Photosynthesis Limiting Factors PDF

Foundation in Science Biology 2 Photosynthesis (PART 3): Photosynthesis limitations and adaptations Prepared by: Pei Ying Ng...

Foundation in Science Biology 2 Photosynthesis (PART 3): Photosynthesis limitations and adaptations Prepared by: Pei Ying Ng [email protected] EXT: #1266/ 03-27317241 Inspire Empower Elevate Learning Outcomes 1. Explain the term limiting 2. Explain how the anatomy factor in relation to and physiology of the photosynthesis leaves of CAM and C4 plants adapt to photosynthesis Learning Outcomes 2 Limiting Factors of Photosynthesis Major factors affecting photosynthesis Light intensity Temperature CO2 concentration Minor factors affecting photosynthesis Water Chlorophyll concentration Pollution 3 Limiting Factors: Light Intensity Light intensity When light intensity is LOW, rate of photosynthesis is PROPORTIONAL to light intensity At higher intensity, rate of photosynthesis become Rate of photosynthesis maximum due to atmospheric CO2 and saturated pigments At very high intensity, pigments may degraded due to light degradation 4 Limiting Factors: Temperature Temperature Rate of photosynthesis increase proportionally to temperature (from 0°C to 25°C) Rate of photosynthesis DOUBLES for each rise in 10°C kinetic energy increases Rate of photosynthesis more effective collisions At high temperature (40°C) rate of photosynthesis decrease, result of enzyme denaturation 5 Limiting Factors: CO2 Concentration Carbon dioxide concentration When the CO2 concentration increases, rate of photosynthesis increases proportionally After certain point, further concentration increased has no effect on rate of photosynthesis due to other environmental limiting factors (temperature/light/etc) Further increase in CO2 reduce photosynthesis rate Rate of photosynthesis this is because CO2 can dissolve in water causing an acidic solution to form. Too much dissolved CO2 can cause a low pH of the surrounding water that cause denaturing of enzymes CO2 Concentration 6 Limiting Factors of Photosynthesis Rate of photosynthesis Major factors affecting photosynthesis Light intensity Temperature CO2 concentration 7 Major Limiting Factors: Summary 8 Adaptations of Photosynthesis Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis On hot, dry days, plants CLOSE stomata o conserves H2O o limits photosynthesis The closing of stomata reduces access to CO2 and causes O2 to build up ▪ These conditions favour an apparently wasteful process called photorespiration 9 Photorespiration Photorespiration Consumes O2 and organic fuel Releases CO2 NOT producing sugar. This will help to limit damaging products (ROS) created by light reactions that build up in the absence of the Calvin cycle. ▪ Photorespiration creates a product that is not sugar and hence reduces the efficiency of the Calvin cycle ▪ Photorespiration reduces levels of photosynthesis by up to ~25% in C3 plants, reducing the overall energy yield in these plants 10 Adaptations of Photosynthesis: C3 plants C3 Plants ❖ Plants that exhibit C3 pathway ❖ Utilise only the Calvin cycle in dark reaction. In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a 3C compound (3-phosphoglycerate) In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a 2C compound (2-phosphoglycolate) Because oxygen acts as a competitive inhibitor for Rubisco, photosynthesis in C3 plants is reduced in the presence of oxygen 11 Adaptations of Photosynthesis: C3 plants C3 plants are less efficient in hot and dry regions, as stomata must remain closed to prevent excessive water loss ▪ When stomata are closed, O2 cannot diffuse out of the leaf, increasing O2 concentration relative to CO2 In these hot and arid conditions, other types of plants have evolved to limit the exposure of Rubisco to oxygen 12 Adaptations of Photosynthesis: C4 plants C4 plants Before photosynthesis, C4 plants use enzyme PEP (phosphoenolpyruvate) carboxylase to form a 4C compound as 1st product of initial fixation of CO2 These plants can then safely transfer the CO2 (stored in the 4C compound) to the Calvin cycle without worry of O2 interference 13 C4 Plants Adaptations: Hatch & Slack Pathway Hatch and Slack pathway Minimize the cost of photorespiration by incorporating CO2 into 4C compounds in mesophyll cells before Calvin cycle This step requires the enzyme PEP carboxylase PEP carboxylase has a higher affinity for CO2 than rubisco does It can fix CO2 even when CO2 concentrations are low These 4C compounds are exported to bundle-sheath cells, where they release the CO2 to be used in the Calvin cycle without O2 competition 14 Adaptations of Photosynthesis: C4 plants C4 plants Exhibit a different arrangement in photosynthetic cells Bundle-sheath cells: tightly packed around veins Mesophyll cells tightly packed outside bundle sheath ❖ Make transferring of CO2 more effective & reduce O2 interference 15 C4 Plants Adaptations: Kranz’s anatomy C4 plants are also well adapted to hot environments high light intensities high temperatures (above ~ 30°C) This is also a feature of the Kranz’s anatomy leaves have common mesophyll cells and a specialized ring bundle sheath surrounding vascular tissue This Bundle sheath have no direct contact with air 16 C3 plants versus C4 plants Kranz’s Hatch & Slack anatomy pathway 17 Knowledge Check X Which of these is a C3 and C4 plant? Give reasons why. Y 18 Knowledge Check 19 Photosynthesis Adaptations: CAM plants Crassulacean Acid Metabolism (CAM) Similar to C3 plants that follow C4 pathway 1. Open their stomata at night, incorporating CO2 into organic acids → Minimizes photorespiration Stomata open at night - PEP bind with CO2 and form oxaloacetate (4P) Oxaloacetate is then reduced to produce malic acid which is stored in sap vacuoles (malic acid formation occurs throughout the night) 20 Photosynthesis Adaptations: CAM plants Crassulacean Acid Metabolism (CAM) Similar to C3 plants that follow C4 pathway 2. Stomata close during the day, and CO2 is released from malate (organic acids) 3. Malate is made in the NIGHT and stored in reservoirs ready to be used during the MORNING. undergoes Calvin cycle in the morning from the CO2 reservoirs of malate stored. 21 Photosynthesis Adaptations: CAM plants CAM have the same 2C-fixing steps that are present in C4 plants, but rather than being spatially separated between the mesophyll and bundle sheath cells, CAM plants have both carbon dioxide-fixing enzymes within the mesophyll cells. 22 Photosynthesis Adaptations: CAM plants Facultative CAM Many CAM plants are facultative: Can switch to C3 photosynthesis during the day when the weather is favourable like after a good rain and temperatures are cooler. 23 Knowledge time Mesembryanthemum crystallinum (Ice plant) Switch photosynthetic mode in response to water and/or salt stress Start as C3 pathway but then switch to CAM later during flowering or under stress. Native to Mediterranean type climates with cool, wet springs and hot, dry summers. Utilises C3 pathway when water is available → increase photosynthetic rates and growth. Increase stress tolerance during drier time periods through CAM pathway. 24 Photosynthesis In C3 plants 25 Photosynthesis In C4 plants 26 Photosynthesis In CAM plants 27 Comparison of adaptations 28 Comparison of adaptations 29 Summary Adaptations Photosynthesis Limiting factors Photorespiration Minor Major Water Light Chlorophyll Temperature Pollution CO2 Conc. Interferes with photosynthesis Decrease CO2 fixation Energy production 30 Thank you class ☺ 31