Key Concepts
• Photosynthesis – process, stages
• Light and dark reactions – process, stages, products
• C4 cycle – process, stages
• CAM cycle – significance, process, stages
• Comparison of C3, C4 and CAM plants
Physiological Metabolism – CAM Pathway
Introduction:
Photosynthesis (photo–light; synthesis – to join) is the process through which green plants make use of energy from sunlight to make their own food. In the presence of sunlight, chloroplasts of green plants synthesize glucose using water and carbon dioxide. During photosynthesis, water gets oxidized, and carbon dioxide gets reduced to form carbohydrates. Photosynthesis forms the basis of all types of food chains and food webs. Photosynthesis produces starch and oxygen required for the survival of an organism. Therefore, photosynthesis supports all forms of life on Earth.
Photosynthesis in Plants:
Photosynthesis is a vital process that occurs in green plants. In the presence of sunlight, plants combine carbon dioxide and water to produce carbohydrates. The extremely significant by-product of photosynthesis is oxygen. In the presence of light energy, water is split to release oxygen. This process is known as the photolysis of water. During the process of photosynthesis, water molecule gets split up to release oxygen, and carbon dioxide forms carbohydrates. Oxygen produced during photosynthesis comes from a water molecule and not from carbon dioxide. In plants, photosynthesis takes place in the green part. Mostly green leaves carry out the photosynthesis process. Sometimes other green parts of plants, such as green stems and floral buds, are also involved in photosynthesis. Chloroplasts are specialized organelles in which the photosynthesis process actually takes place.
Stages of Photosynthesis:
Photosynthesis involves two important processes,
- Light-dependent reaction (Light reaction)
- Light-independent reaction (Dark reaction / Calvin cycle)
Though the entire process of photosynthesis takes place in chloroplast, light and dark reactions occur at different sites. Light reaction takes place in grana, and the dark reaction takes place in stroma regions of the chloroplast.
Light-Dependent Reaction:
Light-dependent reaction is also known as the primary photochemical reaction or Hill’s reaction, or Arnon’s cycle. Light reaction takes place at a faster rate than dark reaction. Light energy is converted into chemical energy during a light-dependent reaction. Light dependent reaction occurs in the thylakoid (thylakoids are stacked up to form grana) region of the chloroplast. Thylakoids contain chlorophyll molecules. Chlorophyll pigments are green in color. These pigments absorb different wavelengths of light and convert them into chemical energy through photosynthesis.
Light-dependent reaction involves four important stages.
- Absorption of light energy
- Splitting of water molecules
- Release of oxygen
- Formation of energy-carrying molecules – ATP and NADPH
Products of Light Reaction:
During light reaction, solar energy gets converted into chemical energy and is stored in the form of energy carrying molecules – ATP and NADPH. During light reaction, water is split up to release oxygen. High energy carrier molecules, ATP, and NADPH are required for the dark reaction, the next stage of photosynthesis.
Dark Reaction/Calvin Cycle:
The second step of photosynthesis is the light-independent reaction. It is also known as the dark reaction or Calvin cycle, or C3 cycle. Calvin cycle refers to the conversion of carbon dioxide to carbohydrate or the fixation of atmospheric carbon dioxide by plants through photosynthesis. Plants that undergo this cycle of reactions are known as C3 plants (Example: rice, wheat, barley, peanuts, spinach, etc.).
Calvin cycle takes place in the stroma of chloroplasts in the absence of light. The overall purpose of the Calvin cycle is to convert atmospheric carbon dioxide into carbohydrate (sugars). Calvin cycle makes use of ATP and NADPH produced by the light reaction to convert carbon dioxide into carbohydrate.
Phases of the Calvin Cycle:
Calvin cycle involves three important phases.
- Carbon fixation
- Reduction
- Regeneration of ribulose1, 5-bisphosphate (RuBP)
During the first phase of the Calvin cycle, carbon dioxide reacts with ribulose1, 5-bisphosphate (RuBP). This reaction is catalyzed by the enzyme ribulose biphosphate carboxylase/oxygenase or RUBISCO(RuBp). Two molecules of three-carbon molecule known as 3 – phosphoglycerate (3– PGA) are produced during this phase. In the reduction phase of the Calvin cycle, 3-PGA molecules (from the carbon fixation phase) are converted into glyceraldehyde-3-phosphate (G3P). ATP and NADPH are utilized for this reaction. As NADPH gets reduced (donates electrons), this reaction is termed as reduction phase. During the third phase, ribulose1, 5-bisphosphate (RuBP) gets regenerated, and the cycle restarts.
Products of Calvin Cycle:
- After each turn of the Calvin cycle, one molecule of carbon gets fixed.
- After three turns of the Calvin cycle, one molecule of G3P is exported into the cytoplasm.
- G3P molecules that leave the Calvin cycle are used for the production of glucose/fructose/ sucrose/starch.
- Two G3P molecules combine together to form one glucose molecule. Therefore, six turns of the Calvin cycle are required to produce one molecule of glucose.
C4 Cycle (Hatch and Slack Pathway):
In 1966, Marshall Davidson Hatch and Charles Roger Slack discovered the C4 cycle. C4 cycle is observed in plants present in the dry tropical region. In order to grow in a hot and dry environment, plants have adapted themselves by following the C4 pathway. The first stable product of the C4 cycle is oxaloacetate. It is a four-carbon compound. Hence the pathway is named C4 cycle.
C4 cycle is a kind of adaptation by plants to survive in a hot and dry environment. C4 plants have more benefits than C3 plants. C4 plants do not exhibit the process of photorespiration. (Photorespiration refers to the oxidation of RuBp in the presence of oxygen). Photorespiration begins when RUBISCO takes up oxygen instead of carbon dioxide. In order to reduce the loss of water, C3 plants close their stomata (pores present in leaves). Photorespiration takes place during this time. C3 plants lose an enormous amount of energy through photorespiration. In order to avoid energy loss through photorespiration, certain plants adapt themselves to C4 and CAM pathways. The crop yield also increases through this adaptation.
Process of C4 Cycle:
In C4 plants, light and dark reactions occur in different regions. Light reaction takes place in the mesophyll cells, while dark reaction/C3 cycle takes place in the bundle-sheath cells. Calvin cycle/C3 cycle is commonly observed in all photosynthetic plants. Whereas the C4 cycle is observed only in C4 plants. C4 pathway is also observed to occur before the C3 pathway.
In C4 plants, the C4 pathway takes place in the mesophyll cells, while the C3 pathway takes place in the bundle-sheath cells. Whereas in C3 plants Calvin cycle occurs in the mesophyll cells. C4 cycle involves four important steps.
- Carboxylation
- Break down
- Splitting
- Phosphorylation
CAM (Crassulacean Acid Metabolism) Pathway:
Photorespiration is an inefficient metabolic pathway through which a lot of energy is lost. Photorespiration begins when RUBISCO takes up oxygen instead of carbon dioxide. In order to reduce the loss of water, C3 plants close their stomata (pores present in leaves). Photorespiration takes place during this time. C3 plants lose an enormous amount of energy through photorespiration. In order to avoid energy loss through photorespiration, certain plants adapt themselves to C4 and CAM pathways. In C3 plants, approximately 25 % of photosynthesis is lost through photorespiration.
Crassulacean Acid Metabolism (CAM) pathway is a special type of carbon fixation pathway. It is observed in plants that grow in dry, semi-arid, or xerophytic conditions. In order to survive in dry conditions, plants adapt to the CAM pathway. Plants avoid photorespiration by using the CAM pathway. The leaves of these plants are found to be succulent or fleshy. Scientists first observed this pathway in the Crassulaceae family of plants (Example: Bryophyllum, Sedum, Kalanchoe). The pathway has been named after this discovery.
CAM pathway is found in Crassulaceae, Cactaceae, Agavaceae and Orchidaceae family of plants. Plants like cacti, orchids, and pineapple are found to exhibit CAM pathway. The stomata of these plants are observed to be scotoactive. Generally, plants lose their water content during the daytime through transpiration. In order to prevent water loss during the daytime, stomata remain closed and are open at night (scotoactive).
Significance of CAM Pathway:
- In order to reduce water loss in CAM plants, stomata remain closed during the day and open at night. Using this adaptation, CAM plants survive in extremely dry conditions.
- CAM plants carry out carbon dioxide fixation in the dark. Hence, they are able to survive in light for a longer time without the uptake of carbon dioxide.
- When stomata remain closed, succulent plants obtain carbon dioxide from malic acid.
- CAM plants uptake carbon dioxide during the night. This limits photosynthesis. In addition, stored carbohydrates and organic acids also limit the photosynthesis process. Hence, the growth of CAM plants is generally slow.
- CAM plants are drought resistant. They possess xerophytic adaptations (For example: thick fleshy leaves).
Process of CAM Pathway:
CAM plants adapt themselves to survive under extreme drought/dry conditions. CAM pathway involves two important steps.
- Acidification
- Deacidification
Acidification:
Acidification occurs during the night. In darkness, the glycolysis process converts stored carbohydrates into phosphoenol pyruvate (PEP). As the stomata of CAM plants remain open during the night, atmospheric carbon dioxide diffuses into the leaves. CAM plants fix the carbon dioxide using PEP. PEP gets carboxylated, and oxalo acetic acid (OAA) is produced. This reaction is catalyzed by PEP carboxylase. The OAA is then converted into malic acid in the presence of malic dehydrogenase enzyme. NADPH produced during glycolysis is used for this reaction. Malic acid gets accumulated in the vacuole and causes an increase in the acidity of the cells.
Deacidification:
The deacidification process occurs during the day. In order to prevent water loss, stomata remain closed during the day. At this time, malic acid undergoes decarboxylation to produce pyruvate and carbon dioxide. This reaction is catalyzed by malic enzyme. As malic acid is decarboxylated to pyruvate, there is a decrease in the acidity of the cell. Therefore, this process is termed deacidification. Carbon dioxide produced during the deacidification of malic acid enters the C3 cycle and aids the production of carbohydrates. Pyruvate is either used for the regeneration of PEP or converted into carbon dioxide through Kreb’s cycle.
CAM pathway is the most useful pathway in succulent plants. In order to reduce water loss, the stomata of these plants remain closed during the day. Therefore, atmospheric carbon dioxide does not enter the leaves during the daytime. However, these plants carry out photosynthesis during the day with the help of carbon dioxide produced by the decarboxylation of malic acid. Atmospheric carbon dioxide is fixed in the form of malic acid during the night. During the day, when atmospheric carbon dioxide is not available, stored malic acid is broken down to release carbon dioxide, which aids photosynthesis. Thus, CAM pathway conserves energy and aids the survival of succulent plants.
Difference between C3, C4, and CAM Plants:
C3 Plants:
In C3 plants, carbon fixation and Calvin cycle take place in the mesophyll cells located on the surface of leaves.
C4 Plants:
In C4 plants, Carbon fixation and Calvin cycle take place in different regions. Carbon fixation takes place in mesophyll cells, and the Calvin cycle takes place in bundle-sheath cells.
CAM Plants:
In CAM plants, carbon fixation and Calvin cycle take place in the mesophyll cells. However, these steps are separated by time. Carbon fixation takes place during the night, and the Calvin cycle takes place during the day.
Summary
• Photorespiration is an inefficient metabolic pathway through which a lot of energy is lost
• In order to avoid energy loss through photorespiration, certain plants adapt themselves to C4 and CAM pathways.
• Crassulacean Acid Metabolism (CAM) pathway is a special type of carbon fixation pathway. It is observed in plants that grow in dry, semi-arid, or xerophytic conditions.
• In order to survive in dry conditions, plants adapt to the CAM pathway. Plants avoid photorespiration by using the CAM pathway.
• CAM pathway involves two important steps – acidification and deacidification
• In order to reduce water loss, the stomata of CAM plants remain closed during the day and open at night.
• Atmospheric carbon dioxide is fixed in the form of malic acid during the night. This process is known as acidification.
• During the daytime, stored malic acid is broken down to release carbon dioxide. This process is known as deacidification.
• In C3 plants, carbon fixation and Calvin cycle take place in the mesophyll cells located on the surface of leaves.
• In C4 plants, Carbon fixation and Calvin cycle take place in different regions. Carbon fixation takes place in mesophyll cells, and the Calvin cycle takes place in bundle-sheath cells.
• In CAM plants, carbon fixation and Calvin cycle take place in the mesophyll cells. However, these steps are separated by time. Carbon fixation takes place during the night, and the Calvin cycle takes place during the day.
FAQs
What is the process of CAM pathway? ›
Crassulacean Acid Metabolism (CAM) Photosynthesis
In this pathway, stomata open at night, which allows CO2 to diffuse into the leaf to be combined with PEP and form malate. This acid is then stored in large central vacuoles until daytime. During the day, malate is released from the vacuoles and decarboxylated.
Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night.
What are the examples of CAM pathway? ›Sedum, Kalanchoe, Pineapple, Opuntia, Snake plant are the examples of CAM plants. These plants also perform double carbon dioxide fixation. The carbon dioxide acceptor in CAM plants is Phosphoenol pyruvic acid (PEP) during the night and Ribulose bisphosphate is carbon dioxide acceptor during the daytime.
What is CAM and describe the CAM pathway of CO2 fixation? ›Carbon Fixation in CAM Plants
CAM pathway of carbon fixation or Crassulacean acid metabolism is present in plants present in arid conditions, e.g. cactus. In the CAM pathway, plants take CO2 during the night through the stomatal opening. It is converted to malic acid (4 carbon compound) and stored in vacuoles.
Steps of CAM Photosynthesis
CAM photosynthesis begins at night, when the plant's stomata open and CO2 gas is able to diffuse into the cytoplasm of CAM mesophyll cells.
CAM plants temporally separate carbon fixation and the Calvin cycle. Carbon dioxide diffuses into leaves during the night (when stomata are open) and is fixed into oxaloacetate by PEP carboxylase, which attaches the carbon dioxide to the three-carbon molecule PEP.
Where does the CAM pathway take place? ›These pathways of carbon fixation, know as the C4 and the CAM pathways, take place in the cytoplasm of the cell.
What is the product of CAM pathway? ›| C3 | C4 | CAM |
|---|---|---|
| First-stable product produced | ||
| 3-phosphoglycerate | Oxaloacetate | Daytime – 3-phosphoglycerate Night time – Oxaloacetate |
| Number of molecules of NADPH and ATP required to produce glucose | ||
| NADPH – 12 ATP – 18 | NADPH – 12 ATP – 30 | NADPH – 12 ATP – 39 |
CAM plants function using crassulacean acid metabolism. Like C4 plants, CAM plants provide a preparatory step for the Calvin cycle. CAM plants are found in hot, dry environments; to prevent desiccation, they keep their stomata closed during the day. They take in carbon dioxide at night while stomata are open.
What are 3 examples of CAM? ›- Acupuncture.
- Ayurveda.
- Homeopathy.
- Naturopathy.
- Chinese or Oriental medicine.
What are 2 examples of CAM? ›
Complementary and alternative medicine includes practices such as massage, acupuncture, tai chi, and drinking green tea. Integrative medicine is an approach to medical care that combines conventional medicine with CAM practices that have shown through science to be safe and effective.
What are the benefits of CAM pathway? ›For terrestrial plants, the greatest benefit of CAM is considered to be increased water use efficiency (WUE) because stomatal opening during the dark period causes much less transpirational loss of water than opening during the light period.
Why does CAM photosynthesis occur? ›CAM Photosynthesis is for Plants Adapted to Dry Environments
CAM plants are often found in desert environments. It is too hot and/or dry to keep stomata open during the day, so they only open them at night. However, there is no light at night to do photosynthesis.
CAM photosynthesis reduces photorespiration
CAM plants have a simple trick that reduces the amount of water lost during gas exchange: they only open their stomata at night. Since the air is normally cooler and more humid at night, these plants can take in CO2 while losing relatively little water.
In the first stage of the Calvin cycle, the light-independent reactions are initiated and carbon dioxide is fixed. In the second stage of the C3 cycle, ATP and NADPH reduce 3PGA to G3P. ATP and NADPH are then converted into ATP and NADP+. In the last stage, RuBP is regenerated.
What are the 4 classical phases of CAM? ›Four temporal Phases of CAM (I, II, III and IV) indicated over a 24-hour photoperiod by the main features of CAM: CO 2 fixation, Rubisco, PEPC and NAD(P)-ME-type or PEPCK-type activities and organic acid and carbohydrate ac‐ cumulation.
What are the 5 steps of photosynthesis in order? ›The different phases of photosynthesis are: Absorption of light, Transfer Of electrons, Production Of ATP, and Carbon Fixation.
How many ATP are used in CAM cycle? ›For every CO2 fixed photosynthetically, C3 plants require 3 ATP and 2 NADPH, whereas the extra enzymatic reactions and compartmentation complexity for C4 plants require 4 or 5 ATP and 2 NADPH, and CAM plants require 5.5-6.5 ATP and 2 NADPH.
What is the explanation of C3 C4 and CAM plants? ›C3, C4 and CAM are the three different processes that plants use to fix carbon during the process of photosynthesis. Fixing carbon is the way plants remove the carbon from atmospheric carbon dioxide and turn it into organic molecules like carbohydrates.
How do CAM plants take in CO2 and prevent the loss of water? ›Unlike plants in wetter environments, CAM plants absorb and store carbon dioxide through open pores in their leaves at night, when water is less likely to evaporate. During the day, the pores, also called stomata, stay closed while the plant uses sunlight to convert carbon dioxide into energy, minimizing water loss.
What enzyme do CAM plants use? ›
In arid conditions, CAM plants fix CO2 by using the PEPC enzyme during the night, thus minimizing evapotranspiration; then, the CO2 is released for the carbon fixation using the Rubisco enzyme during the daytime while the stomata on the leaves are closed (e.g., Cushman and Bohnert, 1999).
What are CAM plants in simple explanation? ›CAM plants are the plants, which fix carbon dioxide by CAM pathway or Crassulacean acid metabolism. It was first discovered in the plants of the Crassulaceae family. They are present in dry and arid environments. The CAM pathway is adapted to minimise water loss and photorespiration.
Which is a CAM plant answers? ›Sedum, Kalanchoe, Pineapple, Opuntia, Snake plant are the examples of CAM plants. These plants also perform double carbon dioxide fixation.
Which are characteristics of CAM plants? ›CAM plants often show xerophytic features, such as thick, reduced leaves with a low surface-area-to-volume ratio, thick cuticle, and stomata sunken into pits.
What are the 4 types of CAM? ›- Circular. Circular cams use an off-centre pivot to cause the follower to move up and down. ...
- Pear. Pear cams are called this as they have the shape of a pear. ...
- Snail or drop. Snail or drop cams have the appearance of a snail shell. ...
- Heart-shaped or constant velocity.
Cam is short for camshaft, the engine part that opens and closes the valves to let the air-fuel mixture in and out of combustion chambers. Every engine manufactured today has, if not one, then at least two or more installed. The camshaft's primary function is to close and open the valves.
What is the most commonly used CAM? ›Prayer is the therapy most commonly used among all the CAM therapies.
What are the two main parts of a cam mechanism? ›Devices that utilize cams to transform one type of motion into another are typically composed of three main parts: the cam, the shaft (or rotating wheel), and the lever (also called a cam follower).
What are the advantages and disadvantages of CAM? ›| Advantages of CAM | Disadvantages of CAM |
|---|---|
| Fast and accurate production | Expensive to set up |
| Machines can run constantly on repetitive tasks | Needs a skilled workforce of engineers |
| Good for producing on a mass/flow production line | Downtime required for maintenance |
During the day, they breakdown the malate and use the released CO2 through Kalvin cycle to produce sugars, similar to C3 plants. So, CAM plants releases oxygen during night.
Why do CAM plants grow slowly? ›
They are ineffiecient at absorbing CO2, however, so they are slow growing compared to other plants. In addition, CAM plants avoid photorespiration. The enzyme responsible for fixing carbon into the Calvin cycle, Rubisco, cannot distinguish CO2 from oxygen.
Why do CAM plants close their stomata? ›CAM plants usually close their stomata during the day and open them at night. When the stomata are closed, water loss is prevented by the process of evaporation. This process prevents carbon dioxide gas from entering the plant's leaves.
How do CAM plants separate the light reactions and the Calvin cycle? ›Instead of separating the light-dependent reactions and the use of CO2 in the Calvin cycle in space, CAM plants separate these processes in time. At night, CAM plants open their stomata, allowing CO2 to diffuse into the leaves.
What is the Calvin cycle easy explanation? ›The Calvin cycle is a process that plants and algae use to turn carbon dioxide from the air into sugar, the food autotrophs need to grow. Every living thing on Earth depends on the Calvin cycle. Plants depend on the Calvin cycle for energy and food.
What happens in the Calvin cycle step by step? ›The Calvin cycle has three stages. In stage 1, the enzyme RuBisCO incorporates carbon dioxide into an organic molecule. In stage 2, the organic molecule is reduced. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue.
What are the steps of the Calvin cycle in order? ›The Calvin cycle reactions can be divided into three main stages: carbon fixation, reduction, and regeneration of the starting molecule.
What is the process of Crassulacean acid metabolism? ›Crassulacean acid metabolism is a carbon uptake system utilized by many succulent plants; these plants fix carbon dioxide during the night when evapotranspiration is relatively low, storing it as organic acids.
How does CAM help the manufacturing process? ›CAM can automate the milling of workpieces in applications where there is a need for subtractive manufacturing. Through CAM, the machinists can accurately remove excess material from workpiece blocks. The use of CAM with CNC machining enables using the data for quick quotes on machining jobs.
What is C3 C4 and CAM pathway? ›C₃, C₄ and Cam pathways are the adaptations that permit several plant species to lessen photorespiration in them. These pathways function in a way such that RuBisCO grabs large concentrations of carbon dioxide and prevents it from binding with oxygen.
Where does photosynthesis occur in CAM? ›Thus, CAM photosynthesis occurs in fleshy green leaves and not in thin green leaves with reticulated venation or Thin green leaves with parallel or thin colored leaves.
What is the importance of CAM plants? ›
For terrestrial plants, the greatest benefit of CAM is considered to be increased water use efficiency (WUE) because stomatal opening during the dark period causes much less transpirational loss of water than opening during the light period.
How do CAM plants avoid water loss? ›Unlike plants in wetter environments, CAM plants absorb and store carbon dioxide through open pores in their leaves at night, when water is less likely to evaporate. During the day, the pores, also called stomata, stay closed while the plant uses sunlight to convert carbon dioxide into energy, minimizing water loss.
What is CAM and its benefits? ›Computer-aided Manufacturing (CAM) is the term used to describe the use of computerized systems to control the operations at a manufacturing plant. These computerized systems assist manufacturers in various operations such as planning, transportation, management, and storage.
What is CAM advantages and disadvantages? ›| Advantages of CAM | Disadvantages of CAM |
|---|---|
| Fast and accurate production | Expensive to set up |
| Machines can run constantly on repetitive tasks | Needs a skilled workforce of engineers |
| Good for producing on a mass/flow production line | Downtime required for maintenance |
Computer-aided manufacturing (CAM) uses machines that are controlled by computers in the manufacturing process. This will reduce the risk of human error and ensures consistency across all products produced. It allows the business to save on labour costs and operate 24/7.
What is the purpose of the CAM and C4 pathways? ›The C4 pathway is designed to efficiently fix CO2 at low concentrations and plants that use this pathway are known as C4 plants. CAM plants live in very dry condition and, unlike other plants, open their stomata to fix CO2 only at night.
What is the difference between CAM pathway and C4 pathway? ›The primary difference between CAM and C4 pathways is that the former (CAM) minimizes photorespiration by selecting a specific time to extract CO2 or carbon dioxide from the environment, whereas the latter (C4) relocates the carbon dioxide molecules to two different cell types in order to prevent photorespiration.
What are the steps of C3 pathway? ›C3 Pathway (Calvin Cycle)
Calvin Cycle occurs in three steps: carboxylation. reduction. regeneration.