CAM Plants: Definition, Evolution, Photosynthesis, Examples

What Are CAM Plants?

The Crassulacean Acid Metabolism (CAM) is among the most unique photosynthetic pathways. It is a characteristic very unique and common among several specially adapted plants which gives excellent performance in dry and semi-arid habitats. Such a pathway confers to the plants' wonderful means through which they can afford and effectively capture and utilise carbon dioxide and still be in a position to conserve water efficiently, hence making them very good at surviving in dry environments. Carbon fixation takes place in CAM plants in a manner quite different from either C3 or C4 plants.

Mechanism of CAM Photosynthesis

Although all photosynthetic plants perform photosynthesis, CAMs go a step further and carry out a very strange photosynthetic activity by which they fix carbon dioxide at night rather than during the day. These adaptations greatly avoid the loss of water due to transpiration, especially in conditions when the atmosphere is hot and dry. The major steps are:

Step 1 – Nocturnal CO₂ Fixation (Night)

In plants with CAM, the stoma opens at night when it becomes cold and humid. Carbon dioxide will gain entry then through the opened stomata. This carbon dioxide is fixed into a 4-carbon compound, normally malate, which is then stored in vacuoles.The malate is thus stored in the vacuoles, and it is to be used at night. Thus, carbon dioxide is saved in a form that can be used both day and night.

Step 2 – Daytime Decarboxylation (Day)

During the day, after stomata have been closed to prevent the loss of water, the stored malate is again re-converted for use as carbon dioxide. This CO2 results in the production of sugar during the Calvin cycle.

Differences Between C3, C4, and CAM Pathways

The difference between C3, C4 and CAM pathways include:

Adaptive Features of CAM Plants

Most CAM plants are succulent—for instance, cacti and some orchids—a characteristic that enables them to store water in their tissue to survive for a long time without water.

Examples of CAM Plants

There are so many plants that are examples of CAM, but some common ones are stated below:

Cacti: The symbolic plants since they can survive in the most dried environment, they fix CO2 through photosynthesis they carry with the use of CAM.

Pineapple: The tropical fruit uses CAM photosynthesis to survive in environments that are warm and humid-tensed, and therefore conserved water.

Orchids: Most orchids have their niches in variable water availability conditions. CAM affords them an advantage in maximizing their efficiency for carbon fixation.

Importance and Benefits of CAM Photosynthesis

The following are some of the benefits that are imparted to plants, which live in dry environments, by the CAM pathway:

Water Conservation

CAM plants can reduce the loss of water to a considerable degree during night carbon fixation, and hence survive in conditions where water is at a minimum.

Better Carbon Fixation

The ability to store carbon dioxide as malate gives CAM plants the ability to fix a lot of carbon during the day even when the stomata becomes closed.

This may therefore make it possible for CAM plants in any other case uninhabitable to thrive, and this will increase the biodiversity in the arid ecosystems.

Survival in Arid Conditions

The succulent tissues and vacuolar storage helps the plants to survive in the drought resistance.

Biodiversity and Ecological Value

CAM plants are present in different ecosystems like desert and coastal which supports the various flora and fauna.

CAM Plants NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Mechanism of CAM photosynthesis

• Difference between C3, C4 and CAM pathway

Practice Questions for NEET

Q1.The plant family that does not show CAM pathway is

1. Crassulaceae

2. Euphorbiacea

3. Cactaceace

4. Gramineae

Correct answer: 4) Gramineae

Explanation:

CAMs are the most adapted xerophytic conditions, with plants from the Crassulaceae, Euphorbiaceae, and Cactaceae families. The stomata of these plants open at night, and the carbon dioxide absorbed is fixed by them in the form of malic acid within the vacuoles. At daytime, the fixed carbon is released and utilized for the C3 cycle, along with photosynthesis. Thus, CAM plants conserve water in arid conditions and can survive in such habitats.

Hence, the correct answer is option 4) Gramineae.

Q2. CAM helps the plants in:

1. Conserving water

2. Secondary growth

3. Disease resistance

4. Reproduction

Correct answer: 1) Conserving water

Explanation:

Crassulacean acid metabolism (CAM cycle) -

• In this pathway, stomata open at night to reduce transpiration and fix CO2 to malic acid which gets stored in vacuoles.

• CAM plants are succulents in the habit and have the slowest photosynthetic rate.

Hence, the correct answer is option 1)Conserving water.

Q3. Which of the following statements is true about the CAM pathway?

1. The CAM pathway is a type of photosynthesis found only in desert plants.

2. The CAM pathway is an adaptation to low CO2 levels in the atmosphere.

3. The CAM pathway involves the storage of CO2 as malic acid during the night and its release during the day

4. The CAM pathway is more efficient than the C3 and C4 pathways in terms of CO2 fixation.

Correct answer: 3) The CAM pathway involves the storage of CO2 as malic acid during the night and its release during the day

Explanation:

The CAM pathway involves the storage of CO2 as malic acid during the night and its release during the day is a true statement. The CAM pathway is a type of photosynthesis found in many plants, including those in arid environments. It involves the storage of CO2 as malic acid during the night when the stomata are open and its release during the day when the stomata are closed, allowing for reduced water loss through transpiration. While the CAM pathway is efficient in terms of water use, it is generally less efficient in terms of CO2 fixation than the C4 pathway and is not typically found in plants adapted to high CO2 levels.

Hence, the correct answer is option 3) The CAM pathway involves the storage of CO2 as malic acid during the night and its release during the day.

Also Read:

• MCQs on CAM Plants

• Difference between C3 and C4 Pathway

• Cyclic Photophosphorylation