1. Explain the structural differences in the leaf anatomy of C3, C4, and CAM plants.
Answer:
C3 Plants:
- Photosynthesis occurs entirely in mesophyll cells.
- Chloroplasts are uniformly distributed.
- Lack Kranz anatomy.
C4 Plants:
- Possess Kranz anatomy with two distinct cell types: mesophyll and bundle sheath cells.
- Chloroplasts in mesophyll cells are smaller, while bundle sheath cells contain larger chloroplasts.
- Bundle sheath cells are tightly packed around vascular bundles.
CAM Plants:
- Similar leaf anatomy to C3 plants but adapted for water storage.
- Large vacuoles to store malate formed during CO2 fixation at night.
- Stomata open at night to reduce water loss.
2. Describe the Kranz anatomy in C4 plants and its significance.
Answer:
Kranz anatomy refers to the arrangement of mesophyll cells and bundle sheath cells in concentric rings around vascular bundles.
- Mesophyll cells: Perform initial CO2 fixation using PEP carboxylase.
- Bundle sheath cells: Perform the Calvin cycle using CO2 delivered via the C4 pathway.
- Significance: Kranz anatomy allows spatial separation of CO2 fixation and the Calvin cycle, minimizing photorespiration and increasing photosynthetic efficiency.
3. How does the spatial separation of photosynthesis processes occur in C4 plants?
Answer:
- CO2 fixation occurs in mesophyll cells using PEP carboxylase to form oxaloacetate, which is converted to malate or aspartate.
- Malate is transported to bundle sheath cells, where CO2 is released for the Calvin cycle.
- This spatial separation ensures high CO2 concentration around RuBisCO, reducing photorespiration.
4. Explain the temporal separation of photosynthetic processes in CAM plants.
Answer:
CAM plants exhibit temporal separation as follows:
- Night: Stomata open, CO2 is fixed by PEP carboxylase into malate, which is stored in vacuoles.
- Day: Stomata close to conserve water. Stored malate is decarboxylated to release CO2, which is used in the Calvin cycle.
- This adaptation minimizes water loss in arid environments.
5. What is photorespiration, and how do C4 plants overcome it?
Answer:
Photorespiration occurs when RuBisCO fixes O2 instead of CO2, leading to the loss of fixed carbon and energy.
- In C4 plants, CO2 is concentrated in bundle sheath cells by the C4 pathway, reducing RuBisCO’s interaction with O2.
- This adaptation minimizes photorespiration and enhances efficiency.
6. Compare the primary enzymes involved in CO2 fixation in C3, C4, and CAM plants.
Answer:
- C3 Plants: RuBisCO catalyzes the carboxylation of RuBP.
- C4 Plants: PEP carboxylase fixes CO2 in mesophyll cells, while RuBisCO operates in bundle sheath cells.
- CAM Plants: PEP carboxylase fixes CO2 at night, while RuBisCO functions during the day.
7. Describe the role of PEP carboxylase in C4 and CAM plants.
Answer:
PEP carboxylase is a key enzyme in C4 and CAM plants that fixes CO2 into a 4-carbon compound:
- In C4 plants, it operates in mesophyll cells, ensuring efficient CO2 fixation even at low concentrations.
- In CAM plants, it functions at night, enabling CO2 fixation when stomata are open.
8. How does the leaf anatomy of CAM plants support their survival in arid environments?
Answer:
- Large vacuoles store malate formed during nocturnal CO2 fixation.
- Thick cuticle and sunken stomata reduce water loss.
- Stomata open only at night, balancing CO2 uptake and water conservation.
9. Why do C3 plants face higher rates of photorespiration compared to C4 plants?
Answer:
- In C3 plants, RuBisCO lacks a mechanism to differentiate between O2 and CO2, leading to oxygenation of RuBP.
- C4 plants concentrate CO2 in bundle sheath cells, reducing oxygenation and photorespiration.
10. Explain the role of malate in CAM photosynthesis.
Answer:
- Malate serves as a temporary carbon storage molecule in CAM plants.
- Formed at night during CO2 fixation, malate is stored in vacuoles and decarboxylated during the day to release CO2 for the Calvin cycle.
11. What adaptations in C4 plants enhance their efficiency in tropical climates?
Answer:
- Kranz anatomy ensures efficient spatial separation of photosynthetic processes.
- PEP carboxylase has a higher affinity for CO2, ensuring fixation even under high temperatures.
- Reduced photorespiration enhances carbon fixation efficiency.
12. How does water use efficiency differ among C3, C4, and CAM plants?
Answer:
- C3 Plants: Moderate efficiency; stomata open during the day, leading to significant water loss.
- C4 Plants: High efficiency due to reduced stomatal opening and photorespiration.
- CAM Plants: Highest efficiency; stomata open only at night, minimizing water loss.
13. Discuss the ecological significance of CAM plants.
Answer:
- CAM plants thrive in arid and semi-arid environments.
- They contribute to carbon sequestration in harsh ecosystems.
- Common examples include cacti, succulents, and pineapples.
14. Why is Kranz anatomy absent in C3 plants?
Answer:
- C3 plants perform all photosynthetic processes in mesophyll cells.
- Absence of Kranz anatomy indicates lack of spatial separation, making them less efficient under high light and temperature.
15. What is the significance of vacuoles in CAM plants?
Answer:
- Vacuoles store malate, a 4-carbon acid formed during nocturnal CO2 fixation.
- This storage facilitates temporal separation of processes, reducing water loss.
16. How does light intensity affect C4 photosynthesis?
Answer:
- C4 plants are adapted to high light intensity and use it efficiently for CO2 concentration and Calvin cycle.
- Higher light intensities improve the efficiency of bundle sheath chloroplasts.
17. Compare the energy requirements of C3, C4, and CAM pathways.
Answer:
- C3 Plants: Lower energy requirement but prone to photorespiration.
- C4 Plants: Higher ATP requirement for CO2 transport and concentration.
- CAM Plants: Energy-intensive due to nocturnal fixation and malate storage.
18. Why are C3 plants less efficient in hot and dry conditions?
Answer:
- Increased temperature enhances photorespiration in C3 plants.
- Limited water availability forces stomatal closure, reducing CO2 uptake.
19. How do stomatal behavior patterns differ in C3, C4, and CAM plants?
Answer:
- C3 Plants: Stomata open during the day.
- C4 Plants: Stomata open during the day but for shorter periods.
- CAM Plants: Stomata open at night to conserve water.
20. Explain the ecological distribution of C3, C4, and CAM plants.
Answer:
- C3 Plants: Common in temperate regions with moderate sunlight and water.
- C4 Plants: Found in tropical and subtropical regions with high light and temperature.
- CAM Plants: Dominant in arid and semi-arid environments, where water conservation is critical.
