4 plants have a photosynthetic efficiency that is 50% greater than C3 plants.
Unlike C4 plants, C3 plants are composed of three carbon atoms in the form of 3-phosphoglycerate.
C4 plants are more robust, regardless of whether the goal function is biomass synthesis or CO₂ fixation.
Unlike C4 plants, C3 plants directly decrease into carbon dioxide in the chloroplast. C3 plants have a more dense structure than C4 plants.
The modularity of C3 plants is lower than that of C4 plants.
C4 plants produce more CO₂ than C3 plants.
C4 plants use less radiation than C3 plants.

Ques. Explain C3 Plants? (3 marks)

Ans. C3 plants are classified as common plants that lack photosynthetic characteristics to minimize photorespiration. These are those that utilize rubisco for carbon dioxide fixing.

The Calvin cycle is responsible for this fixation.
C3 plants account for around 95 percent of all plants, including rice, wheat, soybeans, and all trees.
Photosynthesis occurs when the micropores (stomata) on leaves are open.
The leaves of C3 plants lack kranz anatomy.
It is made up of three carbon atoms (3-PGA).

Ques. What are the chemical reactions carried out in photosynthesis and respiration? (2 marks)

Ans. The chemical reactions carried out in photosynthesis and respiration are as follows:

6CO₂ + 6H₂O + → C₆H₁₂O₆ + 6O₂

C₆H₁₂O₆ + 6CO₂ → 6CO₂ + 6H₂O

Ques. Explain the C4 Plants? (4 marks)

Ans. Light-dependent processes and the Calvin cycle are physically separated in C4 plants. The light-dependent processes occur in the mesophyll cells. The mesophyll cell is a spongy tissue located in the center of the leaf.

While the Calvin cycle takes place in specific cells located around the leaf veins.
These cells are referred to as bundle-sheath cells.
Let's look at how this division helps with C4 photosynthesis as an example.
It begins with the fixation of ambient CO₂ in mesophyll cells, which results in the formation of a simple, 4-carbon organic acid.
It is also referred to as oxaloacetate. PEP carboxylase, a non-rubisco enzyme that does not seem to bind O₂, is responsible for this activity.

Ques. What is the difference between photosynthesis and respiration? (3 marks)

Ans. The difference between photosynthesis and respiration are as follows:

Respiration	Photosynthesis
Respiration is carried out in all organisms.	Photosynthesis is carried out in phototrophs.
The process is carried out in mitochondria.	The process is carried out in chloroplasts.
It undergoes catabolic Process.	It undergoes anabolic process.

Difference between C3 and C4 Plants

Difference between C₃ and C₄ Plants